Output Transformer Changed to a Bassman

Hey, Jeff.

I love your column! I look forward to reading it every month. I have a ’67 blackface Super Reverb that I gig with. Really an awesome-sounding amp!

I just realized that the output transformer has been changed to a Bassman reissue or a Super reissue OT (output transformer). I’m not really big on keeping it original — it doesn’t really matter to me because I will never sell this amp — but like every other tone searcher out there, I want the best possible tone that this amp can achieve. I am curious about changing this out for a higher-quality OT. I heard the Mercury transformers are really good vintage replacements. What kind of differences in sound/tone will I hear by doing this, and is it worth it? Also what kind of tubes do you prefer in these amps? Thanks so much, and keep the awesome columns coming!


Hi Ben,

Thanks for reading PG, and thanks for writing in. It’s the much-appreciated support of the readers that enables all of us to write for such a cool publication. Now… on to that horrible amp you’re forced to gig with. I kid, of course. The Super Reverb is absolutely one of my favorite amps. The multiple 10″ speaker configuration helps give it a unique voice and sets it apart from most other combos using the ubiquitous 12″ speaker. It’s a shame that the output transformer needed to be replaced, but occasionally these things happen. A reissue Bassman or Super Reverb transformer, since they both have an output impedance of 2 ohms, will certainly get the amp working properly, but yes, you can do better.

Mercury Magnetics offers a couple of different lines, and they are some great-sounding replacement transformers. Their ToneClone series transformers are replicas of the original transformer designs, and the Axiom series takes them to the next level with design modifications for tonal improvement. Which one you choose will depend on whether you desire to have the amp sound as good as a great-sounding Super Reverb can, or to, as Emeril Lagasse says, “Kick it up a notch!” Either way, you should notice tonal improvements. Some may be very noticeable, and some may be subtler. Things like tighter, extended bottom end, smoother top end, more harmonic content and better note definition are all improvements you might expect. These attributes can all be affected by the quality of your output transformer. Whether it’s worth it or not is completely dependent on any cost limitations you put on your search for the ultimate tone.

You also asked about tube preference. This is always very subjective and depends on the type of music you play and your expectations of the amp. In general, my preferred preamp tube for amps that were not designed with heavily overdriven preamp sections is the Sovtek 12AX7LPS. Its large plates seem to make it a very full-range tube, so your guitar or effects will be very full bodied. In amps with major front-end gain, this extended frequency range can become too much of a good thing, but that’s certainly not the case with a Super Reverb like yours.

Also, here’s a little helpful tip to remember: Even new tubes can be microphonic. If you install new tubes in your amp and you experience ringing or feedback when the volume is turned up with nothing plugged in, try swapping the positions of all the tubes of a same spec. (In this case, it would be the 12AX7s. The 12AT7 tubes in Supers are in locations that are generally not too susceptible to microphonics, so they shouldn’t be an issue.) Certain locations in the circuit are more susceptible to microphonic tubes than others, so moving them often clears up the ringing, or at least minimizes it.

Preference for output tubes is much more dependent on the use of the amp and style of music. If you play mostly blues or classic rock, I would recommend going with a smaller-bottle tube that will have a nice, smooth breakup that occurs sooner — making it easier for the output stage of the amp to be pushed into clipping and achieve that glorious nirvana that is output-tube distortion! Recommendations might be the new reissue Tung-Sol 5881 or Groove Tubes GT-5881C. If you’re more into big jazz chords or country twang — or if you get your signature tones from stompboxes and prefer that the amp be as big, loud and proud as it can be — you’ll probably want to go with a larger-bottle tube. This generally yields the fullest, cleanest performance. Recommendations here might be the JJ/Tesla 6L6GC or the Ruby 6L6GCMSTR. Another suggestion here might be the new reissue Tung-Sol 6L6GC-STR. I just installed a quartet in a Twin Reverb and it was surprisingly loud ‘n proud. I hope that helps you on your way to a more super Super.

© Mercury Magnetics
  • This field is for validation purposes and should be left unchanged.