1960 Vibrasonic replacement power TF?

[Voxbox]

Hi,

More stuff from this Vibrasonic I have for a check-over.
The power tranny has been replaced with the one in the attached pics -
The voltages in the amp are fine, however the tranny has an extra winding, the unused yellow wires, which I guess its for a 5v heater.

I'd like to be able identify what make the tranny is and if it really is suitable for the amp. No metalwork has been done to install it, so it has slotted straight in without modification, and it looks fairly new. The voltages may be correct, though I'm wondering about its power rating, etc.

There are no markings whatsoever on the tranny.
Does anyone recognise the type from its construction?

[eleventeen]

Without markings...pretty difficult, if not impossible. It really looks like the most typical, generic tranny one might imagine.

Agree that the unused yellows are almost certainly your 5v.

I don't know how you could easily determine whether it's suitable (in terms of ampacity) without performing extensive tests; probably consisting of taking a Twin Reverb or Dual Showman and noting the voltage drop of ITS tranny loaded and unloaded. I guess there might be something to be gained if you could call a buddy with a genuine TR tranny and have him/her measure the DCR of the HV winding...or measure it yourself. That test would not necessarily be conclusive, by the way. I guess you can take slight comfort that you are not using 10 watts because you're not using the 5v winding.

If the tranny fits in the same hole...it's not like mfr "A" had 93% efficient trannys and mfr "B" had 65% efficient ones. The technology really hasn't changed in 50 or so years, maybe more. I would forget about it if the B+ volts do not droop badly when you switch out of standby and if they conform to the levels a called out on the schematic.

[HotBluePlates]

The power tranny has been replaced with the one in the attached pics -
The voltages in the amp are fine ...

I'd like to be able identify what make the tranny is and if it really is suitable for the amp. ...

Agreed that there's no way to know without any markings.

I know Fender had "Export" transformers in the 60's, but I don't know if they were using them as early as this amp. Being you're in the UK, if you're not having to use a step-up transformer, it may explain why the PT was replaced.

I don't know how you could easily determine whether it's suitable (in terms of ampacity) without performing extensive tests ...

If you have to know if it's suitable, try this:

5G13 Schematic shows loaded idle voltages; compare to your amp. You say they're good, so idle conditions seem appropriate.

The schematic shows a bias of -55vdc; maybe you're idling near that, or may less negative voltage.

Attach a dummy load, meter the voltage on the dummy load, also meter the peak voltage at the 6L6 grids. Apply a test signal to the amp such that the peak at the 6L6 grids is about 1v less than the bias voltage (i.e., bias is -55vdc, measure for 54v peak). Check voltage across dummy load to see that output power is 35-40w (probably a reasonable guess for this amp).

For an 8Ω load, 35w would be indicated by:
√(35w * 8Ω) = 16.7v RMS or 23.7v peak

[Voxbox]

Thanks guys,

I can do the load test, which is about the best test I can do, but then I dont know what to expect from an original Vibrasonic TF. As it was designed for clean power, with the large output TF, I guess that there shouldnt be much, if any PSU sag.
I cant test for transformer regulation though.

Its an American transformer with no tap for 240V, so I'm running it through an oversized step-down transformer.

Right now I've stopped putting any time into this amp until the owner discusses the issues its got with the guy he bought it from. The speaker cone is gone, the output transformer isnt original, most of the capacitors and resistors and pots have been changed. The key elements in what makes an amp what it is are not present - the transformers and speaker, and to a lesser extent the caps and resistors.
What I'm doing now is costing what it would take to get it as close to what it was when it was made.

Cheers, VB

[stratele52]

Sure yellow are for tube rectifier 5 volts heater.  Got to hammond Transformer , see some sketch ;

www.hammondmfg.com/pdf/EDB290DX.pdf

[HotBluePlates]

I can do the load test, which is about the best test I can do, but then I dont know what to expect from an original Vibrasonic TF. ...

Sure you do.

If the amp is 2x 6L6 with 450vdc B+, you could reasonably estimate it's a 35w or bigger amp.

If you use 2 meters, you can apply the test signal, monitor peak input to the output tubes, monitor output voltage at the speaker load.

If the PT couldn't hang, you'll get less than the calculated output voltage (implying less than full output power) because the supply voltage is sagging with current demand more than what will allow expected output power. If you get expected output power with the peak input voltage for the 6L6's I mentioned (or less), then the PT is up to the task.

[SoundmasterG]

It looks like a good quality transformer with that copper shield around the gap....are there any EIA codes stamped into it? You can identify the maker and year from those usually....

Greg

[Voxbox]

Hi Soundmaster!

nope, there are absolutely no markings whatsoever. Which is why I have been a bit suspicious of it.
I wonder if I would see any markings under the covers?

However, I did do a full-load test, and the B+ dropped only 40V, less than 10%, so that seems good. i.e 473V to 433V.

Cheers, VB

[eleventeen]

If that's all the drop you got from no load to full load, I say launch it!

[Voxbox]

Yep agree with that.
My customer wants to go ahead with it, and make it as good as possible - see my other post on when is a 1960 Vibrasonic not  a 1960 Vibrasonic for more detail.

This is a really interesting project....the same customer brought me a pristine, virgin, never out of the cabinet,  1966 Pro Reverb recently, so this Vibrasonic is the other end of the spectrum in terms of originality.

I just wish I had an original to compare with.

Is there anyone in the UK that has one that I could look at/ play with/play through??

Cheers, VB

[Guitarzan]

There are no markings whatsoever on the tranny.
Does anyone recognise the type from its construction?

It looks just like a ClassicTone from Magnetic Components. I wonder it you tried taking some paint thinner and a rag and see if you can rub off where someone may have painted over the Classictone Markings? Might be worth a try. Anyway, for what it's worth, that what it looks like to me.

[HotBluePlates]

It looks just like ...

To me it looks just like any E-I core transformer with that style of metal endbell. Hammond, Schumacher, Stancor, Triad and innumerable other makers produce transformers that look the same.

Unfortunately, it is not a unique form-factor like Partridge, UTC, Radio Spares or some other makers. It's just a big black lump, and the only thing we'll have to go on is the electrical performance.

[sluckey]

It looks just like a ClassicTone from Magnetic Components.

It's not that transformer. Not enough wires.

[Guitarzan]

I forgot the metion of a step up transformer. The one I sent you the specs on has the extra wires for the 220v operation. They have the same tranny minus the 220v feature which would mean fewer wires in the primary. Yeah, I know it looks like any number of irons that out there but the Magnetic Components one really is made exactly like that one, to my eye anyway. And...they don't stamp anything into them. They just paint their name and part number on it and that's it. Could be someone thought "ClassicTone" looked cheesy on there and hit it with a spray can of black paint to try and pass it off, at a glance anyway.

[sluckey]

It's not just the dual voltage primary that's different. The high voltage secondary is different also. The one in the pic has 4 wires. The classic tone has 6 wires.

[Voxbox]

Thanks guys,
we are going to go for the MM trannies, so at least it will have some re-sale value, and be a known quantity, not that my customer is planning to sell it though.
I'll post some pics when I'm done.

cheers, VB