Deluxe Reverb plate voltage concern
Moderators: pompeiisneaks, Colossal
Re: Deluxe Reverb plate voltage concern
Yes, the 25mf/25v caps. They degrade w/ time and 40 years is a long time, and the amp gets slowly darker and softer. You barley notice until you replace them and then the amp perks up. E-caps ought to have a date on them usually week-year e.g. 4885 would be 48th week 1985. Your bias range is prolly ok, it's likely all the way over with that pair of tubes. Those tubes may be tired if run for a long time the way they were. A 5ARA will put you close to the SS again I'd stick with the 5U4. I really regret never having grabbed a SFDR when they where $350.
Re: Deluxe Reverb plate voltage concern
I've had quite a few deluxe reverbs that run around 450 plate volts. Use some JJ 6v6s they can handle that voltage.
Re: Deluxe Reverb plate voltage concern
The poster said he the lowest dissapation he could bias the tubes with the 5U4 to was 74% which for most amps would be the upper limit that you'd want your bias to be set. The bias voltage needs to be MORE NEGATIVE to be able to lower the idle current of the power tubes...It needs to be more positive, you do not want the larger tail resistor. With 450v he should not need anything larger than around 12k. Assuming the bias circuit is stock with a 10k pot, a 9-12k bias tail resistor should be plenty.
Thus the tail resistor needs to be a higher value. You could use a decade resistance box to dial in the exact resistor value or try the 22k for starters. Some of the other Blackface Fenders use 22k to 27k for that resistor...
TT
Re: Deluxe Reverb plate voltage concern
Yes, for 6L6 tubes, not the 6V6.tictac wrote:Some of the other Blackface Fenders use 22k to 27k for that resistor...It needs to be more positive, you do not want the larger tail resistor. With 450v he should not need anything larger than around 12k. Assuming the bias circuit is stock with a 10k pot, a 9-12k bias tail resistor should be plenty.
TT
TM
Re: Deluxe Reverb plate voltage concern
Maybe so, but keep in mind the idle current of a particular type of power tube can vary greatly from tube to tube. Which is one reason companies like Groove Tubes have a numerical rating system for thier tubes. This chaps 6V6 pair seems to be idling higher than average. Put these tubes in a Fender that uses 6L6's and they'd probably bias up perfectly...Yes, for 6L6 tubes, not the 6V6.
The fact is the tail resistor on the bias adjust pot for this guy's amp which uses 6V6 tubes needs to be larger than 10k if he's going to be able to adjust the bias in the 50% to 60% plate dissapation range which is a good setting for good tone and longer tube life...
15k to 22k would be my best guess...
TT