Premier 76 temolo not working

[pontiacpete]

I'm trying to get the tremolo working on this amp. There is no schematic so I drew up the wiring of the input and the oscillator.
Sorry it's not the neatest drawing, but I hope someone will take a stab at this. It's an interesting tube configuration.
It uses 3 7F7s for the first 3 tubes and a 7N7 for the PI, 2 6L6s for the output.
The trem tube is a 7F7 and here are the voltages on this tube:

Pin 2 0vdc
pin 3 163vdc
pin 4 -.4
pin 5 0
pin 6 230vdc
pin 7 2.6vdc

I have changed out all the caps in the oscillator. They were domino style mica caps(might well have still been good). Changed
all resistors in the circuit. There are a couple of questionable resistors that were reading up around 500K. One of them was on pin 3 and the voltage there was about 96v so now I'm trying a 47k and it gives 163v , still no trem.
Does this tremolo circuit look like it should work or is there something missing?
Any ideas?
thanks

[Tom Phillips]

Do you know if the tremolo in this amp ever worked? (Or has ever worked after you got the amp)
Your schematic shows the grid of the low Frequency Oscillator triode connected to ground. That would keep the LFO off all the time. Let us know if that's a drawing mistake or if the amp has lived its life so far with a factory wiring mistake. That happens sometimes. Edit: Another possibility is a wiring mistake made during a repair attempt sometime over the long life of the amp.

[pontiacpete]

That's a mistake I made in my drawing, the grid doesn't go to ground in the amp. I'll try to fix the drawing.
I don't know if it had ever worked but it looks like nothing had been altered in the tremolo circuit since it was built.
There was an issue of what the values of the caps should be. I'm not fluent with domino cap value markings, two of them have the colored dots. I measured with the cap meter and decided on those. Would a picture of them help?

[Tom Phillips]

... Would a picture of them help?

Better yet, attached is a document that will tell you how to read the dot code. The actual values are not super critical. First task is to verify that the LFO is running. You are doing a good job by tracing the circuit and generating the schematic. You have a DVM with cap reading capability. Any other test equipment like a scope? I've got to take off now.

Edit: Various pictures of the whole amp and the wiring detail are always helpful and appreciated.

[pontiacpete]

I have a scope.
The LFO is not showing any signs of life. I think you usually see the voltages fluctuating between those caps.
There's nothing happening between the .01s, 0vdc.
Anyway here are some pictures

[Tom Phillips]

Pete,
There is good general LFO information at The Valve Wizard- Tremolo Oscillator . Check it out if you haven't already. I don't have, nor can find any Premier 76 schematics that would seem to cover your version of the amp. I suggest that you clean up the schematic you started and add the tube pin numbers. Then check off all the components and connections in the LFO with a highlighter. Take care to verify that the grounds are all connected and, of course try another 7F7 even if just swapping for another one in the amp.

Additional general comments are:
*I don't see a speed control on your schematic. Does the amp have a speed control?
*By the time I follow the lines and connect the asterisks together you are showing all four cathodes of the tubes in your schematic connected together. That isn't correct.
* I am surprised that there is no cathode bypass cap on the LFO triode. Without it I think that the low frequency gain would be too low to keep the LFO going.

[pontiacpete]

Thanks Tom for the comments and leading me over to Merlin.
Tried changing the tubes, these are the only 3 7F7s that I have, but all 3 perform the same in the trem circuit.
I revised the drawing, made corrections on the cathodes. Notice that I mixed up the cathodes a bit, but there are 3 cathodes connected to the 1K to ground in the first 7F7.
There is only one control for the tremolo. I'm assuming(for what I've seen before in old amps)that there is no intensity but only a speed control, but I could be wrong.
Now having read through Merlin, it looks like the on/off footswitch is on the other triode and not positioned in the oscillator. Wonder if that's wrong. I'll try switching that over.
Here's the revised drawing. Numbered the pins of the tubes but forgot to highlight. (wonder how that will look in a scan)
I have never seen a transformer used this way, in place of the usual capacitors. Could this have an effect on the tremolo circuit in any way?

[pontiacpete]

Finally got back to this. And finally got the oscillator work. Added a 1.5k cathode resistor and a 25/25 bypass cap.
Moved the 1 meg resistor that was between the .02uf and .01uf cap in the oscillator to the plate of the triode and the added a .02 cap in series to the grid of the next triode. Here's the working schematic of this section of the circuit.