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youthnotlost (November 30, 1999 at 12:00 am)
I never worked on the unit. I bought it at a resale store for $15. They were asking $50.00 but when it was plugged in, the lights didn't go on. I noticed the function knob was set where lights didn't show. I had to replace a couple of output fuses and it has worked ever since.
retrochad (November 30, 1999 at 12:00 am)
Thanks for your comments, you are absolutely right. I think I have the problem solved by using 6v6's but slightly reducing the AC line voltage coming in.
retrochad (November 30, 1999 at 12:00 am)
Ok, Thanks...I may need to add a little more cathode resistance to get to 31 ma.
Maxxarcade (November 30, 1999 at 12:00 am)
According to the Weber bias calculator, the ideal cathode current for class AB bias would be around 31ma per tube with 315v on the plates. That was for the 6V6GTA, which I think is the same as a 6V6GT.
retrochad (November 30, 1999 at 12:00 am)
Actually the E=IR calculations ended up with 70-72 ma for two tubes in push-pull and then I divided that by two to get one tube's value.
retrochad (November 30, 1999 at 12:00 am)
What would you recommend for the current...I was experimenting with different values of cathode resistance. I guess I calculated 19 volts at the cathode resistor divided by 270 ohms to get the 36 ma which I assume is what the tube is drawing through the resistor.
Maxxarcade (November 30, 1999 at 12:00 am)
Almost forgot- 36ma at 315v seems a bit high. You may need to change your cathode resistors. Are the plates getting hot?
Maxxarcade (November 30, 1999 at 12:00 am)
Cool, let me know how it holds up :-)
Most amps are ok with today's higher AC voltages, but the ones that already run close to their limits often get pushed over the edge.
Another thing to check is the filament voltage. If it seems noticeably high (say over 6.5v or so), that is another clue that there is still too much incoming voltage.
That problem is one of the reasons I decided to use a new power transformer in my amp instead of a vintage one.
retrochad (November 30, 1999 at 12:00 am)
THANKS Aaron for this suggestion. I put a 10 ohm wirewound resistor in series with the incoming power line and used the 6V6's again and now the plate voltage on the 6V6's is about 315 volts and the cathode current is about 36 ma each. Without the resistor the plate voltage was around 345.
The AC line before the resistor was 119-120 volts and at the output of the resistor is 115.
desertbard (November 30, 1999 at 12:00 am)
When is the last time the alignment had been checked on that FM section. |
