829B like audio amplifier?

[hmtavella]

Somebody knows applications 829B like audio amplifier?
TIA
Regards

Heriberto LU6DBU

[Patrick Turner]

I guess you already have a few 829B and want to know if you can make
an amp with them.
If you dial in "829B amp" into Google, there's lots of hits to help if
you wanna use the tube for an audio amp. But the tube is a twin beam
tetrode with the screens taken to a common pin, so your use with just
one tube is restricted to SE parallel operation of the two tetrodes
using maybe UL, triode or CFB and you'd get maybe 17W of SE PO,
because Pda max is 40W total and maybe needing to use class A2
operation.
For PP, much more PO is available, maybe a good 40W in class AB using
TWO of them, each with their anodes tied together and so you can use
the UL connection if you want. Seems like they are more difficult to
use than octal tubes because of two anode top pins and a strange
socket, but inovation gets you over that hurdle by making you own
connectors if you are keen. Notes I saw that by 1950, the 829B was not
the best large beam tetrode one might use for anything because by then
the makers were using larger anode structures and using say 3
indirectly heated parallel cathodes within to get the gm high and so
the tubes would operate with low voltages below 500V, and at high
currents, so thus making high PO easily and more reliably, usually RF
power. There were quite a large family of BIG glass envelope tubes
which can dissipate quite high PO without forced air cooling and which
ppl can use with similar voltages as one might use with KT88 etc, but
many in the family are like having a couple of KT88 in parallel. They
were extremely expensive and used mainly for tramsmitters in
institutions and for industrial amps and the public never sought to
buy them like they'd buy a 6L6 or KT88 or EL34 etc.

Patrick Turner.

[rrus...@hotmail.com]

On Feb 9, 5:00 pm, Patrick Turner <i...@turneraudio.com.au> wrote:
> On Feb 10, 2:29 am, "hmtavella" <hmtave...@cybertap.com.ar> wrote:
>
> > Somebody knows applications 829B like audio amplifier?
> > TIA
> > Regards
>
> >  Heriberto LU6DBU
>
> I guess you already have a few 829B and want to know if you can make
> an amp with them.
> If you dial in "829B amp" into Google, there's lots of hits to help if
> you wanna use the tube for an audio amp. But the tube is a twin beam
> tetrode with the screens taken to a common pin, so your use with just
> one tube is restricted to SE parallel operation of the two tetrodes
> using maybe UL, triode or CFB and you'd get maybe 17W of SE PO,
> because Pda max is 40W total and maybe needing to use class A2
> operation.

No, you can use them as a single push pull tube. The screens are in
common but that is effectively true with a lot of standard push pull
circuits. The seven pin socket is fairly common and is used by a fair
number of tubes. Just treat it as a pair of 6V6s.

[hmtavella]

"Patrick Turner" <in...@turneraudio.com.au> escribió en el mensaje
news:3c2fd215-48cb-4a8f...@ir9g2000pbc.googlegroups.com...

Thanks Patrick, the case is that I have several tubes 829B and wanted to
give a use them, since here a tube EL34 or similar is but expensive that
829B. - Very detailed its explanation.
Again thank you very much

Regards

Heriberto

[John L Stewart]

There were several of those double Tetrodes made in particular for what
was then VHF RF service. Off the top I can think of some of the most
common such as 829B, 832, 815 & 3E29.

Think the 2nd PA Amp I ever built used an 815. The driver was a triode
connected 6F6 thru a Hammond IT. Don't remember what OPT I used, it may
have been a Jensen 2430, similar to a Hammond 125D.

I wouldn't use any of these now in a tubed AF Amp. Common leads for the
cathodes & screens are very limiting to the serious designer.

But the 815 might look kinda cool to someone who gets a charge out of
cosmetics. Still got one in my stash. And the data shows the 815 in AB2
can kick ass!

My 2 Rasbuckniks, anyway.

Cheers, John




--
John L Stewart

[Patrick Turner]

> number of tubes. Just treat it as a pair of 6V6s.-

OK, sure you could use 1 x 829B as a pair of 6V6, for pure beam
tetrode, but who would want to in a hi-fi amp?

UL is the better way for hi-fi than pure beam tetrode, so you need to
have screens able to connect to two phases of the 40% of the adjacent
anode signal. There is only ONE cathode connection so that outlaws CFB
with one tube.

And because there is only ONE cathode, and if someone wants to be
certain of equal Ia in each tetrode section, the Ia at idle must be
set by monitoring each anode current, and adjusting grid bias voltage
to each tetrode.

Plain cathode biasing could be used for class A if it was assumed that
equal Ia flows in each anode which is how the worst cheapest crummiest
amps made have been set up. Many stereo amps have amps have say 2 x
EL84 or 6V6 per channel, and they just connect all 4 cathodes
together, and run the combined Ia thru a single R&C network to get the
bias. But there's more. The dumber designers use the cathode current
to power heaters of a pair of 12AX7 used in the phono stage, 1 12AX7
per channel, so heaters in series needs 12.6V x 150mA, and each OP
tube gives 37.5 mA. Sure, and pigs also fly. Over time, with just a
single bias RC, OP tubes become unmatched, and Ia can vary by + +/-
60%, not unusual. And Ek can also vary a lot.
If anyone is going to all the trouble of using just one 829B, may as
well be hung for a sheep because stealing a lamb is a hanging offense,
hense I suggest ppl use TWO of them which widens the possibilities,
and allows the two to be run well below ratings, so they might just
last a bit, something one should consider when using what must be 60
year old tubes even if they haven't been ever used.

Even if one uses 2 tubes then connects anode together and then to a
transformer connection, one would still be wise to monitor Ia of each
tetrode. However, some large tetrodes made in the 1950s and 60s which
were designed to operate on anode supplies less than 500V have not
just 2 commoned cathodes, but 3, and just what each one is doing is
anyone's guess. 13E1 has two commoned cathodes. I have not seen any
samples display symptoms of different cathode current. They are not
prone to because the two cathodes have been made in the same batch,
same "stuff" used to make it, and then spent life in the same
temperature and vacuum purity and hours of use, so two cathodes in one
tube tend to age together if both anodes are used similarly. Even with
small signal little tubes like 12AX7 there are two cathodes which can
be commoned for a parallel tube, or for an LTP, etc, without many
problems ever developing.

Pure beam tetrode PP operation with 1 x 829B does not appeal to me
very much but would be fine for a musicians amp where THD/IMD can be
huge. But if enough NFB is used, then tetrode might be OK for hi-fi.
Most amps made with PP 6V6 in beam tet PP mode in 1955 used 20dB
global NFB. 26dB NFB was not uncommon.

Patrick Turner.

[rrus...@hotmail.com]

> > > I guess you already have a few 829B and want to know if you can make
> > > an amp with them.
> > > If you dial in "829B amp" into Google, there's lots of hits to help if
> > > you wanna use the tube for an audio amp. But the tube is a twin beam
> > > tetrode with the screens taken to a common pin, so your use with just
> > > one tube is restricted to SE parallel operation of the two tetrodes
> > > using maybe UL, triode or CFB and you'd get maybe 17W of SE PO,
> > > because Pda max is 40W total and maybe needing to use class A2
> > > operation.
>
> >  No, you can use them as a single push pull tube. The screens are in
> > common but that is effectively true with a lot of standard push pull
> > circuits. The seven pin socket is fairly common and is used by a fair
> > number of tubes. Just treat it as a pair of 6V6s.-
>
> OK, sure you could use 1 x 829B as a pair of 6V6, for pure beam
> tetrode, but who would want to in a hi-fi amp?
>
> UL is the better way for hi-fi than pure beam tetrode, so you need to
> have screens able to connect to two phases of the 40% of the adjacent
> anode signal. There is only ONE cathode connection so that outlaws CFB
> with one tube.
>
> And because there is only ONE cathode, and if someone wants to be
> certain of equal Ia in each tetrode section, the Ia at idle must be
> set by monitoring each anode current, and adjusting grid bias voltage
> to each tetrode.

Yes, but CFB isn't that common. And anode current is easily measured
with a DC current probe, exotic then, but not expensive now.

Audio is not its first best purpose but all these tubes were used as
modulators (i.e., audio power amps) in transmitters for commonality
purposes.

[grumpy]

This tube is same as 3E29 in push pull can produce up to 80 watts pending
class operated on

"hmtavella" <hmta...@cybertap.com.ar> wrote in message
news:4f33...@news.x-privat.org...

[John L Stewart]

Yes, but CFB isn't that common. And anode current is easily measured
with a DC current probe, exotic then, but not expensive now.

Audio is not its first best purpose but all these tubes were used as
modulators (i.e., audio power amps) in transmitters for commonality
purposes.

>>>>>>>>>>>>>>>>>>>>>>>>>>>>..

Because CFB is not common does not preclude its use here. Provided your
OPT has a secondary with zero, 4 & 16 ohm leads, the NFB can be directed
to the driver tube cathodes with very good results. How much depends on
the bandpass of the OPT.

The 3E29 was used as a RADAR modulator. Discharge a charged lumped
constant (LC) transmission line into a magnetron & get a nice steep edged
pulse of RF. The faster the edge the better the resolution of the system.

My 3 & 1/4 Lira, anyway.

Cheers to all, John


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--
John L Stewart