Multi tap or single tap output transformer...what's the difference?

[bluesman714]

I have a question about guitar output transformers. I have posted in the Black Market, looking for a Fender 125A7A 8 ohm output transformer. I am also looking online, since my chances of finding an original aren't great. One online parts supplier offered up a Heyboyer multitap transformer. The seller says its a paper bobbin, interleaved transformer with 4/8/16 ohm taps. Should I expect a sonic difference between using the 8 ohm tap on this transformer as opposed to using a single tap, 8 ohm transformer.

Thanks

 

[abbey road d enfer]

Just because it's a replacement xfmr, made by another mfgr than the original equipment, it would sound different. The incidence of a multitap secondary is that copper is used less efficiently when 4 or 8 ohm is selected, but the difference is very subtle.
The way the xfmr is wound and the nature of the core are much more important than this little detail.

 

[bluesman714]

Thank You for that explanation. The original transformer was supposed to have been a Heyboyer as well, but it was missing from the amp when I found it. Leo was known to be frugal, so who knows what brand was originally in the amp.
I have been advised that the original was actually too small with little iron and would likely saturate easily (like a Bandmaster). I have a new in the box OEM Fender tweed output transformer that I will install the Pro. More iron = more Me!...hopefully

 

[bluesman714]

I'm going to keep looking for an original 1964 125A7A. who knows, I might get lucky enough to find one, If I ever decided to sell it, it would definitely add value to include it in the sale and say that the amp could be put back to stock.

 

[CJ]

There is one on Reverb for 450 which is a rip.

Are you building a Vibrolux 6G11-A with an 8 ohm speaker?

I believe the original was simply wound primary-secondary with no interleaving or secondary taps.

The small core was to protect the single speaker and may contribute to a saturated sound.

An interleaved transformer might sound more hi-fi which could make the amp a little brighter than normal.

Any space in the coil due to
Insulation, air, tape or unused copper constitutes leakage inductance which combines with the leakage capacitance to form a resonant circuit which determines how much ringing and how many peaks and valleys and at what frequency but it should not sound different as there is plenty of power to charge up the stray capacitance which takes leakage C out of the equation, unlike low level audio transformers. This is why a Schumacher output wound pri-sec is flat to 100 kc.

Do you have an original chassis or doing a diy? If you have the chassis measure the mounting holes and that will make it easy to determine the core size. There may be an extra hole for a larger core option like on some other Fender dual 6L6 amps.

 

[bluesman714]

Its a complete 1964 Fender Pro Amp, missing the output transformer. The original was discarded over a decade ago by the technician I bought it from. The original owner didn't want to pay the bench fee for troubleshooting. Its the cleanest one I have ever seen & I seriously doubt it ever left the original owner's home.

 

[CJ]

Cool! Can you measure the mounting holes?

 

[bluesman714]

A quick measurement of the hole spacing is 3 3/4". There are only two mounting holes. I can use at least one of them, meaning I will only have to drill 3 holes to mount the Bassman transformer.

 

[CJ]

I believe the Bassman XFMR uses a 2 ohm output,

Thanks for the measurement , 3 3/4 = EI 100 lam,

 

[abbey road d enfer]

I believe the Bassman XFMR uses a 2 ohm output,

The original one, 4x10", yes. 4 8 ohms in parallels. There were several after that, which had 2x12", for a resulting 4 ohms.

 

[CJ]

and there was a Twin Reverb with a single 15 wtf?

 

[dmp]

The original transformer was supposed to have been a Heyboyer as well,

No, I think it would have been a Schumacher (606 code).
I would not drill holes in the chassis to put the wrong transformer in, if it is a clean '64 amp.
Put in a Mercury Magnetics now, or put a watch on ebay for a vintage one.
If you're patient you can find vintage schumacher transformers.
The pro was 6L6 to 8 ohm.
If you find a 6L6 transformer to different ohms it would still work (pro reverb, deluxe, princeton, vibroverb, vibrolux, etc...) , you'd just need a different speaker.

 

[CJ]

i can spin one if you like.

 

[abbey road d enfer]

and there was a Twin Reverb with a single 15 wtf?
View attachment 107216

That's one of the oddballs.
Actually looks like a CBS 100W Vibrasonic, which had the same chassis shared with the Super6 Reverb, Twin Reverb, Dual Showman Reverb and Quad Reverb. Only the faceplate was different.
Originally, the OT was different on the Vibrasonic, that had a 8-ohm 15".
Mine had a (blown) Cerwin-Vega 4 ohm that weighted a ton. I replaced it with a Jensen Ndym. Made it almost carryable.
It's quite possible that the chassis of the one in your picture has been replaced, or it's a factory hybrid.
Or a recent back-to-the-future "reissue"...?

 

[bluesman714]

CJ, Yes! I would definitely like for you to spin one! Lets work out the details.

 

[bluesman714]

The single 15" Twin Reverb was aimed at the Pedal Steel players. The Peavey Nashville and Session amps seem to be a more popular choice.

 

[13engrsapper]

That's one of the oddballs.
Actually looks like a CBS 100W Vibrasonic, which had the same chassis shared with the Super6 Reverb, Twin Reverb, Dual Showman Reverb and Quad Reverb. Only the faceplate was different.
Originally, the OT was different on the Vibrasonic, that had a 8-ohm 15".
Mine had a (blown) Cerwin-Vega 4 ohm that weighted a ton. I replaced it with a Jensen Ndym. Made it almost carryable.
It's quite possible that the chassis of the one in your picture has been replaced, or it's a factory hybrid.
Or a recent back-to-the-future "reissue"...?

That is a reissue of some sort. the '65 embellishment on the grill is the clue. I've not worked on that reissue.

 

[13engrsapper]

I've got an original 64 blackface bassman laying around and all apart waiting for restoration. If we need any measurements it will be here awhile, it is mine, not a clients. It's already been sitting a decade.

oops my quote reply thing did not work - that was to CJ

 

[bluesman714]

i can spin one if you like.

Yes, definitely! My quote skills required some practice also.
Message me and lets work out the details.
Thanks!

 

[bluesman714]

Yes, definitely! My quote skills required some practice also.
Message me and lets work out the details.
Thanks

And this solution will allow me to keep the amp as "stock" as possible.