Vox Tremolo Problem Troubleshooting HELP Please

[tubenoob]

Hello everybody, excellent information here, I hope someone can help with troubleshooting this oscillator circuit.
I have a Vox Cambridge Reverb here that has a non-functioning tremolo.
I'm familiar with the Marshall 18w and this is similar to that in many ways aside from the old point to point wiring.
I've lurked and read as much on the subject as I could find through searches and tried everything i could think of.
I'm stumped and could really use some help.

Here's what I've done so far
Tried multiple tubes in the position, have a high gain JJ in there now.
Checked to see if circuit was oscillating by strapping a red LED from the cathode to ground.
The LED did not light.
Disconnected cathode resistor and bypass cap and left LED only.
The LED never flashed or lit up.
I measured 1.6v at the cathode prior to altering it (pin 3 v7b)

Replaced all timing caps (twice)
Traced circuit and verified all connections.
Measured all components in the circuit; pots, resistors, caps.
Cleaned pots.
Replaced all electrolytics; power supply and bypass caps.
Verified grounds.
Voltages are all within 10-20v of the schematic.

What puzzles me is I have no oscillation with all new parts in the circuit, I measure voltage at the cathode but it doesn't change with the speed or depth control and the LED doesn't light. Maybe it's bad?

It seems like I've checked everything multiple times, the 220k plate resistor seems fine, the voltage calls for 270v, I measure 280v.
The caps are new, the tube is strong, good grounds in the network.
What am I missing?
Any help would be tremendously appreciated!

[JazzGuitarGimp]

You wired the LED with the corret polarity, yes? LED anode to V7B cathode, and LED cathode to ground. If you accidentally wired it backwards, chances are good the LED was destroyed with 270V across it.

[tubenoob]

Yes it was correct.
The longer lead is the anode right? That connected to pin 3, the other lead to ground.
I replaced the cathode resistor and bypass cap with the LED.
I measured 1.6v, not 270v

Weird thing is I tested the LED with a power supply and it lights right at 1.6v through a 330 ohm resistor but won't light when wired to the tube.

chances are good the LED was destroyed with 270V across it.

[JazzGuitarGimp]

If the connection going to the footswitch jack is grounded, it won't oscillate. Try plugging in a TRS plug with no connection to it, into the FS jack, and see it that gets you going. Or alternately, use an ohmmeter and measure from the junction if R34 and C20 to ground. If you measure 1M, then the plug idea won't help. From the schematic, it would appear that a closed circuit jack, with switch tied to ground, was not employed, but you never know. Even if it isn't a closed circuit jack, there could be a malfunction in the jack. It wouldn't be the first time that has happened....

[tubenoob]

I should have listed that as well.
From what I can tell it should be on without the foot switch but I made a closed shunt (stereo) and tried every combination including grounding it with a wire and I got nothing.
Thanks for the suggestions so far, I'm really scratching my head here

[JazzGuitarGimp]

Yes, that's correct: the footswitch wire needs to be open in order for the oscillator to run - short it to GND to stop the oscillator. I would still ohm-out the top of R34 to GND, just in case there is something hidden from view going on there.

[tubenoob]

R34 R35 and R37 are 1M, 1M & 155k-4.7M (throughout the travel of the pot) respectively.
Does that tell you anything?

[tubenoob]

It's working now, I took a closer look, found an error in the power supply and it sounds great now, thanks for your help.

[JazzGuitarGimp]

Good news! Congrats!

[tubenoob]

Oh if only it were that easy...

Now I have another problem surfacing.
The reverb is noisy.
With the reverb control up there's a hum, maybe this is normal, it doesn't change much or go away if I move the cables around, but there's a distortion with the note when I hit it hard, and there's a runaway oscillation with certain settings; different combinations of reverb and tremolo.
So if the tremolo is on in any setting, there's a place on the reverb control, a little past halfway, that causes trouble, runaway oscillation sounds like a hip hop DJ scratch kinda thing.
What should I be looking for here?
I cycled through a number of 12AX7's (both reverb recovery and tremolo are on one tube) and not much difference.
Should I be suspecting the reverb send tube?

[tubenoob]

Just throughout I'd check in here and finish this saga.
I got the reverb sorted out.
After I fixed the tremolo, the reverb developed a nasty oscillation around 70% on the reverb knob. It would shriek and make a hideous sound as I turned it from 70-100%
I pored over the circuit over and over and couldn't find anything wrong.
Eventually my son suggested trying a different tank, I said there's no way the tank is causing all this mayhem. It was the tank.
I put in an old Hammond I had had laying around, perfect. Tried a newer Mod tank, worked too, no weird noises, nothing but wet reverb (and tremolo) pretty good sounding little amp!
All fixed now.