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Student of the Steel: Zum uni, Fender tube amps, squareneck and roundneck resos, tenor sax, keyboards

The output transformers are the big difference in them. The Pro Reverb and Bandmaster Reverb had the same 4 ohm output transformer (125A6A), very small unit! The Vibroverb had an 8 output transformer, 125A7A

The Super Reverb had a massive piece of iron, the 125A9A output transformer at 2 ohms. Also where a Super Reverb and Bandmaster have a middle control the Vibrobverb and Pro Reverb did not. It is set with a fixed value resistor, 6.8K.

If I had a Pro Reverb with an 8 ohm-15: speaker I would use the output transformer from a Twin Reverb! Been there and done it on several of the Vibroverb clones I built! The Twin transformer is a perfect impedance match for 2-6L6GC tubes and one 8 ohm speaker.

If using the original 4 ohm trasnformer, I would go with a 4 ohm speaker, such as a Black Widow 1501-4SB or the new Eminence Commonwealth 15" speaker.

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Student of the Steel: Zum uni, Fender tube amps, squareneck and roundneck resos, tenor sax, keyboards

[This message was edited by David Doggett on 16 August 2006 at 04:15 PM.]

If you want to "soften" a Pro Reverb with a 15, use a 5751 tube in the V2 slot AND dump the JBL in a lake. A Weber California with a paper dust cap is better IMO - there may be other choices. Call Ted Weber and ask.

Also, a common mod is to sub a Bassman output transformer - it doesn't make the amp "harder" sounding, but tightens the lows a bit and gives it much more midrange punch. Very, very common.

And yes - one speaker should be 8 ohms when you pull two tubes in a Twin..but it should be 4 ohms in a Pro Reverb.

"How different is a Pro Reverb from my 64 Vibroverb?"

Also the Twin Reverb OT has more iron and can handle more wattage. That is what was used in SRV amps with an EVM15L, he ditched the JBL. A Bassman O.T. is a good choice as well, with the multiple taps. There is another OT used in the Dual Professional and Tonemaster amps with multiple taps:

13. FENDER TONE-MASTER CUSTOM SHOP "OUTPUT TRANSFORMER 100W FOR 4/8/16 OHMS", FOR AMPS WITH FOUR 6L6 OUTPUT TUBES, STANDARD UPRIGHT END BELL TYPE, 3.5" BY 2.625" MOUNTING CENTERS. SECONDARY COLOR CODE (4 WIRES): BLACK IS COMMON, THE GREEN/YELLOW STRIPED WIRE IS THE 4 OHM TAP, THE SOLID GREEN WIRE IS THE 8 OHM TAP, THE SOLID YELLOW WIRE IS THE 16 OHM TAP. PRIMARY COLOR CODE: STANDARD RED CENTER TAP WITH BROWN AND BLUE PLATE LEADS (ALSO THERE ARE ADDITIONAL WHITE AND ORANGE WIRES EXITING FROM THE PRIMARY SIDE HOLE BUT THE TONE-MASTER SCHEMATIC SHOWS NO CONNECTIONs FOR THESE-PERHAPS THIS TRANSFORMER WAS USED IN OTHER HIGH POWER FENDER AMPS?). ONE OF OUR ESTEEMED CUSTOMERS, MARK WHITNEY, WRITES: "...the Tonemaster output transformer was also used earlier in the red knob The Twin. The orange and white pair were for a low level unbalanced XLR out." Our customer ED SMITH WRITES: "Thought I would add one more point on the extra output taps. I nocited the comment from your esteemed customer stating that those taps were used for a balanced output on "The Twin". That's absolutely correct the only thing I would add is the white wire is the "in Phase" signal (pin 2 on an XLR jack) and the Orange wire is the "Out of Phase" signal (pin 3 on an XLR jack). Fender typically left pin 1 open on those. Someone might consider adding a ground lift function dependent on the application. Fender listed that connection as a +3dB level." NICE IRON FOR BUILDING POWERFUL 6L6 AMPS WITH MULTIPLE OUTPUT IMPEDANCES? GENUINE FENDER PART #026478.

Here is a web page to a lot more transformer choices for Fender: