Another tube amp project

[blair]

I bought an old Pioneer receiver off a friend for a reasonable price that had an issue with a channel. I'm not into nostalgia, so I cut it up and stole the stuff I wanted Anyway, the output iron ohms out, so I cut a plate and started to mount parts. This project uses 6BQ5 output tubes, and 12AT7 drivers. Very minimalist. Here are a few shots. I can and never will be as good as PWRider/Craig at documenting, so the next images may be completed amp images. Should be good for ~15-17WPC.





I did not do cosmetics on the outputs because they were supposedly made by Tamura.i wanted to keep the numbers there.

Oh, and yeah. I do these completely backwards. I build the amp, and then machine the chassis

[50 watt head]

Re: Another tube amp project

Nice! Nothing sounds sweeter than a push-pull pair of EL84

[blair]

Re: Another tube amp project

I'm sure it will sound good. It, however, will not drive my speakers. Off to Audiogon it will go

I'm saving for parts on my sweep tube project right now.

[blair]

Re: Another tube amp project

Here is a little progress.




It's so hot here that the wood kept getting wet from sweat and then dirt would follow. I decided to lacquer it black. I will probably do the whole thing that way since the look of lacquer on oak is nice in my opinion.

[PWR RYD]

Re: Another tube amp project

I like it Blair! Not to nitpick, but those power supply caps aren't big and bold enough to be top side. The clamps make them look tiny. JMO. I would have tucked them under the skirt so to speak But the iron is awesome!!!. CCS for the output bias? What B+ and is it going to be UL?

[blair]

Re: Another tube amp project

Thanks Craig!

The cap clamps are from the receiver I robbed the iron from. The caps are actually about 3X the capacitance of the ones Pioneer used. Just better cap technology.

I chose the top mount because if real estate. Spece goes fast in a 6" deep chassis

No CCS. Just a pentode wired circuit with a cathode bias resistor between the pair. I added a balance pot in the middle at the cathodes as a tweak. B+ is ~360V with 290V in the screens.

Blair

[PWR RYD]

Re: Another tube amp project

Radio Shack 25 ohm 2w balance pot? I used those pots with my Odd Watt mono blocks and was able to dial in the bias +\- 0.5 mA. Good stuff!

[blair]

Re: Another tube amp project

Nah. I'm not against Radio Shack parts, but I have a surplus store down the toll that has mil spec Clarostats for $.99-1.50.

I'm going to cry if they run out. I get them for bias on my bigger projects where the same pots sell for 8-15 bucks each at AES and fleBay.

[tyger23]

Re: Another tube amp project

It's so hot here that the wood kept getting wet from sweat and then dirt would follow.

Today felt like the hottest day I could remember in quite some time. I think the thermometers were wrong. They only said 104.

[blair]

Re: Another tube amp project

Yea!! Output iron ohm's out cold, but shorts hot pulling the cathodes to stupid current.

Now to figure out what to do to salvage this project

[AJ]

Re: Another tube amp project

Cool project Blair, as always.

I'm saving for parts on my sweep tube project right now.

I have a box full of 13GB5 and 12BQ6GTB sitting here from the dollar store (ESRC). What tubes are you planning on using?

[blair]

Re: Another tube amp project

Hi AJ,

Thanks! It's a bummer that I will have to buy new output iron or find old stock with similar laminations for a transplant, but that's how it goes with scrap

Regarding the sweep amp, I'm going with the 6CB5A. The one obstacle, well to me anyway, is tube cost. A good quad of KT88s is $100 on a cheap day. Right now, at AES, the 6CB5A can be had for just over $3 each.

Iron is a different story, but you don't replace iron unless something horrible happens. I'm looking for 100-150W from the quad on each channel. It's only a 23W tube, but the sweeps were made very conservatively. The plate on a 6CB5 is as big if not bigger than a KT88.

I have all of the iron, I'm just waiting for cooler weather to start machining stuff. These will be my personal amps, so I will pay plenty of attention to detail on the aesthetics.

[tc]

Re: Another tube amp project

Hey Blair,

Where is this surplus store you speak of? I promise not to buy any Clarostats......

[dthomas]

Re: Another tube amp project

Tanners Electronics is one Blair is referring to, they are in Carrollton, TX. Here is a link great place to get capacitors or about anything electronics related. Great store with great folks running it.

http://www.tannerelectronics.com/location.html

[blair]

Re: Another tube amp project

Tanner's Electronics off 35E in Carrollton. Good "stuff" supplier.