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Hello,
I have an RM-100 that according to the owner had been behaving normally then started blowing fuses - It will blow the individual 400ma power tube fuses - at random - and, sometimes it will take out the two 1.6A HT fuses. It has done this on the original EL-34s and on various sets of 6L6GCs. I switched to 6L6GCs to rule out high peak current draw that EL-34s are prone to.
Note - when testing I made sure to set bias voltage to a very conservative starting value to insure low current draw. I did this in standby mode using octal test sockets which gave me easy access to measure grid voltage in case you are wondering.
My gut tells me this is not a tube issue and my next guess would be a shorted filter cap. However, due to the complex design of this amp and the lack of a factory schematic I am hesitant to start shotgunning. It's a lot of work to get those filter caps out and replace.
I would greatly appreciate if someone who has experience with this amp could offer some advice on any other places to look for a major short, and whether anyone thinks it would be best to go ahead with a recap. There's a lot of "stuff" in the power supply = a lot of places where something can go wrong, and without a schematic it's hard to guess where to look for other fault paths.
Much Thanks in advance.
I have an RM-100 that according to the owner had been behaving normally then started blowing fuses - It will blow the individual 400ma power tube fuses - at random - and, sometimes it will take out the two 1.6A HT fuses. It has done this on the original EL-34s and on various sets of 6L6GCs. I switched to 6L6GCs to rule out high peak current draw that EL-34s are prone to.
Note - when testing I made sure to set bias voltage to a very conservative starting value to insure low current draw. I did this in standby mode using octal test sockets which gave me easy access to measure grid voltage in case you are wondering.
My gut tells me this is not a tube issue and my next guess would be a shorted filter cap. However, due to the complex design of this amp and the lack of a factory schematic I am hesitant to start shotgunning. It's a lot of work to get those filter caps out and replace.
I would greatly appreciate if someone who has experience with this amp could offer some advice on any other places to look for a major short, and whether anyone thinks it would be best to go ahead with a recap. There's a lot of "stuff" in the power supply = a lot of places where something can go wrong, and without a schematic it's hard to guess where to look for other fault paths.
Much Thanks in advance.
.
. Do you have more schematics or diagrams, because I think I will need them later also, it will help a technician to fix the real problem, I think I have some bad tubes which resulted the burning fuse. It was a nice surprise to read your helpful tip and see the schematic. I am not really into the technical stuff but I will take it with me to somebody who understand the schematic. It is really hard to find all relevant details and information regarding the Randall RM100. Wish you all a good time later on 
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