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Old 20th June 2009, 10:15 PM   #11
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Good, I'll see if I can find those values at the local parts store...

The tube is an Electro Harmonix... bought at AES. It could very well be the socket. The underside joints looked perfect, and to get at the top side of the PCB would be pretty difficult. But I can ohm out the socket to the PCB...

Sigh, I'd rather be working on the SE chassis.
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Old 21st June 2009, 03:56 AM   #12
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I had some random static in my SSE, it turned out to be a loose mounting nut on one of the input jacks. Took me a while to find it...

Bill
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Old 22nd June 2009, 01:01 AM   #13
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George replies in another thread:

Quote:
I saw this post in a different thread. Try operating the amp without the 12AT7 and see if the static goes away. Of course there should be no sound at all. If the static is still there it isn't the 12AT7. If the static goes away, it isn't the power supply components. The most likely suspect is the tube, or the socket.
So this was an easy test - removed the tube turned on the amp - dead quiet. I'll resolder the socket but it looked fine to begin with. I really hope it isn't a contact issue in the socket.
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Old 22nd June 2009, 03:21 AM   #14
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socket resoldered. The static is better, but still there at a much lower level. Almost bearable.

Replacing the socket will be a pain, but mostly because I will have to disassemble the amp to do so.

I may try a new 12AT7 first, or perhaps bend the leads on the one I have to make better contact.
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Old 22nd June 2009, 03:34 AM   #15
kevinkr is offline kevinkr  United States
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Quote:
Originally posted by oldmanStrat
socket resoldered. The static is better, but still there at a much lower level. Almost bearable.

Replacing the socket will be a pain, but mostly because I will have to disassemble the amp to do so.

I may try a new 12AT7 first, or perhaps bend the leads on the one I have to make better contact.
I'd try a new 12AT7A or equivalent before replacing that socket - it could very well be that tube. Hamfests can be a pretty good source of not too unreasonably priced NOS tubes including 12AT7A/WA or 6201.

You might also try cleaning the tube pins (not socket) very carefully with a very fine emery board. I have run across a few tubes with so much glaze or oxidization on the pins that they were noisy.
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Old 22nd June 2009, 03:37 AM   #16
chrish is offline chrish  Australia
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Looks like you have resolved this to upstream of the input socket. So, it might be the socket, the tube, the volume pot, the input rca shorting to chassis or the wiring between any of these.

I have not built an amp with a volume control, all mine are controlled from a preamp or from the source. I have read people having similar problems if the body of the volume pot is not grounded.

Something also worth checking while waiting for a new tube would be your source and the cables from it to your amp. I have spent hours trying to sort out an amp problem only to find that an external component was to blame...

Best of luck!

Chris
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Old 22nd June 2009, 02:45 PM   #17
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good suggestions. I'll give them all a try.

One thing is the static started getting worse again after a couple of hours last night...

I checked my guitar amp and it uses 12AX7's... only one letter off checking the data sheet, it doesn't look like that would work...
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Old 22nd June 2009, 03:03 PM   #18
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I don't think a 12AX7 will work. You can use a 12AZ7, if you have any of those around.
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Old 22nd June 2009, 03:10 PM   #19
rknize is offline rknize  United States
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Wouldn't hurt to have an extra 12AT7 on hand in any case. You can probably tighten the socket contacts by carefully slipping a fine screw driver between the ceramic and the outside of the pins. I have my doubts that it's the socket contacts themselves...you can try to leave the tube in the socket crooked to see if that makes a difference. What happens to the static if you gently lean the tube while the amp is on?
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Old 22nd June 2009, 04:56 PM   #20
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Quote:
What happens to the static if you gently lean the tube while the amp is on?
What happens? You will have an old man hopping up and down saying "Thats HOT" lol jk.

Ty - I have a couple hundred tubes here, but they are mostly 6Al5, 6CB6, 6AQ5, 6CX8, 6J6... almost nothing in the 12 series....

wait take that back, just found a 12AT6. Yikes, thats a totally different tube - rectifier + gain stage...

I'll play with the tube pins and socket tonight.
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