Buzz and hum are usually connection/ground/shield related...

Newer tubes can have thicker pins; especially the Sovtek 12AX7LPS. Thus, if the sockets were previously "stretched" by thicker pins, these newer tubes should not add noise. In fact, it would be the older, thinner pins on vintage tubes that might have this problem with "widened" sockets. Let us move on...

Are you using the tube shields ? Important detail; for certain....

Are you using the bottom cover securely fastened to the chassis ?

Does the buzz stop when the music plays ? Buzz with cdp too ?

The next troubleshooting would involve "disturbance" testing and/or grounding tube grid or cathode elements, as well as checking for clean connections at all switch contacts. If you ground any 12AX7 grid and the buzz stops, the problem existed at or before that grid. Sherwood decided to split channels within all the 12AX7s, so keep this in mind when grounding both grids in each tube. If you only ground one grid, since the stereo channels exist within each 12AX7, the buzz may not lower in level.

Disturbance testing involves touching single tube elements with an insulated length of metal, like a taped up thin, small screwdriver shaft. If the buzz occurs only with no signal applied, then some high gain stage is probably the culprit. Looking at V5 on the schematic, there is a 2200 pf (.0022 uf) cap semi-bypassing each cathode resistor, at pin 3 or pin 8. There is also the presence switch, which may be dirty or moist, causing some noise.

I have experienced de-oxit and other cleaners actually reducing a connection, causing a noisy or intermittent connection; particularly with old switches. Cleaning with high percentage isopropyl alcohol and forcing significant drying time, assuring no moisture(moisture is conductive but resistive) restored the proper connection.

Check the connections and Best of Luck tracking down the noise...

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Follow Ups Full Thread

Topic - Anyone have the datasheet for the RCA 12AX7 long plates - airtime 15:44:38 09/25/15 (12)

And the answer IS ??????????? - airtime 09:33:39 09/27/15 (5)

RE: And the answer IS ??????????? - Jim McShane 10:41:37 09/27/15 (4)

RE: And the answer IS ??????????? - airtime 11:23:16 09/27/15 (3)

RE: And the answer IS ??????????? - Jim McShane 11:53:13 09/27/15 (2)

RE: And the answer IS ??????????? - airtime 06:41:09 09/28/15 (1)

RE: And the answer IS ??????????? - Jim McShane 16:19:30 09/28/15 (0)

RE: Anyone have the datasheet for the RCA 12AX7 long plates - Michael Samra 09:56:56 09/26/15 (0)

wahat is the specified / as built tube type for that position?? - Timbo in Oz 02:53:12 09/26/15 (1)

as built tube type for that position is 12AX7/ECC83 - Interstage Tranny 16:09:01 09/26/15 (0)

You are not going to find your answer in the datasheet - Chip647 16:47:34 09/25/15 (2)

RE: You are not going to find your answer in the datasheet - airtime 11:11:33 09/26/15 (1)

Buzz and hum are usually connection/ground/shield related... - Interstage Tranny 16:07:40 09/26/15 (0)

Follow Ups

Buzz and hum are usually connection/ground/shield related... - Interstage Tranny 16:07:40 09/26/15 (0)

Buzz and hum are usually connection/ground/shield related...

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