6V6 SET amp with 6SN7 driver

[Eli Duttman]

A choke I/P filter should put you quite close to 250 VDC. The rectifier feeds a LC section plus bleeder resistor. Follow the 1st LC section with 2X LC sections, 1/channel for good separation. A RC section for each driver plate finishes things off.

[camotecue]

Originally posted by Eli Duttman
A choke I/P filter should put you quite close to 250 VDC. The rectifier feeds a LC section plus bleeder resistor. Follow the 1st LC section with 2X LC sections, 1/channel for good separation. A RC section for each driver plate finishes things off.

thanks eli. but as a newbie (please pardon my ignorance), i cant quite understand what you've just mentioned. i would really appreciate if you could put it in schematic form.

[arnoldc]

camotecue,

you said you need a voltage drop of 70V (250-180) and we need the current drain of that stage to compute for the dropping resistor.

if it is 2mA for example, then R = 70V / 0.002A = 35Kohm

i can draw you a schematic as suggested by eli, later.

we will also need the current drain of the power stage to compute for the power supply.

here is the schematic.... it does not include the RC section which would be B+ (from the diagram) ---R (?)--- C (47uF) ---> driver for each channel... oh and i forgot the bleeder on the first cap

[camotecue]

Originally posted by arnoldc
camotecue,

you said you need a voltage drop of 70V (250-180) and we need the current drain of that stage to compute for the dropping resistor.

if it is 2mA for example, then R = 70V / 0.002A = 35Kohm

i can draw you a schematic as suggested by eli, later.

we will also need the current drain of the power stage to compute for the power supply.

here is the schematic.... it does not include the RC section which would be B+ (from the diagram) ---R (?)--- C (47uF) ---> driver for each channel... oh and i forgot the bleeder on the first cap

thanks for your help. do i see three (3) 10H chokes?

[arnoldc]

yes, you do. the value (10H) is a suggestion and what i mostly use. the 5U4G manual also lists that as a typical value if i'm not mistaken.

[Eli Duttman]

Better than 3 10 H. chokes is a 20 H. choke in the 1st position and 2X 5 H. in the 2nd position. A 10 KOhm bleeder resistor is used with a 10 H. choke, while a 20 KOhm bleeder resistor is used with a 20 H. choke. A larger 1st inductor allows you to lower the I^2R losses (heat) in the bleeder resistor.

BTW, an inductor rated for choke I/P service is required in the 1st position. "Beefy" construction is in order to cope with the large AC ripple current that is present. The chokes used in the 2nd position can be of the "ordinary" variety.

[SHiFTY]

Or you could just use something like 20uF-10H-47uF and you would be right. Modelling this in PSUD gives a very smooth power supply.

Voltage would be higher, at around 320V, but you can boost your cathode resistors on the 6V6s to compensate, so you don't go over the plate dissipation rating (12W I think?)

Three chokes is excessive, IMHO.

[Eli Duttman]

Three chokes is excessive, IMHO.

You're going against long established precedent. Older editions of the ARRL Handbook specifically advise that 2 LC sections in cascade be used when choke I/P filtration is employed.

Using a pair a LC sections after the 1st LC section isolates the 2 channels from each other. It's a form of pseudo dual mono power supplies.

CLC supplies are POORLY regulated, while choke I/P supplies are WELL regulated. Another advantage of choke I/P filtration is the ability to access the full VA capability of the power trafo.