Will this output transformer work?

[TarheelTechinTraining]

Yes a bridge rectifier. I'm not sure about 0v reference. Though I'm only using the positive DC side of rectifier

[TarheelTechinTraining]

I kinda figured this PT wouldn't do what I needed. Guess I'll need a new PT. The wife won't be happy, lol

[J M Fahey]

Ok then. I'm finding the JTM60 schematic frightfully hard to interpret. Maybe someone else can make more sense of it.

Nobody can.

That's not a real "schematic" but the printout of the .SCH file used to plot the PCB, so everything going to something which is not physically inside the PCB ends in a connector or at best a wire pad.

At least they label connectors with meaningful names , such as "htr", "HV", etc.

SWR just names them as "Pin1/2/3/4/"etc. and you must be a heck of a Tech to guess: "oh, this capacitor connected to this cathode might be boost/drive/bright/you-name-it

EDIT: no, no a *Tech* but a Psychic; a Tech will still need to see the proper Schematic.

[g1]

The main filter caps in the JTM60 are 550V. In other threads, B+ is reported around 485V.
If you only get 300V B+, either the transformer or your circuit is defective.

[TarheelTechinTraining]

So I looked over the jtm schematic. Is that a jumper on the primary?

[TarheelTechinTraining]

Well I disabled the rectifier and got 385vac at the secondary

[überfuzz]

Unsolder the secondary and measure what you have at the PT, i.e. measure Vac before the rectifier.

[überfuzz]

Well I disabled the rectifier and got 385vac at the secondary

Then your circuit is wonky. You should see well over 500 V after the rectifier. Estimate like this: Vdc = sqrt(2)*Vac

[TarheelTechinTraining]

Right .... Could the lack of an earth on the secondary side cause problems?
I know your math is right just frustrated

[überfuzz]

Lack of ground? I'm not sure I follow you...

Try connecting the rectifier again, but this time unsolder it from the rest of the circuit. You should see something like B+ = 550 Vdc at the rectifier. This is just to rule out anything fishy happening in the rectifier. When you do this step, take the time to check the rectifier very closely. Like... even under board.

If you don't fine anything at this stage, connect the power stage and measure the B+ again. Proceed and connect one stage at the time. By doing this you should be able to pin point where the B+ is drained.

[Chuck H]

I think he's just testing the transformer on a bench, not in an amp.

[Chuck H]

TTT, your filament voltage looks right-"ish" so I think you have the primary hooked up correctly.

385 measured with no rectifier hooked up seems about right. That amp uses a bridge rectifier so you can expect about 1.4x that voltage minus any loading from current as your plate voltage. Previously reported as 480-ish for a jtm60 it looks to me like everything is alright. There may have been an error in how you were implementing the rectifier for the initial tests. And, so, using that PT you can expect about 480Vp!!! No small feat for new production tubes I'll warn. A customer of mine is using a pair of Ruby EL34's (B's?) at that voltage and the amp is doing well with occasional trips into square wave clipping and semi regular gigs.

[TarheelTechinTraining]

380vac at the secondary before rectifier.
And yes Chuck its on the bench.

[überfuzz]

Got any preferences when it comes to power tubes? Your tranny will be just fine! A pair of 6L6 or maybe a pair of EL34.

[TarheelTechinTraining]

I have a pair of E34Ls. So I'm gonna go with those. If they don't sound/feel like what I'm after I'll try 6l6s.