been away for a few years, and now I'm looking to start working on some of my projects. I have two nice unrestored UA-2 amps, as well as an AA-61 (same amp, different color). I want to restore the two UA-2s near stock, but without the goofy current feedback circuit, and without the preamp socket and all its wiring. I bought two new can caps 40-20-20-50 from Hayseed, and now need to order the coupling caps and whatever else I need to get these up and running. Any advice? Anyone have a simplified schematic like I described? I've seen the threads on mods, but want to start stock and go from there.
Thanks in advance!
Steve T
Thanks in advance!
Steve T
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A PP EL84 amplifier. Rip everything out and look to doa variation on El Cheapo, Red Light District, or Baby Huey. 3 VERY modern EL84 PP amplifiers that many here have built.
dave
dave
Dave, I may just do that, with the el cheapo..... Is there a comparison between these three somewhere?
Steve T
Steve T
They are all very good. We base dours on El Cheapo, a Scott chassis and iron, Class A , triode, only 3.2 w but the amplifier is competitive sonically with teh SIT-3 in regular use. I prefer a LTP front end to a paraphase splitter.
dave
dave
from the Sheldon Stokes page: "The UA-1 and UA-2 amps are essentially identical. The only difference between the UA-1 and UA-2 are that Heath increased the value of the cathode resistor on the output tubes because they were running them WAY too hot, and burning them out quickly. The UA-1 had a 130 ohm resistor in the cathode at first. They changed that pretty quickly though, and the schematic here reflects that change. They also reduced the value of the screen grid resistor on the input stage to 680 K ohms."
I imagine my Heathkit AA-151 integrated would be a good donor, right?They are all very good. We based ours on El Cheapo, a Scott chassis and iron, Class A , triode, only 3.2 w but the amplifier is competitive sonically with teh SIT-3 in regular use. I prefer a LTP front end to a paraphase splitter.
dave
Steve T
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Yes, indeed. I an converting a single 2-chassic mono Heath AA-32 into a stereo SE 6V6 if i can figure out how to easily get less voltage from the taro.\
dave
dave
Or doing an Acrosound 20 Frankenstein like I did here:
https://audiokarma.org/forums/index...-1-frankenstein-project.995909/#post-15612335
Won't be disappointed with the sound, that's for sure, just more complicated than the simple original design.
https://audiokarma.org/forums/index...-1-frankenstein-project.995909/#post-15612335
Won't be disappointed with the sound, that's for sure, just more complicated than the simple original design.
planet10,
I was not familiar with the AA-32 schematic, so I looked it up.
But because it uses a 2 diode 2 cap voltage doubler, it is not adaptable to be able to use a choke input B+ filter.
So the series dropping resistor is the only way to reduce the B+ voltage (It will not have enough B+ voltage using a bridge rectifier and single cap input filter).
Use a dropping resistor, or purchase a different power transformer.
Using a 2 diode 2 choke input circuit is not practical, especialy since each arm of that circuit is only half wave.
I was not familiar with the AA-32 schematic, so I looked it up.
But because it uses a 2 diode 2 cap voltage doubler, it is not adaptable to be able to use a choke input B+ filter.
So the series dropping resistor is the only way to reduce the B+ voltage (It will not have enough B+ voltage using a bridge rectifier and single cap input filter).
Use a dropping resistor, or purchase a different power transformer.
Using a 2 diode 2 choke input circuit is not practical, especialy since each arm of that circuit is only half wave.
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