30-09-2019, 10:05 AM
Hi Everyone!
So, I've learned a lot.
TV boost diodes make perfectly good HT rectifiers.
You can use a power transformer as an output transformer for a valve amplifier, particularly useful for push pull.
Recent experiments with the balance circuit earlier in the thread using a half wave power supply (as I intended to use), show that it CAN be able to null hum, but that feature isn't coincident with the standing current balancing that I was aiming for. Maybe it would be possible to combine both, but, it seems an either/or situation to me, and balance of AC at 50Hz and DC together in a power transformer would make me want to go back to building a PP amp.
I've tried several valve types, thanks to a couple of the members here who are super guys and took the time to send me some that I wanted to try (Boater Sam & Ppppenguin) the best for the PP version have been the PCL83, though that's a bit much for what I wanted here.
What I seem to be settled with is the ECL80, despite its shortcomings, a pig to bias, and it's liability to take off at the least excuse, it has a low heater consumption, is not OTT for my application, and, I kind of don't like to be beaten by a dumb valve!
As Kalee20 kindly sent me a small SE transformer to suit my needs I built another version with the ECL80, with no balance feature needed it could be compared with the mains transformer version.
Its rather good!
The frequency response is better, though not going down quite as far as the mains transformer version it appears.
Also it produces approximately a third more power for three quarters of the current consumption....
The penny finally dropped on this one Lawrence! I've incorporated it into the recent version, thanks.
I'm including the update on the attached diagram, one erratum is the cathode capacitor is 470uF not 47uF as the diagram, its needed to stop + feedback.
I will tidy this up for some glamour photos to post when I start putting all the elements of the project together.... Hopefully!
It will be the most complex thing I've built....
Amie.
So, I've learned a lot.
TV boost diodes make perfectly good HT rectifiers.
You can use a power transformer as an output transformer for a valve amplifier, particularly useful for push pull.
Recent experiments with the balance circuit earlier in the thread using a half wave power supply (as I intended to use), show that it CAN be able to null hum, but that feature isn't coincident with the standing current balancing that I was aiming for. Maybe it would be possible to combine both, but, it seems an either/or situation to me, and balance of AC at 50Hz and DC together in a power transformer would make me want to go back to building a PP amp.
I've tried several valve types, thanks to a couple of the members here who are super guys and took the time to send me some that I wanted to try (Boater Sam & Ppppenguin) the best for the PP version have been the PCL83, though that's a bit much for what I wanted here.
What I seem to be settled with is the ECL80, despite its shortcomings, a pig to bias, and it's liability to take off at the least excuse, it has a low heater consumption, is not OTT for my application, and, I kind of don't like to be beaten by a dumb valve!
As Kalee20 kindly sent me a small SE transformer to suit my needs I built another version with the ECL80, with no balance feature needed it could be compared with the mains transformer version.
Its rather good!
The frequency response is better, though not going down quite as far as the mains transformer version it appears.
Also it produces approximately a third more power for three quarters of the current consumption....
(23-09-2019, 09:03 AM)pwdrive Wrote: To avoid using a separate bias supply you could use cathode bias (potential divider)
Lawrence.
The penny finally dropped on this one Lawrence! I've incorporated it into the recent version, thanks.
I'm including the update on the attached diagram, one erratum is the cathode capacitor is 470uF not 47uF as the diagram, its needed to stop + feedback.
I will tidy this up for some glamour photos to post when I start putting all the elements of the project together.... Hopefully!
It will be the most complex thing I've built....
Amie.
