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Funky Project [message #95429]

Wed, 23 March 2022 21:11

gofar99
Messages: 1950
Registered: May 2010
Location: Southern Arizona

Illuminati (5th Degree)

Hi Everyone. This is a project I started a while back and finally am getting around to finish. A push-pull 832 amp. I love the way the tubes look but they are certainly not mainstream audio ones. Typically used for really high frequency radio power amps. Still the current price for such a cutie is only $10 from Antique Electronic Supply. Since I already had them and the amp was at least started I figured it was something to keep me out of trouble. I am actually running the tubes well below their ratings and really just at the bottom of the linear range 250 Volts and 51ma each side. In class A pentode mode I figure on about 7-8 watts. Driver is a 5751 in SRPP mode. The photo is what it looked like when I set it aside. More to follow as I work on it. It was barely operational at the time (hum, noise and so-so sound). I figure I can make it sing with some changes.

/forum/index.php?t=getfile&id=3029&private=0

Attachment: 832 B with CXPP Transformers.jpg
(Size: 393.54KB, Downloaded 419 times)

Good Listening
Bruce

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Re: Funky Project [message #95435 is a reply to message #95429]

Thu, 24 March 2022 09:30

Wayne Parham
Messages: 18791
Registered: January 2001

Illuminati (33rd Degree)

Dude, that's so cool! The tubes look like little glass minions!

You have to think of a fun name for that amp. It's so unique!

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Re: Funky Project [message #95436 is a reply to message #95435]

Thu, 24 March 2022 09:45

Rusty
Messages: 1192
Registered: May 2018
Location: Kansas City Missouri

Illuminati (3rd Degree)

I think you've just named it. That really is unique. Very creative.

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Re: Funky Project [message #95444 is a reply to message #95436]

Fri, 25 March 2022 21:47

gofar99
Messages: 1950
Registered: May 2010
Location: Southern Arizona

Illuminati (5th Degree)

Actually I'm thinking of Quercus. That is the genus for Oak trees which naturally are the source of acorns. The 832 has lots of names but the one that comes up frequently is an acorn tube. Rolling Eyes

Good Listening
Bruce

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Re: Funky Project [message #95445 is a reply to message #95444]

Sat, 26 March 2022 08:48

Wayne Parham
Messages: 18791
Registered: January 2001

Illuminati (33rd Degree)

Very cool. Those tubes do look like glass acorns. Love it!

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Re: Funky Project [message #95591 is a reply to message #95445]

Fri, 06 May 2022 12:44

gofar99
Messages: 1950
Registered: May 2010
Location: Southern Arizona

Illuminati (5th Degree)

Hi Everyone,
Well.....some things are not quite as expected. This amp is one of those. First you would expect a pair of beam tetrode RF sections to deliver a bunch of power in push-pull. Even if it is class "A" operation. Well 4 watts clean and a max at 5% distortion of 6.5 isn't exactly a lot of power. A pair of EL84s can do that in a similar circuit. Granted the 832s are really neat looking though. On the brighter side of things the response, signal to noise and sound are all good. Except for some 60HZ at -75 db the rest of the range is nearly -90db. Not too shabby for a small amp. Response is equally good. -0.9db at 20HZ and -0.5db at 30HZ. Everything from there up to past 30KHZ is within 0.1db. To me the sound is well rounded. No obvious anomalies. The "color" of the sound if you want to use such terms is largely determined by the driver tube choice and the coupling capacitors. If you fiddle with them then you can alter the sound from warm to cool. Your choice. I used Auricap capacitors and JJ ECC802S driver tubes. Sensitivity is around 1 volt for full output. You can use ECC803 types and get more gain at the expense of a higher noise level. Since nearly any decent source can deliver 1 volt I figure that this is not really an issue. So while really cute and a worthy project, I figure there are better ways to make sound.

/forum/index.php?t=getfile&id=3056&private=0

Attachment: 832 Consolidated Schematic May 6 2022.jpg
(Size: 155.33KB, Downloaded 270 times)

Good Listening
Bruce

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Re: Funky Project [message #95592 is a reply to message #95591]

Fri, 06 May 2022 14:12

Wayne Parham
Messages: 18791
Registered: January 2001

Illuminati (33rd Degree)

But dude, it's so unique looking!

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Re: Funky Project [message #95596 is a reply to message #95429]

Sat, 07 May 2022 08:29

Barryso
Messages: 205
Registered: May 2009

Master

Like Wayne said, it's a great looking amp. Those tubes are exotic, at least in the looks department.

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Re: Funky Project [message #95599 is a reply to message #95596]

Sun, 08 May 2022 14:15

gofar99
Messages: 1950
Registered: May 2010
Location: Southern Arizona

Illuminati (5th Degree)

Hi, The tubes were pretty cheap about three months ago. One site had them for under $10 each NOS. BTW the amp is a pretty good heat source on cold days. This one seems a bit less efficient that most of my other similar designs. As class "A" U/L amps they are not efficient to start with.

Good Listening
Bruce

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