Quandary regarding power up with variac & amp meter

[Bigdrums]

Well at this point I measure only +/- 27vdc from the power supply with the leads disconnected. I'm certain I had +/- 37 as shown on each of the various schematics. Strange. Power supply leads connected it's + 9vdc -15vdc. Obviously that has to be fixed first. Not sure how this happened. I was able to get to the point where I was able to just turn it on without ramping, but never had output.
And I see it is drawing too much current based on the amount of glow from the limiter, and the amp meter, about .4 amps at idle. Not sure what to do at this point as I don't measure any shorts from the B+ and B- leads either to ground or across them. Feel free to comment. I know I've got to get the P/S working right though.

[Helmholtz]

What about a schematic?

[g1]

Of course it's possible that the power amp is not balanced at low voltages because some auxiliary voltage is missing, a zener not conducting yet etc.
In that case some circuits may tend to latch on one rail.

This could be the reason.
All I know is some perfectly good amps will come up on a limiter lamp with full bright bulb (when a load is connected). And some don't like to come up slow with variac.
In this case he mentioned the bulb limiter, so I'm guessing it was in use when the issue arose.

[Bigdrums]

I am concerned I may have damaged the power transformer. this particular one is for either 117vac or 100vac so there is the one unused wire on the primary side being blue. Green is the 117v rating with white being the common. Secondary is center taped (black) with 2 orange coming out to the rectifier board. Any way to verify what the AC output voltage from the transformer should be?
BTW, the plate on the back panel is missing so I don't know what the serial number is but believe it to be a latter model. There are quite a few variations of this unit and just as many schematics floating around. I'll try to include one here:
SM_JC-120_11052.pdf

[g1]

Should be in the ballpark of 30VAC at each end of secondary (to ground), or 60VAC between the two.

[loudthud]

Some solid state amps don't like being brought up slowly on a variac. These typically make a loud thump when being turned on or off while connected directly to the mains.
There will be DC on the output until the rails come up to about half the final value and this can show up on a meter connected to the output that doesn't filter out the DC.

Here is a thread that discusses the reason for the DC: https://music-electronics-forum.com/...ops-on-shutoff

Sorry, the link to my attachment in the above linked thread is broken.

[Bigdrums]

Ac out of the transformer is 29.6 volts per leg. Since the rectified voltage can not be greater than the AC supply, the +/- 27v makes some sense. But the schematic and my recollection was it's supposed to be +/- 37v. Uniformity of the 2 AC legs implies transformer is not damaged.

[Bigdrums]

Should be in the ballpark of 30VAC at each end of secondary (to ground), or 60VAC between the two.

To achieve the +/- 37 vdc on the schematic wouldn't the AC out of the transformer need to be 45v per side or so?

[eschertron]

The rectified voltage starts at the peak voltage, not the RMS value. Or so I've been told.

[g1]

Yes, rectification is calculated from peak. Schematic shows +/-37V DC.
If you are on limiter bulb, and it is glowing some, then you can't expect full voltage. So that would explain the +/-27V.

[Tom Phillips]

To achieve the +/- 37 vdc on the schematic wouldn't the AC out of the transformer need to be 45v per side or so?

No.
If you Google terms such as "Power supply" +"Full wave rectification" +"smoothing & filtering" you will find good tutorials with the information about what is really happening. As has been pointed out above, a key bit of information to learn is the distinction between RMS AC voltage and peak AC voltage. It should be a fun and worthwhile learning experience.
Cheers,
Tom