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More specific the long black plate version. Not the A short plate version?
I'm trying to figure out what is so unique about that tube that does not cause a buzz in the V5 position of my Sherwood S-5000. When I use any other tube but that one it buzzes and hums - yes both!
charle
Follow Ups:
Improper tube shielding.
I improvised and used tin foil to wrap the V5 tube and put the metal cage back on. Nothing like tin foil and a few hundred volt pins in proximity.
It was dead quiet with the Gold Lion ECC83/B759. And there was still a faint hum with the TungSol ECC803S/12AT7. So that was the problem and now I can tube roll to my hearts content.
So I have to find a set of tube shields.
Thanks for all your help
charles
There apparently is a fairly strong hum field in that location. The Genalex has a spiral wound heater which is less vulnerable to hum than the ECC803S/12AX7 which does not. That would explain the difference.
If you can't find a suitable shield drop me a note - I may have something that will work for you.
On of the trannies is about an inch or so away from that V5 tube. I have no idea why that didn't even cross my mine???????????
I'll contact you. I have to put in a Christmas order soon anyway.
For now can I use tin foil - As unsettling as that sounds????
Also can those tubes be mixed and matched? eg V4 and V5 tubes have to be matched but the V3 can be different?
For V3 it MAY have some effect if the sections are matched internally but it does not need to match any other tubes in the amp.
Jim can you put two of the Gold Lion B739s aside for me for Christmas. I want to finish a complete set of three for my Sherwood. I'll be putting an order in around thanksgiving.
There are some numbers on the box I'll send you if you need them.
thanks
charles
You have mail.
It sounds like you need to tension the pins in the amp..The pin size of the black plates could be slightly different and that's possibly where we are getting this issue from.Try changing other tubes as well.
Nobody ever went broke underestimating the intelligence of the American public
H. L. Mencken
I'm sorta thinking it's a 12Au7?
Am I right?
Warmest
Tim Bailey
Skeptical Measurer & Audio Scrounger
at least for the S-5000s using 7189s....
The answer is that they are either just really good tubes from the hey day of US tube production, or they are about used up and do not have the gain to buzz and hum.
Probably the latter.
When I use new tubes, eg TungSol, Gold Lion, I get the hum/buzz
When I use vintage tubes, eg Bell&Howell, RCA, Zenith, I get NO hum/buzz
SO what characteristic does the old tube have over the new tubes.
And the RCA has "low mileage".
charles
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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