• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

832A Push Pull 5W

Follows the schematics of a 5W amp I have built using the 832A transmitting double tetrode. The original schematic belongs to Ultra Analog whose site is off line for some time now.

Sounds fairly good.
 

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Pics plz! Good stuff, I thought the 832A was a HV tube? Does it oscillate much?

It is. The 832A was intended for VHF, PP Class C operation. The typical operating voltage for that is 400 -- 750V(DC). It also looks like the grids are loaded down pretty good, so that it doesn't oscillate. I doubt he has a problem with it, although I'd certainly be looking for that if I built one.
 
SHiFTY said:
Pics plz! Good stuff, I thought the 832A was a HV tube? Does it oscillate much?

Sorry for the delayed responce.

Originally there were no oscillation problems. Applying NFB with 4K7//100pF everything seemed ok in the lab. Connecting the amp to my system with hi capacitance speaker cables did oscillate like hell. Removing the 100pF is quiet as dead. Now I have a 220K pot to adjust the feedback with no cap in parallel. Amp is stable down to ~1K setting. I like the sound with the minimum amount. Applying more firms the bass and stereo imaging but some how dries out the music.
 

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morfeas said:
No balancing for the output.
But there is a balance in the phase splitter which I didn't include in the schematic. :rolleyes: The anode load of the input valve (not the grounded grid one) is 18K||200K pot.

Also the feedback is not included in the schematic even thu I tend to no feedback.

Updates schematic follows

So how is the DC balance through each of the output tubes?

Best
Robert Morin
 
832 PP amp

Hello,

I build a PP 832 based amp from this schematic during the few las months. It's my first amp! I'm very impressed and happy about the sound of it. Quite powerful and lots of air on sound stage.

http://www.audiohobbyist.com/projects/832.htm

The only modifications I did :
- Upgraded filter cap to 2900uf - 400 V
- Add a serial resistor and switch for slow charging of the filter cap
- Add a switch and parallel resistor for filter cap discharging at shutoff
- Add a switch for power on (after charging)
- Add a separate transformer, voltage regulator and filter cap for 12AT7 filaments.

I plan to replace the PS transformer. It's underamp and overheating. I'll go for Hammond 261M6.

Nice project to work on. Great sound for the price! Go for it

.. and best regards to the author who gave me excellent advice during assembly.

For a few pics of it :

http://membres.lycos.fr/fpelletier/832/832/

Francois