Fender Twin transformer runs hot?

[gregsk777]

Hi, I have a 135 watt silverface twin reverb and the ultralinear power transformer seems to get hot. After about 1 hour it gets warm and at about 1 1/2 hours it starts to get hot? Everything else in the amp works perfect (the quietest amp I have ever owned!) and I have never had any problems using it 1 hour at a time.

Also last time I checked, the plate voltage was about 575V! Which to my knowledge seems way too high!

Besides replacing it with an expensive Mercury Magnetics transformer what else can I do or check first?

[gregsk777]

Any thoughts anyone?

Should I just keep on using it till one day it blows! Or should I investigate?

[gregsk777]

Any thoughts anyone.

I jammed with it for 2 hours today and everything sounded perfect. When to see how the power transformer was doing and it was HOT! It took about 45 minutes for it to finally cool down to room temperature.

Ideas anyone?

[52 Bill]

Any thoughts anyone.

Your transformer gets hot because it either is being stressed by too much current draw from the circuitry or due to an internal fault.

If you let the amp idle for a little while how hot does it get?

[gregsk777]

Hi, Thanks for your reply.

I have never idled the twin in the standby mode for more then ten minutes. I will experiments and leave it in standby for an hour and see if the transformer starts to get hot.

Some other info about the twin is that it does not have any bias adjustment it is fixed bias. It just has a hum balance pot and "output tubes matching" pot on the back. Because of the high plate voltage (around 575V) I tried to the the most rugged tubes I could find (SED Winged C's).

If the transformer is being stressed do you think it could be the tubes? I have run other amps unbiased and with mismatched tubes but have never seen a power transformer get hot?

[mac1amps]

????....Power transformers ALWAYS get hot after an hour or two of "normal" operation. It wouldn't hurt to install a bias adjustment control, which on THOSE Twins, basically involves replacing the resistor on the "output tubes matching" control (between wiper and ground) with a trim-pot. If I owned one of those, I would also install a cooling fan. It would [at LEAST] triple the life of your power tubes (but be sure not to use an "overkill" fan, or it'll affect your sound...just a nice QUIET small fan to keep the air moving)......BTW, "ultra-linear" refers to OUTPUT transformers, not power transformers.

[krhnyc]

Those silver panel fender's were designed to run the old USA Sylvania Coke Bottle 6L6. Those tubes could handle to ungodly high PV. You may still be able to source some from Boogie. Old MKI's also used those tubes, for the same reason... crazy high PV. I had a load of Boogie tubes back in the 80's, but I sold them or used them.

BTW, if you have a silver panel deluxe or princeton (both of which run around 475 PV!) I have had good luck with the EH 6V6. Don't know anything about thier 6L6 though.