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John L Stewart John L Stewart is offline
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Aw Yes, the wondrous Wobulator!

Patrick mentioned a very useful piece of test equipment. I built one around 1956 to be used to align IF Transformers in AM receivers. To avoid the mess of mechanically wobulating, the circuit used a reactance modulator.

Tuneable over the range of 450 to 475 KHz with a regular variable cap to go to the IF center frequency, the reactance circuit driven by a handy sine or triangular wave oscillator did the rest.

The sine wave also drove the X-axis of a scope rather than the internal timebase. A plug-in slot, such as an octal socket provided a place where a crystal of say 465 KHz could be plugged in. That way a birdie showed up on the display to indicate mid-band.

The schema is long gone. Think it was published in Audio Magazine. It used a 6BA7. But I expect a search on the web would find something.

Cheers to all, John
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John L Stewart John L Stewart is offline
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Originally Posted by John L Stewart View Post
Aw Yes, the wondrous Wobulator!

Patrick mentioned a very useful piece of test equipment. I built one around 1956 to be used to align IF Transformers in AM receivers. To avoid the mess of mechanically wobulating, the circuit used a reactance modulator.

Tuneable over the range of 450 to 475 KHz with a regular variable cap to go to the IF center frequency, the reactance circuit driven by a handy sine or triangular wave oscillator did the rest.

The sine wave also drove the X-axis of a scope rather than the internal timebase. A plug-in slot, such as an octal socket provided a place where a crystal of say 465 KHz could be plugged in. That way a birdie showed up on the display to indicate mid-band.

The schema is long gone. Think it was published in Audio Magazine. It used a 6BA7. But I expect a search on the web would find something.

Cheers to all, John
Here is a tubed Wobbulator for discussion. Still haven't found the schema for the version I built way back when.

Cheers, John
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patrick-turner patrick-turner is offline
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On Thursday, 31 October 2013 12:03:54 UTC+11, John L Stewart wrote:
Aw Yes, the wondrous Wobulator! Patrick mentioned a very useful piece of test equipment. I built one around 1956 to be used to align IF Transformers in AM receivers. To avoid the mess of mechanically wobulating, the circuit used a reactance modulator. Tuneable over the range of 450 to 475 KHz with a regular variable cap to go to the IF center frequency, the reactance circuit driven by a handy sine or triangular wave oscillator did the rest. The sine wave also drove the X-axis of a scope rather than the internal timebase. A plug-in slot, such as an octal socket provided a place where a crystal of say 465 KHz could be plugged in. That way a birdie showed up on the display to indicate mid-band. The schema is long gone. Think it was published in Audio Magazine. It used a 6BA7. But I expect a search on the web would find something. Cheers to all, John +-------------------------------------------------------------------+ |Filename: KLIBAN KAT A.jpg | |Download: http://www.audiobanter.com/attachment.php?attachmentid=359| +-------------------------------------------------------------------+ -- John L Stewart


About 17 years ago I built a two band RF oscillator with 300-500kHz and 530-1,650kHz. It was limited in usefulness so I added grid modulation for AM in 6BX6RF amp. Then I added a detector and applied NFB and reduced envelope THD and increased max mod to 95% without more THD than could be expected in most radios I serviced.

But for a wobbulator, I created a saw tooth gene which altered the biasing of 8 paralleled 68V x 5W zener diodes arranged to make a vari cap which could not conduct with the 20+ Vac generated in the Hartly LC oscillator tank.
This allowed me to FM modulate the low band up to +/- 10% at centre 455kHz, and then I could see the effects of alignment as obviously as dogs balls.
It was interesting to build, and sometimes useful, but the other way to align IF of AM radios is to shunt the AGC voltage, set a low level of RF below which overloads anything, and then use 455kHz applied to the antenna with set tuned low as possible, and then adjust for max AGC voltage generated starting with IFT2 grid, then plate, then IFT1 gid then plate, then repeating 3 times to make sure you have the best. Then apply square wave AM at 50% and the square wave audio detected should show little over shoot of detector output of set.

Having done that, then use an non AM RF input to antenna at 900kHz, or away from any station frequency ( to avoid any beating or chatter ) and then use F counter to ensure IT is 455kHz, then re-tune the 4 IF coils for max Vagc.
But then the tracking must be adjusted, so then you use 550kHz RF input, and tune set to that for max agc, and adjust the RF input coil ferrite slug to change coil inductance for max Vagc.

Sets with ferrite rod antennas need to have their coil located about 1/3 the way along the rod so that inductance adjustment is done by sliding the coil slightly one way or other on the rod. Rods are directinal, and so adjustments must be done with positions kept constant.
Then set F gene to 1,600kHz, and tune set to the 1,600kHz and adjust the trim cap on the tuning gang for RF input coil so max Vagc is attained.
Then move F back to 900kHz, and Vagc should be high, between the other two values. If you have a set that was designed well and which didn't suffer during the manufacturing process, then Vagc might be say -5Vdc +/- 1V for the whole AM band. But you will be very lucky to get this, and usually you must fiddle around a lot to get the tracking correct enough for say between 650kHz and 1,200kHz, outside of which the gain of the set seems to fade because tracking cannot be got right as RDH4 says it ought to be.
Once everything is tuned optimally for most gain, maybe the darn set oscillates at part of the band causing whistles while you tune, so stagger tuning the IFTs may help, and it ma be what was done originally. Maybe put 4k7 in series with IFT1 grid coil and IF amp tube, anyway, you can sure waste much time getting AM radios to work properly.
aodbout all Agc made

As I said, tracking is rarely perfect in many AM sets. You can try to calculate L&C values you should have to get good tracking. But accurate calculations don't correspond to perfect tracking, where the tuning gang has two equal C gangs, and a series C is used for the higher F of oscillator coil. When you replace the RF coils used in AM radios with ferrite rods ( to get rid of hum modulated AM waves caused by flourescent lamps et all ), then the turns of the coil on rod must be very carefully adjusted to suit the existing vari cap gang and get good tracking.

I've never bothered to make an audio F wobbulator which would be useful for speaker testing if the change of centre F is sufficient to prevent waves reflected off room walls etc to interfere with response measurement. But one could be made using a crystal oscillator at say 100kHz, and then have a VFO which has its output with FM, and the two signals are mixed to give a difference F which is detected with diode detector, and the FM is done using RF FM techniques. Some gear was sold with this idea.

But I just use pink noise for testing speakers and a switched F BPF with Q = 12 to plot speaker response with 33 F between 20Hz and 20kHz.

So, I avoided the need of an audio F wobbulator. Nothing I ever read on the subject led me to believe I was wrong.
Patrick Turner.
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Phil Allison[_3_] Phil Allison[_3_] is offline
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Default Wobulator


"patrick-turner"


( snip 7K of self indulgent reminiscing and
wanking from an aging, retarded brick layer )


** My ****ing god, the excruciating, long running

" Turneroid Concerto for Solo Trumpet "

is reaching *megalomaniacal* proportions.

When will it ever ****ing finish ??????
--------------------------------------------


FYI:

I am just longing to hear the PT's last post.

Pun massively intended ......




..... Phil




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patrick-turner patrick-turner is offline
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Phil resounded with a near zero content post of....


"patrick-turner"
( snip 7K of self indulgent reminiscing and
wanking from an aging, retarded brick layer )
** My ****ing god, the excruciating, long running
" Turneroid Concerto for Solo Trumpet "
is reaching *megalomaniacal* proportions.
When will it ever ****ing finish ??????


Unfortunately, Phil has a limited visioin of the world, and about any of its peoples, but then all opinions are "limited" in veracity or plausuibility..

But I take issue with Phil's phrase " ** My ****ing god "

Unfortunately, despite millions of years passing since our species evolved to consider the possibility of a spirit world and a god of some sort or other, or many others, there has never been convincing demonstration by anything supernatural ever having existed. THEREFORE, how on earth does Phil's god copulate, ie, ****, root, pharque, poke etc ?

Being Sunday, and a time to consider religious matters if one wishes, then I invite Phil to talk more to us about his copulating god, and discuss the properties of the god, and of the copulation methods and details.

I am just longing to hear the PT's last post.
Pun massively intended ......

Weel keep longing, but the world moves on Phil......

Meanwhile, I have tried unsuccessfully to get a transistor based Schmitt trigger square sine wave to square wave converter to work up to 2MHz, using 3 x PN100 transistors, and produce +/-10V peak, with 20V rise time of 0.05uS, and with good symmetry and without having a huge number of R&C compensation networks and a lack of readiness to work properly above 300kHz.

Perhaps the PN100 ( said to be equalivalent to 2N2222 and many other types ) is something that is allergic to working much above 1MHz, and seems like its gain rolls off and base current increases renderig it impossible to use in the many Schmitt Trigger circuits displayed when Googling. NONE if the displayed websites have a complete circuit showing details of operation with all voltages and wave forms and the F range over which reliable operation can be had. In other words, there is a huge anount of regurgitation of basic info that is practically useless, a typical feature of how the Internet displays mostly crap that IS CRAP because most essential details are never included and test results never given.

What would Phil have us drink about Schmitt triggers? A bowl of sour and bitter un-helpful bull**** perhaps?

Now stay calm Phil, and, in your own words, and, in your own time, post something genuinely helpful, please......

Meanwhile, in the absense of anything really helpful online about trying to make square waves up to 2MHz, I'll explore what a 4093 chip will do, and maybe get a +/-3.3V pk swing which can be amplified to be +/-10Vpk, and thus match the +/- 10Vpk swing of the sine wave oscillator I just made with tubes.

The harmonic content of a square wave is well posted online and consists of fundemental sine wave and odd harmonics of the fundemental frequency, Ff. If Vf = 2MHz, then for a FAIR looking square wave we need the correct relative levels and phase of 6MHz, 10MHz, 14MHz, 18MHz. The devices which produce or amplifiy the square wave must therefore not attenuate the harmonics, and should be able to handle 10 times the Ff.
I think a PN100 is dismally incapable of what I wish it to do.

If Phil or anyone else would not wish to use a 4093, or 74LS14, what device would they use?

I do not wish to have to pioneer the use of say 2 x 6CM5 or 2 x 6CL6, EL86 etc, to make reasonably good looking square waves between 1Hz and 2MHz. The little BJTs are OK for 1Hz to say 250kHz, but beyond that they really struggle.

Patrick Turner.


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Alex Pogossov Alex Pogossov is offline
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Default Wobulator

The best square wave you can get using a CMOS Schmitt trigger. Using 74HC14
you can get about 6ns rise and fall time. If this is not enough, use more
advanced 74LVC14 -- 3ns. The above assumes the load is under 100pF.

A limitation is that you have 5V rail for the former and 3.6V rail for the
later. So the amplitude can not exceed 2.5V or 1.8V respectively. But it is
usually enough.

Another issue -- 50% duty cycle. It is possible to achieve it by using an
op-amp based bias control servo loop, or by using a high speed comparator in
front of the Schimitt trigger, e.g. MAX941 or even something more exotic if
operation above 10MHz is required.

Making Schmitt triggers of discrete transistors nowadays is laughable.

Regards,
Alex



"patrick-turner" wrote in message
...

Phil resounded with a near zero content post of....


"patrick-turner"
( snip 7K of self indulgent reminiscing and
wanking from an aging, retarded brick layer )
** My ****ing god, the excruciating, long running
" Turneroid Concerto for Solo Trumpet "
is reaching *megalomaniacal* proportions.
When will it ever ****ing finish ??????


Unfortunately, Phil has a limited visioin of the world, and about any of its
peoples, but then all opinions are "limited" in veracity or plausuibility.

But I take issue with Phil's phrase " ** My ****ing god "

Unfortunately, despite millions of years passing since our species evolved
to consider the possibility of a spirit world and a god of some sort or
other, or many others, there has never been convincing demonstration by
anything supernatural ever having existed. THEREFORE, how on earth does
Phil's god copulate, ie, ****, root, pharque, poke etc ?

Being Sunday, and a time to consider religious matters if one wishes, then I
invite Phil to talk more to us about his copulating god, and discuss the
properties of the god, and of the copulation methods and details.

I am just longing to hear the PT's last post.
Pun massively intended ......

Weel keep longing, but the world moves on Phil......

Meanwhile, I have tried unsuccessfully to get a transistor based Schmitt
trigger square sine wave to square wave converter to work up to 2MHz, using
3 x PN100 transistors, and produce +/-10V peak, with 20V rise time of
0.05uS, and with good symmetry and without having a huge number of R&C
compensation networks and a lack of readiness to work properly above 300kHz.

Perhaps the PN100 ( said to be equalivalent to 2N2222 and many other types )
is something that is allergic to working much above 1MHz, and seems like its
gain rolls off and base current increases renderig it impossible to use in
the many Schmitt Trigger circuits displayed when Googling. NONE if the
displayed websites have a complete circuit showing details of operation with
all voltages and wave forms and the F range over which reliable operation
can be had. In other words, there is a huge anount of regurgitation of basic
info that is practically useless, a typical feature of how the Internet
displays mostly crap that IS CRAP because most essential details are never
included and test results never given.

What would Phil have us drink about Schmitt triggers? A bowl of sour and
bitter un-helpful bull**** perhaps?

Now stay calm Phil, and, in your own words, and, in your own time, post
something genuinely helpful, please......

Meanwhile, in the absense of anything really helpful online about trying to
make square waves up to 2MHz, I'll explore what a 4093 chip will do, and
maybe get a +/-3.3V pk swing which can be amplified to be +/-10Vpk, and thus
match the +/- 10Vpk swing of the sine wave oscillator I just made with
tubes.

The harmonic content of a square wave is well posted online and consists of
fundemental sine wave and odd harmonics of the fundemental frequency, Ff. If
Vf = 2MHz, then for a FAIR looking square wave we need the correct relative
levels and phase of 6MHz, 10MHz, 14MHz, 18MHz. The devices which produce or
amplifiy the square wave must therefore not attenuate the harmonics, and
should be able to handle 10 times the Ff.
I think a PN100 is dismally incapable of what I wish it to do.

If Phil or anyone else would not wish to use a 4093, or 74LS14, what device
would they use?

I do not wish to have to pioneer the use of say 2 x 6CM5 or 2 x 6CL6, EL86
etc, to make reasonably good looking square waves between 1Hz and 2MHz. The
little BJTs are OK for 1Hz to say 250kHz, but beyond that they really
struggle.

Patrick Turner.


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