Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Bassden on December 03, 2021, 09:16:21 am
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Thank you for any information you may have. Sorry this is long however, I do not know how to make it shorter.
I am attempting to duplicate a Hammond AO44 amp conversion with the Steve Luckey AO-44 Pee Wee Build. I cannot find a same standard power transformer and found this toroidal power transformer. It looks like it will work and I have one installed in a new build.
The red and black primary wires are both red wires to hot black of the power cord and both black wires of the power transformer to the neutral, white wire of the power cord.
On the secondary I have one white and one yellow connected together for the center tap and the other set of yellow and white wire going to the plates of the 6CA4 rectifier.
I already have an AO44 amp I converted without the Fender preamp and measured the B+
voltages. on the first connection before the filtering on the AO44 amp that's working I get 302vdc
under load and 320vdc not under load.(no tubes except the rectifier and the CT off the first B+)
On the new one I'm building with the new toroidal transformer I'm getting 370vdc not under load. 50vdc more. All the B+ voltages are the same, 370dc. The only thing I can figure is the PS filtering caps are not the same manufacture but measure x3 30mf and x1 20mf two of the center caps at 30mf are twice the physical size of the other 30mf and 20mf. I would not believe that should matter. The Antak tech I've been emailing says, "Your need to consider the voltage drop on the tube and transformer. The AS-1T250 will give your about 300Vdc with load on your circuit. I understand the regular voltage drop of about 20vdc. But this is still 50vdc higher than that.
With everything reconnected and the tubes in I turn on the amp and my light bulb current limiter never lights. As the tubes warm up and conduct it sounds like, coming from the new Antek power transformer
a vibration noise that progressively gets louder so I shut it off within a couple seconds.
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Public service post # 1 of the month
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After measuring the existing Hammond AO44 power transformer on the working amp I have I used this to compare. It looked like a good match. I got 302vdc with load on, on the output of the rectifier.
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edited
Sorry, I don't have time to give your problem justice. Rather than rush an answer, I'm gonna back out.