5f1 build, s

[pontiacpete]

I put together a 5F1 and it's not doing so well.
Very distorted.
These are my voltages

6V6:
pin 3 - 478v
pin 4 - 458v
pin 5 - 0 v ?
pin 8 - 58v

12AX7

pin 1 - 254v
pin 2 - 2v
pin 6 - 254v

these seem high,
any suggestion?
thanks
pete

[loudthud]

Pin 2 of the 12AX7 should be 0V. What are the 12AX7 voltages on pins 3, 7 and 8?

[pontiacpete]

I made a mistake. the 12ax7
pin 3 - 2.0v

and
pin 7 - 0v
pin 8 - 1.9v

thanks
pete

[loudthud]

Those voltages are pretty high! The one that is suspicious is pin 8 of the 6V6. Measure the resistance to ground of that point with the power off. Your meter may not give a stable reading with the capacitor in the circuit. If you can't get a stable reading, unsolder one side of the cap.

[pontiacpete]

thanks loudthud,

I unsoldered the 25uf/25v cap and measured 460K to ground from pin 8 of the 6V6.

pete

[loudthud]

That resistor is supposed to be 470 ohms 5 watts.

[pontiacpete]

that was it, I put a 470K in by mistake. I put a 470 ohm 3W in(that's all I have on hand) and it's working fine. Thanks!
If I want to use a 6L6 instead of the 6V6, how do I figure the size of that cathode resistor?
pete

[loudthud]

A 6L6 will draw more current and there will be more voltage across the resistor. If I remember correctly most people stick with the 470 ohm value (do a search to confirm) but the increase in current dictates a 5 or 10 watt part. Generally the power is calculated as voltage squared divided by resistance and then use a part roughly double that power for reliability.

[pontiacpete]

Thanks Loudthud! I'll wait on that until I get some higher wattage 470's.
I'm putting this amp together because I have this idea of making a battery powered tube amp using the following circuit to supply B+ and eliminate the PT. How do you think it will work? Is it possible using a couple of 12v gel rechargables.

[loudthud]

A 3 watt 470 ohm will be fine for a 6V6, use a 5 watt to be safe for 6L6. Fender used a 2W in the Champ.

That power supply will probably work. You'll need to find a NOS 12V6GT so you can run the heater directly from the battery and just use the 12AX7 in the 12V mode. I'm not sure exactly how the supply regulates. If it just cuts the oscillator off when the output voltage is high enough, there can be random sounding noise on the output that you may hear through the speaker. Better to use one of the chips designed to be a regulator that use pulse width modulation to regulate.

[pontiacpete]

thanks again Loudthud,
I didn't think of the 12v6 , the first amp I was thinking of doing this with was the 5e3, however since the champ is a single ended amp and has only one 6v6 I'll have to change that out to the 12v6 to make the heater set up easier. thanks.
I'll, also, look into the pulse width modulation to regulate.
I'm sure I'll be posting more on this project soon with questions.

pete