Regal 500 on the bench

[TubeGeek]

I have an old Canadian amp on the bench I am trying to sort out.  I have done a little work to it so far.  I installed a grounded power cord, changed the bias resistor from 420Ω to 500Ω and added a 25µF bypass cap to bump up the gain at the owner's request and finally replaced all electrolytics.


The thing that has me stumped is the tremolo...


When the tremolo is switched on, the tremolo comes in audibly and then quickly fades away.  The tremolo does work steadily when the chassis is out of the cabinet and on my bench but as soon as I re-installed the chassis into the cabinet, the tremolo starts acting up.  I'm scratching my head on this one.


Schematic attached.

[sluckey]

Put a jumper across S2 switch contacts. Swap 6AV6 tubes around.

Does the oscillator (V5) quit when the trem fades away? The voltage on V5 pin 7 will be changing at the trem rate when the oscillator is working but will become steady when the trem quits.

[TubeGeek]

Put a jumper across S2 switch contacts. Swap 6AV6 tubes around.

Does the oscillator (V5) quit when the trem fades away? The voltage on V5 pin 7 will be changing at the trem rate when the oscillator is working but will become steady when the trem quits.

Swapped tubes around, no difference.


Tried a couple other tubes from my stash, same thing.


Yes the oscillator does quit when the trem fades away.  When I switch the trem on there is a second of wiggle and then it's gone. The voltage on v5 pin 7 is 235 when trem is off and 158 when trem is switched on.

[sluckey]

Replace C5. Any better?

[TubeGeek]

Replace C5. Any better?

This was the first thing I did to the amp, thinking along the same lines.  It did not fix it.


I have been tracing things out and while doing that I found that one leg of c2 wasn't making a good connection to the terminal strip so I replaced it with and OD.  It didn't seem to help but after a few minutes it started wiggling.


I thought I had it sorted out but then the tremolo faded away for a bit and then it came back.  There is a gremlin inside this amp and it is taunting me.


I'm gonna take a break and come back to it later.  As of right now the tremolo is working.  I have to switch the tremolo on and then turn the pot to max, wait for it to wiggle quickly and then back it off just a tad to get a slower tremolo.  It's holding at the moment. Later on? we'll see. It seems to be finicky.

[jjasilli]

The tremolo does work steadily when the chassis is out of the cabinet and on my bench but as soon as I re-installed the chassis into the cabinet, the tremolo starts acting up.


* When the chassis is out of the cab on your bench, is it oriented so the tubes are pointing down?  If NO, orient it that way, out of the cab, to see if the trem still works.
* I'm thinking maybe something is shorting out somewhere, lead, jack, pot, even a tube internally???
* What are the plate & cathode voltages of V4 & V5 when the trem is: i) Working?  ii) Not working?

[sluckey]

Replace C2, C3, and C11.

[TubeGeek]

Replace C2, C3, and C11.

Yeah.  I figured it was headed here. 


The tremolo is now solid after replacing these caps.  In fact, it was too fast so I connected a decade box and selected a larger value for c11 in order to slow the trem down to a useable speed.  0.1µF did the trick.


I can button this amp up now. 


It sounds fantastic, a bit hummy but it has a nice raw tone.  I think it'll be perfect for the cigar box guitar I voiced it for. The owner is going for a raunchy tone and this nails it. Oh and he bought this last week for $20!


Thanks guys for the help.

[TubeGeek]

The tremolo does work steadily when the chassis is out of the cabinet and on my bench but as soon as I re-installed the chassis into the cabinet, the tremolo starts acting up.


* When the chassis is out of the cab on your bench, is it oriented so the tubes are pointing down?  If NO, orient it that way, out of the cab, to see if the trem still works.
* I'm thinking maybe something is shorting out somewhere, lead, jack, pot, even a tube internally???
* What are the plate & cathode voltages of V4 & V5 when the trem is: i) Working?  ii) Not working?

The only explanation I have for this is the caps on the oscillator were causing the weirdness.

[jjasilli]

  I wonder why it worked with the chassis outside the cab? Gremlins!!!