I have a Mark III Simuclass Collesuem series long body head with reverb. It runs 2 pair of 6L6's and a pair of EL34's with 5 AX7's. I finally replaced the entire set of tubes as the tone wasn't sounding as good as it used to. Anyway, I noticed that one of the EL34's weren't glowing blue. I took the chassis out and found that one of the resistors was blown (reading 1) on the EL34 socket. It is a red resistor with a blue, white (looks like white), black, gold stripe. This supposedly tells me it is a 69ohm +/- 5% resistor. The good one reads .182. I replaced the blown one with the 69ohm brown body resistor and all tubes lit up blue for 10 seconds than the fuse blew. Does anyone know what this resistor actually is. Thanks in advance. Paul
Mark III EL34 socket resistor question
- Thread starter oneaussie
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Boogiebabies
Well-known member
There is no 69 Ohm resistor in the MK III schematics. Take a picture and post it.
Ok just took these with a 10.2 mega pixel HD camera and still hard to shoot. The dioide/resister is circled that I need to replace. It is on pin 8 of the tube socket. These diodes are only in #3 & 4 (el34s) socket but not 1,2,5 or 6 (6l6s). If someone can tell me what it is it would be much appreciated.
Restless Rocks
Well-known member
The brown resistor is a carbon comp and the white resistor is a metal film. Pull the tubes before attempting to read the resistance across the resistors. Neither "looks" burned. You are correct they are 69 ohm and are connected between the cathode and ground. If one of them is indeed "Open" replace them both with a matched pair of 1watt metal film. If you are able to gain the assistance of a tech I suggest you do so to avoid personal injury and further damage to the amp if you don't really know what you're doing.
John
John
Restless Rocks
Well-known member
Just noticed also that you have your DMM set on the diode setting: Duh! to read a low ohm resistor set it on the 200 ohm scale. Then set the meter on the 2K scale and test the screen resistors. If you don't know what they are then back to my original suggestion of finding a tech who does. Sorry don't mean to offend but you are out of your league.
Np. Yep I know, thats why I am asking here. I did take the old resistor to a repair shop and it should be a 68 ohm resistor although it measured in the 80s. He gave me 2 replacements and I will solder them in. He also suggested a tube could be bad, I will have them tested.
Thanks restless, I replaced the pair as you said they are a lot bigger and a different body color, but all powers up without blowing a fuse. The original one that I replaced I found out was a 1/2 watt and than the fuse blew. So much trouble for the cost of a whopping $2 for 2 resistors and 5 fuses. I will sound test tomorrow. I think the monster is back 
Restless Rocks
Well-known member
I'm still not sure what your mod is there with the double pot; ist that a post phase inverter master volume? or has someone tried to rig a dual bias adjustment? Any way I've not seen a Coli with the semi cathode biased class A sockets. I'd thin tkhe cathode resistors would have been at least 5 watt each to handle the power there. I'd still contact Mesa to see if there are any updates you might want to have done to the amp.
Still possible you have a shorting tube or something else. It's hard to tell without checking for voltages etc.
Still possible you have a shorting tube or something else. It's hard to tell without checking for voltages etc.
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