orange thunderverb

[lowell]

I can't get a schematic for this amp. The tubes are not glowing and the power light won't come on. Mains fuse, Ht fuse, filament winding fuse are all good. I see no disconnected wires or issues. No ac voltage on filament secondary ends. There is 3v on the filament center tap. 120v IS getting to the primary winding. I've yet to pull the tubes but the only way I can see this changing things is if the filaments are in series which I highly doubt is the case. A schematic would help as this pcb is tough if not impossible to visually trace.

[Prairie Dawg]

How about firing up that old Simpson and check from the tube sockets to the source of power? That ought to be easy enough even if the board's painted black. It should serve to localize the problem.

[J M Fahey]

Befoere anything else: do you have continuity across the primary?
More specifically: across hot and neutral power plug legs?

[lowell]

There is continuity from heater winding to all heater pins. There is also continuity from hot to neutral power legs.

[J M Fahey]

There is 3v on the filament center tap.

Relative to what?
A single wire has no voltage by itself.
What about other secondary voltages?

[lowell]

Isn't it a given that a stated voltage is relative to ground unless otherwise specified? I'm not trying to be a smart ass, isn't it though? In any case there is 3v on the filament ct relative to ground. Not sure bout other voltages yet as I'm not with the amp.

[Prairie Dawg]

You might be able to get a voltage indication yet there's not enough current to do anything. Seems to me I had a similar problem on a Peavey Classic 30 a while ago.
At any rate unless you have a schematic you're going to have to trace it out, either visually or by any other means. I've got a pair of test leads I made up for that task. I took alligator clips and soldered sewing needles to them. Bam! Goes right through that lacquer they put all over boards. I'd be looking at the connecting points and at any place a component is connected to the filament circuit. IIRC on the Classic 30 there was a small capacitor that had never been properly soldered and was kind of flopping around. The filaments were in series as well.

[J M Fahey]

Isn't it a given that a stated voltage is relative to ground unless otherwise specified?

Not necessarily.
Even less so here where:
1) Since we are checking whether this transformer furnishes voltage (and current) or not, useful measurements are wire-to-wire.
It's somewhat irrelevant where some of those wires might be connected externally, we're checking something internal to the transformer itself.
In fact, and to avoid clouding the problem, I would measure that transformer with only primary leads connected and all others "floating in the air"; as I said I'm interested in the transformer itself; it would not be referred to ground (or anything else).
2) In case you were measuring it still connected to the rest of the circuit, center tap *is* "ground", it *must* be showing 0V referred to it, so what you post is baffling , meaning it's something that must be investigated and explained, it may very well be a direct part of your problem.
3) *If* the transformer secondaries are floating, connecting a modern multimeter (*very* sensitive, *very* high impedance) from ground to any single lead *may* indicate a random voltage, as Prairie Dawg correctly indicated, but it shows electrostatic coupling or imperfect insulation, nothing else.
It may even not be enough to light a test screwdriver neon lamp.
Good luck.

[lowell]

Well the heater fuse was blown. It looked fine visually and I was getting continuity across it but that's because of the low DC resistance of the heater winding. Whoops. Thanks for the help guys. I may not have found the issue had I not shown a flashlight under the board to reveal the shadows of underboard traces.

thanks JM
thanks Prairie Dawg that's a good idea with the needles.

[lowell]

Well the heater fuse was blown. It looked fine visually and I was getting continuity across it but that's because of the low DC resistance of the heater winding. Whoops. Thanks for the help guys. I may not have found the issue had I not shown a flashlight under the board to reveal the shadows of underboard traces.

thanks JM
thanks Prairie Dawg that's a good idea with the needles.

[Prairie Dawg]

I cannot tell a lie, Lowell. I bought an ESR tester from Radio Devices in Russia, and that's how the test leads are set up. I thought it was a good idea So when you were testing the fuse your current from your multimeter was 'going 'round Cape Horn" so to speak.

-

[Dave Curtis, dB AudioTech]

A blown fuse will show voltage across it; a good fuse won't.

[Steve Conner]

For the sake of our less experienced members, I should mention that that applies when the fuse is in the circuit with power turned on, not sitting in a drawer.

[Prairie Dawg]

Correct. But let's posit an open fuse and all the tubes installed, no power on the system, you would see continuity but via a long path. You of course would not see voltage if the system was powered up. All's well that ends well though.

[lowell]

"A blown fuse will show voltage across it; a good fuse won't. "

Very good point!

"For the sake of our less experienced members, I should mention that that applies when the fuse is in the circuit with power turned on, not sitting in a drawer."

Hilarious!