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Old 7th November 2010, 08:11 PM   #11
M Gregg is offline M Gregg  United Kingdom
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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!

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M. Gregg

Last edited by M Gregg; 7th November 2010 at 08:23 PM.
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Old 7th November 2010, 08:41 PM   #12
M Gregg is offline M Gregg  United Kingdom
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O.K.

here is the link found it:

http://music-electronics-forum.com/a...ng_100_212.pdf

Is this correct?

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M. Gregg
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Old 7th November 2010, 08:48 PM   #13
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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.
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Old 7th November 2010, 08:56 PM   #14
M Gregg is offline M Gregg  United Kingdom
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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

Last edited by M Gregg; 7th November 2010 at 09:02 PM.
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Old 7th November 2010, 09:04 PM   #15
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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.
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Old 7th November 2010, 09:14 PM   #16
M Gregg is offline M Gregg  United Kingdom
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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?

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M. Gregg
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Old 7th November 2010, 09:19 PM   #17
M Gregg is offline M Gregg  United Kingdom
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Does the fault occur on clean and overdrive channels?
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Old 7th November 2010, 09:31 PM   #18
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Definately clean, I dont know about O/D tho. Want me to check?
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Old 7th November 2010, 09:33 PM   #19
M Gregg is offline M Gregg  United Kingdom
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normaly the clean channel is the key issue if its on the clean its going to be on overdrive!
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Old 7th November 2010, 09:34 PM   #20
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Great place to start!! Actually it DOES happen on both channels.
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