An interesting 6aq5 SE amp.

[Carbsandcaps]

I came across this cool looking 6aq5 single ended amp on eBay made by yellow springs instrument company of yellow springs Ohio. No info on it at all. I believe it was used with microphones. It had 800 ohm output transfomers (if it was using an 8 ohm speaker). It might make more sense to use a 3200 ohm into a 32 ohm speaker. It had a gain control in between the 2 triodes of the 12ax7 preamps. It was clearly removed by force from something on the back because half of the rivets were still there.

Through the help of some others on here I decided to use a cathode follower then volume pot then normal triode on the 12ax7’s. Then regular 6aq5 circuit and set the bias. I tried a few output transformers but just didn’t sound right plus there was very little room with the original ot’s being tiny. I had an idea to tear apart an old se 6BM8 Lafayette receiver I had and use this ot’s. They were about 4300 ohm and sound great! I’m very happy with the outcome for the small amount of money I put into it. I’ve heard good things about se 6aq5 amps and they weren’t lying! I threw in some yellow LED’s where the balance control and mic level pots were they’re a little bright but I figured I’d pay tribute to the yellow springs instrument company.

Yellow springs instrument company is still around but they sure don’t make amplifiers.

 

[dsndblm]

Nice save and build. Any chance of posting a schematic with your changes? The 6AQ5 is one nice sounding tube. They don't get much love because of limits on plate voltage? The amp in my avatar was built for my son about 15 years ago. It's push pull, triode strapped. It's sounds good, I'd like to try a SE 6AQ5 build.

 

[ceylon]

this sure is interesting. cant say ive come across a SE 6AQ5 amp yet.

 

[Bill Ashton]

I wonder if she wasn't originally built as an audio amplifier but for some instrumentation purpose? In any event, very nice save!

 

[gadget73]

possible, normal plate load for that would be about 5k, which is a 50 ohm load. Could have been used as a buffer to get a small signal down a coax line or whatever.

 

[Mr Boochie]

Maybe it's simply a mic pre-amp section to a larger unit?

 

[Lavane]

A few years ago I put a little 6AQ5 SE amp together and thought it sounded pretty good. I wound up taking it apart and using the power trany for a SE guitar amp.
I noticed in your pictures you had that amp fired up without speakers connected.
Did you wire some load resistors connected to the output trany speaker taps?

 

[Mr Boochie]

A few years ago I put a little 6AQ5 SE amp together and thought it sounded pretty good. I wound up taking it apart and using the power trany for a SE guitar amp.
I noticed in your pictures you had that amp fired up without speakers connected.
Did you wire some load resistors connected to the output trany speaker taps?

Prolly needs a different OPT to match today's instrument speakers impedance.

I've made or fixed a few 6AQ5/6005 push-pull amps. The TungSol (USA) 6005 is one hell of a tube. It can make a great recording amp in the Champ power range.

 

[ceylon]

Maybe it's simply a mic pre-amp section to a larger unit?

but it has a pair of OPTs

 

[egellings]

possible, normal plate load for that would be about 5k, which is a 50 ohm load. Could have been used as a buffer to get a small signal down a coax line or whatever.

6AQ5 is a 6V6 in a peanut pentode bottle.

 

[nikon f]

I have a Magnavox 8802 amplifier that I use 6AQ5's instead of 6V6 tubes, it produces a nice quality of sound.

 

[Carbsandcaps]

The outputs transformers are about 4.3k into 8 ohms. The original tiny transformers were 800 ohm into 8 ohm. Here’s the original pictures.