Traynor Custom Reverb trem always "on"

[Cups]

Hi folks
On to another repair. Did a lot of work on this one: replaced reverb tank, recap, reground to galactic ground, individual 1k screen resistors. Added cathode resistor to bright channel and such

Sounds great. And quite quiet. This amp would be a keeper (aren't they all though - especially after you fix 'em)

There's always a throbbing trem sound though and I know I'm being lazy but instead of poking around I thought I'd ask here first.

I know it's bias modulated but I don't get trems enough to know where to start

Thanks in advance guys.
Patrick

[Cups]

I should include shcem: http://www.webphix.com/schematic%20heaven/www.schematicheaven.com/bargainbin/traynor_customreverb_ysr1.pdf

[HotBluePlates]

Both of those schematics show an oscillator setup where you need the footswitch to turn the trem off, just like a Princeton Reverb.

Does turning the Intensity down to 0 not silence the trem?

[Cups]

Intensity at 0 there is still a pulse.
I'll try a footswitch. 

[PRR]

Do you have a ceiling fan?

Did you re-cap the bias supply? If the cap at the -38V point is lame, trem will leak.

But it may be leaking other ways. Agree that it may be best to kill the trem with the footswitch.

[HotBluePlates]

I suspect the different load impedance seen from the trem/bias point to ground may result in the thumping.

What I mean is You have the resistors going from the common trem/bias point to each grid, which are in parallel with the phase inverter plate loads via the coupling cap.

I wonder if differences in the 100k resistors, coupling caps or the intended difference in the long-tail plate loads keep the two sides of the trem unequal, resulting in failure to cancel at the output stage.

I dunno, cause I've never investigated this situation. Try the stuff PRR mentioned first. I do notice that Fender generally saved bias-vary trem for non-long-tail amps, which makes me wonder...

[Cups]

Feel a little silly.
It does need a footswitch. Quiet with a switch. If it was a keeper I'd mod it for a slower pulse but it's fixed and out the door.

Another funny quirk with this amp is the "tall" el34 won't fit in this amp. I guess just a shorter 6ca7 will fit. Do they have a shorter el34??