Having a strange problem with a Marshall JMV410H. At irregular intervals there is a pop sound. The sound is the same as when you switch off the standby button. Like a small pistol shot, but with a silencer. Several minutes may pass between each time it happens. All volume controls are set to infinity. Any suggestions? No flash in powertubes
-
We are looking to make improvements to the Classifieds! Help us determine what improvements we can make by filling out this classifieds survey. Your feedback is very appreciated and helpful!
Take survey
Marshall JMV410H
- Thread starter rbotn
- Start date
This site may earn a commission from merchant affiliate links like Ebay, Amazon, and others.
Kuga
Well-Known Member
- Joined
- May 21, 2023
- Messages
- 1,219
- Reaction score
- 1,957
adjust a proper bias current on it. Always when you install a new power tubes set it's a good think adjust bias trim pots to low setting before turn on the amp. Then adjust It properly.One step closer. Connected a cathode current meter to the tubes. Measured about 40mA. Then the current started to rise on V3 and V4 to about 50-55 mA. The pop sound came and the cathode current dropped to about 40mA. After a while it rose again and the same thing happened. V1 and V2 were normal.
Kuga
Well-Known Member
- Joined
- May 21, 2023
- Messages
- 1,219
- Reaction score
- 1,957
I'm not an amp tech but looks like you have an issue on bias circuit. Test measuring the voltage(VDC) on pin 5 of each power valve socket without any power valve in it. Does it still current drop on V3 and V4?
Best of luck
Last edited:
Mike_LA
Well-Known Member
I am also Not an amp tech but sounds like a bad capacitor.
guitardude57
New Member
- Joined
- Nov 29, 2016
- Messages
- 27
- Reaction score
- 6
Sounds like a power rail cap is bad…
Spanngitter
Well-Known Member
intermittent popping normally indicates a bad cap, so check if your JVM still has C7/C8 equipped near the Bias Probe Connector.
They can fail (had this already twice) and will draw the Bias to the positive side, hence current to your valve will increase (in one of my cases it burnt one side of a set twice before i noticed, I anticipated a bad coupling cap first). For testing these can be snipped out (later Revisions apparently do not have these anymore).
They can fail (had this already twice) and will draw the Bias to the positive side, hence current to your valve will increase (in one of my cases it burnt one side of a set twice before i noticed, I anticipated a bad coupling cap first). For testing these can be snipped out (later Revisions apparently do not have these anymore).
dtier
Well-Known Member
Sounds like a good tip for a failing C8 cap and easy to clip out. It may not be necessary if later versions omitted them. The 410h does appear to have separate bias supplies for v1,2 and v3,4. C22 is the bias supply cap for v3,4. It could be failing as well. They will often show leakage if they are failing but not necessarily.
