Heathkit AA-151

[WA4SWJ]

Brad,

Sounds good. I would still check it out and look at a square wave on the output with and without the network. More curiosity than anything else. Like I mentioned, it does roll off the high frequencies a little.

Great job on the amp so far. Glad it's working! Lots of fun this is! (Yoda language)

Regards,

[ecir38]

Thanks Ed,

Would it be alright to use Shannon's bias circuit for a pair of EL84's by changing the 470 ohm to around a 220 ohm resistor? Then adjust them to .70v and 200 ohms.



Brad

[ecir38]

Change the 470uF to a 150uF too.

Reason being I am not sure yet if four will fit in the space I would like to put them. Probably will order parts for dual and quad bias then fiqure it out..

Brad

[TerrySmith]

I think Shannon is going to do away with the bias circuitry and just have a 400 ohm resistor and a 470uf cap.

Anyway the 470uf x4 caps will fit, I uploaded pics of my modded AA-151.

The third pic is the VA-PI section with a 9A based tube.

[WA4SWJ]

OK Guys,

QUIT THAT!!!!

You're putting the rest of us to shame!

Great job fellas. The amps look great!!

Regards,

[ecir38]

Sweet, I love pics!!! I would like to rebuild one as an intergrated in the future thanks for sharing the pics.

Did you keep the rca phono stage?

Brad

[ecir38]

After looking at your pics again, I can see where I will be adopting allot from them. I particularly like the ground bus by the output tubes and the color scheme of the wiring makes it easy to figure the schematic :).

Brad

[TerrySmith]

Yes it has a phono stage, copied from the RCA tube manual. It sounds way better than the stock circuit. The linestage now starts at the 6AV6 tube. Also did away with the tone PEC's and used discreet parts, I'm going to re-do that part to make it look neater. The "stereo-mono-left-right-up-down-forward-backward" switch is disconnected.

Pic of the phono circuit:


Tone controls:




Picture of my Corvair:

Sorry, I just had to include it!

[WA4SWJ]

Terry,

Your amp is beautiful. Nice job!!!

[Vince]

Terry,
Thanks for posting the pic of the car. I thought it was a Corvair but wasn't sure. Nice piece!!!

Do you have a schematic of your altered AA-151? Thanks, Vince

[TerrySmith]

The rest of the circuit is basically stock except leave out the screen resistors and bypass caps for the 6AU6 and 6AN8 tubes. Since the line level lost a gain stage, I changed the divider resistors at the input jacks from 470k / 33k to 470k / 470k and omitted the 33pf caps.

In the power supply I added a 22uf cap at the 5AR4 then to a C-354 choke then to the rest which is stock values. Both filament circuits are paralleled into a bridge rectifier for DC at all preamp circuits. AC on the EL84's.

[mesherm]

Terry, that wouldn't be one of the turbocharged Corvairs would it?

[TerrySmith]

It's not the turbo, it has the 140hp 4 carb engine.

[EWBrown]

Saw this beauty parked under the pines at the NEAR-fest hamfest in May, at the Deerfield NH fairgrounds.




I can only wish that it were mine... These babies start out around $120K



/ed B

[TomMcNally]

Oh please Ed ... stay on topic !