Peavey Valveking 100- static sound during warm-up

Rotus623

Member
2010-09-20 4:34 am
I checked all of my speaker wiring,and no problems. For some reason, when I fire up the amplifier, as it warms up I hear static like there is a loose wire connection and someone is wiggling it around. When the amp is warmed up, it doesnt make any of those sounds. Does anyone know what components that I should check first?
 

Rotus623

Member
2010-09-20 4:34 am
So guys, I tapped all of the tube and none of them are microphonic. I was jamming today at 3 or 4 and the gain started fading out. I kicked it over to clean channel, and the volume was significantly lower than it was when I started playing. This was in a period of about 10 minutes. Does anyone have any that would lead me to pre or power amp tubes? Id like to narrow it down to tubes before I drop 1XX dollars into tubes.
 
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Rotus623

Member
2010-09-20 4:34 am
So check these out guys, upon further inspection this is what I saw. Is this what it looks like when the vacuum seal has a leak?
PA120038.jpg

PA120037.jpg
 

Rotus623

Member
2010-09-20 4:34 am
Okay, well I changed all of the tubes out and now I still have a static noise during the warm up phase. Except now it takes a lot longer to go away. Any suggestions why the amp is making a static noise when the volume is turned all the way down? When it is in standby mode it is totally quiet.
 

M Gregg

Disabled Account
2010-06-28 11:04 pm
UK
Rotus,

The reason you hear nothing in standby is the HT is off! Only heaters are on!
I have found a schematic "I think" on the web if interested PM me your E-mail I will send it to you.
I would post the link, however I can't find it again sorry. If this is the correct circuit then we can possibly post some info and progress!

Regards
M. Gregg
 
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Rotus623

Member
2010-09-20 4:34 am
Thanks! So M, what do you think these symptoms mean? I hear a static noise like there is a loose jack for the first minute or so when the amp is just turned on. After that, no issues, the amp plays and acts fine. Before I changed the tubes, i was playing for 15 minutes or so at 3 or 4 volume, and the volume kind of dropped off. Then is almost sounded like I had the reverb on just a tad. Very strange.

I have an inkling that the guy I bought the amp from was running the wrong impedence speakers at high volumes if that helps at all.
 

M Gregg

Disabled Account
2010-06-28 11:04 pm
UK
This kind of fault is always difficult to track down. As stated by others mechanical damage in a tube would cause it however it would normaly continue after warm up. The picture you posted of the output tubes shows no red plates "Anodes" so it could be a coupling cap. It could also be a bias problem, if it is a bias problem then you will have to take some measurements. Have you ever worked on tube circuits before?
The output tubes look O.K. in the photo, this is good however this means it is probably going to require measurements.

Also is the schematic correct?

Regards
M. Gregg
 
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Rotus623

Member
2010-09-20 4:34 am
This is the schematic of my amp. Actually I have done work on tube circuits. I have done more with solid state components. I actually just put an adjustable bias mod into this amp and checked all of the output tubes for bias and they are all very similar. Another issue that I had with this amp was that the two power tubes on the right hand side (as you look from the rear of the amp) look like they had lost their vacuum seals. (If that helps at all) But this is not a tube issue. I changed the tubes out and it actually took longer for the static noise to go away.
 

M Gregg

Disabled Account
2010-06-28 11:04 pm
UK
If you have checked the bias on the output tubes and that is ok, you have removed that avenue. So you have to start at the simple and work up. Have you tried all the simple things like cleaning the pots? Also you say you have changed the tubes did this include the small pre-amp and drivers?

Just a safety issue does the amp hold HT after power off?

Regards
M. Gregg