Tube pops upon power on?

[Gene]

Hi,

I just rec'd a quartet of 1957 RCA 6V6GT blackplates. I put it into my amp and when you first turn the amp on, there is a pop. The amp plays fine though and sounds great.

Is this something to do with getters? I haven't experienced this with my other tubes.

 

[doctord02]

I dont know what it is, but I do know it's not related to the getters. Getters only matter the very first time the tubes ever get voltage applied to them at the factory. Does the amp pop with a different set of tubes?

 

[Gene]

Nope. It is the tubes. I tried it with a different amp and when you first turn it on, the amp makes a "pop" sound and then plays normal. I can alleviate this annoyance by having the volume on zero when turning on the amp.

Weird. Could it be related to gas or air in the tube? Maybe it is a bit leaky after 52 years.

 

[doctord02]

Hmmm. Does the amp have a stand-by switch? Odd that it's just that set of tubes. I wonder if they draw significantly more or less current that your other 6v6's do...

Edit - they likely arent leaky, 'cause they work. Leaky tubes just dont work at all...

 

[Gene]

No standby. I tried it in 1983 Fender Princeton II, 1966 Champ, 1964 Gibson GA-19RVT.

These pull significantly less current than the RCA grey plates I had in the Princeton. About 10ma less. Which is perfect for the PR II.

The tubes sound great, though. I love these tubes. I got a quad match for like 12 bucks each.

The thing is I remember a thread here with someone with a similar issue. I think one of the tube gurus around mentioned this was quite normal for a tube back then and not to worry about it. But I'd like to know for sure.

 

[Trout]

It might not be the 6V6's. It is very possible that a weak rectifier is being exposed by the new output tubes load differences.

It also could be a shorted tube. Once hot it clears up. I have seen lots of pre-amp tubes make sizzles and pops during heat up, often for up to a minute, Not a good thing, but common.

 

[Gene]

It is very possible that a weak rectifier is being exposed by the new output tubes load differences.

On 3 different amps? PR II has a solid state rectifier. The Champ and Falcon has 5y3.

Wouldn't a shorted tube not work at all? I think it would start taking out other components in the amp. I played it for 4 hours straight, no problem.

 

[rockon1]

Just curious-does the amp physically pop or does it pop thru the speaker? The reason I ask it that if I turn on my Peavey Classic 50/50 power amp without using the standby (usually by accident of coarse) the amp physically "pops" not thru the speakers! - more of a loud "bonk" actually. Sometimes I think the amp would actually jump if it wasnt so damned heavy! Wierd but its been that way for 16 years now. Bob

 

[Structo]

Sometimes depending where the standby switch is in the circuit, when the first filter cap charges, it can cause a thump in the speakers.

But, no standby and no rectifier, would most likely eliminate that.

Weird, never heard of something like that where it would be the tubes.

The only other thing would be a carbonized socket but you say the pop follows the tubes no matter where you put them.

 

[slider313]

If they're pulling 10ma less then your plate voltage is higher. Did you measure it? That could be an issue.

 

[Gene]

does the amp physically pop or does it pop thru the speaker

Through the speakers. If I turn on the amp with volume at 0 and give it a minute, no problem.

 

[Gene]

If they're pulling 10ma less then your plate voltage is higher. Did you measure it? That could be an issue.

Yes, the plate voltage goes up about 15 volts. But well below 400 volts.

 

[Gene]

I found the culprit. It is one of the tubes. As you turn the amp on, I see sparks in the tube but then settles down and plays fine. What is that? A shorted tube?

 

[Trout]

Swap the tube to a different socket, if the arc follows the tube,replace the tube.
If the arc is common of that socket, you will need to dig further.

Remember, when a tube arcs inside, in 95% of the cases the output transformer is being exposed to transient voltages that can and often do damage it.

If you put it on a peak capturing scope you will see spikes in excess of 2KV, this can take out the insulation in the output transformer fairly quickly.

 

[Gene]

Yes, it is a bad tube. It would arc once or twice upon power and then settle and sound fine. The seller is sending me a replacement.

Thanks, everyone for your response.