My amp has the wrong rectifier tube, is that a big deal?

[Burstbucker]

I just worked out a trade for a 1969-70 Fender Vibrolux Reverb amp, I just started cleaning her up and I noticed that the tube chart says to use a GZ34 for the rectifier but somebody went and put in a 5U4 instead. Is this a potential problem to the health of the amp or maybe to the way it performs?

I'm not sure if I need to replace this tube right away or if it's okay to use a 5U4 rectifier tube in this amp.

[jcs]

absolutely install a gz34-5ar4 preferably a mullard-amperex 60s production with a usa production as 2nd choice..

you will need to check plate-screen volts-current bias of your amp too.

[Blue Strat]

You're probably ok, but you may want to consider using the correct tube to hear what the amp is supposed to sound like.

A Mullard/Amperex would be great but very expensive. The JAN Philips is a much less expensive and high quality alternative.

[donnyjaguar]

I'd say only change it if the amplifier isn't serving up the volume you're looking for.

[Burstbucker]

Thanks for your comments!

This little amp sounds amazing but it's a little bit shy on volume IMHO. I plan on doing a complete cap job, replace both power tubes and rebias, and I'm also going to try putting in a GZ34 in there to see how I like it.

I've got a feeling that this little bit of maintenance work is long over due and should liven up the amp too.

[hunter]

In 68 Fender issued the AB568 Schematic. That scheme depicts a 5U4GB. Fender also issued an AB568 Layout. That layout depicts a GZ34. That should clear things up. In 70 the AA270 scheme AND layout call for a 5U4GB.

Fender is well known for using up what they had including tube charts. I'm not sure I'd consider the tube chart to be the authoritative source for rectifier tube info.

I know this doesn't help much but I'd at least suggest proceeding with caution. I believe there is a chance your amp was built to use a 5U4GB. You could check plate voltages and maybe compare some scheme values to try to get an idea which scheme and components (mainly PT) your amp was built around.

At any rate just use a little caution. A GZ34 could pump your plate voltage up to levels that give your power supply caps problems as well as other components. If you can live with the voltage you get from a GZ34 (and you rebias accordingly) everything else should be OK.

hunter