Hi all. I built the JE 2A3 amp many years ago, using a single Hammond 272 BX. I just scrapped a different project that also uses the same transformer (I have 2) , so I want to rebuild this into two mono blocks.
I'm not a tube circuit expert, just a guy that like to solder every now and then, so please excuse me if these are dumb questions:
1) With only a single channel running from the PS, I'm assuming I can just eliminate the second resistor and capacitor (circled in red)?
2) Since each amp will only use 1/2 of the 6SL7, I assume I would just ground the pins from the unused half?
With Christmas coming up, I want to re-use as many components as possible.
I'm not a tube circuit expert, just a guy that like to solder every now and then, so please excuse me if these are dumb questions:
1) With only a single channel running from the PS, I'm assuming I can just eliminate the second resistor and capacitor (circled in red)?
2) Since each amp will only use 1/2 of the 6SL7, I assume I would just ground the pins from the unused half?
With Christmas coming up, I want to re-use as many components as possible.
1) no. 330V supplies the output tube at the output transformer, and 325 is filtered to provide B+ to the input gain stage/driver tube.
You can remove the second 12K3W resistor below the circled 1.2K 3W resistor as well as it's associated 20uF cap as this was for the second channel. The 330Supply is for both channels so no changes there.
You may ground the pins, but a better solution might be to redesign the circuit slightly by reducing the anode resistor from 100K to 50K (47K closest value),and the cathode resistor from 1K to 500R (470R closest value). Then parallel the two tube sections.. Increase the 100uF cap to 220uF at the same time.
It looks like the cathode resisstor in the center tap of the filament transformer should be two 1.5K resistors in parallel for 750R as this is the recommended catoode bias resistor value for a 2A3.
You will get a bit of hum from this bias/filament suppll scheme as there is no hum balance.
You can remove the second 12K3W resistor below the circled 1.2K 3W resistor as well as it's associated 20uF cap as this was for the second channel. The 330Supply is for both channels so no changes there.
You may ground the pins, but a better solution might be to redesign the circuit slightly by reducing the anode resistor from 100K to 50K (47K closest value),and the cathode resistor from 1K to 500R (470R closest value). Then parallel the two tube sections.. Increase the 100uF cap to 220uF at the same time.
It looks like the cathode resisstor in the center tap of the filament transformer should be two 1.5K resistors in parallel for 750R as this is the recommended catoode bias resistor value for a 2A3.
You will get a bit of hum from this bias/filament suppll scheme as there is no hum balance.
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Thank you, this is very helpfull.
I think the resistor and cap you suggest deleting are the same values as my deletion (1.2k and 20uF.) Its hard to see because of the low res schematic - sorry, It's the best I could find.
I'll definitely parallel the 6SL7 as suggested.
I did have a little hum with my original amp. I'm hoping cleaner wiring will help a little. There is an updated version of the circuit, with hum pots. I don't want to use this, simply because I'd need to buy more stuff, but would it be as simple as adding a 50-ohm pot?
I don't mean to have people design my amp for me, I just want to be sure I don't do something stupid.
I think the resistor and cap you suggest deleting are the same values as my deletion (1.2k and 20uF.) Its hard to see because of the low res schematic - sorry, It's the best I could find.
I'll definitely parallel the 6SL7 as suggested.
I did have a little hum with my original amp. I'm hoping cleaner wiring will help a little. There is an updated version of the circuit, with hum pots. I don't want to use this, simply because I'd need to buy more stuff, but would it be as simple as adding a 50-ohm pot?
I don't mean to have people design my amp for me, I just want to be sure I don't do something stupid.
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