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I got it fixed few weeks ago. Today I got finally to try it at full blast and it sure works! I don't know what was exact failure but.. I replaced those infamous tantalum caps (besides one, 'cause gain boost wouldn't have work) with matching Mallory caps. Replaced three tube sockets; V1, V2 &...

Yeah, thanks.. I don't replace stuff just for fun. There's is/was flavor of rust about everywhere when I first started working my amp. If there have been burnt or faulty looking part in circuit board I would have rip it of without delay. There wasn't so, I don't think it is bad idea to replace...

here's some voltages I measured: Standby - 470V relay coil - rhythm ch 8.4V / lead ch 5V V3 pin 1 - 179V By now I replaced all diodes except ones near filter caps. I've cleaned tube sockets but if nothing else helps gonna replace those too.

little update.. I still haven't found the problem. Meanwhile.. I re-soldered the whole thing, put some new pots and wires there. There's one wire that is question mark to me.. Grey (double) cable that comes from V3, socket pins 6 and 7, If I remember correctly. Middle wire (red) goes to middle...

Yes, I will. Indeed, seems like we have same problem. By now, I've found, broken channel switch relay and 470uf/16v cap was also burnt. My amp was giving little smoke when problems started and I tought it was power on/off switch (witch was also worn out). I later figured out it was that 470uf cap.

I replaced the relay. It's not tubes. I've tested it with many spare tubes, many times. this thing is driving me nuts. I've spend days now with this crazy little machine. I've opened and cleaned pots also. Found one bad resistor but that didn't fix the problem.. would have been far too easy...

Serial no. is 10727. It's 1983 model, no EQ/reverb. 60 w. Problem is definitely in preamp section. Adding gain and treble makes it worse. Kinda resonating distorted sound. And only when I hit chords in lead channel. it's not really bad but it is definitely there. I just changed new relay cause...

I just changed new filter caps to my boogie. Although it was major upgrade to sound, there's still something going on when I'm hitting chords in lead mode. A kind of sound like speaker is broken. It's not and and tubes are ok too. ..and while changing filter caps I noticed.. there's 2 resistors...

I'm fine with analog delay and phaser in front of amp but I'm now thinking of buying MXR EQ. What's the odds for tone loss if I put EQ in effects loop with two short high quality cables?

I have original IIb footswitch and I could sell it.

I have these in my Mark IIb V1 Tung Sol 12ax7 V2 NOS 12at7 V3 Tung Sol 12ax7 V3 NOS 5751 JJ 6l6s

I'm thinking of buying 2x12" closed back cabinet for my Mark IIb 60w combo. Any experience, is 60w enough for all 3 speakers?

seems to only work for lead channel. IIb, ser.no. 107xx

Welcome cmc64 !! I just updated my fav settings. Mark IIb manual says to set bass and middle about 2 each and treble to about 7 and I think that's pretty much it. Good starting point at least to rock / blues tones. It's easy to get bad and unmusical tone out of this amp but when you find right...

Rolling Stones used Mark IIb Coliseums in their 81-82 tour. Keith, Ronnie and even Mick have used Mark I and Mark IIb over the years but never Mark III.

My Mark IIb is currently dialed like this Vol 1.= 7 Treble = 7,5 Bass = 3 Middle = 0 Master 1 (pulled) = 3-4 Presence = 8

I have matched pair of JJ's in my Mark IIb. These tubes work really well in this amp and I would suggest you to get pair of these. I don't like Str 440's at all... :?

I have Eminence Black Shadow MS-12 in my Mark IIb. Eminence Red White & Blues in 1x12" external cabinet. MS-12 works great for me although I don't have much to compare it with.

Yes, it was really pleasant surprise to find her name when I opened my amp week ago. I actually found some old thread about of her. She must have good hands :) BTW. Merry Christmas to my MKII friends & all boogie lovers!! http://forum.grailtone.com/viewtopic.php?f=3&t=1645

Here's mine.