Randall RM guys inside, got a problem.

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Loudness250

Loudness250

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Ok, I screwed up and I think I know what I did. I was putting el34's in my RM100 for the first time. I just threw the tubes in without lowering all the bias pots which I know is pretty damn stupid, but I figured the tubes would handle for a minute until I turned it down. Go ahead laugh, it's ok. I never do anything that stupid so I deserve it, mock me. lol. Anyhow, you guessed it , hit the standby off and pop pop pop arc, tube failure light and I turned the switch back on standby right away. And immediately began cussing myself out. So I replaced all the fuses on the back of the amp. put my old 6l6's back in and fired it up, but did not get sound. So then I took the amp out of the chassis and examined those fuses and the board. The mains fuses looked good and so did the slo blow ones and the 2 under the midi board. Anybody have any suggestions? Maybe I should just replace all of the fuses just to make sure? I actually do have a good amount of experience with biasing and a pretty good tube knowledge I just did something really stupid even though I do know what I'm doing. I gambled on the tubes being able to handle for a sec while I turned them down. I believe it was the outer pair that were the problem, they are Ruby STR el34's with a bias rating of 1 "which makes me even more stupid for doing what I did". I'm really hoping that it's just one of the slow blow's and that I just didnt look closely enough. I'm going to replace them all in the morning and fire it up, I know the 6l6's that I have in there now are fine and biased correctly. Damn, I can't believe I did that. Anyhow Randall MTS guys please chime in with your experience on blown fuses in this amp and such, thanks.
 
I'm surprised that the El34s would blow strictly off an incorrect bias setting that quickly. Typically EL34 type tubes are biased hotter than 6L6 types in the RM amps so I don't think thats your problem. I say this because I popped a 5881 at a gig recently in my Mod 100 and didn't have a good spare. I did have a duet of EL34s and I popped them in mid show, didn't bias and the amp performed fine. Didn't sound as good, but no fireworks. I know that the bias readings will change when you change tube type and can be substantially higher when you go to bias them, but this kind of trouble doesn't sound right. When you pulled the chassis out did you look at the bias resistors visually or with a meter? Any charring near the tube socket solder points?
I would replace all the internal fuses he tube fast blo fuses as well. You are using 400A fuses right? 250A will blow quick as shit in the RM and Bruce has said to use 400A for the tubes fuses.
 
If you can track Pete down or any of the Egnater people that roll around here you can get the answer easily...I'm guessing that you should just replace all of the fuses first. Just because a fuse physically looks good doesn't mean it's always good...
 
Test all the fuses with a multimeter, looking at one doesn't count. Be sure you find ALL the fuses too, there a shit-ton of them around that midi board... do a search on mtsforum.grailtone.com, I posted a thread there years ago with pics on where to find them all.

You may have had a bad set of EL34s... the only times I've ever had tubes actually cause problems at a gig, it was EL34s. They just aren't as robust overall IMHO as 6L6s.

Pete
 
Thanks guys. After a good night sleep and reading that I feel better. I'll just replace the rest of the fuses. Yes I did examine the board especially around the sockets and did not see any burn marks. Well, when I just popped them in without turning down the bias first I naturally kicked myself for that, because I was not really sure but I figured 6l6's would be biased a little hotter than el34 but not much, but one of the pairs of el34's had a bias rating of 1 on the Ruby box so I figured also that this pair might be a high breakup tube that would be even lower on the bias than the other pair I was putting in. But as was stated I don't really know, it might be a faulty tube. I will pick up some 400ma fast blow. And some slow blows and just replace all of them. I definitely saw a blue arc when this happened and it came from one of the rubys on the outside pair and then the opposite tube on the outside pair's tube failure light came on. I'll let you know how it turns out.
 
Yup........I had some problems and it was always the Internal fuse that gave me a headache.
I Swapped out the tubes to 6L6's and never had that problem again.
I think for a couple years there were some bad Tubes floating around out there. ;)
 
Ok, after looking at that thread at Mts Grailtone I have a couple questions. Do the fuses not indicate the values? don't they say what they are when you read what it says on the fuse? There were a few confused people responding to that thread. It looks like, you can replace the tubes fuses with 400 ma, I can see that. It looks like the mains fuses are 10 amp 250v slo blo so that should be easy to spot. The one behind the impedence selector says what to replace with 250ma 250v I believe. But the other 5 internal fuses seem like they might be confusing if it is not indicated what goes where. It's only 3pm here in Hawaii so I was going to go up and do this but I'm not sure what I'll be looking at once I get up there to work on the amp. I guess I'll look at that thread again and write down the description that gives me the best shot at figuring it out. Thanks though for the link, it definitely let me know what I'm up against.
 
Loudness250":8elzmwin said:
Ok, after looking at that thread at Mts Grailtone I have a couple questions. Do the fuses not indicate the values? don't they say what they are when you read what it says on the fuse? There were a few confused people responding to that thread. It looks like, you can replace the tubes fuses with 400 ma, I can see that. It looks like the mains fuses are 10 amp 250v slo blo so that should be easy to spot. The one behind the impedence selector says what to replace with 250ma 250v I believe. But the other 5 internal fuses seem like they might be confusing if it is not indicated what goes where. It's only 3pm here in Hawaii so I was going to go up and do this but I'm not sure what I'll be looking at once I get up there to work on the amp. I guess I'll look at that thread again and write down the description that gives me the best shot at figuring it out. Thanks though for the link, it definitely let me know what I'm up against.
Click to expand...

Remove the Midi board and underneath that board you'll find the AC fuses on the rectifer board.
ACFusesRM100.jpg
 
Thanks Jimmie, but I understood already that I need to take the midi board off and that there are fuses under there, if you go on that link further up on the thread, it explains all that but if you read further on that link you will see many confused people who kind of further confuse the facts about fuse values and such. That's where my problem is now, but I think I have a good shot at figuring it out with info I got from that thread. thank you though, I know you were just helping. And hopefully those 2 under the board are the whole problem!
 
Loudness250":2p94r4ap said:
Thanks Jimmie, but I understood already that I need to take the midi board off and that there are fuses under there, if you go on that link further up on the thread, it explains all that but if you read further on that link you will see many confused people who kind of further confuse the facts about fuse values and such. That's where my problem is now, but I think I have a good shot at figuring it out with info I got from that thread. thank you though, I know you were just helping. And hopefully those 2 under the board are the whole problem!
Click to expand...

I blew up my RM100 as you did, got the big blue flash and a scorched Power Distribution board (RM100-A). Initially I replaced everything that I could "see" but was still dead in the water. The AC fuse shown in the pic, powers the trans that supplies the tubes with +500 volts and is what solved it for me. Mine blew with the master volume at 12:00 and the Module at 12:00. A lot of folks say its the EL34's. I replaced the Power Distribution board (the one that the Tubes plug into) with newer revision boards, but again tonight I was running her hard checking out my Riot pedal, master and volume at 12, and again I got the distinct odor telling me to back it down.
:doh:

Good luck
 
Amp Fixed! Yes it's true. Thanks to everybody who helped. I don't know what that guy on the MTS grailtone thread was talking about "the guy who says he doesn't know what fuse goes where", The fuses are labeled, it's not a problem. You just take them out one by one and look at the label on each fuse which is what I originally would have thought but that guy had me tripping out. And Jimmie, yes those were the 2 fuses that blew and also 2 of the tube fuses blew but I already knew about those. So what I did was stick 2 of the 6l6's that I had been using already in the outside pair and my RFT el34's that I just got in the inside pair. crossed my fingers and fired it up and it was fine. WELL ALMOST FINE, I should say, one of my 6l6's won't bias up all the way, which is really wierd, I tried 3 different 6l6's in that same socket after I noticed the weak bias level, and none of them would bias up above 20mv. The other 3 sockets are fine. Anybody got any input on this new problem?
 
Bump, anybody , ideas about the weak bias on one power tube? I have an idea it might be a burnt resistor and I should check the resistors around that tube socket. But That's all I can think of .
 
Loudness250":118yzw0q said:
Bump, anybody , ideas about the weak bias on one power tube? I have an idea it might be a burnt resistor and I should check the resistors around that tube socket. But That's all I can think of .
Click to expand...

Did you find the schematic on the site? It helped me trace out my problems. I'd check the voltages on all of the tubes to see if you have consistancy, perhaps one of the tubes was damaged when the arc occured? You could always perform the "process of elimination" method and pull the tube in question and replace it with a known to be good part, I'd be remised not to say "be careful," theres more than enough potential in there to seriously harm or even kill you.
:scared:
 
Jimmie":13qnw34i said:
Loudness250":13qnw34i said:
Bump, anybody , ideas about the weak bias on one power tube? I have an idea it might be a burnt resistor and I should check the resistors around that tube socket. But That's all I can think of .
Click to expand...

Did you find the schematic on the site? It helped me trace out my problems. I'd check the voltages on all of the tubes to see if you have consistancy, perhaps one of the tubes was damaged when the arc occured? You could always perform the "process of elimination" method and pull the tube in question and replace it with a known to be good part, I'd be remised not to say "be careful," theres more than enough potential in there to seriously harm or even kill you.
:scared:
Click to expand...

Thanks, no problem I'm aware of the high voltages and very cautious , I've poked around in some pretty dangerous amps , I don't take any chances. I've messed with old fenders but I won't go into it right after it's been on and even then I'll check for voltages, I'd rather blast a multimeter than get a shock. Yeah, I tried swapping 3 different 6l6's in that same tube socket and it was a weak bias on all of them, so it's not that. I'll have to pull the chassis again and test resistors, I'll also search at MTS grailtone again.
 
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