power transformer bad?

[TarheelTechinTraining]

This pt doesn't have a center tap on Vac. Does that matter? This pt is from a jtm 60

[loudthud]

We can't help you if we don't know exactly how you amp is wired. A transformer without a center tap won't work with the schematic you have referenced. Neither will the bias supply.

[TarheelTechinTraining]

Yeah I thought that might be the case.
No problem I'll just get the correct tranny

[The Dude]

If no center tap, you will need to go with a bridge rectifier or some other arrangement. If you pulled the tranny from a JTM60, just look at that schematic and build something similar to that supply.

[TarheelTechinTraining]

So this pt has a 43vac center tap. I need to rectify it and supply the bias, right?

[TarheelTechinTraining]

Or do I run Ht to a bridge rectifier and ground the negative DC?

[J M Fahey]

I apologize for having posted in the wrong place. I'm debugging my first build, a jcm800. My question is should it take a minute or two for the voltage to reach 500 Vdc. This is after rectifier but before stand-by. Going through 100uf capacitor before stanf-by. Thanks for the help, Greg

What do you mean by through?
Do you have a cap in series with your high voltage line?

Plus when I take it off stand-by the voltage drops unless the 50uf caps are disconnected

What does that mean?

No the caps and pt don't share a ground

In the M Huss schematic you are following, PT center tap is grounded.
Capacitors negative terminals are also grounded.
That may be described as "sharing a ground".

Measuring the AC on the transformer secondary, how long does it take to reach it's max output?

Are you talking a single winding?
A center tapped one?

382 vac instantly

Single 382VAC winding? (meant for bridge rectification)
382+382 VAC? (meant for 2 diode full wave rectification)
Not the same.

This pt doesn't have a center tap on Vac. Does that matter?

Yes, of course it does.
Then you can NOT match M Huss'schematic.
Then you are NOT following M Huss'schematic.

The schematic I'm using is a 2204 by Marc huss. Only difference between it and mine is stand-by placement.

You have more important differences than that.

LOUDTHUD said:
We can't help you if we don't know exactly how you amp is wired. A transformer without a center tap won't work with the schematic you have referenced. Neither will the bias supply.

+ 3

So this pt has a 43vac center tap. I need to rectify it and supply the bias, right?

No such thing as 43vac center tap

Please draw the actual circuit you built.

No need to master a schematic drawing program, hand draw it on a sheet of paper and send a picture of it.

Take it under very good light, outside if possible, and in focus, so it's not fuzzy unreadable.

I suspect you have a single secondary 385V transformer, and you simply wired both ends to a 2 diode full wave rectifier, didn't ground the center tap because you don't have one, and the first capacitor is slowly charging just through transformer insulation losses, measured in microamperes, that's why it takes a couple minutes to reach 500V .
Of course as soon as you turn standby switch on, that voltage collapses, it can drive no real world load, except your multimeter's 10M (or 1M) input impedance.

[TarheelTechinTraining]

I see what I screwed up. Yes it needs a bridge rectifier so it has a ground,duh. So the bias will still be powered from ac side of bridge rectifier, right?

[Justin Thomas]

Oops, simulposted. if there's a 43VAC tap it's for biasing &/or powering SS components. The schem shows a third winding. Are you sure it's not a 43-0-43 winding? There's no voltage listed on the schem for that third winding. Anybody know what that third winding is for? I only looked at the one page w. the PT & OT wiring on it.

Justin

[TarheelTechinTraining]

My bad. Its 43-0-43. I think it ran switching and reverb.

[Justin Thomas]

You could still use that winding as a bias supply. OR derive it from the AC side of HT as in the original schem. You have options now!

Justin

[TarheelTechinTraining]

Thanks for that. I feel like a dope for forgetting the ground. Keep looking at it wondering were it was. Now I'm on track. Thanks again, Greg

[TarheelTechinTraining]

Now we're cooking with gas! I've got 545 vdc before stand-by. Isn't that kinda high?

[J M Fahey]

-WHAT-DID-YOU-ACTUALLY-DO-?

-POST-THE-SCHEMATIC-

"Cooking with gas" isn't an acceptable description.

OR derive it from the AC side of HT as in the original schem.

If you are referring to the M Huss schematic, no, he can't.

[TarheelTechinTraining]

I'm sorry for being such a newbie, Juan. Short and long, I'm using the PT and OT from a jtm60 in a jcm800.