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previous: Rick Erickson Plug into the second input jack and... -- 3/14/2004 12:49 AM

Re: Now there is sound, but bad.

3/14/2004 5:39 AM
nic	Re: Now there is sound, but bad. Thanks Rick, The high gain jack is the one that is getting the strongest signal through the amp. I hacked the OT from a JCM900 in there just to test before I blow money on a new one and I am getting the same results; nasty low volume distortion. So now I know for a fact that it is probably not the OT. Lacking the tools here at my apartment to do sophisticated tests I have done the old school meter signal trace from the power stage up to the preamp. I find it sorta interesting that the one 1K 5W resistor on the power tube nearest the inverter was open (not to mention was different size from the others) so I temporarily put in a couple 470 ohms in series to see if that helped any. When doing the signal trace test this side was substantially quieter than the other pair. I measured the pins on the inverter tube and they seem to be WAY higher (like 200-300) than the 90V or so I am seeing on schematics. When I went to signal test the preamp stages, the signal was extremely loud on pin one of the first tube. Almost like when an amp is cranked and you touch the tip of the plug. SO I suspect a couple of things. A.)something in that inverter B.)something in the preamp, like I ought to be looking for more broken board traces. I have swapped all the tubes and with either set they work in the 900 and not as the ought to in the 800. What could I be missing? nic

3/14/2004 5:39 AM

nic

Re: Now there is sound, but bad.

Thanks Rick,

The high gain jack is the one that is getting the strongest signal through the amp.

I hacked the OT from a JCM900 in there just to test before I blow money on a new one and I am getting the same results; nasty low volume distortion. So now I know for a fact that it is probably not the OT.

Lacking the tools here at my apartment to do sophisticated tests I have done the old school meter signal trace from the power stage up to the preamp.

I find it sorta interesting that the one 1K 5W resistor on the power tube nearest the inverter was open (not to mention was different size from the others) so I temporarily put in a couple 470 ohms in series to see if that helped any. When doing the signal trace test this side was substantially quieter than the other pair.

I measured the pins on the inverter tube and they seem to be WAY higher (like 200-300) than the 90V or so I am seeing on schematics.

When I went to signal test the preamp stages, the signal was extremely loud on pin one of the first tube. Almost like when an amp is cranked and you touch the tip of the plug.

SO I suspect a couple of things.

A.)something in that inverter
B.)something in the preamp, like I ought to be looking for more broken board traces.

I have swapped all the tubes and with either set they work in the 900 and not as the ought to in the 800.

What could I be missing?

nic