Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: dude on May 13, 2021, 11:45:00 am
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A friend of mine picked up an unmolested AO-44, he asked me if I could do anything with it. I found Sluckey's PeeWee conversion. Seems pretty easy as most of the existing circuit is kept. Adding the Fender preamp AB763, I noticed the cathode caps have been excluded, I assume the amp had too much gain or was bass heavy..? Steve, if you read this, any other suggestion you would recommend?
I also didn't see a CT on the filaments but your conversion's schematic has a CT, I didn't see any 100 ohm R's, is the CT internal or not needed...? I don't have a variact and hoped to use the original can, anyway to reform it a bit, or just hit it with HT and hope for the best.
Don't know if PT wiring can be seen in pic but didn't see a filament CT, correct me if I'm wrong.
Thanks,
al
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I actually removed the typical Fender 25uF cathode caps to reduce the bass.
Look at the original AO-44 schematic included in my docs and you'll see the filament CT is internally connected to the HT CT (red/yel wire). Verify by measuring the resistance from either filament lead to chassis. You should read nearly zero ohms.
I've never reformed caps with the following method but I've read that others have had success... Put a 1M resistor between the rectifier cathode and the first cap.
Specifically for this amp, disconnect the red wire and 1K from the recto pin 3. Leave the red wire connected to the 1K and let them dangle safely. Now connect the 1M resistor between pin 3 and the dangling red wire/resistor. Power up and let it sit for a couple hours. Turn it off to drain caps. Replace the 1M with a 100K and repeat. Replace the 100K with a 10K and let it sit overnight. Hopefully the caps will be recharged and you can reconnect the red wire and 1K to pin 3. If this doesn't work, don't blame me. I'm just passing on some net lore. :l2:
As much as you love tinkering with this stuff you should really own a variac. You can find some 10A ones at a reasonable price these days. So, save your money. Sell some AO-43s.
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Thanks, l take it slow voltage over time not only “maybe” reforms old cap cans but reforming the first cap in the can does them all... l hear ya on the variac, l have a box full of nice old Mallory cans, money saved if they reform is well worth the cost of the variac :icon_biggrin: . As far as bass heavy, l can always try a lower gain tube, maybe 12ay, coupling caps changes too might help. The guy is a blues player, he likes his bass tight, might not be for him, ha. I’ll just keep it, ha.
Those AO43’s are narrow but using 1” standoffs on the PT opens up a lot of room. Did the Plexi thing with them, lot of work but enjoyable for me, l got nothing else to do in retirement, :l2: . Too old to gig anymore, too old to do much of anything l use too, just an old fart now. You are quite the go to man, thanks for everyone for your sharing. Cheers, l’ll drink to that...
al
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If this works then all caps on the B+ rail should be affected. I'd pull all tubes except the recto to do this. You know that PeeWee became a donor for my Magnatone M2?
Cheers back at 'cha dude...
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Hello,
I modified a leslie 760 because the treble amplifier was lazy.
I replaced it by an amp like this.
It is not complicated and the result is wonderful.
JP