Fender Custom Deluxe Reveb

[bsco]

Good afternoon...to everybody....A customer has been complaining about the loud pop in his amp when switching to standby....Fender does not acknowledge that this an issue....and I have read numerous articles that state this is normal.....but, is there something that can be done to eliminate this......the amp is not under warranty so it won't void any Fender warranty....and the owner really wants me to try to get rid of it.....any suggestions greatly welcome and accepted....
Cheers

Just found something on line...I used a .047/600V cap in parallel with a 220K/2W resistor in parallel and connected across the standby switch....pop is gone......but Fender will not authorize this when under warranty....go figure.....

[xtian]

Tape the standby switch in the ON position and tell owner not to touch it.

[pdf64]

I don't think that your fix would do any harm; Merlin suggests a 47k 'trickle charge' resistor across such a standby.

[bsco]

I don't think that your fix would do any harm; Merlin suggests a 47k 'trickle charge' resistor across such a standby.

47K?? what I had saw on line used anything from 220k to 250K.......... anyway.....thank you for your reply......by the way...who is Merlin??
Cheers

EDIT!! I will pick up some quick connects/dis-connects and make up something that can easily be installed or removed...and insulate everything.....gotta be safe......

[eschertron]

I don't think that your fix would do any harm; Merlin suggests a 47k 'trickle charge' resistor across such a standby.

It depends on if the customer uses the standby as a performance-time mute switch. I'd think a value as low as 47k will allow the amp to function, even if it's much quieter than normal. Personally, I'm ambivalent towards the classic standby switch. A more usable mute switch can be done that has no HV popping on and off... if that's the desire.

[bsco]

It depends on if the customer uses the standby as a performance-time mute switch. I'd think a value as low as 47k will allow the amp to function, even if it's much quieter than normal. Personally, I'm ambivalent towards the classic standby switch. A more usable mute switch can be done that has no HV popping on and off... if that's the desire.

Ahhhh. I just saw your post.....thank you for your reply...

[g1]

The only real downside to such a mod is that it might cause a bit of grief to a tech who expects the caps to discharge when the unit is in standby.
There is always a trickle charge there for the caps if the unit is on but in standby mode.
Not saying it's right or wrong to make that assumption, but we do make assumptions based on what we are used to.

[eschertron]

47K?? what I had saw on line used anything from 220k to 250K.......... anyway.....thank you for your reply......by the way...who is Merlin??
Cheers

EDIT!! I will pick up some quick connects/dis-connects and make up something that can easily be installed or removed...and insulate everything.....gotta be safe......

My suspicion is that the circa. 220k value is a bleeder on the cap, which is the active element. The 47k resistor above is the active element, if it's installed without a parallel cap (which is my understanding). 's funny, using a 47k or lower jumper is almost like what xtian suggested, basically bypassing the switch altogether.

[bsco]

The only real downside to such a mod is that it might cause a bit of grief to a tech who expects the caps to discharge when the unit is in standby.
There is always a trickle charge there for the caps if the unit is on but in standby mode.
Not saying it's right or wrong to make that assumption, but we do make assumptions based on what we are used to.

Ok. This is the stuff I wanted to hear.....So you are saying that the filter caps will always be charged even in standby with this type of mod.....so is it possible to just put a cap across the switch?? oh wait...then the filter caps would charge up when in standby?? I will go ahead and put one together and just test it to see what happens to the filter caps with this installed across the switch with the standby switch in both positions....Thanks for pointing that out to me g1.....much appreciated.....

[nevetslab]

Turn-On Pop's origin in the circuits

Ok. This is the stuff I wanted to hear.....So you are saying that the filter caps will always be charged even in standby with this type of mod.....so is it possible to just put a cap across the switch?? oh wait...then the filter caps would charge up when in standby?? I will go ahead and put one together and just test it to see what happens to the filter caps with this installed across the switch with the standby switch in both positions....Thanks for pointing that out to me g1.....much appreciated.....

Having gone down this road with a Fender Twin Reverb, and with the assistance of nickb and others, we found the source of the popping to be the potential at the grids of the power tubes. As the circuit topology is essentially the same, though different power tubes (6V6GTs and only a pair in the case of the Deluxe & Custom Deluxe Reverb amp), coming out of standby, the DC potential at the grids are very different.



Looking next at the plates of the driver tube V6, we find the real issue, since the input caps on the driver tube grids are 1nF & 100nF.



After adding an additional 200uF across the output filter cap following the inductor (C33 on the Custom Deluxe Reverb, C32 on the Twin Reverb), it reduces the large overshoot transient on the negative driver's plate @ Pin 6:



It didn't totally eliminate the pop, but vastly reduced the transient. Similar improvements can be made by reducing the 100nF cap on the neg driver's grid. The Driver tube's source impedance ahead of the grid coupling caps are quite different, which is part of this turn-on transient seen at the output of the driver tube.

I'll have to look up the thread from which these images were gathered....sometime last year. I'll add that thread shortly.

NOTE: Previous thread where this Turn-On Pop and related artifacts found on the output tubes: https://music-electronics-forum.com/...ad.php?t=47438

[Randall]

FWIW, I tore down and rebuilt on garolite turret board a DRRI last year, new OT and PT, the works. It had a loud pop going into standby before the build, and after the build. Fortunately the customer isn't worried about it, so I didn't address it.

[Tony Bones]

This is fascinating! Another good reason not to have a SB switch in the HT supply.