epi valve std question

[mik]

hi all. i'm new here and need some of your knowledge and help/advice on the valve standard.

what is happening is that with the amp with the gain at 9 o'clock and MV at 12 o'clock, for a nice clear sound, after a couple of hours playing the volume will begin to decrease and the sound starts breaking up quite quickly. turn the gain up some more it comes good for a few minutes only to again break up. turn the amp off, let it cool down and it's fine again. until it's been played for a couple of hours.

i'm not much of an electronics person so any help would be very much appreciated.

is it the output transformer or valves we are looking at here? or is something else?

[cGil]

The fuse holder on the orange wire under the power transformer is a prime suspect. The fuse itself isn't the issue, the pressure contact pads for it inside the holder are the real perpetrators. They often have some kind of varnish that'll need to be cleaned off with steel wool or a scotchbrite pad.

 

That's been a problem with these amps since the version 1 VJr. Try buffing those pads. Then reinsert the fuse, and try it out.

 

If it still craps out, then on to suspect #2. There are quick connectors all over the board for the transformer hookup. If it isn't the fuse holder, then it'll probably be a bad solder joint underneath one of those connector lugs. They're also known for causing problems like this. You're gonna have to pull the board to reflow solder to those connections, and doing so put's more stress on the connector solder joints that haven't broken yet. Be very careful getting those connectors apart. Pry the clips loose with a poker of some sort, so they just slide apart easy without any effort. Then you can pull the board and reflow the solder. After that, just crimp the connectors a little before you reconnect them.

 

Gil...

[mik]

thanks gil i'll do that. i hope it doesn't get to the re-soldering of the connectors but if so i'll get it to the amp tech. it seems that i have 2 yellow and 1 blue wires with fuses. no orange wire but i'll do these anyway.

i probably wont be able to run it for the required couple of hours to check it out until the weekend but when i do i'll let you know the outcome.

thanks again gil.

mik.

[cGil]

Oh that's right. Sorry. Had VJr's on the brain again. The Valve Standard color codes are different. And there are fuses inside the amp on the board. My VStandard PT walked out the door in a recent 18watt lite project, but there's a label on the PT that gives you the color codes to look for. Just follow the appropriate colored wire into the amp, and it'll lead you to the offending fuse clip.

 

Gil...