Standby sw wirinq question

[catalin gramada]

Hello. Trying to put a standby switch in the circuit above. I cannot get rid of "popping" at startup. The actual wiring layout is like in top drawing and I wonder if I do the wiring like in second drawing will do a difference, please ??. Thanks

[catalin gramada]

No, didn.t works no matter how is wired. Do You have any ideea why? Just power stage was connected so any possible grounding issues are excluded. snubbering network over contacts just help me to get rid of popping when is switched off but pops when switched on. I have not ideea how can diagnose where the source of the problem is. Share some help, please ? Thanks

[Enzo]

However you switch it, it pops because the voltage changes instantly from something to something else.

Why do you consider this a problem? I assume you are not flipping the standby switch while playing.

[catalin gramada]

However you switch it, it pops because the voltage changes instantly from something to something else.

Why do you consider this a problem? I assume you are not flipping the standby switch while playing.

Thanks Enzo. So You consider is normal to get a little thump at startup in this configuration, please? I just thinking is not a good way for a standby switch implementation...and maybe is better to move it into DC side as anyone do

[Enzo]

I do. Not every amp pops, but many do.

If an amp pops when you switch channels, I look for a solution. If an amp pops when you turn it on, I don't even notice.

[catalin gramada]

That can be true for me aso. I worked at this amp last week and quick wired the switch temporary without snuber for a test and didn.t notice the noise. Trying to finish I noticed now . Damn..I don.t remember if it pops before or not...

edit: anyhow is irelevant as cannot be sure if I waiting to heat the tubes till starts to conduct..

[TonyZ]

I had a SS Marshall which had a REALLY loud pop, more of a bang, it actually made me nervous when I knew I had to switch it off (on wasnt so bad - making vs braking) so I stuck a couple of high value caps across the switch terminals and that sorted it right out. I was a bit reluctant as it seemed like bad practice in case they fail, but there seems to be plenty of examples of people doing this and you should probably have it unplugged before you go poking around either way! There are caps you can buy rated to fail open which would probably be appropriate here

[alexradium]

try a 47/100k in parallel with the switch.

[J M Fahey]

1) the top and bottom circuits are exactly the same, so you shouldnīt expect any functional difference.

2) the wiring shown is wrong, and can be dangerous because it can give you a false sense of security: the bottom capacitor is switched ON-OFF but the top one is *always* charged to 280V DC.
You might think: "I switched AC standby OFF, now itīs safe to work" .... it is not.

3) a minor point: voltage ratios between caps are 3:2 , so bleeder resistors should also be roughly 3:2 ; say 220k on top, 330k on bottom. Not a big deal but since we are analyzing the circuit

4) yaībuilding a Hiwatt?

5) for proper standby action either use a double switch "DPST"
, each half switching one HV AC secondary, or each half switching one HV rail.

Personally I would not use standby, not sure what HiWatt did about it, but of course itīs your choice.

[catalin gramada]

1) the top and bottom circuits are exactly the same, so you shouldnīt expect any functional difference.

2) the wiring shown is wrong, and can be dangerous because it can give you a false sense of security: the bottom capacitor is switched ON-OFF but the top one is *always* charged to 280V DC.
You might think: "I switched AC standby OFF, now itīs safe to work" .... it is not.

3) a minor point: voltage ratios between caps are 3:2 , so bleeder resistors should also be roughly 3:2 ; say 220k on top, 330k on bottom. Not a big deal but since we are analyzing the circuit

4) yaībuilding a Hiwatt?

5) for proper standby action either use a double switch "DPST"
, each half switching one HV AC secondary, or each half switching one HV rail.

Personally I would not use standby, not sure what HiWatt did about it, but of course itīs your choice.

Thanks JMF. It is not a Hiwatt but 120w 2xKT88 amp. The stb sw. into a Hiwatt looks different. My friend who asked for amp want a stb sw. I usually don.t use. Simple or double switch over both rails didn.t do any diference in term of startup "popping"- I allready try it. It is not a safe break circuit so did not found any reason to cut all voltages inside the amp from a standby switch, this is a consequence, the only reason is to mute it from a standby switch -of course the power switch act over hot and neutral, both, for safety reason. The voltage over anodes are not shared equal over stacked rails so did not see any reason to use equal resistors but it can be as well. It acts just as bleeders, not to balance the voltage over caps, so I think can consider to use any values as time not draw too much current. It just was very convenable to me to choose that point for a standby switch from wiring/layout reason.
I can use a double switch and calculate the bleeder resistors values in respect with current over each caps. Do you think it will stop the annoing "pop" ? I thinking more to put a "X" type cap over secondary...
I still consider those "pop" as a transient, a disfunction but have not ideea how to identify where coming from..

[catalin gramada]

try a 47/100k in parallel with the switch.

alex, 10nF meant allready 300k arround over switch for 50cps operation, Do you think reducing to 100-47k arround will help ?

[Enzo]

If you must cure it, then FIND OUT where it is coming from. Do not assume the standby switch is the problem. Leave the standby on, and just cycle the power switch on. Does it still pop that way? Same trick for turn off pops: just pull the plug from the wall outlet instead of turning off the switch. Does it still pop?

[catalin gramada]

You might think: "I switched AC standby OFF, now itīs safe to work" .... it is not.

Wow!This is most dangerous way of thinking! If someone thinking like that should be imediatly disqualified to work into a tube amp. just my 2 cents. If have to work into live amp, leave it on. Othervise take the mains out and always check the caps if are drained first Never ever count on switches. I have friend who cut his fingers trying to replace a disc on angled grinder which was pluged. The switch looks very solid...still

[Enzo]

That is the problem: No one has to be qualified. On this forum we have some very experienced techs, and we have guys who are lifting a volt meter for the first time. None of them had to get qualified to jump into an amp.

[catalin gramada]

If you must cure it, then FIND OUT where it is coming from. Do not assume the standby switch is the problem. Leave the standby on, and just cycle the power switch on. Does it still pop that way? Same trick for turn off pops: just pull the plug from the wall outlet instead of turning off the switch. Does it still pop?

Thanks Enzo. I allready check it, fliping the power switch few times, stb,sw engaged, tubes well heated, it not "pop", no blowed fuses..., the problem comes just from engaging standby switch.

late: I will wire a separate transformer for bias voltage and leave the caps to discharge a little more if it have any sense...
No problems with stb.sw tured off. It was think sort of inductive coupling somewhere but was cured with snuber network. Anyhow was diferent manifestation. when turned off "the popping" had higher pitch like arcing. This turned on "pop" is a "muffled thump"-hope understand my representation