WTF!

[Bewitagos1]

You wait and wait for your RM-100 to arrive. She does, you plug her in, she purrs like everyone says she would and even better. The Marshall 1960A cab never sounded so good. 5 minutes into playing, you already want to hear more. Its a Randall, shes built to deliver, right? so you slowly ease her up to about half way into the Master Volume. Wow, bliss...I can like this, ALOT!

Then....dead silence...horror overwhelms you, you want to break something, but cool reason prevails and you sit down and explain your situation to someone who might be able to tell you what the F*$&%^K just happened.

?
grrrrr :twisted:

 

[okstrat]

Your amp could have taken several knocks in shipping and could have damaged a power tube. the way to kill/prematurely age a power tube is vibration and/or heat. Could happen to any tube amp... Or you may have bought a used amp that had an existing problem. Kinda hard to tell with the info we have so far.

Pete

 

[Bewitagos1]

Your amp could have taken several knocks in shipping and could have damaged a power tube. the way to kill/prematurely age a power tube is vibration and/or heat. Could happen to any tube amp... Or you may have bought a used amp that had an existing problem. Kinda hard to tell with the info we have so far.

Pete

Thanks for getting back with me Pete, I did buy a used amp and have attempted to contact the seller about it. I noticed a hint of burnt electronics smell and immediately shut her down. all of the tubes were still glowing before I shut her down. I realize that isn't much to go on. I'll have to wait and see what he says before I open the case. Fingers crossed.

 

[Bewitagos1]

Anyone help me determine what might have caused this? Its located under the third tube.

Any help will be greatly appreciated.

Thanks,
Jimmie

 

[JKD]

Did you check the bias before turning it on?

I'd say the tube in that socket went tits up and caused that.

It's possible that the fuses in there are too high rating or wrong type I guess...

 

[Bewitagos1]

Did you check the bias before turning it on?

I'd say the tube in that socket went tits up and caused that.

It's possible that the fuses in there are too high rating or wrong type I guess...

Thanks again Pete, upon further inspection, I noticed the Transformer in the photo below was loose from the case, without a schematic in front of me, is the trans supposed to be grounded, and if so, could an EMF have occured due to a faulty ground?

 

[JKD]

It's possible it took a bash in shipping..

I think I'd be more worried about where the missing nut and bolt are - inside the chassis? eeek.

It's not good to have that much weight possibly bouncing around but there;s still 3 in place presumably if a ground connection is important there...

Time tp start cjecking all the fuses.....if I were you, I would not use the tube in that socket again though.

You can run the amp on two power tubes, so long as you pull a pair...inside 2 or outside 2 depending on which one is failed. If you do this, remember to set the amp impedance at 1/2 of what the cab load says.

 

[Bewitagos1]

It's possible it took a bash in shipping..

I think I'd be more worried about where the missing nut and bolt are - inside the chassis? eeek.

It's not good to have that much weight possibly bouncing around but there;s still 3 in place presumably if a ground connection is important there...

Time tp start cjecking all the fuses.....if I were you, I would not use the tube in that socket again though.

You can run the amp on two power tubes, so long as you pull a pair...inside 2 or outside 2 depending on which one is failed. If you do this, remember to set the amp impedance at 1/2 of what the cab load says.

Thanks JKD for replying. the Seller is contacting Randall regarding warranty, better him than me. the trace that burned is off the Plate of the EL34B. I've retreived all of the loose hardware. Fuses are all good. may have just been a faulty unit.

The only reason I posted this here is I know you guys (and gals) have probably seen it all when it comes to the RM100, if not, well, heres one more to add to your list.

Thanks,
Jimmie

 

[Julia]

Any amp can do bad stuff. So don't think that we've "seen it all" here. I have horror stories about a Marshall. I got a serious crash course in amps during that time. I didn't really want to learn all the technical crapola. I just wanted to plug and play. But as luck would have it, I learned about bias feed circuits, main bias circuits, how not to bias tubes (I haven't biased anything except on the LB), how not to test for microphonic tubes (by watching someone else do it). And how to read an amp schematic and ask questions that smoke out people who don't know what they're doing. I'm really good at playing dumb.

UPS can do a lot of damage in transit. It's not that I don't think they care, it's that I don't think they care.

 

[Ulvo]

Seems to me the fried trace is the one leading from the plate of V3 to the output transformer (the brown lead seated on the connector in the pic).
I?m not sure what might have caused this, but i guess a shorted tube might be guilty.

Another possibility is that there might have been a tiny crack in the trace.
The voltages at the plates are about 500V in these amps, so any bad connection would cause quite a lot of heat.

 

[Bewitagos1]

Any amp can do bad stuff.

I think I bought a large percentage of them over the years. Fender, Mesa Boogie, Marshall and now add Randall to the list. Sigh

 

[Bewitagos1]

FedEx kicked the **** out of it, you're probably right Ulvo, thanks for the tip.

 

[Bewitagos1]

still no further in getting this problem solved. So I tore it apart and snapped off this photo. Pin three on Tube 3 is the plate, the trace that is burned also connects to the plate on pin 3 of the 4th Tube. Both tubes are EL34s. QC9A is the male connection to the brown wire routing to the Trans. For whatever reason the plate voltage jumped across the trace and through the foil to ground under the resistor. Thoughts?

 

[Julia]

Was the amp shipped insured? I hope it was. If so file a claim with FedEX. You do have photos.

 

[Jeff Hilligan]

I will go out on a limb. Since we have fixed about 12 amps with sections blown up on the board both Randall and Egnater. It's the fricken EL 34's. They suck right now. All of the board blows we have taken in were caused by a 34!

 

[JKD]

Ya know what, now that I think abou it, it was a pair of EL34s that were in my RM50 that died too.

They were GT-EL34 (6ca7) ... but still... :?

 

[Bewitagos1]

I will go out on a limb. Since we have fixed about 12 amps with sections blown up on the board both Randall and Egnater. It's the fricken EL 34's. They suck right now. All of the board blows we have taken in were caused by a 34!

(no saw in hand) Thank you Jeff, so you think if I replaced the tubes, (6L6's) repaired the trace I'd be ok? Or do you see more damage occuring than on just the RM100-A circuit board?

I understand theory enough to know that when the plate(s) saturated, excess current saw the next available source to ground by arcing across the trace, or is that the other way around believing that electricity actually flows from negative to positive. But thats another debate for different forum...

thanks much!
Jimmie

 

[Julia]

I will go out on a limb. Since we have fixed about 12 amps with sections blown up on the board both Randall and Egnater. It's the fricken EL 34's. They suck right now. All of the board blows we have taken in were caused by a 34!

How about EL34L's? That's what I've got right now. So do I replace them with 5881s or 6L6s should one blow?

Mike Soldano recommends the Tung Sol 5881 for tube replacements on his amps (Hot Rod 50 series).

 

[Ampoholic]

How about EL34L's? That's what I've got right now. So do I replace them with 5881s or 6L6s should one blow?

Mike Soldano recommends the Tung Sol 5881 for tube replacements on his amps (Hot Rod 50 series).

I have a pair of those in the basement. Anybody ever mixed 6L6s and 5881s?

 

[RD/Steve]

by the looks of all that, it might have been the bolts from the transformer that caused an arch inside the chassis.

regardless...contact service at 847-643-5120. they will be bale to help you out.