Question about interchanging transformers? Any help appreciated!!

[guitarhvac]

I want to build a blackface vibrolux.  I have a question.  I think the answer is no, but i wanna be sure.
I have a silverface twin reverb and i want to know if there's ANY way that i can use the power or output transformer
out of the twin in the vibrolux.  I guess my question could be- " can i step down the voltage on the twin transformer to make it usable
on a vibrolux?
Thanks a lot!!

[jjasilli]

I think the short answer to the question is Yes.  But, note that the basic Fender circuit is the same across the various models of amps.  One of the differences is the trannies used in the different models.  Twins are clean machines.  I don't think that's true of the Vibrolux.  I assume your Twin has 4 power tubes, so its PT must handle all that current.  It will not sag.  The OT will have a primary impedance mismatch and will not saturate.  If you build a Vibrolux with the Twin trannies it will work; you may even love it.  But it will not be a Vibrolux.

[Raybob]

The physical size of the twin trannies, both PT and OT would never fit in a SF Deluxe.  If you hacked away the metal, you could squeeze in the PT but you'd have to move your tubes somewhere else.  The OT could squeeze in but you'd have to change the baffle board to have speaker completely to the end of the amp.

You can put the PT and OT from a Vibrolux Reverb into a Deluxe, but you need to enlarge the hole for the PT and drill new mounting holes.  The OT needs to be re-located.

Raybob

[guitarhvac]

Hey jjasilli thanks for your reply!  I have been told that the GZ34 tube rectifier in the vibrolux is what gives the amp so much natural compression, which is what i'm after.   It's probably not possible to use a GZ34 with the twin reverb power transformer is it?
Sorry to be asking ignorant questions but this is my first amp project and i don't wanna tie up money in a new transformer if i can use the one(s) out of the twin reverb that i already have!
Thanks!!

[guitarhvac]

I know the physical size is different on all the transformers.  I'll make it fit or get another chassis.  So i just need to know if they're interchangable and if i can use the GZ34!

[guitarhvac]

I guess my question could be-" can i step down the voltage on the twin transformer to make it
usable for the vibrolux?"
thanks

[jeff]

I have a silverface twin reverb and i want to know if there's ANY way that i can use the power or output transformer
out of the twin in the vibrolux.  I guess my question could be- " can i step down the voltage on the twin transformer to make it usable
on a vibrolux?

I think so When you use the rectifier tube instead of diodes the voltage will go down.

You'd need a seperate 5V transformer to heat the rectifier tube but I think you could do it.

By the way I'd suggest if you are going to do this to steal the transformers and build a new chassis. I had a PA100 that I totally rewired. I was young and dumb and a tweak here a tweak there led to a total rewire. The amp sounds great but I totally destroyed its value. Leave the Twin intact. You can always put the transformers back in and sell the amp as original.

Actually a twin isn't that different than the vibrolux schematically. If you reuse one of the power tube sockets for the rectifier it's not too invasive. Just don't do anything that you can't easilly undo.

The Twin used 4 power tubes and I believe a 4 ohm speaker load. You are using only 2 power tubes so use a 8 ohm speaker load.

Side note: Make sure your caps are discharged. When removing the output transformer remove the center tap first/connect CT last. Sometimes even though you discharge the caps they can build a small charge. If you remove the plate taps first and they touch ground any stored voltage on the caps will be discharged through the windings. I'm pretty sure that's what happened to my Univox transformer. [quote

[jjasilli]

Hey jjasilli thanks for your reply!  I have been told that the GZ34 tube rectifier in the vibrolux is what gives the amp so much natural compression, which is what i'm after.   It's probably not possible to use a GZ34 with the twin reverb power transformer is it?

Part of the difference in tone between the Vibrolux vs. Twin probly lies in power and clean headroom.  The the Twin has more of both.  Of course some of the Twin's extra power comes from the 2 extra power tubes.  But the Twin also has 460 plate volts vs. 410 for the Vibrolux.  One can expect the Vibrolux to sound more bluesey.  Also, for 2 power tubes in push-pull, the amp's output power in watts =  (plate voltage)² / nominal impedance of the OT primary.  So a lower plate voltage makes for less output in Watts.  The Twin's OT is well rated for say 100 Watts.  Per the above formula the Vibrolux is 25 Watts.  It seems to be a waste of iron, and backstrain, to use a 100 watt OT on a 25 watt amp.  There's also no chance to saturate the 100 watt OT, with only 25 watts.  It will work and probably sound good in itself.  Again, it won't be a Vibrolux.

The GZ34 can easily handle the voltage and the current draw from 2 power tubes.  Generally, in place of of SS diodes, the GZ34 will drop the B+ voltage by about 30 volts.  But in your case, with 2 less power tubes, the draw on the Twin PT will be less.  This may result in a higher voltage to offset the drop caused by the GZ34.

A 25 watt 6L6 power amp is a great platform.  IMHO it is beafier sounding than a 6V6 amp of near-equal wattage.  Especially if you want to saturate the OT.  Once you have that basic design concept, you then need to pick the right iron.  There is no good way to compensate for iron which is widely mismatched to the design concept.  

You can also use VVR or power scaling to drop the B+ voltage, but this won't cure the issue of the over-rated OT.  And, for the cost of a VVR or power scaling kit, you're well on the way to buying the correct iron for a Vibrolux.

In conclusion, you can build the amp that you propose, with the Twin's iron, a GZ34, and 2X 6L6's.  It will probably sound fine, maybe great.  But it won't be a Vibrolux.  

Also note that 2 less power tubes will cause a 2:1 impdedance mismatch.  This is acceptable but may result in some hi & lo frequency loss (not terrible for a guitar amp); on the OT secondary side, a 4 ohm tap would become an 8 ohm tap, etc.

[guitarhvac]

Thanks for your replies guys!!  I'm gonna do some thinking on this.  This is my first amp and I appreciate the help!!!!