Standby to play mode - switch thud

[Bob M.]

Hi,

I've got a BF Pro Reverb on my bench that my client thinks has too big a thud/thump coming from standby to play mode. I've told him many amps do this and the amp is fine electronically but it bugs him and I have to say that it's a louder thump/thud than normally encountered. Also, coming from play mode back to standby produces a 'pop' of medium volume (a bit more high endy sounding). I've replaced the amp's standby switch 2 or 3 times without any change in this sound so I'm looking into different things to tame the thud. I've read that a cap can be placed across the standby switch but at what value? I would think maybe .022 or .047uf @ 1kv. Or possibly adding another stage of filtering, pre-standby, just off the rectifier tube (5AR4A/GX34) at pin 8 to ground might help. Any suggestions are welcome, especially successful ones to 'stop the pop'.

Thanks,

Bob M.

[The Dude]

Try this.

https://robrobinette.com/Generic_Tub...#Pop_Reduction

[Bob M.]

Thanks, Dude, that's a good website - I bookmarked it.

Bob M.

[The Dude]

He's a smart fella and a member here.

http://music-electronics-forum.com/member.php?u=41785

[cerrem]

Not a fan of using a resistor.... You simply put a .047uf to .1 uf 600V film cap across the standy terminals...
No more thump...

[The Dude]

I have no beef with either solution.

[pdf64]

Err, how about not using standby?
I’m not aware of any technical benefit in the use of standby with an amp that has a indirectly heated rectifier.
Yes I’m calling out BS on many tube guitar amp user handbooks.
I think the ‘cathode stripping’ issue invalid in our application, evidence that myths spread quite effectively pre internet.

[g1]

Err, how about not using standby?

Some guys still want to mute their amps without shutting them off for breaks etc.
I think the guitar cords that have the mute switch on the guitar end are a good solution for this. Yank the cord out of the guitar and it mutes the amp.

[cerrem]

Err, how about not using standby?
I’m not aware of any technical benefit in the use of standby with an amp that has a indirectly heated rectifier.
Yes I’m calling out BS on many tube guitar amp user handbooks.
I think the ‘cathode stripping’ issue invalid in our application, evidence that myths spread quite effectively pre internet.

I hear ya...
The reason for the stand-by switch is not necessarily for prevention of Cathode Stripping..... I agree that is a weak argument... However the main reason is for the tubes to warm up just long enough so that they present a LOAD to the power supply, when the STND-BY switch is hit....
One customer who removed his stand-by switch would have about 540V B+ across every node in the amp...until the tubes warmed up to provide a suitable idle load to keep voltages in check..
He blew his 500V filter caps and also blew up his V2 tube.....multiple times...
The V2 cathode follower had arcing between the cathode and heater ....since it is ratted at +/-200V ...... Well before the tubes are warmed up, the power supply is working unloaded....and the cathode will sit at 540V in his case, before warm-up... Same goes for amps with Cascode circuits.... If power supply voltages are applied before the tubes are capable of conducting ...then you get some flash-overs....

[Leo_Gnardo]

Well before the tubes are warmed up, the power supply is working unloaded....and the cathode will sit at 540V in his case, before warm-up... Same goes for amps with Cascode circuits.... If power supply voltages are applied before the tubes are capable of conducting ...then you get some flash-overs....

Bring back spark gaps! Technology, forward - into the past.

[Bob M.]

Hi pdf64,

The amp in question is a 1965 blackface Fender Pro Reverb. Leo, in his wisdom, mounted a standby switch on this (and most other models) amp. The guy who owns and uses the amp likes the standby and just wants it work so the associated noises with it don't make him nervous (so he can concentrate on his playing and not be thinking his amp is about to die/explode). I can see his point. If I was building an amp from scratch, I may not include a standby, depending on a few other things in the design. This standby thing has been debated for a pretty long while around here (Are standby switches really necessary?) but many, many amps already have them and it would be good if they all worked as intended with a minimal amount of extra noise and hoopla. Given the choices of sending my client to a standby re-education seminar or fixing the the thud, I think I'll just fix the thud.

Bob M.

[alexradium]

having a tube rectifier like the 5AR4 in this amp,at startup there is no HV problem,because it takes a minute to heat up and conduct,so you could easily let it always in play mode,same thing happens in the Vox AC30 that never needed standby.
Another technique i like is to use the standby switch to cut only the power tubes screen grids line,that reduces a lot the problem.

[J M Fahey]

Hi pdf64,

The amp in question is a 1965 blackface Fender Pro Reverb. Leo, in his wisdom, mounted a standby switch on this (and most other models) amp. The guy who owns and uses the amp likes the standby and just wants it work

Ok, so Leo though a Standby switch was fine.
Won´t argue that.
Leo must have also noticed that standby switches *pop/thump* some.
Clearly HE thought it was no big deal or he would have corrected it some way or the other.
Are we playing the "Authority" card here? ("Leo did it").
Ok, I can also play with those cards: Leo did nothing special to avoid it.
No caps, switches, screen mute, anything. How´s that?

so the associated noises with it don't make him nervous (so he can concentrate on his playing and not be thinking his amp is about to die/explode).

Well, it won´t.

many, many amps already have them and it would be good if they all worked as intended with a minimal amount of extra noise and hoopla.

Oh, they DO work as intended, any doubt about that?
Less noise than what´s normal for that kind of circuit?
Sure, but you´ll have to reengineer a Sacred 53 y.o. circuit.
I wonder what´s the point of using a Vintage Original amp then

Given the choices of sending my client to a standby re-education seminar or fixing the the thud, I think I'll just fix the thud.

It ain´t exactly "broken" so I wonder what exactly are you "fixing".

Side comment:
* the thump is real and natural.
* balancing power tubes will minimize it, in a very favorable case it will disappear, since it is applied common mode to both halves of a balanced circuit so it self cancels.
* I can trust both transformer windings to be quite well matched , they will certainly have same number of turns, wound out of phase.
The tubes? ... not so much.
^^^^^^^^^^^^^^^^^^^^ .................. I´d call this a hint

[cerrem]

Bro...
Just put solder a .047uf to .1uf 600V film cap across the stand-by switch terminals...
Simple, non-invasive and no redesigning of the circuit ......
Gets the amp off your bench in under 5 minutes and a happy customer..
Sometimes there is a "death" cap in these NON-grounded Fender amps..
I sometimes will put a grounded cord in the amp chassis...then remove the "death" cap and re-use it across the Stand-By switch...
A Stand-By switch does not always have an logical electrical reason, especially when there is a tube rectifier in the circuit...however, it is used for a player that want to shut-down the audio so they can change out guitars and be able to flip back ON in an instant..without changing the volume setting..
I love the Stand-By switch in my gigging situation....because I use 4 different guitars and have like a few seconds to change out the guitars between songs...
I looked at using the guitar cable with the switching plugs but the cable quality was crappy.... I bought a few Switchcraft #182 silent plug with internal dead switch and I also purchased roll of Mogami cable...this way I can make some decent cable to use that will switch-OFF when I pull them from the guitar jacks.. Ill see how that works... The Switchcraft #182 looks to be a fatter diameter plug, wondering if it will fit into the Strat jack ???

[Dave H]

I love the Stand-By switch in my gigging situation....because I use 4 different guitars and have like a few seconds to change out the guitars between songs...

If the amp doesn't have a standby switch I just pull the jack plug halfway out of the amp's input to mute it before changing guitars.