Tube Questions... Fender Amp


Hello... looking for some feedback (pun intended)

Although I have owned plenty of tube amps. My knowledge of tube themselves is really limited. Other that what I have read.

I have a 60 watt 1990 Fender Super 112 amp with original:

2 x 12AX7 - pre amp tubes
2 x 6L6gc - power tubes

I love this amp and it sounds great. It does have a hum powered on with or without a guitar plugged into it. I have taken the amp to other power sources and it still has the hum with proper grounding. Other than it being painfully heavy and loud the amp has no issues. I know the red knob Fender's have had a bad rep but this amp is special... at least to my ears.

Is it possible the hum would disappear if I swapped out the tubes?

The amp has a fixed bias... would I just install the tubes without adjustment?

What band tubes should I buy? I have looked into it and there are so many choices it's confusing (almost as bad as pickups).

Would there be any benefits to replacing the tubes anyway?

I play mainly Allman bros/country rock/classic rock and blues... no overly distorted metal. It I had the cash I would definitely take the amp to a professional but I'm out of work right now and would like to handle it myself if possible.



Yes tubes can become noisy.
Tubes are always the first suspect, try known good tubes.
Fixed bias is frequently misunderstood.
Think of it as Fixed Voltage. But the voltage is adjustable.
If you change power tubes you need to check and adjust the bias.
What brand of tubes?
That is very subjective. JJ's, EH, Tung Sol all get decent reviews.
Lately I really like the SED Winged =C= 6L6's in an amp I have.
Tubes wear out over time, sometimes so gradually that you don't notice unless one fails completely.
Preamp tubes generally last a long time, power tubes - 6 months to 2 years depending how often and how hard you play.


1) Is the hum 120 Hz (assuming you're in a 60Hz country)? Remember that the low A on a guitar is 110Hz.
2) Does the amp have a hum balance adjust on the rear panel? If so, see if it makes any difference...if not, put it back to where it started.
3) It could be a tube. If you have any other amps, swap the 12ax7s around in an attempt to isolate a bad one. If you have another 6L6 amp, swap both tubes at once.
4) For 6L6GC, use SED a.k.a. =C=, for 12ax7 get whatever Mike K (KCA tubes) is recommending.



Thanks guys

1) yes
2) No
3) I have no other tubes to test with.
A tube amp owner should ALWAYS have a back-up set. Make sure you have at least one pre, and a good set of power tubes on hand, never know. The Winged C's are very good. The Tung Sol 12AX7 reissues sound decent, too. Asking Mike at KCA is a great way to go.


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