Deluxe reverb power transformers

MrCoolGuy

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When Fender switch to the Silverface Deluxe Reverbs, they started using 5U4 rectifier tubes, but did they change the power transformer? Every schematic for a deluxe reverb that I can find AB763, AA763, AB868, A1172, A1270... all have the same power transformer "125P23B".
Am I missing something?

I only ask because multiple people have told me not to use a 5U4 in this old 64 deluxe. Its schematic calls for a GZ34... but it seems to be the same power transformer. So it should be fine running 5U4's, correct?
 

SoK66

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From about 1970 when Fender started using 5U4 recifiers instead of GZ34s the PTs were wound to generate more B+ to compensate. The part #'s didn't change. But what also happened in that era, wall voltages started to climb up to the 120vac+ levels we see today. So on a DR, even with a 5U4 you will get B+ in the 460vdc range. With the earlier amps like your '64 using a 5U4 will bring down the B+ into maybe the 425 - 440vdc range. Although the 5U4 is a 3A tube the PTs are more than capable of handling the extra draw.

The best way I've found to deal with the whole B+ thing on vintage Fenders is to feed the amp the wall voltage it wants to see using some sort of buck transformer. (A buck transformer lowers voltage rather than increasing it.) I've used Carl Hartman's "Amp Preserver" for years, but there are others out there including variacs and even a homemade option. (Google "Vintage Voltage.") Dial in the amp's desired wall voltage using the heater voltage. The closest you can get to 6.3vac is the sweet spot.
 

MrCoolGuy

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From about 1970 when Fender started using 5U4 recifiers instead of GZ34s the PTs were wound to generate more B+ to compensate. The part #'s didn't change. But what also happened in that era, wall voltages started to climb up to the 120vac+ levels we see today. So on a DR, even with a 5U4 you will get B+ in the 460vdc range. With the earlier amps like your '64 using a 5U4 will bring down the B+ into maybe the 425 - 440vdc range. Although the 5U4 is a 3A tube the PTs are more than capable of handling the extra draw.

The best way I've found to deal with the whole B+ thing on vintage Fenders is to feed the amp the wall voltage it wants to see using some sort of buck transformer. (A buck transformer lowers voltage rather than increasing it.) I've used Carl Hartman's "Amp Preserver" for years, but there are others out there including variacs and even a homemade option. (Google "Vintage Voltage.") Dial in the amp's desired wall voltage using the heater voltage. The closest you can get to 6.3vac is the sweet spot.
Yes, I understsand. I have done it each way: bucking xformers, zener diodes, changing rectifier tubes...
But this isn't my amp. Trying to help the owner.
 

2L man

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If mains voltage stay stable and only B+ are too high there is no need for bucking transformer. Just installing series resistors to rectifier tube anode circuits drop voltages, lessen hum, increase sag-effect and lengthen rectifier tube life.
 




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