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Re: Biasing problem with '62 Princeton 6G2

6/26/2004 8:20 AM
Wild Bill	Re: Biasing problem with '62 Princeton 6G2 Chris, 198 volts on the 6V6 plates doesn't really sound right! You really should go to the Fender Field Guide and d/l the schematic. The factory voltages are almost double what you found. The only way you could get such low plate voltage is if when you wired up the can you crossed something somewhere. Double and triple check it - especially the bias tap on one plate of the 5Y3. If you didn't have enough negative bias voltage in the first place tacking in a pot won't help. If there's not enough there's not enough! I'd first try pulling the output tubes and measuring the voltages along the filter cap string. If they aren't starting off at nearly 400 volts with no 6V6 loads I'd definitely want to know why! Then I'd check that bias voltage. The print says about -35 volts - how much do you have? If it's too low the 100k dropping resistor from the 5Y3 could be damaged or maybe even the bias supply diode. Check the bias stuff AFTER you find out what's wrong with the B+ voltages! The low voltages might be screwing up the bias supply and after things are corrected the bias might come back to normal. HTH ---Wild Bill

6/26/2004 8:20 AM

Wild Bill

Re: Biasing problem with '62 Princeton 6G2

Chris, 198 volts on the 6V6 plates doesn't really sound right! You really should go to the Fender Field Guide and d/l the schematic. The factory voltages are almost double what you found.

The only way you could get such low plate voltage is if when you wired up the can you crossed something somewhere. Double and triple check it - especially the bias tap on one plate of the 5Y3.

If you didn't have enough negative bias voltage in the first place tacking in a pot won't help. If there's not enough there's not enough!

I'd first try pulling the output tubes and measuring the voltages along the filter cap string. If they aren't starting off at nearly 400 volts with no 6V6 loads I'd definitely want to know why!

Then I'd check that bias voltage. The print says about -35 volts - how much do you have? If it's too low the 100k dropping resistor from the 5Y3 could be damaged or maybe even the bias supply diode.

Check the bias stuff AFTER you find out what's wrong with the B+ voltages! The low voltages might be screwing up the bias supply and after things are corrected the bias might come back to normal.

HTH

---Wild Bill

Replies:

Chris >Chris, 198 volts on the 6V6 plates... -- 6/27/2004 6:22 AM