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FDP Forum / Amp Mods, Repairs, and Projects / DRRI noisy static

Contributing Member

Memphis, TN

Jul 4th, 2017 06:18 AM   Edit   Profile  

Amp has gotten a staticy light crackling type noise that's been going on for awhile now.

Note: I don't use the reverb channel so V2 is not used.

Quick troubleshooting:

Replaced V1 and V6 (Phase inverter) - no difference.

Changed power tubes - no difference

Removed V1 and powered it up. Still noisy.

Removed V6 and dead quiet

Did not replace tube rectifier yet.

I've ordered all new filter caps, but wondering if screen resistors might be accounting for this

R60 and R61 ?

R62 and R63 ?

Thanks !

(This message was last edited by Stratmanx at 08:39 AM, Jul 4th, 2017)



Jul 4th, 2017 07:14 AM   Edit   Profile  

How about if the amp is operated without a tube in the V4 socket?
V2, V3, V4 and V5 being specific to the reverb/trem channel.

Contributing Member

Memphis, TN

Jul 4th, 2017 08:37 AM   Edit   Profile  

Give that man a cigar for V4 !

Stock Fender Groove Tubes junk.

I can see by the schematic where that could bleed into the circuit all the time whether you used the Reverb channel or pulled V2.

Not sure how much tone shaping this will give so just putt a JJ in there.

I've got good RCA grayplates but don't think I would need to sacrifice them in this position ?



Jul 4th, 2017 09:31 AM   Edit   Profile  

The noise MAY be due to a bad plate resistor, so whatever tubes are used could result in the noise.

Really, I suggest not to use anything more than an 'adequate' tube in V4 if you're not using that channel, anything should be fine.
However, V2 and V4 both still need to have reasonably low noise and microphony.

Check if the amp sounds as good with V2,3 and 4 sockets empty; if so, consider leaving it like that, as speaker vibration and operational hours will gradually kill them.



Jul 5th, 2017 08:26 AM   Edit   Profile  

I guess I'm not clear on something.
Did V4 fix the problem?

Contributing Member

Memphis, TN

Jul 5th, 2017 08:31 AM   Edit   Profile  

Yes it did.

It was a wonky Fender Groove Tubes 12ax7.

I decided to yank it after replacing it with a known good tube. No sense in wear and tear on a tube if its not needed.

the plus is a wee bit more gain in the normal channel.

I also pulled V3 and found that also added a tad bit more gain, but found it was just a hair too much, so I put a NOS RCA in there and it seemed to just give the overall tone a bit more clarity.

Probably imagination with the V3 in or out of the circuit, but yeah, the faulty V4 was the one giving me the fits !

FDP Forum / Amp Mods, Repairs, and Projects / DRRI noisy static

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