High rectifier voltage on standby

[Choan]

Hey yall, I have a Fender Deluxe AB868 (non reverb, with vibrato) that I’m checking voltages on. It was brought to me and wasn’t powering up, a quick check revealed the power switch is non functioning, easy enough fix. I jumped over the switch to get some readings. The only one that concerns me is the amp runs 513dc on the rectifier output (JJ5u4), and drops down to about 470 fully loaded and powered up. Secondary rectifier input is around 360 I believe, about 30v high. The FT caps are rated at 500 +30% so not so worried about that. Does that standby voltage concern anyone? Preamps looks good, power tubes are 425dc, biased at 23ma. It looks like the filter section has been modified to have a 27k resistor in addition the normal 10k next to it, maybe someone tried to drop the B+ before. Another anomaly is the pair of 100 ohm artificial center resistors appear to be a pair of 2k, oddly. Anyways it sounds good, no red plating, I’m just a little concerned about the 5u4 getting bbq’d.

[shooter]

easy enough fix.

yep, just use the SB switch to fix the power switch, problem solved!


original Fender or homemade version of?


didn't look at the rectifier datasheet, find max volts into a cap load

[Choan]

That is a great solution 😅😅

The JJ data sheet uses ‘Ua invp’, mind helping me understand that? on rectifier reference sheets it says 450maxpv, but I know JJ is known to be rated higher. The JJ sheet says Ua inpv=1550 into 40uf.

https://www.jj-electronic.com/en/5u4gb

[Merlin]

The JJ data sheet uses ‘Ua invp’, mind helping me understand that? on rectifier reference sheets it says 450maxpv, but I know JJ is known to be rated higher. The JJ sheet says Ua inpv=1550 into 40uf.

Ua invp is the max peak inverse voltage. Max RMS voltage is therefore about 550V per plate for choke input, although 450V for cap input. Either way, well above what you have. Vintage datasheets are much better!
https://frank.pocnet.net/sheets/127/5/5U4G.pdf

[Choan]

Thanks for the insight fellas, I’m in a safe range! Cheers.