RM50 Issues - Any ideas?

[kbause]

Ok so my RM50 has a problem.

I got a new headshell made by a local guy.
Came out great actually.

Anyway, ever since its been in the new head shell its had problems.
I didn't realize before I plugged it in, that during the installation into the new headshell that both the power AND standby buttons had been switched to the on position.

So as soon as I plugged it it, it gave a pop sound.

Since then, its been REAL finicky. It'll work fine, for a little bit sometimes. Then bam its 1/4 of the volume and just sounds like a tin can.

I've changed EVERY tube, and checked every fuse. No luck there.

Whats strange is if I just hit some chords and kinda mess with the preamp volume, its like it shocks it to life.

It does this with every mod I have, so its not the mods.

Anyone have any ideas before I take it in and spend a bunch of $$?

 

[kc2eeb]

O.K. I've got something similar with my RM50.
Amp plays fine for 5 min. then loud hum, even with all the knobs off.
Pull the chassis out, play it for an hour, no problem,then, put it back in,
hum is back. No blown fuses. What's going on!!!!!

 

[nixerx]

O.K. I've got something similar with my RM50.
Amp plays fine for 5 min. then loud hum, even with all the knobs off.
Pull the chassis out, play it for an hour, no problem,then, put it back in,
hum is back. No blown fuses. What's going on!!!!!

Both of you check for grounding out. Could be a wire touching something or even a loose wire..


BE CAREFUL WHAT YOU POKE AT ESP the CAN CAPS!!!

 

[kbause]

O.K. I've got something similar with my RM50.
Amp plays fine for 5 min. then loud hum, even with all the knobs off.
Pull the chassis out, play it for an hour, no problem,then, put it back in,
hum is back. No blown fuses. What's going on!!!!!

Both of you check for grounding out. Could be a wire touching something or even a loose wire..


BE CAREFUL WHAT YOU POKE AT ESP the CAN CAPS!!!

I've worked in repair before so I know the basics, I just know very little about tube amps.

Nothing is grounding out that I can see, everything is tightly connected as well.

 

[Julia]

Speaking of the can caps....

I had a computer one time that did the POP thiing. It still ran, but would bog down after a bit. Turns out that when we inspected the top of the smaller can caps were "raised" a bit, meaning they were blown, and this meant a new motherboard. Check them on both the amp and the modules. If this is the problem it's amp tech time.

No poking is necessary. Just visual.

 

[kbause]

I couldn't see any of the components being visually fried.

 

[JKD]

The input jack is faulty?

One of the effects loop jacks is faulty/dirty?

The connections to your reverb tank got messed up when you were moving around back there?

Hopefully something simple like that...

 

[kbause]

The input jack is faulty?

One of the effects loop jacks is faulty/dirty?

The connections to your reverb tank got messed up when you were moving around back there?

Hopefully something simple like that...

The jacks are all straight my friend.
I didn't hook the verb tank back up after removing it from the combo, could this be part of my problem?


I think its a blown cap of sorts, from going straight from off and unplugged fora few days to ON/Standby RIGHT AWAY.

 

[kc2eeb]

First,
Unless the speakers were not connected, you're not going to hurt anything other than the output tubes by having the amp turn on with the standby switch in the play position. Check the series effects loop. The series loop has switching built into the jacks that are supposed to close the loop if nothing is plugged in. To test, just plug in a guitar cable into the send and return and see if it makes any difference.
Second,
If the new box is vinyl covered, make sure none if it is rubbing anything on the chassis like the caps, wires, connectors, etc.
Third,
Back to the problem with my RM50,
I noticed a rub mark on C15, 100mfd 350 V, cap which is in line with the
screen grid supply circuit.
This was caused by the vinyl covering pealing back and I think when the chassis was initally installed in the box, it flexed the cap, fracturing the solder connection.
I'm going to pull the board and look underneath.

 

[kc2eeb]

Just to reiterate,
The reason for the standby/play switch is to save wear on the tubes, not the caps. It's to allow the heaters to warm up before applying the plate voltage and also to have the amp "warmed up" and ready to play.
What I found so far in my RM50 was that one of the two screws that ground the power supply board to the chassis was loose.
My theory is that the vinyl that peeled back inside the cabinet pushed on the caps and flexed the board. With the one ground screw loose. it lifted the board off the threaded post which caused an intermittent ground connection.
This is the one behind the 12 V DC heater regulator, to the right of the AC
Mains socket. I also re-routed some of the wiring away from the heater supply heat sink.
So far, the amps been on 4 hours, no hums or buzzes.
Tomorrow we turn it up!
If you mess with the preamp volume and it suddenly comes to life, you have a continuity problem somewhere.
You have to look at everything.

 

[kc2eeb]

It's fixed!

 

[kc2eeb]

Did the person making the new head box have your amp while they were making the box?
They may have inadvertently pulled a connection and did not put it back correctly or in the right place.

 

[kbause]

No nothing like that happened.

I'm gonna really dig into this ******, anyone have a schematic or know where I can get one?