Hey RATs:

Been messing with my 6v6 amps again, this time in the power supply.

Originally, a 340-0-340 transformer to a 5y3 giving 375v to a CRC filter
(10uf/5.6k/40uf) for 365v on the plates. I was able to scrounge a couple of
4H/137ma/95.5ohm chokes with plans of adding a choke input to the above. I
realise the choke value is a bit small, but was hoping I could make it work.

Does dividing 375v by 4Hy mean a 95ma load is needed at the choke output to
prevent voltage runaway? Could that be done with a 5k 25w bleeder resistor,
or is that asking too much for the power transformer to put up with?

Inserting a 95ma current tap after the choke in Duncan's Psud gets me a
simulation that works, knocking the plate voltage from 365v to 276v.

Ultimately trying to bias up close to Class A PP.

Thanks for any knowledge anyone can pass on.

dre

"dre7" wrote in message
om...
Hey RATs:

Been messing with my 6v6 amps again, this time in the power supply.

I presume these are 2 x 6V6 in PP.

Originally, a 340-0-340 transformer to a 5y3 giving 375v to a CRC
filter
(10uf/5.6k/40uf) for 365v on the plates.

I assume plates to the rectifier cathode, rest of circuit fed after
the 5.6K. If so, likely quite a lot of ripple on the plate B+.

I was able to scrounge a couple of
4H/137ma/95.5ohm chokes with plans of adding a choke input to the
above. I
realise the choke value is a bit small, but was hoping I could make
it work.

Small P/S chokes are better than no P/S chokes!

Does dividing 375v by 4Hy mean a 95ma load is needed at the choke
output to
prevent voltage runaway? Could that be done with a 5k 25w bleeder
resistor,
or is that asking too much for the power transformer to put up with?

I don't understand what you are trying to say. Regardless, don't put
in any 5K bleeder! You can't afford a 70 mA or so drain on the B+.

Inserting a 95ma current tap after the choke in Duncan's Psud gets
me a
simulation that works, knocking the plate voltage from 365v to
276v.

Experiment! I would first put in one choke as a choke input (no
resevoir cap - just connect it with a pair of wires to the choke
standing at the side of the chassis, one wire from the rect. cathode,
other to present reservoir cap.) and see what voltage you get. My
guess is close to 320 VDC at the 6V6 plates. Not as good as 365 VDC
but less ripple. You could also try two chokes in series (they seem
to be "free", or do you need one each for stereo monoblocs?) Then add
a capacitor from between the chokes to ground but now we're getting a
bit excessive

Ultimately trying to bias up close to Class A PP.

Ah, well, that's your decision. I would run them in AB1 or AB2 but
use scads of NFB (I trust you have enough first stage gain for this
and a decent OPT - check for stability on a 'scope), but then I
believe in designing power ampfliers as "thick wires with gain".

Thanks for any knowledge anyone can pass on.

dre

Legal Disclaimer: these are high voltage circuits that can give lethal
shocks. Only work on them if you are competent to do so.

Good luck and cheers,

Roger

Good advice in previous message.

I would try replacing the resistor with the choke. Your output voltage on
the PI filter will be higher than the resistor filter.

To reduce your ripple further, and drop your voltage down to previous
levels, use the output of the first PI filter as the input to a second PI
filter (since you found two chokes) with 40mfd caps on both sides. If you
still need to reduce plate supply voltage insert a series resistor between
the PI filters. BTW, you will get a different inductance in the second PI
filter depending on the orientation, placement, and lead connection with
respect to the first filter due to the inductive field interaction.
Experiement to see what works best. DON'T use any bleeder resistors.

"Engineer" wrote in message
news
"dre7" wrote in message
om...
Hey RATs:

Been messing with my 6v6 amps again, this time in the power supply.

I presume these are 2 x 6V6 in PP.

Originally, a 340-0-340 transformer to a 5y3 giving 375v to a CRC
filter
(10uf/5.6k/40uf) for 365v on the plates.

I assume plates to the rectifier cathode, rest of circuit fed after
the 5.6K. If so, likely quite a lot of ripple on the plate B+.

I was able to scrounge a couple of
4H/137ma/95.5ohm chokes with plans of adding a choke input to the
above. I
realise the choke value is a bit small, but was hoping I could make
it work.

Small P/S chokes are better than no P/S chokes!

Does dividing 375v by 4Hy mean a 95ma load is needed at the choke
output to
prevent voltage runaway? Could that be done with a 5k 25w bleeder
resistor,
or is that asking too much for the power transformer to put up with?

I don't understand what you are trying to say. Regardless, don't put
in any 5K bleeder! You can't afford a 70 mA or so drain on the B+.

Inserting a 95ma current tap after the choke in Duncan's Psud gets
me a
simulation that works, knocking the plate voltage from 365v to
276v.

Experiment! I would first put in one choke as a choke input (no
resevoir cap - just connect it with a pair of wires to the choke
standing at the side of the chassis, one wire from the rect. cathode,
other to present reservoir cap.) and see what voltage you get. My
guess is close to 320 VDC at the 6V6 plates. Not as good as 365 VDC
but less ripple. You could also try two chokes in series (they seem
to be "free", or do you need one each for stereo monoblocs?) Then add
a capacitor from between the chokes to ground but now we're getting a
bit excessive

Ultimately trying to bias up close to Class A PP.

Ah, well, that's your decision. I would run them in AB1 or AB2 but
use scads of NFB (I trust you have enough first stage gain for this
and a decent OPT - check for stability on a 'scope), but then I
believe in designing power ampfliers as "thick wires with gain".

Thanks for any knowledge anyone can pass on.

dre

Legal Disclaimer: these are high voltage circuits that can give lethal
shocks. Only work on them if you are competent to do so.

Good luck and cheers,

Roger