Current draw in primary of unloaded PT?

[turbofeedus]

Just picked up a ~74 Traynor YGL-3A.
Album.
Schematic.
I've completed the work I wanted, mostly just replacing e.caps.
I also modded the bias supply to be a bit safer (adjustment pot is now a variable resistor, rather than the bias being supplied from the wiper)
I was forming up the new caps, and noticed that the current draw was significantly higher than I was accustomed.
I started removing components that were loading the PT; cooling fan, bias supply, even the neon indicator lamp.
I finally completely desoldered the primary from any components, and clipped in straight from my variac.

PTtesting-1.JPG

The following is a graph I made showing the current draw vs primary voltage.
This is completely unloaded, in standby.

Traynor YGL-3A Primary current draw unloaded.png

This was based off measurements on the multimeter I have installed on my variac.
The current draw is rock steady, it was running for over an hour as I was slowly forming the caps.
Worth noting the PT is also creating an audible buzzing, not loud, but noticeable.
The PT is also getting, I would say, slightly warm. Not cool to the touch like the OT, but nowhere near uncomfortable to touch.
Like when you make a coffee, but then forget to take it back to your desk for an hour, and you go back, and it's like, ugh I guess I could microwave it but I really need to get back to the desk, so you bring it back but by the time you get there it really is too cold now, so you just end up not drinking it at all. Like that kind of warm.

I suppose the question is; how concerned should I be? Is this the sign if the insulation breaking down in the transformer? Is this some electromagnetic wizardry I don't understand?

[sluckey]

The tube filaments is a considerable current draw. Just the 4 EL34s present a 37 watt load on the PT. That would be .3A @120V in the primary even if the PT was perfect and had no losses. I'm not even gonna add in the other six tubes. So, the filaments of just the EL34s account for almost half of the current shown on your graph. I would not be concerned at all.

EDIT... Ignore the filaments ramblings above. I just noticed the octal sockets are empty.

BTW, you cannot reform any B+ filter caps in that amp while in standby mode.

[thetragichero]

recapped a yba-1a last night and i wondered why my lightbulb limiter was going crazy. turned out the three diodes on one side of the full wave rectifier failed short (so one of the ht secondary taps was shorting to ground via the filter caps)
not saying this is your issue but worth a test

[turbofeedus]

The tube filaments is a considerable current draw. Just the 4 EL34s present a 37 watt load on the PT. That would be .3A @120V in the primary even if the PT was perfect and had no losses. I'm not even gonna add in the other six tubes. So, the filaments of just the EL34s account for almost half of the current shown on your graph. I would not be concerned at all.

EDIT... Ignore the filaments ramblings above. I just noticed the octal sockets are empty.

BTW, you cannot reform any B+ filter caps in that amp while in standby mode.

Yep no tubes, also the forming was done off standby.

I wanted to show completely unloaded (or at least theoretically), so I put it on standby for the test.

recapped a yba-1a last night and i wondered why my lightbulb limiter was going crazy. turned out the three diodes on one side of the full wave rectifier failed short (so one of the ht secondary taps was shorting to ground via the filter caps)
not saying this is your issue but worth a test

I actually replaced the entire rectifier circuit, and the bias diode.

[xtian]

I commonly see 7-15 watts drawn by unloaded PTs of various sizes. So your 0.8A draw is not outside the norm.

[turbofeedus]

I commonly see 7-15 watts drawn by unloaded PTs of various sizes. So your 0.8A draw is not outside the norm.

Gotcha, it's a bit less, 0.66mA, but I hear you.
Just to be 100% sure, I disconnected all the secondary taps, thinking maybe something wrong with the standby switch, or filament winding. No change.
I'm gonna hook it back up and roll with it.

[pdf64]

If there was an actual PT fault such as shorted turns, the PT would be drawing very high current, and blow the fuse.

[turbofeedus]

If there was an actual PT fault such as shorted turns, the PT would be drawing very high current, and blow the fuse.

That's what I was thinking too. I did fully fire it up, drawing about 1.4A at 118V, with ~5V on the screen dropper resistor.

Side note, how does the biasing procedure work? It states;
" Set bias for 8V drop across R23. (120mA plate current for 4 x 6CA7)"
R23 is 470R, so that's 8/470 = ~17mA screen current.
But if screen current is ~5.5% of plate current, then that's only 93.5mA, not 120mA as Traynor states?
What am I missing? Is this Traynor just trying to keep things conservative?

[thetragichero]

the yba-1 i had called for way cooler bias than i would've liked on the factory schematic so that's very likely. i added 1 ohm resistors between pins 1 and 8 (one per pair would work in your case) obviously have to rewire what goes to ground but that and the tube bias calc on robinette's site make biasing a whole lot easier for me to understand
the yba-1a called for a similar thing, adjusting until there is a 4v drop through the shared 470r screen resistor
i'm not familiar with your model (aka too lazy to pull up the schematic) but these bassmasters are FANTASTIC amps. LOVE the huge Hammond transformers (so much so that i have one from the combo version going into a 50w build)

[turbofeedus]

the yba-1 i had called for way cooler bias than i would've liked on the factory schematic so that's very likely. i added 1 ohm resistors between pins 1 and 8 (one per pair would work in your case) obviously have to rewire what goes to ground but that and the tube bias calc on robinette's site make biasing a whole lot easier for me to understand
the yba-1a called for a similar thing, adjusting until there is a 4v drop through the shared 470r screen resistor
i'm not familiar with your model (aka too lazy to pull up the schematic) but these bassmasters are FANTASTIC amps. LOVE the huge Hammond transformers (so much so that i have one from the combo version going into a 50w build)

From the bit I know about Traynor, they supplied much of the backline for Canada. I could see Pete wanting to protect the amps from gung-ho roadies, even to the point of a little white lie on the schematic.