'79 Silverface Deluxe Reverb Tremolo Problem

[Johnrcurry]

I am working on a '79 Silverface Deluxe Reverb. When using the tremolo there is no discernable tremolo effect until about 6 on the "intensity" dial. In addition, when the tremolo effect does come on, there is a very large drop in overall volume; I'd estimate it drops to about half what it is without the trem. I've swapped in a known good tube for V5 with no difference. Any ideas what the problem may be? I've attached a schematic and a couple of shots inside the chassis. (By the way, the wiring looks pretty messy to me. Is this typical of this era Deluxe Reverb?).

Thanks

John

[52 Bill]

With the exception of the power tube sockets and related resistors, the chassis looks to be typical of that era. The weak tremolo sound like a bad photocell in the optoisolator, "bug". Replace it with a new one or cut open the heatshrink and replace just the photocell.

[Jazz P Bass]

. (By the way, the wiring looks pretty messy to me. Is this typical of this era Deluxe Reverb?).

Thanks

John

Yeah, 79 Silverface amps are a real rats nest.
And yet they do not hum
Go figure.

[Johnrcurry]

Bill52, you mentioned the work done on the power tube sockets (which is evident from the the photos). What they've done is:

1) removed the 1200pf capacitors from pin 8 to ground and replaced them with 10 ohm resistors; and

2) changed the resister between pins 4 and 6 from 470 ohms to 2.2K ohms.

I'm guessing that the resistors on pin 8 is to provide some place to check the bias, although I've generally seen people use 1 ohm resistors when adding bias test points. Would it work the same with a 10 ohm resistor, only moving the decimal point when taking a reading? If not, is there some other reason to add that resistor?

Also, have you seen this sort of change to the resistor value between pins 4 and 6 before, and what would be the reason/effect of that?

Thanks.

John

[Johnrcurry]

Jazz P Bass. You're right about that. The wiring is messy, but it doesn't hum.

John

[52 Bill]

Would it work the same with a 10 ohm resistor, only moving the decimal point when taking a reading? If not, is there some other reason to add that resistor?

Yes it will work in place of the more common 1 ohm value.

Also, have you seen this sort of change to the resistor value between pins 4 and 6 before, and what would be the reason/effect of that?

I've never seen a value that high used for a screen grid resistor.

[Johnrcurry]

Bill, does it make sense to change the screen grid resistor back to the stock 470 Ohm? Is there any reason not to?

Thanks

[52 Bill]

I'm a traditionalist when it comes to Fender Deluxes, so I prefer the sound of the 470 ohm value. The larger values may help increase tube life by controlling the current a little better, but there are sonic tradeoffs, like compression of the signal. I think that Marshall used that value in some of their amps back in the days when they were having EL34 tube failure problems, (maybe the early '90s?).

I'm sure that some of the others here will have opinions about this.

[Johnrcurry]

I've ordered a new optoisolator to see if that solves the tremolo problem, and I will change the screen grid resistors back to stock. In the meantime, the amp has developed another problem, for which I've started another thread. Thanks for your help with this.