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well I finally pulled out that mystery resistor and took a photo of it, it only measures 2.2 ohms on my multimeter and judging by the colours it should be a 90kohm or a 900kohm resistor right? The colours are: 1) grey or silver 2) white 3) gold or yellow 4) red or orange 5) silver What do you...

Well I did pull all the pots, switches and unsoldered the lamp wires and succeeded in pulling the board out.... great experience!! Yeah the radial cap underneath is a real PITA to get at without taking the board out.... does your amp have 6800uf 16 v caps or are they 6.3volts aswell??

Yeah well I did get some 6800uf 25 volt caps but they're way too tall, I think that's why mesa chose to put 6.3 volt caps instead. I think the ones in there are original..... does anyone know a safe way of pulling the board out of this amp?

I suppose MEsa used this method inorder to keep V1 as quiet as possible using DC heater voltage.... I'm having a hard time finding those 6800uf caps and another strange thing I noticed is that the schematic rates them at 16 volts, whereas the caps on the board are 6.3volts.

Well when I received the amp there was no volume jump, the rhythm channel acted properly just with more hiss than the supposed to be more noisier lead channel. I changed out the 100k resistors as advised by monsta tone and that's when I started having other problems. So it could be a short along...

Well the wires all give continuity untill they get to the rectifiers and caps so my guess is that one or both of the caps has failed or the diodes aren't doing what they're supposed to do. BTW the diodes are soldered to the main heater line... so that means V1 is probably getting 3vDC and not...

I'm getting close to no readings on all 3 heater pins, 0.1vAC, where do you think the problem could be, in the bridge rectifier or the 6800uf caps?

Ok everyone, I've taken the board out of the amp and the first thing I've noticed is that the heater connections on V1 are very different and not connected to heater paths of the other 5 tubes. Here are some photos: http://www.flickr.com/photos/73835524@N00/3322375700/...

Yes all the other tubes inluding the EL84's correctly have heater voltages! This is really strange, does anyone know for sure that V1 should have heater voltages?

Ok folks here's a really good question for you all.... the schematic states that heater voltage is to reach from V2-V6, I suppose that's a writing error, but in that case I'm not getting heater voltage on V1...... any ideas?

Well I also took the readings of all pre-amp tubes and mainly pins 1 & 6 of all pre amp tubes were slightly under the readings stated on the schematic: Tube Pin 1 Pin 2 Pin 3 Pin 4 Pin 5 Pin 6 Pin 7 Pin 8 Pin 9 V1 125 ---- 1.0 0.1 0.1 125 --- 0.7...

Well today I found out what the bias problem actually was, the power tube board had been screwed in too hard and caused the circuit paths to break and scratch off, so with a bit of wire I re-wired the paths and now the bias problem has disappeared but the hiss problem is still there!!

Well I took all the readings on the power tubes and here's what I found: V7 Pin 2 = -10.74 voltsDC Pin 7 = 438vDC Pin 9 = 378vDC V8 Pin 2 = -10.57vDC Pin 7 = 433 Pin 9 = 378 V9 Pin 2 = no voltage??? Pin 7 = 436 Pin 9 = 379 V10 Pin 2 = -13.1vDC Pin 7 = 437 Pin 9 = 378 Obviously V9 is the...

Well thanks for all the tips, most of the electrolytics in the signal path are actually tantalums so they should be ok, there is only 1 electrolytic 1uf 50v on V6 that looks suspicious. Anyways got another one up for grabs.... I changed out those 100k plate resistors on V1a, V4a & V4b and when...

Well where the resistors were reachable I did take one end out, and the 1st 2 of the suspect list were tested that way. I also tested the 2x 220uf 63v caps (one for the bias and the other for low voltage) and they are giving me around 160uf..... time to change?? :) The battery in my tester is...

Well I just checked all the resistors in the rhythm channel and they all test ok except for the following 3: 1) 1.5megaohm resistor on pin 2 of V1a tests 600kohms 2) 1 megaohm resistor on pin 2 of V1a tests 594kohms 3) 150k resistor in the treble, bass & mid control measures 134k I couldn't...

Well that bypass didn't do much for the hiss on rhythm channel.... but I discovered that it did make both lead channels noisier (not hiss but a loud hum) so that could be a lesson to all those who are having hum problems :) As for my problem well it's still a mystery.... another thing I noticed...

Well I did follow your tube swapping instructions but the problem is always only present on the rhythm channel, the tubes are new. I'll try bypassing that mystery resistor and see what happens thanks

Well since I'm writing from Italy I don't think I could call them up without paying big $$$, that's why I wrote up my problem here. If anyone knows about that mystery resistor being or not being stock please let me know.

I've done somemore circuit checking comparing it to the schematic and here's what I found: Looking at the rhythm channel pre-amp section the input is wired directly the 1.5Mohm resistor (in parallel with the 180pf cap). Looking at the circuit board the input wire is soldered to a mystery...