Taming The Acrosound Model 20-20

Thank you.

Yes you need new boards on those as they ran the output tubes to hell and back, therefore generating a lot of heat cooking the old boards.
Today's boards are quite good: those are 1.6 mm thick, 2 Oz copper thick, lead free with double layers. glass epoxy rated to 140C.
I added a hole at the bottom of each tube for heat ventilation.
Those with Dave's changes will make the amp run forever.

You should have bought one, they sound marvelous :)
 
Hi guys,

Latest chapter on the Acrosound 20-20 adventure.

I installed the new boards: no issue there.

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Then I change the high voltage supply to a full wave doubler. I first used diodes but looked messy. I set my choice on a rectifier bridge. I could re-use the 200uF originally from the Authenticap can so I only had remove C4 and install a 200 uF for the other side of the doubler. The rest remained untouched.

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Then I replaced the wire wound chassis resistor with Caddock thick film (non inductive). I started with a 2.5K but the bias was too high (35mA).
So I added in serial another Caddock 360R and it worked nicely. I now cruise at 30+ mA per tube for a cathode resistor of 2.86K
Those Caddock resistors are nice but get hot.
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That's pretty much it.
I installed vintage NOS GE 12AX7 and TAD EL84STR. Note that the balancing of tubes also depends on the 12AX7 tube, as well as the bias level.
But by picking the right cathode resistor, the max cannot be exceeded so all tubes will now work nicely in this amp.

Sound wise this little guy pack a lof of punch and has fast transients, like all Acrosound amplifiers. It's a really good little amp.

Thanks to Dave and others for helping me with this little terror.

Some pics before I put it away :).

Cheers.

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Looks good.

I bought a Pilot SA-260 instead. I figured I had enough EL84 amps at the time, and I wanted something with a little more grunt.
 
Thanks guys,
Yes it does.
Please swing by and we can do an EL84 amp contest with your nice heathkits :)
 
At some point probably in the middle of this happening i ran across (or perhaps spoke to on Phone, i don't remember) Brice. I thought i was paying attention but somehow i missed this whole thread.
:dunno:
As always a great read. Boards look great!:thumbsup:
 
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