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Another homebrew stereo

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Another homebrew stereo Empty Another homebrew stereo

Post by tubesrgr8 on Thu Feb 27, 2014 7:07 pm

Understanding just a little about second harmonics and Class A single ended triodes, I decided to build a single ended triode amp. Here's the result, "boasting" about 3 watts per channel. Feeding Jensen 15" speakers, it can make some pretty good sounds. It's admittedly far from the craftsmanship I see in Sal Brindisi's KT88 amp, but in all fairness, it has gone over 5 years without a problem. While listening to Big Bands, Jazz, Swing, and assorted Classic and other LP's, I usually end up with three or four dogs in the recliner with me, which does make it interesting when changing records...Another homebrew stereo Photo-14
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Post by Bill Cahill on Thu Feb 27, 2014 8:11 pm

Nice amp. May we see the innards??

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Post by tubesrgr8 on Thu Feb 27, 2014 8:48 pm

Here it is, sounds better than it looks  Wink . Inputs using 6SL7GTs, and 6SN7GTs driving the 6A5Gs. The output tubes are a story in itself. I bid on a batch of 24 on eBay, won them, and found them to be in the original wartime WWII cartons, padded in shredded vintage newspaper!Another homebrew stereo Photo-15
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Post by Bill Cahill on Thu Feb 27, 2014 8:57 pm

Thanks. Much appreciated.............

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Post by N7ZAL on Thu Feb 27, 2014 9:48 pm

Workmanship looks fine to me. Great job !
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Post by tubesrgr8 on Fri Feb 28, 2014 2:45 pm

Thanks, I appreciate the kind words.
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Post by Dr. Radio on Sat Mar 01, 2014 7:38 pm

That is beautiful work.
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Post by DrRick on Sun Jul 22, 2018 4:02 pm

Your amp looks great! I’d like to copy it if I may?
Do you have a schematic?
I’ve got some 6A5Gs.
Do you have any more of the output xformers? If so I’d like to buy or trade for a pair.
Thanks in advance,
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Post by tubesrgr8 on Sun Jul 22, 2018 4:59 pm

DrRick, I'll see what I can find, if I still have the whole thing on one schematic LOL. The transformers were ordered online from One-electron. UBT-3 specs at: http://one-electron.com/Trans/UBT3_10.pdf
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Post by tubesrgr8 on Sun Jul 22, 2018 10:02 pm

DrRick, what I think I remember doing (not having a schematic for such a project) was to take individual circuits like from the RCA Receiving Tube manual and "patch" them together using the suggested component values for the voltages I was using. Kinda fiddled with the cathode resistors for the 6A5G to keep appropriate grid bias. Would be interesting to run some distortion tests but hey, it sounds fine to me, and that's what counts LOL.
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Post by DrRick on Mon Jul 23, 2018 1:08 am

Thanks so very much for taking the time to respond.
I’m your post you mentioned some transformers you bought a bunch of on eBay. I thought you mentioned they were outputs.
What were they and do you had any more?
How’s the hum level? Did you use separate filament xformers for each 6A5Gs?
Thanks for your help!
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Post by tubesrgr8 on Mon Jul 23, 2018 10:54 am

It was the 6A5G's that I got on eBay. The transformers are specially for the SET configuration probably not found on eBay, especially two of the same LOL. Nice thing about the tubes, I kept enough for replacements in the foreseeable future, and sold the rest for more than I gave for the whole batch originally! Hum level is inaudible (to me, again not measured on test equipment), same filament source for both output tubes. Pwr supply filtering (capacitor input) with 5H choke and 100+100mfd caps. Additional RC filtering for input/driver stages with 50+50mfd cap. Hope that's not too vague...
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Post by tubesrgr8 on Mon Jul 23, 2018 2:33 pm

I did a quick listen for hum, what I thought at first was hum, was the A/C compressor running outside LOL. At the speaker furthest from the outside wall no hum that I could hear. YMMV if you have better hearing than mine... Now that it's fired up again, I put on one of my Time-Life Swing records. Love that sound.
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