power supply on Champ build

[john_t]

I have an extra circuit card for a 5e1 champ. Iam using 16uf and 8 uf caps. no choke. What size wattage do you recommend in the power supply. Also are my 25uf 50 caps ok as opposed to 25 25'  thanks john

[bigdaddy]

Do you mean voltage?

If so then it depends on your B+. For the first cap I would go with 500. After that 450 is probably OK but it really depends on your PT and what your B+ is.

Yes 25 50 or 25 is OK on your preamp but on the bias for the power tube no less than 50v.

[john_t]

Bigdaddy, Thanks for the help. Once again I was not clear with my Question. I have 475 & 450 volt capacitors in the power supply. 16-475 8-450v and 8-450v. I will be using Dougs 125p1b pt. MY .022s are 600v. I have the mallory and the sprague. Not sure which to use (soundwise) I meant to ask about the wattage on my resistors. Most are !/4 watt. What should my 470 be on the bias. I have 3 watt, also not sure on the supply caps, That is  was what I meant to ask.

[Fresh_Start]

470/1-watt should work fine on the 6V6 cathode.  Personally, I'd use 1-watt resistors on the power rail (B+ line) too for the 5F1 circuit.  Or you can do the math:  each 12AX7 triode draws up to 1.5ma, the 6V6 screen can pull up to 6ma and the plate can pull up to 35ma.  Ohm's Law 
Frank's tube data sheet search

If you don't want to use a choke like the 5E1 or 5F2 do, I'd suggest a pi filter (C-R-C) before the power tube plate like the 5C2 HERE.  It will make a significant difference in the noise level.  You can put the "extra" cap & resistor on a tag strip.  I've tried both a pi filter & a choke before the plate node and either one is a big improvement in my opinion.

Also, Hoffman's PT is 320-0-320.  That will put voltages with a 5F1-type circuit 25-50 volts higher than vintage.  If you put a 1K-5 watt resistor in that pi filter it will drop the voltage a bit more than the 470 shown in the earlier Champ (40 volt drop +/- vs. 20 volt drop +/-).  Using an NOS 5Y3 rectifier will also drop about 25 volts compared to the new Sovtek "5Y3" tubes which don't conform to vintage specs at all.  To my ears, aiming for the voltages shown for the 5E1 and 5F2 schematics produces a warm, Tweed tone.  You may like the higher voltages used in the Blackface Champ, so don't take this as gospel.

Technically, adding a dropping resistor before the plate(s) might add some "sag" to the amp.  It's debatable whether that happens in a single-ended amp, and I liked the effect, if any, myself.

A 5F2-A was my first build and it's been re-built at least 3 times (so far ), so I'm just sharing what I thought worked well.

Cheers,

Chip

[john_t]

fresh start thanks. Wow I don't know so much. I have a 22k 3 watt and 10k 3 watt I was going to place in the power supply vs the choke. That was based somewhat on Webers 5f1 version. What do you think. Thanks for the help.

[Fresh_Start]

3 Watters are fine in those two spots

Volts * Current = Watts

Current * Resistance = Volts

Current * Current * Resistance = Watts

One 12AX7: 3ma squared * 22k = .198 watts, so 1/2 watt would work fine there

One 12AX7 + 6V6 screen:  9ma squared * 10K = .81 watts, so use 1 watt or 3 watt depending on how much cushion you want.

12AX7 + 6V6 plate & screen:  44ma squared * 1.5K = 2.9 watts, so 5 watts would be needed for a dropping resistor before the plate. 

You want at least a 10% cushion on any resistor's wattage rating IMHO, and I want more room than that on the power rail.  Also, these current estimates aren't cast in stone.  They're based on the data sheets at specific voltages.  The only way to know for sure exactly how much current draw there is, you have to build the amp and measure the actual voltage drop across each resistor.

Took me a while to understand this myself, so I figured the concrete example would help.

Cheers,

Chip

[john_t]

Fresh Start, thanks so much for the help. I just finished my ga-5 build. which by the way I really like so far. I had so many parts left over I decided to build the 5e1 for a friend. il keep everyone posted on my results. I could not do this without all the help. Having fun thanks again.