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Re: still perplexed but a step closer


 
11/3/2003 10:44 AM
db
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Re: still perplexed but a step closer
Hi Matt,  
 
Yeah I musta done something wrong with the Cliff jacks ground, I'll double check that tonight.  
 
Thanks
 
11/3/2003 10:58 AM
Dai Hirokawa
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simon dumblar, the reclusive amp operative ;)
 
11/3/2003 10:23 PM
db
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Still nuthin, the jacks are well grounded and they are wired correctly.  
Strange that with all the tubes pulled and the amp in standby I get -.8 volts on the plates of the 12AX7 and all the b+ line. Looking for the elusive miswire or bad part but haven't found it yet.  
With the tubes in channel one does read a higher voltage at the input than channel two but still not sure where it's coming from.  
 
I gotta go over the whole amp tonite  
 
David
 
11/4/2003 1:48 AM
db
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Got it! I think.. haha
Hey I might be on to something, well actually I have no idea what I did but the readings are much better. tube 1 was the original valve which has the least voltage at the input jack, go figure and 2 was for comparison. this is with the amp on.  
It probably was the ground as I did reflow some solder joints and did a lot of prodding . Is there supposed to be any voltage at the jack tip?  
 
Thanks a million for the tips :)  
 
David  
 
 
 
 
tube 1  
 
CH1 / CH2  
hi= .092 / hi=.037  
low= .007/ low=.003  
 
tube 2  
 
 
CH1 / CH2  
hi=.121 / hi=.008  
low=.008 / low=.003
 
11/4/2003 1:05 PM
Dai Hirokawa
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Right at the grids, with no signal, I think it's usually like you have on the "low" readings above (.007 volts? = 7mV?, etc.). ".092" and ".121" look a bit high (or maybe too high) but IME, you can still have a bit of leakage (from the cap) and it still sounds alright. If I saw, say ".3V", that would be way too high and most probably sound bad too. By any chance did you re-flow the joints on the tube pins, and did you take out the tube when you did? I'm not 100% certain on this, but I take out the tube to avoid possible damage (maybe the grid is most sensitive?--since it's a spiral of wire). I used to use a Sovtek 12AX7WA (temporarily in the tube slot when soldering the pins) which I didn't care about but now I use a plug with a bolt in it (so there is something to hang on to when pulling it out (makes it easier esp. w/bayonet shield). Maybe I'm completely wrong (wouldn't be the first time, lol), but it's something else to consider. Wonder what it is. Hope you can figure it out so we can all get a mental note on an actual/potential problem.  
 
Dai
 
11/4/2003 11:20 PM
db
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Dai,  
 
Yes I did reflow the solder joints on the socket (without tube). Though better than before I think that you are right that the readings (.092 and .121 ) do seem too high especially compared to my JTM50 clone with .013 on the #1 hi input. I also reflowed the jack connections and changed the coupling caps. Even though everything "looked good" on the initial build I believe some of the solder joints weren't as good as they should have been but this still didn't completely solve the problem.  
This is the first time I've encountered this problem so I'm not sure what "normal voltage" is and what the cause of the problem might be. Doh, I didn't measure right at the grids rather the tip of the input.  
 
 
Back to the bench  
 
 
db
 
11/5/2003 8:38 PM
Andrei
Maybe the tube socket is going bad.(arcing) Try replacing it.
 
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