[flipper]

Okay, so I like to make up cutesy names

I wanted to do 'something' with a 6ME8 so I tried using it for an AM
transmitter and the first prototype works rather well. Bandwidth is
'too much', less than 1 dB down at 18 KHz, but we'll worry about that
later.

This is a 'dollar days' special, 2 whole bucks worth of tubes, and L2
is a UHF converter coil scramble rewound, so that was 'free'. Power
supply is from the same converter and if the remaining issues get
worked out it'll probably end up in that cabinet as well (but where to
put the air variable?).

The schematic is rough, but should be rather self explanatory, and the
ganged tuning hasn't been fleshed out yet. I'm still using separate
caps while jiggling things around.

Orphaned web page, not yet ready for prime time, has a recording of it
playing through a table radio.

http://flipperhome.dyndns.org/Beamus.htm

[Doug Bannard]

"flipper" wrote in message
...
Okay, so I like to make up cutesy names

I wanted to do 'something' with a 6ME8 so I tried using it for an AM
transmitter and the first prototype works rather well. Bandwidth is
'too much', less than 1 dB down at 18 KHz, but we'll worry about that
later.

This is a 'dollar days' special, 2 whole bucks worth of tubes, and L2
is a UHF converter coil scramble rewound, so that was 'free'. Power
supply is from the same converter and if the remaining issues get
worked out it'll probably end up in that cabinet as well (but where to
put the air variable?).

The schematic is rough, but should be rather self explanatory, and the
ganged tuning hasn't been fleshed out yet. I'm still using separate
caps while jiggling things around.

Orphaned web page, not yet ready for prime time, has a recording of it
playing through a table radio.

http://flipperhome.dyndns.org/Beamus.htm



Nice design work...and around inexpensive NOS tubes as well! That's a great
looking output waveform. I'll bet that it'll sound great playing through a
vintage receiver!

Best Regards : Doug Bannard

[flipper]

On Sun, 10 Jun 2012 19:48:23 -0400, "Doug Bannard"
wrote:


"flipper" wrote in message
.. .
Okay, so I like to make up cutesy names

I wanted to do 'something' with a 6ME8 so I tried using it for an AM
transmitter and the first prototype works rather well. Bandwidth is
'too much', less than 1 dB down at 18 KHz, but we'll worry about that
later.

This is a 'dollar days' special, 2 whole bucks worth of tubes, and L2
is a UHF converter coil scramble rewound, so that was 'free'. Power
supply is from the same converter and if the remaining issues get
worked out it'll probably end up in that cabinet as well (but where to
put the air variable?).

The schematic is rough, but should be rather self explanatory, and the
ganged tuning hasn't been fleshed out yet. I'm still using separate
caps while jiggling things around.

Orphaned web page, not yet ready for prime time, has a recording of it
playing through a table radio.

http://flipperhome.dyndns.org/Beamus.htm



Nice design work...and around inexpensive NOS tubes as well! That's a great
looking output waveform. I'll bet that it'll sound great playing through a
vintage receiver!

Best Regards : Doug Bannard


Thank you.

Yes, it does sound good though my Zenith 845 but by the time I got
through the cornucopia of recording problems it ended up on a circa
80's Panasonic clock radio, which is a fairly decent one with a 6x4
speaker. The single speaker helped with mic directional problems.

[Alex Pogossov]

"flipper" wrote in message
...
Okay, so I like to make up cutesy names

I wanted to do 'something' with a 6ME8 so I tried using it for an AM
transmitter and the first prototype works rather well. Bandwidth is
'too much', less than 1 dB down at 18 KHz, but we'll worry about that
later.

This is a 'dollar days' special, 2 whole bucks worth of tubes, and L2
is a UHF converter coil scramble rewound, so that was 'free'. Power
supply is from the same converter and if the remaining issues get
worked out it'll probably end up in that cabinet as well (but where to
put the air variable?).

The schematic is rough, but should be rather self explanatory, and the
ganged tuning hasn't been fleshed out yet. I'm still using separate
caps while jiggling things around.

Orphaned web page, not yet ready for prime time, has a recording of it
playing through a table radio.

http://flipperhome.dyndns.org/Beamus.htm

But the smartest arses (aussies of course, he-he!) put their AM transmitters
in the vintage radio cabinets.
http://www.ebay.com.au/itm/140770446...84.m1555.l2649

[flipper]

On Mon, 11 Jun 2012 12:50:03 +1000, "Alex Pogossov"
wrote:


"flipper" wrote in message
.. .
Okay, so I like to make up cutesy names

I wanted to do 'something' with a 6ME8 so I tried using it for an AM
transmitter and the first prototype works rather well. Bandwidth is
'too much', less than 1 dB down at 18 KHz, but we'll worry about that
later.

This is a 'dollar days' special, 2 whole bucks worth of tubes, and L2
is a UHF converter coil scramble rewound, so that was 'free'. Power
supply is from the same converter and if the remaining issues get
worked out it'll probably end up in that cabinet as well (but where to
put the air variable?).

The schematic is rough, but should be rather self explanatory, and the
ganged tuning hasn't been fleshed out yet. I'm still using separate
caps while jiggling things around.

Orphaned web page, not yet ready for prime time, has a recording of it
playing through a table radio.

http://flipperhome.dyndns.org/Beamus.htm

But the smartest arses (aussies of course, he-he!) put their AM transmitters
in the vintage radio cabinets.
http://www.ebay.com.au/itm/140770446...84.m1555.l2649



Interesting you bring that up because it was my original 'cost saver'
idea before the UHF converters and I even bought a supposedly non
working Philips radio to use. Turned out the radio only needed one
tube, which I had. It could also use a recap but it's in good enough
shape I didn't have the heart to scavenge it.

I might resurrect the idea for the air variable and dial indicator but
the biggest problem is I want power transformer isolation and most
don't have one (at least not the AA5s), nor 'extra room' to fit one. I
notice that Little Nipper does but it's 240 VAC.

I think my 2 bucks 2 tube Beamus scope shot looks as good as his 5
tube job

[Alex Pogossov]

"flipper" wrote in message
...
On Mon, 11 Jun 2012 12:50:03 +1000, "Alex Pogossov"
wrote:


"flipper" wrote in message
. ..
Okay, so I like to make up cutesy names

I wanted to do 'something' with a 6ME8 so I tried using it for an AM
transmitter and the first prototype works rather well. Bandwidth is
'too much', less than 1 dB down at 18 KHz, but we'll worry about that
later.

This is a 'dollar days' special, 2 whole bucks worth of tubes, and L2
is a UHF converter coil scramble rewound, so that was 'free'. Power
supply is from the same converter and if the remaining issues get
worked out it'll probably end up in that cabinet as well (but where to
put the air variable?).

The schematic is rough, but should be rather self explanatory, and the
ganged tuning hasn't been fleshed out yet. I'm still using separate
caps while jiggling things around.

Orphaned web page, not yet ready for prime time, has a recording of it
playing through a table radio.

http://flipperhome.dyndns.org/Beamus.htm

But the smartest arses (aussies of course, he-he!) put their AM
transmitters
in the vintage radio cabinets.
http://www.ebay.com.au/itm/140770446...84.m1555.l2649



Interesting you bring that up because it was my original 'cost saver'
idea before the UHF converters and I even bought a supposedly non
working Philips radio to use. Turned out the radio only needed one
tube, which I had. It could also use a recap but it's in good enough
shape I didn't have the heart to scavenge it.

I might resurrect the idea for the air variable and dial indicator but
the biggest problem is I want power transformer isolation and most
don't have one (at least not the AA5s), nor 'extra room' to fit one. I
notice that Little Nipper does but it's 240 VAC.

I think my 2 bucks 2 tube Beamus scope shot looks as good as his 5
tube job

Apparently, the more tubes -- the more "decent" and "professional" it might
look... But your 2-tube solution looks like gives clean modulation due to
the feedback.

However, the biggest (potential) problem of your design is frequency
instability. If you have a parasitic coupling between the aerial and the
oscillator coil, you will get the "frequency pull". If you touch the antenna
(changing the voltage on it) -- you will get a frequency shift! This pull
will also be modulated, so you will get a spurious FM. Probably acceptable
for an AM radio, but will sound crap on an SSB receiver. So your major goal
is to shield your oscillator circuit (L1, C1b and other components). And
even if you make a perfect shielding, you will not be able to completely
avoid parasitic coupling through the shaft impedance of the dual gang
variable capacitor.

[flipper]

On Mon, 11 Jun 2012 14:16:59 +1000, "Alex Pogossov"
wrote:


"flipper" wrote in message

I think my 2 bucks 2 tube Beamus scope shot looks as good as his 5
tube job

Apparently, the more tubes -- the more "decent" and "professional" it might
look... But your 2-tube solution looks like gives clean modulation due to
the feedback.

Yep, NFB is the key to getting g1 linear. I did the same thing on my
reactance tube FM transmitter. And the Twin Triode Transmitter, come
to think of it.

For not being an 'RF guy' I sure have done a lot of RF lately.

However, the biggest (potential) problem of your design is frequency
instability. If you have a parasitic coupling between the aerial and the
oscillator coil, you will get the "frequency pull". If you touch the antenna
(changing the voltage on it) -- you will get a frequency shift! This pull
will also be modulated, so you will get a spurious FM. Probably acceptable
for an AM radio, but will sound crap on an SSB receiver. So your major goal
is to shield your oscillator circuit (L1, C1b and other components). And
even if you make a perfect shielding, you will not be able to completely
avoid parasitic coupling through the shaft impedance of the dual gang
variable capacitor.


That sounds a lot like the old joke "Doc, it hurts when I poke a stick
in my eye, What should I do about that?

Don't poke a stick in your eye."

Don't touch the antenna.

I do intend to shield the LO and, for cost reasons, dropping the gang
tuning idea. (Maybe I should blame it on a 'bean counter', eh?)

There's been a revision. The 70 uH was low and the scramble wind on a
UHF core not so hot, which was causing low plate swing. So I've now
gone to a 250 uH ferrite rod antenna for the plate load and am getting
80 Vpp at idle. And, good as it was, modulation depth also improved.
It's now so close to 100% you can't tell the difference unless you
blow the scale up.

Looks to me like this one is a winner but, of course, I'm a bit biased


Revised schematic is posted http://flipperhome.dyndns.org/Beamus.htm

[Patrick Turner]

On Jun 11, 12:50*pm, "Alex Pogossov" wrote:
"flipper" wrote in message

...





Okay, so I like to make up cutesy names

I wanted to do 'something' with a 6ME8 so I tried using it for an AM
transmitter and the first prototype works rather well. Bandwidth is
'too much', less than 1 dB down at 18 KHz, but we'll worry about that
later.

This is a 'dollar days' special, 2 whole bucks worth of tubes, and L2
is a UHF converter coil scramble rewound, so that was 'free'. Power
supply is from the same converter and if the remaining issues get
worked out it'll probably end up in that cabinet as well (but where to
put the air variable?).

The schematic is rough, but should be rather self explanatory, and the
ganged tuning hasn't been fleshed out yet. I'm still using separate
caps while jiggling things around.

Orphaned web page, not yet ready for prime time, has a recording of it
playing through a table radio.

http://flipperhome.dyndns.org/Beamus.htm

But the smartest arses (aussies of course, he-he!) put their AM transmitters
in the vintage radio cabinets.http://www.ebay.com.au/itm/140770446...ELX:IT&_tr...- Hide quoted text -

- Show quoted text -

Hmm, I must qualify as a dumb-ass aussie because I've not tried to
make an AM transmitter in such a nice package, all kinda trick stuff.
But you know, I recall that while I studied FM tube radios so I could
service them properly in 1995, I mentioned production of an FM test
signal by means of a reactance tube FM modulator to a bunch of radio
enthusiasts at a ham gathering one evening to see if they had any
schematics or knowhow. None did, and one said "Mate, waddia wanna vary
frequency for? We jus wanna keep the frequency stable, eh..." Well,
OK, they were stuck back in 1955, most were over 70 in 1995. Now most
are dead, and I'm still lingering with audio F stuff, having
farnarkled muchly with RF home brew testorator checker thingies.
But I was about 15 when I made my own transmitter out of an existing
old radio set. I got my sister to talk into the crystal mike while
walked up the street to see how far it broadcast, using my mum's new
Japanese 9 transistor portable. After I'd gone about 1/4 mile dear
sister starts saying "This is the illegal broadcast by Patrick Turner
from No ----- street....." and then I qualified for the Olympics 400M
getting back home to shut the sister up. Females can be cheeky, and
sis was no exception.

I have an idea to make another modulator which might work merely by
having 3 cascaded variable µ pentodes, each contributing about 30% AM.
maybe it works, maybe it don't, but it'll have to wait until so many
other things more worthwhile are completed.

In Canberra we get ABC Radio National on 845kHz AM with AF BW allowed
to be 9kHz, so my AM radio has 10kHz BW using variable selectivity in
the 1st IFT by varying the distance between the coils. But one could
always use the Internet to get the podcasts at
http://www.abc.net.au/radionational/podcasts/program/
And you just subscribe. In many places RN is broadcast on FM, and now
in digital stations.

So I guess one could tune into RN on the digital and use the audio to
modulate a carrier for the AM radio to pick up, and that should sound
better than if one tries to pick up the local AM radio station pumping
out 5kW, and only 4km away.

Just don't ask me to describe how digital radio works. I looked for
radio schematics and found none, seems like secret business nobody
wants me to know, but seems like the digital band is at UHF or around
250MHz, and just what the wave forms look like I don't know.

Patrick Turner.

[John Byrns]

In article ,
flipper wrote:

Okay, so I like to make up cutesy names

I wanted to do 'something' with a 6ME8 so I tried using it for an AM
transmitter and the first prototype works rather well. Bandwidth is
'too much', less than 1 dB down at 18 KHz, but we'll worry about that
later.

This is a 'dollar days' special, 2 whole bucks worth of tubes, and L2
is a UHF converter coil scramble rewound, so that was 'free'. Power
supply is from the same converter and if the remaining issues get
worked out it'll probably end up in that cabinet as well (but where to
put the air variable?).

The schematic is rough, but should be rather self explanatory, and the
ganged tuning hasn't been fleshed out yet. I'm still using separate
caps while jiggling things around.

Orphaned web page, not yet ready for prime time, has a recording of it
playing through a table radio.

http://flipperhome.dyndns.org/Beamus.htm

Hi Flipper,

Dropping the ganged capacitor was probably a good idea, if it was a
superheterodyne capacitor there was probably no way you could have made it track
correctly. Did you ever think of using a crystal in the oscillator circuit,
that way there would be only one tuning adjustment? What is the potentiometer
in the oscillator screen circuit all about, what is the criterion for adjusting
it?

You state that 80 Vpp on the plate equates to about 35 mW, how did you calculate
that?

--
Regards,

John Byrns

Surf my web pages at, http://fmamradios.com/

[flipper]

On Wed, 13 Jun 2012 15:48:48 -0500, John Byrns
wrote:

In article ,
flipper wrote:

Okay, so I like to make up cutesy names

I wanted to do 'something' with a 6ME8 so I tried using it for an AM
transmitter and the first prototype works rather well. Bandwidth is
'too much', less than 1 dB down at 18 KHz, but we'll worry about that
later.

This is a 'dollar days' special, 2 whole bucks worth of tubes, and L2
is a UHF converter coil scramble rewound, so that was 'free'. Power
supply is from the same converter and if the remaining issues get
worked out it'll probably end up in that cabinet as well (but where to
put the air variable?).

The schematic is rough, but should be rather self explanatory, and the
ganged tuning hasn't been fleshed out yet. I'm still using separate
caps while jiggling things around.

Orphaned web page, not yet ready for prime time, has a recording of it
playing through a table radio.

http://flipperhome.dyndns.org/Beamus.htm

Hi Flipper,

Dropping the ganged capacitor was probably a good idea, if it was a
superheterodyne capacitor there was probably no way you could have made it track
correctly. Did you ever think of using a crystal in the oscillator circuit,
that way there would be only one tuning adjustment?

I wanted the frequency, at least some degree, tunable.

What is the potentiometer
in the oscillator screen circuit all about,

That adjusts osc RF amplitude to the deflector plates.

what is the criterion for adjusting
it?

I'm still pondering that a bit but current procedure is to run it up
to near max mod and adjust for maximum peak to peak.

You state that 80 Vpp on the plate equates to about 35 mW, how did you calculate
that?

That's guesstimated EI across the plate load.

[Patrick Turner]

On Monday, 11 June 2012 03:39:00 UTC+10, flipper wrote:
Okay, so I like to make up cutesy names

I wanted to do 'something' with a 6ME8 so I tried using it for an AM
transmitter and the first prototype works rather well. Bandwidth is
'too much', less than 1 dB down at 18 KHz, but we'll worry about that
later.

This is a 'dollar days' special, 2 whole bucks worth of tubes, and L2
is a UHF converter coil scramble rewound, so that was 'free'. Power
supply is from the same converter and if the remaining issues get
worked out it'll probably end up in that cabinet as well (but where to
put the air variable?).

The schematic is rough, but should be rather self explanatory, and the
ganged tuning hasn't been fleshed out yet. I'm still using separate
caps while jiggling things around.

Orphaned web page, not yet ready for prime time, has a recording of it
playing through a table radio.

http://flipperhome.dyndns.org/Beamus.htm

I couldn't download Fliper's page above on his transmitter last week but can now, and the circuit looks well. Possibly some improvement could be to used cathode followers to drive each beam delctor plate.

If he has 35mW and say 50Vrms anode signal at antenna output, then
0.035 = 50 x 50 / RL so RL = 71kohms. This is rather high but the tuned tank circuit probably has such a high Z at Fo.
The comments made about coils are of interest, and it should make no difference what type of core is used, because 270uH is easy to achieve with many recipes. But in the best old radios the 455kHz and MW RF coils are pie wound windings using litz wire and large Al cans to keep the Q high, ie, RF resistance low. In an AM receiver I built from scratch in 1999, I made copper cans for two RF input coils and I wound solid wire on 50mm long x 10mm dia pieces of ferrite rod normally used for ferrite rod antennas. The Q became higher than using air cored windings on say 20mm PVC pipes. In my receiver, the Q was so high the BW was less than 15kHz, giving slight cutting of sidebands and thus reducing possible audio BW, so I used TWO such coils, and a 3 gang cap, with 2 gands devoted to the the two RF coild and the other to the oscillator. To overcome the reduction of BW, I used antenna input to a tap on one coil, then a resistor from top of coil to top of next coil and then I tuned the coils so they were "stagger tuned", ie, slightly apart at the low end of the band where the LC Q is higher than at above say 1.2MHz. All that worked well, but compact fluorescent lamps and other junk creates a rectified version of incoming RF and I've had to change to a long rod ferrite antenna with a shielded coil and very short wires to keep out electrostatic portion of RF wave.

In my RF generator which I could use as transmitter, I get the same very nice AM wave on the CRO as Flipper's site shows. I have a 6BX6 for the RF output tube, and the coil is a hand wound thing on ferrite with 3 layers of not very tightly wound windings of solid wire, and with PVC tape used between layers. The self capacitance of the coil must be kept low if you wish to be able to tune the tank to as high as possible, say 1,750kHz.
Many old radios went from 550kHz to maybe 1,550kHz, a 3 fold F increase. Say you have 20pF for coil self C, then if the cap gang = 365pF max, then total max C = 385pF. Say the coil turns or ferrite position adjusted for Fo = 530kHz, then L must be 234uH. Say the C gang min C = 25pF, and you have 20pF self C
then Cmin total = 45pF which gives Fo = 1,551kHz, and not as high as anyone should accept. If C minimum could be reduced to 22.5pF, Fo = 2,194kHz, but you will never see this, and besides, one has to be able to use a trimmer cap to set the top of the F range. So the less stray C or coil self C, the better.

Keep the coil cans as big as possible, and never use iron cans.

Patrick Turner.

[flipper]

On Thu, 14 Jun 2012 22:23:29 -0700 (PDT), Patrick Turner
wrote:

On Monday, 11 June 2012 03:39:00 UTC+10, flipper wrote:
Okay, so I like to make up cutesy names

I wanted to do 'something' with a 6ME8 so I tried using it for an AM
transmitter and the first prototype works rather well. Bandwidth is
'too much', less than 1 dB down at 18 KHz, but we'll worry about that
later.

This is a 'dollar days' special, 2 whole bucks worth of tubes, and L2
is a UHF converter coil scramble rewound, so that was 'free'. Power
supply is from the same converter and if the remaining issues get
worked out it'll probably end up in that cabinet as well (but where to
put the air variable?).

The schematic is rough, but should be rather self explanatory, and the
ganged tuning hasn't been fleshed out yet. I'm still using separate
caps while jiggling things around.

Orphaned web page, not yet ready for prime time, has a recording of it
playing through a table radio.

http://flipperhome.dyndns.org/Beamus.htm

I couldn't download Fliper's page above on his transmitter last week

Sorry about that. Every once in a while the servers is offline for
various reasons.

but can now, and the circuit looks well.

Thanks.

Must say I'm rather pleased with the deep mod and excellent bandwidth
using only two 1 buck tubes.

Possibly some improvement could be to used cathode followers to drive each beam delctor plate.

Well, as is, there isn't a signal to put into a CF for the other
deflector plate. They're being driven single ended.

I've considered that driving the deflectors with a PP transformer
might improve RF harmonics, and maybe a CF to drive it's primary, but
I think it might be possible to simply wind a PP secondary on the osc
coil. However, I'm not convinced it's worth the added complexity.


If he has 35mW and say 50Vrms anode signal at antenna output, then
0.035 = 50 x 50 / RL so RL = 71kohms. This is rather high but the tuned tank circuit probably has such a high Z at Fo.

That's 80 volts peak to peak (Vpp) so RMS is 28 V. Guesstimating
1.25mA gives the 35 mW figure and resonant impedance around 22.4 k but
I think the current guess was a tad high so impedance is probably a
bit higher.

The comments made about coils are of interest, and it should make no difference what type of core is used, because 270uH is easy to achieve with many recipes.

I don't know why you say that. It isn't a matter of 'achieving' 250
uH, at least on an LCR meter, it's how it behaves at that frequency.
For example, I talked to Bob Weaver about that and he confirms
'switching power supply' ferrite cores (which I also tried) soak up RF
like, his words, "a sponge." Now, I don't know whether the UHF coil is
doing the same thing or exhibiting some other 'problem' at MW
frequencies but the volts weren't there.

Might perform better if I had some Litz wire but I'm using a ferrite
antenna for the coil now and AES has them for 3 bucks so it isn't
worth spending moolah on Litz when buying the thing 'ready made' is
just as cheap.

But in the best old radios the 455kHz and MW RF coils are pie wound windings using litz wire and large Al cans to keep the Q high, ie, RF resistance low. In an AM receiver I built from scratch in 1999, I made copper cans for two RF input coils and I wound solid wire on 50mm long x 10mm dia pieces of ferrite rod normally used for ferrite rod antennas. The Q became higher than using air cored windings on say 20mm PVC pipes. In my receiver, the Q was so high the BW was less than 15kHz, giving slight cutting of sidebands and thus reducing possible audio BW, so I used TWO such coils, and a 3 gang cap, with 2 gands devoted to the the two RF coild and the other to the oscillator. To overcome the reduction of BW, I used antenna input to a tap on one coil, then a resistor from top of coil to top of next coil and then I tuned the coils
so they were "stagger tuned", ie, slightly apart at the low end of the band where the LC Q is higher than at above say 1.2MHz. All that worked well, but compact fluorescent lamps and other junk creates a rectified version of incoming RF and I've had to change to a long rod ferrite antenna with a shielded coil and very short wires to keep out electrostatic portion of RF wave.

In my RF generator which I could use as transmitter, I get the same very nice AM wave on the CRO as Flipper's site shows. I have a 6BX6 for the RF output tube, and the coil is a hand wound thing on ferrite with 3 layers of not very tightly wound windings of solid wire, and with PVC tape used between layers. The self capacitance of the coil must be kept low if you wish to be able to tune the tank to as high as possible, say 1,750kHz.
Many old radios went from 550kHz to maybe 1,550kHz, a 3 fold F increase. Say you have 20pF for coil self C, then if the cap gang = 365pF max, then total max C = 385pF. Say the coil turns or ferrite position adjusted for Fo = 530kHz, then L must be 234uH. Say the C gang min C = 25pF, and you have 20pF self C
then Cmin total = 45pF which gives Fo = 1,551kHz, and not as high as anyone should accept. If C minimum could be reduced to 22.5pF, Fo = 2,194kHz, but you will never see this, and besides, one has to be able to use a trimmer cap to set the top of the F range. So the less stray C or coil self C, the better.

I don't really care what the 'top end' is as this isn't to 'test'
radios, its a broadcaster, and being able to find a 'quiet spot' on
the dial is the only reason for tuning.

The 'problem', so to speak, isn't the local osc but the plate tank
because a 10 ft wet noodle wire antenna comes in at 30 pF-35 pF before
you even get to cap minimum, stray, and coil self capacitance.

I'm not sure yet but may go to another slug coil on the plate because
even though less inductance lowers voltage swing, hence generated
power, that may be better than cap tuning because, in that case, most
of the circulating current ends up in the tuning cap rather than the
antenna.

On the other hand, I'm getting sufficient range even with closed
plates so it may be a case of "don't fix it if it ain't broke."

Btw, I've tweaked/padded values around the existing coils and caps to
avoid the irritation of being able to 'dial' a frequency you can't
peak on the antenna tank so the tuning range is now narrowed down to
roughly 600 KHz to 1100 KHz. So, now, if you can dial it you can peak
it. Basically I put 100 pF in parallel with the osc cap and lowered
the coil to 190 uH.

I'm listening to it at about 680 KHz as I type.

Keep the coil cans as big as possible, and never use iron cans.

Patrick Turner.

[John Byrns]

In article ,
flipper wrote:

Okay, so I like to make up cutesy names

I wanted to do 'something' with a 6ME8 so I tried using it for an AM
transmitter and the first prototype works rather well. Bandwidth is
'too much', less than 1 dB down at 18 KHz, but we'll worry about that
later.

This is a 'dollar days' special, 2 whole bucks worth of tubes, and L2
is a UHF converter coil scramble rewound, so that was 'free'. Power
supply is from the same converter and if the remaining issues get
worked out it'll probably end up in that cabinet as well (but where to
put the air variable?).

The schematic is rough, but should be rather self explanatory, and the
ganged tuning hasn't been fleshed out yet. I'm still using separate
caps while jiggling things around.

Orphaned web page, not yet ready for prime time, has a recording of it
playing through a table radio.

http://flipperhome.dyndns.org/Beamus.htm

Hi Flipper,

This transmitter has been bouncing around in the back of my head for the past
week because something didn't seem quite right but I couldn't put my finger on
it until this morning when I jumped out of bed.

The problem is that there is nothing wrong with the transmitter concept, except
that it doesn't take advantage of the 6ME8 in the way one might have hoped based
on your previous comments on the tube.

Applying the modulation to G1 doesn't take advantage of the beam deflection
capabilities of the tube and instead uses it in a way that a more ordinary tube,
like a dual control pentode, could serve.

Why not connect the 6ME8 cathode-grid circuit as a Hartley oscillator circuit,
as I think you have suggested in earlier posts, and connect the modulation
signal to the beam deflection plates? I suppose the downside of this scheme is
that it would require a balanced push pull RF output transformer to achieve full
modulation, and building such an RF transformer could be a non trivial project
in itself.

I forgot where you are buying your 6ME8s for a dollar apiece, could you refresh
my memory?

--
Regards,

John Byrns

Surf my web pages at, http://fmamradios.com/

[flipper]

On Mon, 18 Jun 2012 10:26:44 -0500, John Byrns
wrote:

In article ,
flipper wrote:

Okay, so I like to make up cutesy names

I wanted to do 'something' with a 6ME8 so I tried using it for an AM
transmitter and the first prototype works rather well. Bandwidth is
'too much', less than 1 dB down at 18 KHz, but we'll worry about that
later.

This is a 'dollar days' special, 2 whole bucks worth of tubes, and L2
is a UHF converter coil scramble rewound, so that was 'free'. Power
supply is from the same converter and if the remaining issues get
worked out it'll probably end up in that cabinet as well (but where to
put the air variable?).

The schematic is rough, but should be rather self explanatory, and the
ganged tuning hasn't been fleshed out yet. I'm still using separate
caps while jiggling things around.

Orphaned web page, not yet ready for prime time, has a recording of it
playing through a table radio.

http://flipperhome.dyndns.org/Beamus.htm

Hi Flipper,

This transmitter has been bouncing around in the back of my head for the past
week because something didn't seem quite right but I couldn't put my finger on
it until this morning when I jumped out of bed.

The problem is that there is nothing wrong with the transmitter concept, except
that it doesn't take advantage of the 6ME8 in the way one might have hoped based
on your previous comments on the tube.

Applying the modulation to G1 doesn't take advantage of the beam deflection
capabilities of the tube and instead uses it in a way that a more ordinary tube,
like a dual control pentode, could serve.

A DC pentode might work similar but I'm not sure the plate/screen
current transfer is as balanced as the 6ME8 deflection plates. I
wondered about that, though, but the final deciding factor was 'non
technical': I wanted to use a 6ME8

Might be interesting to try because I'd think it would take less RF
amplitude but, ironically, it looks like a DC pentode might pull more
B+, even without 'wasting' the 6ME8 plate two power, because it's
screen pulls so much current. It also looks like the 6ME8 might have
better plate impedance but it's hard to tell because there are no
plate curves down at the relatively low voltages it's being run on.

Why not connect the 6ME8 cathode-grid circuit as a Hartley oscillator circuit,
as I think you have suggested in earlier posts, and connect the modulation
signal to the beam deflection plates? I suppose the downside of this scheme is
that it would require a balanced push pull RF output transformer to achieve full
modulation, and building such an RF transformer could be a non trivial project
in itself.

That was my first thought too although you may be remembering the FM
stereo multiplex discussion, where we needed DSB-SC output, because I
think that's the only one I posted a (conceptual) schematic for.

However, unbalancing the deflectors and then 'subtracting' one plate
from the other via a PP transformer was, indeed, what I proposed to
Patrick for the '100% mod' solution back when he was tinkering with an
AM modulator for, I think, 'testing' AM radios. I did wonder, in that
discussion, what the effect of the 'extra' side bands might be. I
mean, you have, in essence, DSB with 'partially suppressed carrier'. I
may still try that some day but, yes, the PP RF transformer kind of
put me off and I'm glad I tried this one first because of what I
learned: the pot core I bought for that very idea, and would have
used, wouldn't have worked well at all.

The other 'advantage' would be self excite but everyone keeps telling
me "don't do it." Self excite 'FMs'.

It could also be done 'single ended' but then you have large audio
swing required and deflector 'non-linearity at the extremes with no
'simple' means of NFB.

So, this topology was picked because it seemed 'simpler', reduced the
number of "never done this before" things that could go Murphy's Law
wrong, and required no 'special' parts. Doubly so because I already
had them.

I forgot where you are buying your 6ME8s for a dollar apiece, could you refresh
my memory?

ABC vacuum tubes and ESRC1 vacuum tubes (which seem like maybe they're
the same people). Both sites have a perennial !dollar days! section,
which says qty 10 minimum but I've also been able to get a few tossed
in when buying others at 'normal' price. However, since those are
'normally' $3 (occasionally $4, as with the 6ME8) you really only have
to want '4' (maybe 3), and get 'extras' to make up 10, to come out
ahead.

vacuumtubes.net has no !dollar days! section but pretty much the same
tubes simply listed for 1 buck in their normal price lists, but I've
never tried ordering from them. I normally use ABC, mainly out of
habit.

[John Byrns]

In article ,
flipper wrote:

On Mon, 18 Jun 2012 10:26:44 -0500, John Byrns
wrote:

Why not connect the 6ME8 cathode-grid circuit as a Hartley oscillator
circuit,
as I think you have suggested in earlier posts, and connect the modulation
signal to the beam deflection plates? I suppose the downside of this scheme
is
that it would require a balanced push pull RF output transformer to achieve
full
modulation, and building such an RF transformer could be a non trivial
project
in itself.

That was my first thought too although you may be remembering the FM
stereo multiplex discussion, where we needed DSB-SC output, because I
think that's the only one I posted a (conceptual) schematic for.

However, unbalancing the deflectors and then 'subtracting' one plate
from the other via a PP transformer was, indeed, what I proposed to
Patrick for the '100% mod' solution back when he was tinkering with an
AM modulator for, I think, 'testing' AM radios. I did wonder, in that
discussion, what the effect of the 'extra' side bands might be. I
mean, you have, in essence, DSB with 'partially suppressed carrier'. I
may still try that some day but, yes, the PP RF transformer kind of
put me off and I'm glad I tried this one first because of what I
learned: the pot core I bought for that very idea, and would have
used, wouldn't have worked well at all.

The other 'advantage' would be self excite but everyone keeps telling
me "don't do it." Self excite 'FMs'.

Would "FMing" actually occur with a "Self excited" oscillator built with a beam
deflection tube, or would the grid-cathode oscillator circuit be isolated from
modulation effects that would cause "FMing", by the construction of the beam
deflection tube? Since the sum of the plate currents for both plates remains
constant with modulation applied to the beam deflection electrodes, I would
think that the cathode-grid oscillator circuit wouldn't even see the modulation
applied to the deflection electrodes. G3, the accelerating electrode probably
provides further isolation between the oscillator and modulation effects.

The 6SA7/6BE6/6SC6 family of heptodes would also seem to provide isolation
between a cathode-grid "self excited" oscillator circuit and modulation applied
to G3 as the total cathode current appears to be largely independent of the
voltage on G3, minimizing "FMing". If this weren't the case, the local
oscillator frequency, in an AM receiver using one of these tubes, would vary
with changes in the AGC voltage due to fading.

Both of these schemes differ from the common phono oscillator circuit in that
they require two tuned circuits, one for the oscillator and a second for the
plate circuit feeding the antenna, the plate current can be completely cut off,
neglecting leakage and so forth, without affecting the oscillator circuit to any
great extent. The single tuned circuit approach of the common phono oscillator
circuit would have a greater sensitivity to "FMing", and the oscillator dies
completely when the plate current is cut off.

--
Regards,

John Byrns

Surf my web pages at, http://fmamradios.com/

[flipper]

On Sun, 24 Jun 2012 15:59:48 -0500, John Byrns
wrote:

In article ,
flipper wrote:

The other 'advantage' would be self excite but everyone keeps telling
me "don't do it." Self excite 'FMs'.

Would "FMing" actually occur with a "Self excited" oscillator built with a beam
deflection tube, or would the grid-cathode oscillator circuit be isolated from
modulation effects that would cause "FMing", by the construction of the beam
deflection tube? Since the sum of the plate currents for both plates remains
constant with modulation applied to the beam deflection electrodes, I would
think that the cathode-grid oscillator circuit wouldn't even see the modulation
applied to the deflection electrodes. G3, the accelerating electrode probably
provides further isolation between the oscillator and modulation effects.

The 6SA7/6BE6/6SC6 family of heptodes would also seem to provide isolation
between a cathode-grid "self excited" oscillator circuit and modulation applied
to G3 as the total cathode current appears to be largely independent of the
voltage on G3, minimizing "FMing". If this weren't the case, the local
oscillator frequency, in an AM receiver using one of these tubes, would vary
with changes in the AGC voltage due to fading.

Both of these schemes differ from the common phono oscillator circuit in that
they require two tuned circuits, one for the oscillator and a second for the
plate circuit feeding the antenna, the plate current can be completely cut off,
neglecting leakage and so forth, without affecting the oscillator circuit to any
great extent. The single tuned circuit approach of the common phono oscillator
circuit would have a greater sensitivity to "FMing", and the oscillator dies
completely when the plate current is cut off.

Well, your logic is pretty much what mine was, plus the same 'constant
current' theory applying to dual control pentodes as well, but over at
radiomuseum (plus others) I read an exhaustive thread where the poster
said "will NEVER try THAT again." I can't find the link off hand.

He did try to theorize some kind of miller interaction but was vague
enough that I couldn't quite follow the logic. He also dealt with your
idea 'that can't be' or else a typical radio wouldn't work right. His
argument was the only reason it did work was the small RF levels and
LO carrier being suppressed.

Anyhow, everyone tells me don't do it but I might try anyway

As for the 6ME8, I thought, like you, cathode current should be
'constant' since the 'beam' is just being 'deflected' to the two
plates but was surprised to find gobs of RF on the cathode. I guess
the modest deflector bias, which is changing with RF, does affect it.
Maybe it wouldn't if I drove both.

Btw, my instinct was to 'clean it up' but that made things worse so I
finally decided to not try 'fixing' what ain't broke.

I'm also going to try the DC pentode because, like you said, it seems
to me that ought to work about the same.

[flipper]

On Sun, 24 Jun 2012 19:01:43 -0500, flipper wrote:

On Sun, 24 Jun 2012 15:59:48 -0500, John Byrns
wrote:

In article ,
flipper wrote:

The other 'advantage' would be self excite but everyone keeps telling
me "don't do it." Self excite 'FMs'.

Would "FMing" actually occur with a "Self excited" oscillator built with a beam
deflection tube, or would the grid-cathode oscillator circuit be isolated from
modulation effects that would cause "FMing", by the construction of the beam
deflection tube? Since the sum of the plate currents for both plates remains
constant with modulation applied to the beam deflection electrodes, I would
think that the cathode-grid oscillator circuit wouldn't even see the modulation
applied to the deflection electrodes. G3, the accelerating electrode probably
provides further isolation between the oscillator and modulation effects.

The 6SA7/6BE6/6SC6 family of heptodes would also seem to provide isolation
between a cathode-grid "self excited" oscillator circuit and modulation applied
to G3 as the total cathode current appears to be largely independent of the
voltage on G3, minimizing "FMing". If this weren't the case, the local
oscillator frequency, in an AM receiver using one of these tubes, would vary
with changes in the AGC voltage due to fading.

Both of these schemes differ from the common phono oscillator circuit in that
they require two tuned circuits, one for the oscillator and a second for the
plate circuit feeding the antenna, the plate current can be completely cut off,
neglecting leakage and so forth, without affecting the oscillator circuit to any
great extent. The single tuned circuit approach of the common phono oscillator
circuit would have a greater sensitivity to "FMing", and the oscillator dies
completely when the plate current is cut off.

Well, your logic is pretty much what mine was, plus the same 'constant
current' theory applying to dual control pentodes as well, but over at
radiomuseum (plus others) I read an exhaustive thread where the poster
said "will NEVER try THAT again." I can't find the link off hand.

He did try to theorize some kind of miller interaction but was vague
enough that I couldn't quite follow the logic. He also dealt with your
idea 'that can't be' or else a typical radio wouldn't work right. His
argument was the only reason it did work was the small RF levels and
LO carrier being suppressed.

Anyhow, everyone tells me don't do it but I might try anyway

As for the 6ME8, I thought, like you, cathode current should be
'constant' since the 'beam' is just being 'deflected' to the two
plates but was surprised to find gobs of RF on the cathode. I guess
the modest deflector bias, which is changing with RF, does affect it.
Maybe it wouldn't if I drove both.

Btw, my instinct was to 'clean it up' but that made things worse so I
finally decided to not try 'fixing' what ain't broke.

I'm also going to try the DC pentode because, like you said, it seems
to me that ought to work about the same.

I found the page.

http://www.radiomuseum.org/forum/gra...ansmitter.html

Down at the bottom, "The sharp-cutoff heptode solution" by Jacob
Roschy. His second circuit is "The cathode oscillator attempt." "Since
this resulted simultaneously with the desired amplitude modulation
into a strong undesired frequency modulation, I abandoned this
experiment and scrapped this circuit very soon, I will never try this
any more !"

[Alex Pogossov]

"John Byrns" wrote in message
...

The 6SA7/6BE6/6SC6 family of heptodes would also seem to provide isolation
between a cathode-grid "self excited" oscillator circuit and modulation
applied
to G3 as the total cathode current appears to be largely independent of
the
voltage on G3, minimizing "FMing". If this weren't the case, the local
oscillator frequency, in an AM receiver using one of these tubes, would
vary
with changes in the AGC voltage due to fading.

Of these tubes only 6CS6 (not 6SC6) is suitable as it has sharp cut-off on
G3.
With 6BE6 it is almost impossible to cut it off completely, so 100%
modulation os impossible, and deep modulatio will be distorted, even with
feedback.

By the way, in this case NFB shall be applied from the plate of a heptode,
not from its cathode.

It is better to use a separate oscillator and geef it to G3 of a heptode,
while feeding audio to G1. In this case any heptode can be used. NFB can be
taken from the cathode since plate current is *sort of* proportional to
cathode current. Do not forget to decouple G2+G4 to cathode (!), not to GND
and use a large electrolytic for passing AF as well, not RF only. But still
it is better to take NFB from the plate (I mean AF component, not RF).

Even in a best heptode, even with a separate oscillator you will have
residual FM -- due to space charge and stray capacitances. A small FM of say
100...1000Hz is acceptable for listening on an AM radio, but will not be
listenable on a synchrodyne or an SSB receiver.


Both of these schemes differ from the common phono oscillator circuit in
that
they require two tuned circuits, one for the oscillator and a second for
the
plate circuit feeding the antenna, the plate current can be completely cut
off,
neglecting leakage and so forth, without affecting the oscillator circuit
to any
great extent. The single tuned circuit approach of the common phono
oscillator
circuit would have a greater sensitivity to "FMing", and the oscillator
dies
completely when the plate current is cut off.

--
Regards,

John Byrns

Surf my web pages at, http://fmamradios.com/

[flipper]

On Mon, 25 Jun 2012 19:36:07 +1000, "Alex Pogossov"
wrote:


"John Byrns" wrote in message
...

The 6SA7/6BE6/6SC6 family of heptodes would also seem to provide isolation
between a cathode-grid "self excited" oscillator circuit and modulation
applied
to G3 as the total cathode current appears to be largely independent of
the
voltage on G3, minimizing "FMing". If this weren't the case, the local
oscillator frequency, in an AM receiver using one of these tubes, would
vary
with changes in the AGC voltage due to fading.

Of these tubes only 6CS6 (not 6SC6) is suitable as it has sharp cut-off on
G3.
With 6BE6 it is almost impossible to cut it off completely, so 100%
modulation os impossible, and deep modulatio will be distorted, even with
feedback.

By the way, in this case NFB shall be applied from the plate of a heptode,
not from its cathode.

Yes, audio to G3 is the most common implementation with people looking
to the G3 curve for linearity, which is why dual control pentodes seem
to be the preferred choice. For one, as you mentioned, the 6CS6 is one
of the few sharp heptodes, the ECH84 being the only other one I can
think of off hand, and there's more DC pentode choices. Second, the
dual control pentode G3 'linear' region remains relatively constant
over bias while the 6CS6 cutoff region shifts with screen volts and
bias.. That makes the DC pentode easier to bias.

There's a ton of Dual Control Pentode AM broadcaster schematics online
and I've breadboarded a couple of them. In fact, my LO was originally
developed for a 6GY6 version using a 1 MHz brick osc.

It is better to use a separate oscillator and geef it to G3 of a heptode,
while feeding audio to G1. In this case any heptode can be used. NFB can be
taken from the cathode since plate current is *sort of* proportional to
cathode current. Do not forget to decouple G2+G4 to cathode (!), not to GND
and use a large electrolytic for passing AF as well, not RF only. But still
it is better to take NFB from the plate (I mean AF component, not RF).

This, using a dual control pentode, is what John was suggesting as an
alternate to my 'Beamus' 6ME8 modulator. It does seem like it ought to
work similarly.

I managed to get a dual control pentode (6HZ6) model working with
Circuitmaker, although I'm not sure how 'good' it is. At any rate, it
seems to not like going over 80%, or so, mod. Can't drive it to near
cutoff. Another thing, input impedance to G3 seems incredibly low, at
least at RF, and, if the simulation is even remotely accurate, there's
no way my LO can drive it.

Both those 'problem's may be the model, so I'll probably try building
it anyway, but if the simulation is valid then the 6ME8 works quite a
bit better.

Even in a best heptode, even with a separate oscillator you will have
residual FM -- due to space charge and stray capacitances. A small FM of say
100...1000Hz is acceptable for listening on an AM radio, but will not be
listenable on a synchrodyne or an SSB receiver.

I'm curious how space charge makes it across to a separate LO.
Modulating grid capacitance, which is coupled to the LO tank?


Both of these schemes differ from the common phono oscillator circuit in
that
they require two tuned circuits, one for the oscillator and a second for
the
plate circuit feeding the antenna, the plate current can be completely cut
off,
neglecting leakage and so forth, without affecting the oscillator circuit
to any
great extent. The single tuned circuit approach of the common phono
oscillator
circuit would have a greater sensitivity to "FMing", and the oscillator
dies
completely when the plate current is cut off.

--
Regards,

John Byrns

Surf my web pages at, http://fmamradios.com/

[Patrick Turner]

On 19 June, 01:26, John Byrns wrote:
In article ,





*flipper wrote:
Okay, so I like to make up cutesy names

I wanted to do 'something' with a 6ME8 so I tried using it for an AM
transmitter and the first prototype works rather well. Bandwidth is
'too much', less than 1 dB down at 18 KHz, but we'll worry about that
later.

This is a 'dollar days' special, 2 whole bucks worth of tubes, and L2
is a UHF converter coil scramble rewound, so that was 'free'. Power
supply is from the same converter and if the remaining issues get
worked out it'll probably end up in that cabinet as well (but where to
put the air variable?).

The schematic is rough, but should be rather self explanatory, and the
ganged tuning hasn't been fleshed out yet. I'm still using separate
caps while jiggling things around.

Orphaned web page, not yet ready for prime time, has a recording of it
playing through a table radio.

http://flipperhome.dyndns.org/Beamus.htm

Hi Flipper,

This transmitter has been bouncing around in the back of my head for the past
week because something didn't seem quite right but I couldn't put my finger on
it until this morning when I jumped out of bed.

The problem is that there is nothing wrong with the transmitter concept, except
that it doesn't take advantage of the 6ME8 in the way one might have hoped based
on your previous comments on the tube.

Applying the modulation to G1 doesn't take advantage of the beam deflection
capabilities of the tube and instead uses it in a way that a more ordinary tube,
like a dual control pentode, could serve.

Why not connect the 6ME8 cathode-grid circuit as a Hartley oscillator circuit,
as I think you have suggested in earlier posts, and connect the modulation
signal to the beam deflection plates? *I suppose the downside of this scheme is
that it would require a balanced push pull RF output transformer to achieve full
modulation, and building such an RF transformer could be a non trivial project
in itself.

A balanced RF tranny that is tuned requires coil with more turns on
the same core to get twice the inductance, fairly easy if you start
with a ferrite rod.
I'd probably say the best wire for low capacitance of the coil is
solid telephone hook up wire, or strands taken from a cat5 cable.
You then need two tuning gangs, 20-365pF are OK. The cap frame and
moving plates are at 0V and if you want to avoid B+ across the tuning
caps, then cap frame is bolted to chassis and 0.1uF caps from coil to
fixed plates. Maybe put 2M2 from fised plates to 0V to bias them down.
This allows you to have a 3 gang cap and use one gang for the
oscillator coil.

The old HP606 I have has this sort of set up. It used 6B4 to cathode
modulate a pair of 6CL6. Oscillator is PP type using maybe 12AT7, I
forget, but its designed for many ranges from 300kHz to 65MHz, all
with well calibrated dial. The whole thing has very high electro-
mechanical integrity; must have cost a huge amount in 1955. Its got
NFB around the modulator to make the AM more linear. But my home brew
SE pentode modulator also works just as well for 2 bands up to 1.7MHz
so I can test the BC band or any IF channel. I don't need the more
complex HP PP circuit. I can't see any problem having NFB around ANY
form of AM modulator because whatever triode is used to as a modulator
can be one of a pair of triodes in an LTP with TWO input ports, and
one port is for the detected AF NFB signal, and the other is for AF
input, so the modulator amplifies the difference between input and FB
signal and applies a correction signal at the output.
Such an LTP for an SE modulator isn't really a pair, because you only
need one anode's output with the other anode grounded via electro cap.
But the two available output could be used for a PP modulator.

I forgot where you are buying your 6ME8s for a dollar apiece, could you refresh
my memory?

What other beam deflector tubes are usable?

BTW John, be careful jumping out of bed. Lotsa guys come to grief that
way :-).

Patrick Turner.