OK, I just had to ask this. Has anyone ever tried using big glass RF
amplifier tubes as audio amps? Maybe a tube such as the 3-500Z, which
is rated at about 500 watts of plate dissipation?

On 12 Apr 2005 10:17:31 -0700, "Billy Boy (78's Rule!)"
wrote:

OK, I just had to ask this. Has anyone ever tried using big glass RF
amplifier tubes as audio amps? Maybe a tube such as the 3-500Z, which
is rated at about 500 watts of plate dissipation?

Sure you can use it as an an audio power amp. Interesting set of
design challenges though. Anode voltage around 3000 and a current of
300mA. You will need a good output transformer. You will also need a
high power (25 watts) driver stage to feed it.

d
Pearce Consulting
http://www.pearce.uk.com

Thanks for the interesting reply, Don. Have you ever seen a pair of
3-500Z's in service in a Heathkit SB-220 RF amp? I feel that Heath
proved in the '220 that with proper design techniques, the power supply
need not cost an arm and a leg. But tell me this: would it require a
special audio transformer in order for its primary to avoid breakdown
at 3000VDC, since obviously that primary is going to be in the plate
circuit? I would like to build an audio amp like that someday, just
for fun. I've had Peter Dahl build special transformers for me in the
past. They aren't that terribly expensive.

"Billy Boy (78's Rule!)" wrote in message
oups.com...
: Thanks for the interesting reply, Don. Have you ever seen a pair of
: 3-500Z's in service in a Heathkit SB-220 RF amp? I feel that Heath
: proved in the '220 that with proper design techniques, the power supply
: need not cost an arm and a leg. But tell me this: would it require a
: special audio transformer in order for its primary to avoid breakdown
: at 3000VDC, since obviously that primary is going to be in the plate
: circuit? I would like to build an audio amp like that someday, just
: for fun. I've had Peter Dahl build special transformers for me in the
: past. They aren't that terribly expensive.
:
You need _special_ everything ! That is special wiring, sockets, transformer,
power supply capacitors, even resistors .. and forced air cooling and a hefty
filament supply. Did i mention the voltages in the circuit are absolutely deadly
?

It would be a DIY project in the same sense as making nitroglycerin in your
home lab - unless you've worked with 'lesser evils', a lot, *and* know what
you're doing,
don't even think about it !

Fun is fun,
but dead is dead
Rudy

Oh, yes, I've built high-power RF amps before. Right now I'm using an
SB-220 in my amateur station. Those 3-500-Z's are such
IMRESSIVE-looking tubes! But thanks for the warning.

"Billy Boy (78's Rule!)" wrote in message
oups.com...
: Oh, yes, I've built high-power RF amps before. Right now I'm using an
: SB-220 in my amateur station. Those 3-500-Z's are such
: IMRESSIVE-looking tubes! But thanks for the warning.

...i found myself speeding through the Ardennes one night, 100 mph or so,
at the wheel an ex-cab driver. he thought it more fun, to do that
without the headlights on..

...guess he knew what he was doing :-)
Rudy
:

"Billy Boy (78's Rule!)" wrote in message
oups.com...
OK, I just had to ask this. Has anyone ever tried using big glass RF
amplifier tubes as audio amps? Maybe a tube such as the 3-500Z, which
is rated at about 500 watts of plate dissipation?


Glass Audio 1997 (Volume 9, #1) had an article by Michael Burrows detailing
the contruction of a PP amplifier around the 4-250A beam tetrode by Eimac.
It looked to be quite a beast, ~ 150+ wpc. Great article, lots of detail.
You can get the CD ROM of 1997 GA for ~$20 from www.audioxpress.com if your
interested. The OPT was sourced from Audio Electronic Supply. I'm pretty
sure its still available.
Mark

Hi, Mark, and thanks for the info on audioxpress.com. I will check it
out. I looked up the 4-250A because I hadn't seen one in a long time.
The Eimac spec sheets do list it in audio amp service A pair of them
is rated at 1040 watts max output in class AB2 with 3 KV on the plates,
but the THD figure is 4.5%. My two present power amps are rated at
..01-.1% and .2%, respectively. The lowest THD figure for the 4-250 is
2% with 2500 plate volts in class AB1. A pair of 3-500Z's is rated at
1,420 watts max output in class AB2 audio amp service, but the Eimac
sheet doesn't list its THD figures as an audio amp. I dunno, those THD
figures don't seem so great to me; what do you think? In the meantime,
I am going to see if I can get a copy of the article you're referring
to. Thanks again. Bill

Hey Billy Boy,
I have a couple of pieces of test gear that I do not know the purpose fo
that use QE08/200,aka7378.The things have a OPT that will work at 8
ohms.They seem to be a pretty typical PP circuit with neg and pos feedback
adjustments.They seem to be some kind of high current signal generator.The
controls seem to indicate audio spectrum use.
What a couple of beasts! I can barely get one on the bench.I have looked at
the tube spec's and they do call out for audio.They call for 750 volts. That
seems in the realm of sanity.But I am not going to mess with them untill I
grow up.They are just so massive they scare me a little bit.The OPT's are
huge as well as the PTs and chokes.I need a spare as one of mine is gassey.
I see them for sale online now and then.But the places that a search turns
up want way to much for them.
Anyway you might look at these as a big tube project.There might be others
that do not require as high as a voltage as the ones you mention but I think
the big power ham tubes generaly require the frankenamp type power supplies.
Just rambling.I really am just a newbie tube freak.But it would be cool to
have a massive tube amp without eight 6550's or some such thing.
WesJ.......



"Billy Boy (78's Rule!)" wrote in message
oups.com...
Hi, Mark, and thanks for the info on audioxpress.com. I will check it
out. I looked up the 4-250A because I hadn't seen one in a long time.
The Eimac spec sheets do list it in audio amp service A pair of them
is rated at 1040 watts max output in class AB2 with 3 KV on the plates,
but the THD figure is 4.5%. My two present power amps are rated at
.01-.1% and .2%, respectively. The lowest THD figure for the 4-250 is
2% with 2500 plate volts in class AB1. A pair of 3-500Z's is rated at
1,420 watts max output in class AB2 audio amp service, but the Eimac
sheet doesn't list its THD figures as an audio amp. I dunno, those THD
figures don't seem so great to me; what do you think? In the meantime,
I am going to see if I can get a copy of the article you're referring
to. Thanks again. Bill

Billy Boy (78's Rule!) wrote:
OK, I just had to ask this. Has anyone ever tried using big glass RF
amplifier tubes as audio amps? Maybe a tube such as the 3-500Z, which
is rated at about 500 watts of plate dissipation?


3-500Z is no good. Theres plenty of people using 833As or rare 212s. By
far the most popular is the russian GM70. Its cheap and seems to perform
well. High mu transmitting tubes and class A2 are a good mix.


Adam

Heathkit kinda proved you don't need a huge, really stiff plate supply
for these tubes, as long as you have plenty of capacitance in the
filter. You can use a voltage-doubler supply and the huge charge
stored in the filter will carry the amp along.
When I was 14 years old, I built my first kilowatt RF amp, and
accidentally took the 3KV across my arms (I thought for SURE that
center-tap wasn't grounded!). I was lucky that my muscular contraction
made me throw the wire away (otherwise I think I would have been killed
for sure), but it pulled an arc to the tip of my right index finger as
it flew off, and burned the tip of my finger off (it healed fine). But
I learned my lesson about being careful around HV B+ supplies.

This'll get your fans blowing:

http://groups.yahoo.com/group/bigvalveamplifiers/

"Billy Boy (78's Rule!)" wrote in message
oups.com...
Hi, Mark, and thanks for the info on audioxpress.com. I will check it
out. I looked up the 4-250A because I hadn't seen one in a long time.
The Eimac spec sheets do list it in audio amp service A pair of them
is rated at 1040 watts max output in class AB2 with 3 KV on the plates,
but the THD figure is 4.5%. My two present power amps are rated at
.01-.1% and .2%, respectively. The lowest THD figure for the 4-250 is
2% with 2500 plate volts in class AB1. A pair of 3-500Z's is rated at
1,420 watts max output in class AB2 audio amp service, but the Eimac
sheet doesn't list its THD figures as an audio amp. I dunno, those THD
figures don't seem so great to me; what do you think? In the meantime,
I am going to see if I can get a copy of the article you're referring
to. Thanks again. Bill

Bill,
I think most any transmitting tetrodes will require generous NFB to get
decent distortion figures, especially AB2 operation. Maybe the transmitting
triodes would be better from that stand point but then you'll need quite the
driver stage for those guys. I admit, building an amp with these type tubes
is something I've given thought to. I always thought an 813 would be a good
tube to start with, work out the bugs with the $50 Chinese tubes then spring
for some NOS when ready. NOS would probably out live me under audio
conditions.
Mark

"Billy Boy (78's Rule!)" wrote in
oups.com:

OK, I just had to ask this. Has anyone ever tried using big glass RF
amplifier tubes as audio amps? Maybe a tube such as the 3-500Z, which
is rated at about 500 watts of plate dissipation?


I have built a guitar amp using an ABB T-1000 which is a radiation cooled
glass job. About 1200 watts plate diss. I had an eimac 3-1000 to choose
from and also a similar EEV and the French one (forgot the brand) but the
ABB has a neat looking graphite anode so this was the choice. I have these
available where I work, I would not consider buying one. Topology is single
ended class A. Transformer I wound myself on a large C-core. It has an
airgap and is interleaved. 3db response is about 40 Hz to 30 kHz. In
hindsight I might not interleave a guitar amp tranny since a had to roll
the highs off anyway. Filament is running 8V at 22 amps DC. B+ is 700V and
output power is 60 watts. That is plenty for a guitar amp. Was fun to bulid
and use, took about 10 nights to make but the outer box is not finished
yet. I had a piece of Pyrex bent up to put in front on display. A couple of
pics are at webshots.com, just search using "triode" and "single ended" I
think.

I think you can get reasonable RF tubes from places that make furniture out
of ply, they are used for dielectric heating and at lower B+ than this app,
they may work.

Ruud Broens wrote:

It would be a DIY project in the same sense as making nitroglycerin
in your
home lab - unless you've worked with 'lesser evils', a lot, *and*
know what
you're doing, don't even think about it !

I don't know about making 'making nitroglycerin in your home lab'
because, since I owned the entire computer installed at the university,
I didn't have a lab at work and at my racing team we weren't fancy
enough to call the workshop or the dyno room a 'laboratory'; once, when
I referred to the engine assembly space as "the clean room", one of my
mechanics whispered to another one, "He isn't queer, is he?" But I do
have experience of making DIY nitroglycerine.

My brother, Bullseye Johnny, was given the contract for killng all the
crocodiles on the Oubangui River by Moise Tsombe in return for a favour
(the favour was not shoving his rifle up Tsombe's arse for Moise being
rude to the wife of one of Johnny's men--Moise also gave Johnny's
askari a little baggie of diamonds to sooth his wounded pride; Moise
didn't think it was funny when I remarked that he put rather a high
price on his arse). Some Chinese, who lost face when they tried not to
pay a gambling debt to "a student" and I then turned up with enough
force to make them pay, and for wasting my time made them kneel in
dog**** in the street while their customers watched and I read a poem I
had written (the poem was about how their dicks were smaller than their
skill at cards), had put a price on my head. So in the college vac,
while it all blew over, I went with Johnny to shoot a few crocodiles.
It turned out there were 1.2m crocs; the reason they had to be removed
was that they were eating quite a few people. It was impossible to
shoot them all. By the end of the second day our hands were so swollen
from firing rifles it was impossible to carry on. We had some sticks of
dynamite though. The problem with dynamite is that it is slow to work
with and not all that explosive; the upside is that it is safe if you
keep it cool. I got the idea of the nitroglycerine from wiping down a
stick of sweating dynamite and flicking the sweat beads, nitro, from my
fingers agains a treetrunk, which suddenly went missing, with this huge
bloody tree toppling over on us. I immediately sent all our 30 trucks
to the capital to fetch more dynamite, since we had only a couple of
cases for blowing up big rocks on the road and blasting highwaymen's
houses if they held us up unreasonably on the road. (Unreasonably is
defined as pointing a firearm at us or any of our men, or trying to
negotiate the toll on the road longer than ten minutes, or touching any
of the women in the party.)

DIY NITROGLYCERINE FROM STICK DYNAMITE:
Build a fire with hardwood that will make coals or start with charcoal.
Arrange several sticks of dynamite in a frying pan, not too tightly.
Place on coals. Don't worry, it won't blow up while it is still
dynamite. The nitroglycerine sweats out and runs around in the bottom
of the pan. Carefully pour off the nitroglycerine into a mason jar
(like your granny used for fruit preserves), making sure to fill level
to the top so there is no slosh room or there won't be enough of you
left to slosh in a doggie baggie. When the jar is full put on two or
three sealing rings (for bump isolation when you screw on the top),
screw on top carefully. Do not bump this bottle or the frying pan.

(OPTIONAL) KILLING CROCODILES WITH YOUR BOTTLES OF NITROGLYCERINE
Put a dozen halfpound bottles (halfpound contents; the glass weighs
more) in the bottom of the boat. Carefully tie together with string. It
helps to pre-knot the string to the desired interval between bottle so
you aren't dropping loops of string on the bottles while you stand
around measuring. Scull gently across river. Try not to hit anything.
On the way back to whichever side of the river your camp is on (we made
camp both sides of the river in case someone should have an accident
with the nitro) gently lower your bottles of nitro into the river.
Remove your boat from the river. Stand well back and throw a log into
the river. Catch a big bath. Next day pick up your dead crocodiles
downriver, their skins beautifully preserved and whole. The are killed
by the compression of the water.

Do only one or two rows of fruitjars across the river at a time, about
a hundred feet apart. On our first try we laid eight lines across along
about a kilometre of river and the resulting tsunami swept away two of
our trucks that were parked a hundred paces onto dry land. I crawled
out of the river eight miles down with a live croc snapping at my heels
and I can tell you it was long, lonely crawl back to our camp with
pygmies hunting me (blowtorch poison darts, you suffocate terminally in
eight minutes) and black treesnakes hanging down to inspect my nose (no
antidote to its bite, you suffocate terminally in four minutes). Talk
of adventure holidays!

RECIPE FOR CROCODILE EGGS
We eat all kinds of eggs of course, from chicken and other birds, fish
(caviar, roe), and so on. Most of the rarer eggs are too rich for most
people's bland taste. Ostrich and crocodile eggs need to be diluted
with milk to make them palatable. Ostricheo have six-inch long
forward-facing nails and will of course kick you to death for stealing
their eggs; nasty brutes, ostriches; I used to ride the big males in
races and we kept an ambulance on standby because it wasn't advisable
to fall off; one poor bugger got ripped from his sternum to under his
chin: I scooped his guts and other organs back into his stomach with my
hands and the surgeons sewed him together so neatly we nicknamed him
"The Zipper". Crocodile eggs are buried in mud or on sandy banks beside
rivers. Unfortunately, crocodiles are good mothers. You need to be
nimble to collect enough crocodile eggs for breakfast for a large
party. All four the cooks on the crocodile expedition had scars on
their legs. Collecting crocodile eggs is not like going to the market
garden...

I hope this information helps, Rudy. If you have children and you want
to keep them, you should of course not show them this message, nor give
them enough pocket money to buy dynamite.

Andre Jute
PS I related the experience at greater length in a book under a
pseudonym: African Revenge by Andrew McCoy, published by Secker &
Warburg, London about 25 years or so ago, also in several paperback
editions and translations. John Braine, a novelist I have always
admired, wrote in his review of African Revenge in The Telegraph, "He
goes places where no sane man goes except in divisional strength and
with air cover." I thought at the time, It wasn't *that* dangerous. (1)
Wouldn't do it today though; learned my lesson; do something safe and
responsible instead: I build kilovolt amps.

(1) It is true there were rather a large number of people trying to
take the crocodile skins from us, and they were all armed and
short-tempered and very trigger-happy and given to ambushes, which
****ed my brother off, and since he earned his nickname by shooting
first and asking no questions, not too many of them survived their
greed. Johnny's askari, who were Swahili from the other side of the
continent, were of the opinion we should have let the crocodiles eat
them. Still, it probably wasn't as dangerous as going to Denver to buy
tubes for your geetah amp...

Ruud Broens wrote:
"Billy Boy (78's Rule!)" wrote in message
oups.com...
: Thanks for the interesting reply, Don. Have you ever seen a pair
of
: 3-500Z's in service in a Heathkit SB-220 RF amp? I feel that Heath
: proved in the '220 that with proper design techniques, the power
supply
: need not cost an arm and a leg. But tell me this: would it require
a
: special audio transformer in order for its primary to avoid
breakdown
: at 3000VDC, since obviously that primary is going to be in the
plate
: circuit? I would like to build an audio amp like that someday,
just
: for fun. I've had Peter Dahl build special transformers for me in
the
: past. They aren't that terribly expensive.
:
You need _special_ everything ! That is special wiring, sockets,
transformer,
power supply capacitors, even resistors .. and forced air cooling
and a hefty
filament supply. Did i mention the voltages in the circuit are
absolutely deadly
?

It would be a DIY project in the same sense as making nitroglycerin
in your
home lab - unless you've worked with 'lesser evils', a lot, *and*
know what
you're doing,
don't even think about it !

Fun is fun,
but dead is dead
Rudy

Daddy not pay enough attention to you when you were young?


Adam

Billy Boy (78's Rule!) wrote:
OK, I just had to ask this. Has anyone ever tried using big glass RF
amplifier tubes as audio amps? Maybe a tube such as the 3-500Z, which
is rated at about 500 watts of plate dissipation?


What I was wondering is--would it be possible to use two television
picture tubes as audio amps? What makes me wonder this is that I can
hear sounds as my computer monitors turn off and on, from the picture
tubes. High-pitched sweeps falling down; which leads me to think that
they could give off sounds directly, if fed audio signals. So would you
even need speakers? Wouldn't be hi-fi I'd guess, but still. It would be
pretty interesting to see/hear,,,,,

Dear Doug: Your hearing must be slightly deteriorated. If you could
hear better, you would hear your computer monitor talking to you at
this very moment, saying, "It's not nice to post sarcastic replies to
Billy Boy's posts." I would rather use one impressive-looking tube
than all the nondescript output tubes they use on OTL amps.

I think I can hear sounds from the picture tubes. High-pitched sweeps
falling down; which leads me to think that they could give off sounds
directly, if fed audio signals.

DougC wrote:

Billy Boy (78's Rule!) wrote:
OK, I just had to ask this. Has anyone ever tried using big glass RF
amplifier tubes as audio amps? Maybe a tube such as the 3-500Z, which
is rated at about 500 watts of plate dissipation?


What I was wondering is--would it be possible to use two television
picture tubes as audio amps? What makes me wonder this is that I can
hear sounds as my computer monitors turn off and on, from the picture
tubes. High-pitched sweeps falling down; which leads me to think that
they could give off sounds directly, if fed audio signals. So would you
even need speakers? Wouldn't be hi-fi I'd guess, but still. It would be
pretty interesting to see/hear,,,,,

Well no doubt a picture tube could operate as a triode amplifier.
And maybe give some weird wacky colour effects as well.

I know a guy who has synethesis, ie, his senses cross over a bit,
and not only does he hear what comes from his fab hi-hi system,
but he sees colours coming from the speakers as well.
Some ppl find light changes make sound they can hear.

So speakers that lit up in all sorts of strange ways but in time with the
music
might be interesting. Its been attempted before though......

Patrick Turner.

"Billy Boy (78's Rule!)" wrote:

Dear Doug: Your hearing must be slightly deteriorated. If you could
hear better, you would hear your computer monitor talking to you at
this very moment, saying, "It's not nice to post sarcastic replies to
Billy Boy's posts." I would rather use one impressive-looking tube
than all the nondescript output tubes they use on OTL amps.

I think I can hear sounds from the picture tubes. High-pitched sweeps
falling down; which leads me to think that they could give off sounds
directly, if fed audio signals.

The only high pitched sweep I have ever heard fall down was
when Kylie came around to sweep my chimney.
Some how she lost her footing half way down, and fell to to the hearth
in a cloud of dense black soot, "
SSSHHHeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeTTT!"
she screemed in a high piched tone.
She went in as a blonde, and came out a changed woman.

But I sorted her out in the shower, scrubba dub rub.......

Patrick Turner.

It seems You are aiming at The Final Single-Ended Triode. There are
metal/ceramic ones, but they do not glow, therefore 50% of the magic gets
lost. There are "customary" big ones (211, 845, 813, GM-70 etc.), but it
seems You want something really weird, and this could lead to some
disappointment because large transmitting tubes are not necessarily good
sounding, since linearity was not required for their intended purpose.
Among the glass monsters I saw used for their SET amps by some senior-league
weirdos, there's the 833A (still produced in Ukraine as GU-48 and available
at fair prices), the Russian GM-100 and the terribly expensive 4212.
Somebody managed to get FOUR (yes, to have spares) former Royal Navy STC
4212 to make a 100W SE, but I suppose I'd be kicked out of my home's door if
I blew 4 or 5 kilo-euros in tubes.
There are many others big radio bottles, say 100TH or the "800" series ones
(805, 809, 810...), but most of these are still in the 100 - 150W range,
therefore they have no advantage over the GM-70 (125W).

Problems (apart from electrocution-related risks):
- power consumption/heat/weight (the filament of a GM-100 takes 300W just
to light up!): better make the whole amp as a series of modules to be
installed in a fixed HV cabinet or to provide wheels to move it from the lab
to the listening room (my wife wouldn't allow forklifts to run across the
carpet..)
- output transformer performances: it has to handle maybe 500mA DC at 2kV,
this means A LOT of iron and copper. Getting a good bandwidth will be a
pain in the bottom.
- driver stage: when using radio tubes, positive grid is usual, which means
that the driving stage needs to supply a substantial amount of current.
Indeed, it must be a smaller power amp.

Briefly: I suppose that the best is to use a couple of GM-70 (or 845) tubes
in PP class AB1. This will provide more than 200W with a substantial amount
of class A @ say 1% THD with NO overall feedback and NO DC thru the OPT.
Furthermore, these tubes need a big driving voltage swing, but they do not
need to be driven into positive grid and, as a safety bonus, they do not
have unprotected anode caps.
This way, it is feasible to make the best possible OPT and the best possible
driving circuitry at a "viable" cost and to make a mono amp weigh less than
100# ...
If the circuit is really good, I bet it is absolutely impossible to hear
that it is not SE as long as it operates in class A (add a differential amp
as a driving stage to make sure, see Williamson).
Larger power (350-400W) can be obtained by using tetrodes in B class, say
813 or GK-71, but these will need a large amount of feedback.

Ciao

Fabio


"Billy Boy (78's Rule!)" ha scritto nel messaggio
ups.com...
Dear Doug: Your hearing must be slightly deteriorated. If you could
hear better, you would hear your computer monitor talking to you at
this very moment, saying, "It's not nice to post sarcastic replies to
Billy Boy's posts." I would rather use one impressive-looking tube
than all the nondescript output tubes they use on OTL amps.

I think I can hear sounds from the picture tubes. High-pitched sweeps
falling down; which leads me to think that they could give off sounds
directly, if fed audio signals.

Patrick Turner wrote:

"Billy Boy + Patrick Turner....



Well I did not suppose it would sound GOOD, but that it "sound". -Would
*be audible*. Tube-microphony? Tube-speakerphony?
-----
Not loud enough for regular room-listening perhaps, but other
possibilities. "Here, stick these in your ears and tell me how it
sounds...."

What is this piece of test gear?