Standby switch, snap, crackle, pop?

[Trout]

I have one of my Deluxe amps that has me pulling hairs trying to pinpoint.

When I put the amp/switch into standby, It get a fairly loud pop.
I have also noticed that I get a slight arc inside of the rectifier tube when this happens.

Going into standby interrupts the B+ directly between the 5Y3 and the first PS Cap.

Now, it does not do this every time I use the switch, If the amp has been sitting In standby mode, and I go to the ON position, It appears to be fine. No Pops, No Noises, No Arcs.

I have tried 2 different NOS Jan/Hytron 5Y3's, both arc, Then I tried a Raytheon 5Y3, No visible arc, but the pop still occurs.

Could this be caused by the standby switch itself?


Trout

[kevinkr]

I think the safest place to put the standby switch might be in series with the center tap connection.

I wonder whether when you open the switch the sudden collapse in the transformer's magnetic field (due to abruptly removing the load) is not causing a large voltage excursion on the secondary (flyback effect) and resulting in a momentary transient across the rectifier, and that switch.. IMO that can't be good for either the rectifier or the switch.

Perhaps a simple rc snubber across the transformer secondary and/or across the switch would help. (Something like a 10K 1W and 0.047uF 1KV ceramic in series across the HV secondary? Or 10 ohm and 0.1uF 500V across the switch.)

You might want to wait for George (tubelab) to weigh in on this issue.

[Trout]

I Thought about putting a ceramic cap across the switch, maybe a .01/1600V which is somewhat common in guitar amps. I guess my principle concern is It only 1 amplifier out of the 4 sitting here that has the problem.

If that stops the arc, I would not have any problem adding it.

I do know that it does cause a fuse blow unless it is a slo-blow fuse.
I had a few 1amp non-slo-blow and It blew that every third or fourth cycle.

Its better to interrupt the CT instead of the B+?
If so, I will just start using that for the standby, It should not be difficult to change.

Trout

[kevinkr]

Same power transformer in all 4 amplifiers? Small differences in leakage inductance and inter/intrawinding capacitance between power transformers could account for a lot of the difference.

I have run into similar issues in production MI amplifiers where a certain % of otherwise identical amplifiers would exhibit a very specific symptom. The problem would be very repeatable in some amplifiers, sporadic in others, and non-existant in the rest. Usually it would turn out that there was a minor design error responsible or an unauthorized part substitution (bad buyer LOL) had occured. The fix of course would then be applied to all amplifiers, not just the ones exhibiting the problem.

I would fix the problem even in amplifiers that don't exhibit the specific symptom as I suspect HV transients are occuring that could ultimately damage the transformer's insulation system and result in a HV secondary short.

[Trout]

OK Good Idea,

These are all Hammond 272BX Transformers, I bought a couple cases of them and out of 8, only 1 has given me this problem.

I have however run into this problem on an entirely different amp with entirely different transformers. In all cases however the standby switch is interrupting the B+ prior to the first cap.

Which is the better appoach, Cap on the switch, Or use the Center tap instead of the B+?

I am using CARLING SWITCHES which " Should" have been up to the task. They are basically standard equipment in most older Fender amps.

Trout

BTW Thanks for the input!!

[refference]

Hi Trout ,

Sorry for the delayed input . But I’m going to say to you
that all you had described in your first post , is not
totally ANOMALOUS .
The phenomenon is more problematic , when you turn OFF.

The rectifier tube , the output tubes and the power trans-
former are not the guilties .

First of all , your stand-by switch is in the wrong position , it won’t
work properly , if connected as above ( between the rectifier
and first cap. ) , because the + B line of an audio amplifier
has a very , very high sensitivity to any “disturb” ( due to the
high impedance of all plate’s circuit ) , then a simple
switch interrupting the circuit , will be multiplied many , many
times , causing an “overshooting” , that will be amplified many
times and overcharges the output tubes , causing arcs into them ,
and a very loud “pop” on the speakers .

As kevinkr said , try to put the switch , in series with the center
tap connection ( between center tap and ground connection ) with a 0.01 uf x 1600 V cap , connected in the two switch’s tap .

Try this “trick” , and give us a feedback , if the problem was
solved .

Regards ,

Carlos

[Trout]

After looking closely at my chassis layout, Using the CT for the standby actually eliminates about 4-5 inches of extra wire! Thats always a good thing.

I am going to head in that direction, I should have it wired up fairly quick. Will put cap on switch also, no sense skimping at this point. If it helps save the tubes and possible transformer damage it is well worth the extra .15 cents.

Trout

[Tyimo]

Hi!
I built the Tube Preamp for SEWA (designed by Gregg, Thanks!!) and I have some strange problem.
The tubrepre works very good but not with every amp!
With some power amps it has loud noise.
It is not a 50-100Hz "humm". It is something around 1000 Hz
"brzzzz" noise.
The bigest problem that the worst and loudest noise is with the SEWA!!

I tryed with many diffrent amps. DIY and commercial too. With most of the amps the system was deadly quiet!!

I tryed to grunding the tubepre (PSU negative rail to case via 1Meg resistor bridged with a 0.047uF film cap), but I think it was not the real problem.
Here are the test:

-With my SEWA it has noise and when I turn on my CDplayer the noise is getting louder 2-3 times! With the grounding the result was even worse!

-With my Zen Lite the noise was very little, absolute on acceptabel level!

-With my Aleph5 it was also very quiet!!!

-I tryed the tubepre without grounding to case and mains safety earth and with the last 2 power amps the result was very good!!!!!
Every time I used the same wall connector, interconnect cables, CDplayer, etc.

The Zen Lite and the SEWA amps has the same ground plan. RCAs are isolated from the metal case, PSU ground connected via diode bridge to the case (I learned this from Nelson Pass.) and to mains safety earth. Like in the attached image.
Tha Aleph5 has 10R 20W power resistor instead of the diode bridge, but the rest are the same.

-In another system with non earthed ZV9 (in wooden case) was the best result!

-With a commercial Pioneer amp and Philips DVD was also 100% good!! (Both are not earthed)

-With another earthed ZV9 has noise again!

So, I am afraid that the problem is in my SEWA amp or even worse: the SEWA and Tubpre could not working 100% together ?!?
Could it be the problem that I didn't use the 50K input pot???? I use the CDplayer's output pot.
Need I use the 2.2uF input cap?

BTW, the preamp has superb sound and can drive easy the Mosfet amps!! Except the SEWA!!!!!

Could somebody help me??

Greets:

Tyimo

[refference]

Hi Tyimo ,

Excuse me , but the grounding circuit that you have attached ,
makes NO SENSE to me .

The wall outlet’s ground pin ( central pin ) must be connected
to the chassis or to the metallic box of an electro / electronic
equipment , with the aim to protect the owner against electrical
shocks . It is the ONLY thing to do !!! Nothing more !!!

Take off the bridge rectifier in the grounding circuit , because
your power supply ground , is at least 0.7 Volts above ( or below )
the chassis potential , what is bad enough to introduce “hummm” , “bzzzzz” , “shhhh” , “brrrrrr” , and a lot more of alias noises .

If any noise persists , connect the power supply ground , DIRECT
to the chassis or metallic box ( please , NO bridges , NO resis-tors, NO capacitors , NOthing ) .

I hope it helps , give us a feedback .

Carlos

[Tyimo]

Hi Carlos!

- First: I don't know why my post is here in this thread, because I posted it in the Tube Preamp for SEWA thread!

- Second: Thanks for your kind answer!!! I learned this grunding from Mr. Pass and all my amp are built like this and have no problems. I was thinking a lot about the different grunding variations and I am totaly agree with your oppinions!
I will try and report you!

Thanks again!!

Greets:

Tyimo