Power transformer fails

[Oddvar R]

my experience with a weber twin PT was that it got hot and sagged a lot with 230v/50hz. the next transformer sagged way less, something that gave more power and punch. but you do loose some breakup, compression and mids. Perhaps that was what Oddvar was after here?

That might be it. It had the best guitarsound ever.

[bepone]

my experience with a weber twin PT was that it got hot and sagged a lot with 230v/50hz. the next transformer sagged way less, something that gave more power and punch. but you do loose some breakup, compression and mids. Perhaps that was what Oddvar was after here?

That might be it. It had the best guitarsound ever.

then maybe you like more compression in sound.. this means thinner wire in power transformer secondary high voltage winding , which have more resistance.. affecting also attack,

this is also doable, just to take bigger core and keep the total losses low to avoid overheating

[pdf64]

Or just use a regular transformer and add external series resistance to taste.
Copper losses should be pretty straight line linear, so a resistor should provide a very close result.

[Oddvar R]

So, that seems to be very good advices. Any suggestions on what transformer that could be?

[Roe]

So, that seems to be very good advices. Any suggestions on what transformer that could be?

which one did you not like? see if you can either add series resistance or find a transformer with lower voltage and/or more sag (less regulation and less current ability)

[guitarmike2107]

I have a vibrolux custom here, when distorting the 2 6L6's the are drawing 100mA each and the PT runs very hot and sags from 425v down to 380v and lower. Quite a lot for a little 6L6 amp. I suspect that is the sound that Oddvar likes. If you want the sag fitting some resistors before the diodes will help get you the feel without the burn.

That 48mm stack height is fine for 50 hz if the PT is made with m6 laminations, Check out TAD Bassman or Super Reverb PT for direct replacements.
I make my Bassman PT's with a 2" stack and M6 core and it really is over rated for the job.

[Oddvar R]

I have a vibrolux custom here, when distorting the 2 6L6's the are drawing 100mA each and the PT runs very hot and sags from 425v down to 380v and lower. Quite a lot for a little 6L6 amp. I suspect that is the sound that Oddvar likes. If you want the sag fitting some resistors before the diodes will help get you the feel without the burn.

That 48mm stack height is fine for 50 hz if the PT is made with m6 laminations, Check out TAD Bassman or Super Reverb PT for direct replacements.
I make my Bassman PT's with a 2" stack and M6 core and it really is over rated for the job.

That must be the case, the difference in PY*s what greater than anything I have heard. And do you make your own PT's?

(What resistors shpild be ok for the diodes?)

[guitarmike2107]

Measure the voltage drop and current with the Weber PT if you can still make it work, then with a new PT measure the voltage drop and current when playing or with signal and work out what resistor size you need. otherwise you will just have to take a guess.

You could probably measure the secondary resistance too on both PT and put a resistor in for the difference as a good guess to start.

Yes I make PT and sell them, but I am not here to promote business.

[Stevem]

Keep in mind that overall your talking about power/ wattage.

When you look at ohms law you see that voltage and current dictate the wattage produced, so manipulating the amount / level of either will change the wattage.

What also needs to be kept in mind is the power transformers for guitar amp use are not rated for constant peak service .

You could for example have two different transformers both rated for 100ma and only one of with a CCS rating .

The one with the CCS rating if run flat out all the time will live forever, where as the non CCS rated transformer will burn up at some point.

[Roe]

Measure the voltage drop and current with the Weber PT if you can still make it work, then with a new PT measure the voltage drop and current when playing or with signal and work out what resistor size you need. otherwise you will just have to take a guess.

You could probably measure the secondary resistance too on both PT and put a resistor in for the difference as a good guess to start.

+ 1 measure voltage at idle. Then turn the multimeter to the the minimum setting if you have that, connecting it safely to the B+, then add signal (e.g. from looper) and watch the voltage sag. Fender style PTs sag 10% or slightly more but Marshall ones sag 20% or so in the 100w amps

[bepone]

transformer arrived finally, disasembling started

[bepone]

how i see here, there is some short circuit on everything , looks like condensation?

IMG_20231209_103530.jpg

IMG_20231209_103542.jpg

[bepone]

I was suspicious before, but now I can see..everyone who commented something about voltages, power and currents was wrong
because they were talking about ideal working conditions, of course that doesn't exist...

[bepone]

fault looks like HV winding to the laminations (chassis), carbonisation and short circuit

IMG_20231209_111228__01.jpg

[bepone]

no normal thick interlayer insulation, only poly tape, 5V winding is also shorted to sec., looks like winder didnt understand that 5v winding is floating on hi voltage (+400v dc and is not low voltage 5v ac). 6,3VAC on picture, 5V removed. wires exit from the bobin not in sleeve, non insulated, shorts to the bottom layer also there..

IMG_20231209_124316__01.jpg