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832A power amp

ab0ez

ab0ez

AB0EZ
Here are some pictures and the schematic for a pair a of 832A power amps I finished a couple of days ago. Well, sort of of finished. I still have to add the oak frame.....

I started off with the schematic from a well known site and builder (just google 832 amp) and then modified it for monoblock construction and a tube rectifier with a choke in it's power supply. I also beefed up the capacitance filtering a bit.

If the chassis looks familiar, that's because it is a Hammond AO-40 6BQ5 PP chassis. I'm running about 330 volts on the plates and 240 on the screens, so it is a little bit more powerful than the original version shown on the webpage.

I am really impressed with this amp and my hat is off to the designer of the original 832 amp. I am using this to power two of my Khorns that have the EV T-350 tweeter. These amps are so quiet that I have to get within a foot of the tweets to hear anything. The sound is really crisp and not harsh at all. It's not really a big bass amp (probably because of the original Hammond organ transformers), but I can listen to it for hours on end and not get listening fatigue. This isn't to say the amp is bass-shy (especially with khorns!), but rather to say that the bass is very neutral.
 
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Nice work man, and that 832 is way cool. It's really amazing how quiet tubes can be with proper filtering and lead dress. I would bet you are right about the OPTs being the limiting factor on the bass, but the older I get, the more "neutral" I like my bass. I think this circuit is going on my short list of amps to build. Thanks for posting, Jay
 
I was printing off the schematic and it made me wonder how critical it is to have close matching sections in the 832? I don't think I have a way to test those.:scratch2: Also, how much power do you think it's making?
 
I see 832 equivilants from Russia for about 6 bux a tube on epray. Are you running a certain brand, or could you give any advice on brands? BTW, I also saw a tube tester adapter for Hickoks TV3 at Triode.:scratch2:
 
Since the screens and cathodes are shared between sections, there isn't any easy way that I know of to match sections. I haven't had any problem thus far with one set of plates glowing red and not the other. The brands I have used so far are RCA, National Union, and the GE GL series. The GE GL832A is my favorite. I don't think I paid more than a few dollars each for these tubes. The more I listen, the more impressed I am. Just a wild guess based on some preliminary numbers, but I am thinking it makes 12-15 watts.....more than enough for my Khorns.
 
On my list of projects is to build another pair of these amps using a Pair of Eico HF81 output transformers that I have sitting around. We'll see what that does to the overall sound.
 
Man I am kicking myself, about three months ago I stopped at a yard sale and there was a box of 6 of those tubes GE brand new in box had 5 bucks on the box, but I did not know what they could be used for.
 
Endspec said:
Man I am kicking myself, about three months ago I stopped at a yard sale and there was a box of 6 of those tubes GE brand new in box had 5 bucks on the box, but I did not know what they could be used for.
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Go knock on the door! :yes: Hey, shoot me your address, I think i lost it.
 
Don't kick yourself too hard, they are still available at very reasonable prices.

Heck, we've all passed on stuff we've later kicked ourselves for.....like a WE 300B I passed on years ago for $10.......
 
I did go back few days later to get a maggi console but the house was empty, It was a moveing sale and they said they would be there for about one more week,
 
I think when I build the next pair of 832A monoblocks with the Eico HF81 OPT's, I will configure them as an adjustable tube regulated fixed bias, probably with a circuit similar to a Bogen DB130. Comments? Questions? Suggestions?
 
ab0ez said:
I think when I build the next pair of 832A monoblocks with the Eico HF81 OPT's, I will configure them as an adjustable tube regulated fixed bias, probably with a circuit similar to a Bogen DB130. Comments? Questions? Suggestions?
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Not familiar with that circuit, could you post a schematic?
 
Shoot, I must be getting tired. I meant to say fixed bias adjustable tube regulated screen voltage circuit! I'll post a schematic in the morning.
 
ab0ez said:
Don't kick yourself too hard, they are still available at very reasonable prices.

Heck, we've all passed on stuff we've later kicked ourselves for.....like a WE 300B I passed on years ago for $10.......
Click to expand...

I remember those days too: "Why in God's name would I want a 5W, high distortion amp?" Pass!

I can also remember buckets full of 832's & 829's being given away at nearly any hamfest I went to in the 80's. "RF double power tube, oh yeah, that's what I want....."

:headscrat

Can someone put up the schemo for this? When I open it I am told by adobe the file is busted & cannot be repaired.
 
That's a very cool amp. I got some junked transmitters a couple weeks ago and they were each powered by two of those things. Unfortunately all the 832s were either missing or broken. Got a couple ceramic 832 sockets out of em though. I wondered at the time whether the tubes would be good for audio.
 
Here is the schematic in JPG format. Funny about the 829B......I have a box of them and some OPT's that just might work! Hmmm, ~600 volts on the plates, 240 regulated on the screens.....

I played the Eagles "One of these nights" CD (boy, do I wish it was available on SACD!!!) last night. Outstanding resolution. Listened to the entire disc. I think I really like this little amp.
 
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I have an 829B sitting on my desk at work, similar looking tube but taller. I think I have an 832 at home. Nice looking amp.
 
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