pop noise during warmup

[shel50]

I'm currently using Gold Lion KT77 tubes--they sound wonderful but I notice there is a slight "pop" noise in the speakers
during warm up when the amp is turned on. Only happens with these tubes. The pop is slight but I can't help wondering if this
is normal or can it cause speaker damage?

 

[Republicoftexas69]

Even with volume down?

 

[shel50]

Even with volume down?

yes. completely turned down

 

[shel50]

Even with volume down?

yes

 

[Another Johnson]

Usually popping noises come from failing small driver tubes. Like 12AX7s, 6H30Pis, 6922s, etc. KT77 is a kinkless triode . It might arc, red plate, motorboat, etc. Seems unlikely to just pop during warmup with no input.

 

[Another Johnson]

From Upscale’s website about current crop of Gold Lion KT77s:

Notice: We supply the very finest KT77s that you can get and our testing is the best. Period. Statistically, they are not as dependable as the Mullard EL34 reissue. This has increased lately. Even if you have a PrimaLuna which runs tubes really easy you need to know these can fail more often. If you understand that and love them anyway, party on.

 

[shel50]

Usually popping noises come from failing small driver tubes. Like 12AX7s, 6H30Pis, 6922s, etc. KT77 is a kinkless triode . It might arc, red plate, motorboat, etc. Seems unlikely to just pop during warmup with no input.

only happens with the KT77---KT 88's quiet which eliminates driver tubes

 

[shel50]

From Upscale’s website about current crop of Gold Lion KT77s:

Notice: We supply the very finest KT77s that you can get and our testing is the best. Period. Statistically, they are not as dependable as the Mullard EL34 reissue. This has increased lately. Even if you have a PrimaLuna which runs tubes really easy you need to know these can fail more often. If you understand that and love them anyway, party on.

yes I read that They assured me a soft noise as such will not harm a speaker--just not loud enough to cause damage

 

[sparkie]

I'm currently using Gold Lion KT77 tubes--they sound wonderful but I notice there is a slight "pop" noise in the speakers
during warm up when the amp is turned on. Only happens with these tubes. The pop is slight but I can't help wondering if this
is normal or can it cause speaker damage?

There are a few things it could be, but it sounds like inrush current on cold tubes. Does this have a solid state power supply?

 

[shel50]

There are a few things it could be, but it sounds like inrush current on cold tubes. Does this have a solid state power supply?

probably is SS power supply----Primalina HP premium integrated--built like a tank like all
Primaluna amps.......Changed tubes to Shuguang KT88 tubes--dead quiet

 

[dtbradio]

There are a few things it could be, but it sounds like inrush current on cold tubes. Does this have a solid state power supply?

Would in-rush cause a sharp pop? Even with solid-state supply, wouldn't the change in current be slow enough that it would sound softer than a pop?

To the OP, have you tried different tubes of the type causing the pop?

 

[sparkie]

Would in-rush cause a sharp pop? Even with solid-state supply, wouldn't the change in current be slow enough that it would sound softer than a pop?

To the OP, have you tried different tubes of the type causing the pop?

A solid state supply is very hard on tubes. the instant the power is turned on, is the second the plate gets hit with voltage, Also, this voltage spike appears on capacitor coupled inputs and cathodes at the same time. Tube rectifiers slow start and softly ramps the voltage.

 

[dtbradio]

A solid state supply is very hard on tubes. the instant the power is turned on, is the second the plate gets hit with voltage, Also, this voltage spike appears on capacitor coupled inputs and cathodes at the same time. Tube rectifiers slow start and softly ramps the voltage.

I do understand all of that. However, the tube isn't conducting anything until it warms up, and it doesn't instantly warm up. Where would such a fast transient happen in the tube itself during warm-up that it would cause a sharp pop? Especially curious since the OP's info narrows it down to a tube problem as his other tubes don't show the symptom. As always, I'm trying to learn things.

 

[sparkie]

I do understand all of that. However, the tube isn't conducting anything until it warms up, and it doesn't instantly warm up. Where would such a fast transient happen in the tube itself during warm-up that it would cause a sharp pop? Especially curious since the OP's info narrows it down to a tube problem as his other tubes don't show the symptom. As always, I'm trying to learn things.

the tube circuit doesn't have to be started for effects like exceeding cathode to heater voltage rating to happen.

 

[treitz3]

Could you not just put your pre on "mute" when this happens?

Tom

 

[sparkie]

Could you not just put your pre on "mute" when this happens?

No because its still going to do it regardless if you hear it or not. Eventually you see it when it destroys the tubes. Usually what happens first is the heater flash glow.

 

[treitz3]

My point is to eliminate any other damage to your system. If you like said tubes?

Carry on...

Tom

 

[sparkie]

My point is to eliminate any other damage to your system. If you like said tubes?

Carry on...

Tom

depending on where the inrush current sinks, people have applied thermistors to absorb it. Quite frankly, its better to use the correct technology in the first place and avoid adaptations that add complexity and more avenues of hardware failure.

Power Thermistor

Since this is an amp with an inductive load, you can just add one in series with the bridge to soft start the dc supply.

 

[sparkie]

another way would be to add a time delay relay in as a B+ standby switch. But I would put something like a 47K across the contacts to soft start

 

[shel50]

Would in-rush cause a sharp pop? Even with solid-state supply, wouldn't the change in current be slow enough that it would sound softer than a pop?

To the OP, have you tried different tubes of the type causing the pop?

The GL KT77's were the only ones it happens with. And yet not all the time....Today in the morning did not hear any pop. Later in the day I did---
That being said I'm friends with the amps actual designer who said not to worry----its not a loud noise that can stretch a voice coil-------and a fair amount of people experienced this.....