Page 1 of 1
100 WATT MV COMES TO LIFE (Need help)
Posted: Wed Dec 16, 2009 8:49 pm
by 9VOLT1967
I finally got my amp up and running. I had initially had a problem with the output level and found the input jack shorted by the 500 pf/470K ohm combo intended for the low sensitivity jack. All of my voltages were normal and it biased in at 35ma at idle with JJ EL34's. I played it for a couple of minutes and let it sit idle and I started hearing a popping noise and noticed V4 & V5 were glowing red. I double checked the bias and V6 & V7 were at 35ma and V4 and V5 has no bias reading at all. What do I do? Why would I lose the bias to these tubes? Thanks
Re: 100 WATT MV COMES TO LIFE (Need help)
Posted: Wed Dec 16, 2009 10:12 pm
by 9VOLT1967
I let the tubes cool off and I re-checked the bias and the reading stabilized at (V4-25.
(V5-27.4) (V6-33.0) (V7-32.
. The amp sounds O.K. and the tubes are no longer red plating. Maybe the bias was too hot and caused the previous stituation. I'll continue to check bias for stability and try to get closer to the 35-36 range. Is it typical the the tubes to break in? Thanks!
Re: 100 WATT MV COMES TO LIFE (Need help)
Posted: Wed Dec 16, 2009 10:21 pm
by Flames1950
You could still have issues with the tubes themselves when they get good and hot. If it happens again, mark the tubes with a Sharpie or something, so you can mix and match them in the different sockets to see if one or two particular tubes cause this trouble, or if certain sockets seem to have trouble no matter which tubes are in them.
Be sure the solder joints on the sockets are looking good too, poor joints that get hot and vibrate as the amp is played could be trouble too.