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hotbox help

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11/3/2002 4:46 PM

hotbox help

Hi I just have finished the hotbox. Some mistakes solved and now it is working. I love the sound, only one problem. When I am turning up the gain and get to the middle, a very treble beep starts (is it what is called oscillation?), but the guitar is still sounding. And a little bit more of gain and ... no sound at all. If I turn down the gain and wait for some seconds, I got the sound again, but if I turn up the gain the same happen again. I got a B of 227 Vdc and A 207 Vdc. Should I rise up this voltages?. Is this the problem?. I don't know much about valves, perhaps the second triode passes from active to cut?.
Thanks for your help and solidarity.
Javier

11/4/2002 3:19 PM
griff	it could be many things, from microphonic tubes to oscillations in places. Are you using shielded wire? Does the problem vary with how loud your amp is? How is your lead dress? griff

11/5/2002 1:26 PM

Thanks Griff.
Yes I use shielded wire from input and output jacks to pots and board. I joint the shields and joint them to ground in only one point.
I don't know if the problem vary with how loud is my amp. I will try it this night. Also I will change valves to avoid microphonics.
I don't know what is 'lead dress'.
Anyway, why does the sound dissapears when the gain is high, and later come back if I turn down the gain?.
Javier

11/5/2002 6:15 PM
frank_clarke	Does your plate voltage vary with gain? You could have a leaky capacitor at the plate, especially if it isn't rated for high voltages.

1/20/2003 9:37 PM
javier santana	Frank, thanks to you and Griff for your help. Finnally I found the problem. I joint the resistor to the first triode's grid with a long cable. So much noise. I solded to the valve pin, and ... great, good sound and no oscillation at top of gain. Thanks

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