carvin x100b reoccuring issue... heat related?

[methodofcontrol]

well... this amp is back on my bench!

R113 and R115 (now 1k/5w's) have un-soldered themselves!

simply resoldering them will buy some time, but of course things will continue to unsolder themselves if i don't find a permanent solution.
any ideas as to why only R113 and R115 would be an issue and not R114 and R116 as well?

[Jazz P Bass]

The tubes related to R114 & R116 are to be considered suspect.

Where is the 'Output Power Switch' set at?

[g1]

Any chance the user is pulling a pair of tubes to run at lower power?

[tedmich]

Same old EL34s? Don't waste good solder (and components) on bad tubes, they all fail and need replacement eventually; never get attached to tubes

[Jazz P Bass]

It would surely be interesting to know the amps usage.
It was last repaired 8 months ago.

Where is the output power switch set?
Is the amp being run balls to the wall?
Is the owner pulling tubes?

[nickb]

It would surely be interesting to know the amps usage.
It was last repaired 8 months ago.

Where is the output power switch set?
Is the amp being run balls to the wall?
Is the owner pulling tubes?

..and add "what is the load impedance?" To that list. Too high will tend to make the user turn it up. That will cause the plate to go voltage lower and the screen current goes up.

[methodofcontrol]

amp is being used on a 5150 4x12 (16 ohms, i believe), power setting is on "full" with all tubes in place, used in the rhythm channel with the volume on 2 or 3 with distortion pedals for dirt.

amp is used for a few hours a week at rehearsal. i'd say FIVE hours per week max.

i'm perplexed.

[g1]

Anything about the layout of the board that would put more heat in those locations?

[bsco]

I am by no means an expert here......I come here quite often for advice and I have learned alot from the guys here.....I had a bunch of weird problems with another repair.....You say this amp is old??? has been in storage for a fairly long time??for what it's worth.....did you try using just two tubes and measure the voltage drop across R121??..(Thanks to Enzo for this brainstorm)... then switch the two tubes out with the other two and check the voltage drop across R121 again??? (use the same sockets) and then do it again with the other two sockets....I could be wrong but it is possible it could be socket related..when testing the current draw make sure to rattle or wiggle the tubes to see if the current jumps....could be tubes or it could be sockets...... .just a thought that Enzo inspired......

[nickb]

amp is being used on a 5150 4x12 (16 ohms, i believe), power setting is on "full" with all tubes in place, used in the rhythm channel with the volume on 2 or 3 with distortion pedals for dirt.

amp is used for a few hours a week at rehearsal. i'd say FIVE hours per week max.

i'm perplexed.

Is the amp also set to 16 ohms?

[Jazz P Bass]

well... this amp is back on my bench!

R113 and R115 (now 1k/5w's) have un-soldered themselves!

simply resoldering them will buy some time, but of course things will continue to unsolder themselves if i don't find a permanent solution.
any ideas as to why only R113 and R115 would be an issue and not R114 and R116 as well?

How did you come to the conclusion that the resistors 'unsoldered themselves'?

If the head sits on the speaker cabinet, I would think vibration.

Are the 1K/ 5 watters sitting up in the air?

[J M Fahey]

Molten solder + vibration surely helps explain that.

I have also had similar problems, always because of screen overcurrent.

[Jazz P Bass]

Molten solder + vibration surely helps explain that.

I have also had similar problems, always because of screen overcurrent.

Caused by a bad tube(s), no?

[R.G.]

A sneaky thing to do is, along the lines suggested already, heat sink the resistor. Cement resistors can have an aluminum "U" attached with high temperature (>200C) adhesive and vastly increase the surface area to get heat out, or you can attach a flag of metal, ideally flattened copper sheet (from copper tubing/pipe, maybe) to the resistors leads when you stand it up off the board. If you do this, solder the heat sinking flags to the leads with high-temp melting solder, perhaps (real, not fake 2%) silver solder.

Or use a TO-220 case power resistor that gets to 20-50W rating with a heat sink bolted to the flange of the resistor.

Or make a "hanging garden" of four 350/5W in series/parallel standing off the board. Or...

They say necessity is the mother of invention. That's not true. *desperation* is the mother of invention.

[Jazz P Bass]

Which begs the question: "Why are they getting so hot?"