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I suspect a problem with some Vactrols (LDR) in my Mark IV and I'm wondering if there is a way to test an LDR without removing it from the circuit ? Any tips ?

I'm also experiencing a major power loss with my mark IV. Also, the presence pull-shift does not have any effect anymore. I tried a new set of tubes and connected a preamp directly into my fx return without any success. I crank the amp to 10 and the sound is very low. I can see a small...

I remember a couple of time that I experienced sound cuts after connecting/disconnecting devices from my effect loop. I will check the loop like you told me and hope I will get bakc my Mark IV power and also resolve the presence pull-shift problem. Thanks for your help !

hey Boogie experts...no solution yet ? I will replace some Vactrols and see if it will resolve the power and presence pull-shift problems. I will also change the power tube sockets since the contacts are in a very bad shape. Prefer to go the cheaper way first, then If I don't find the problem...

I measured voltage of power tubes at pin 4 (all 6L6): V8 (A) Tweed : 385 v Full power : 459 v V6 (B) Tweed : 387 v Full power : 461 v V7 (C) Tweed: 387 v Full power : 463 v V9 (D) Tweed : 385 v Full power : 457 v

Seeking some help ! My mMark IV (A) has very low power when Level cranked to the max on all channels but still have a nice lead preamp sound. I also noticed that the "Presence Pull-Shift" has no effect on LD channel. I installed a fresh set of power and preamp tubes and connected another...

When using time delay or modulation effects with distortion, some says that if you want to preserve clarity of power-tube saturation, these effects must go after *all* types of distortions, so basically, the delay must be ideally positioned after the mic, in the console fx-loop. Maybe this as...

If you can afford a 4x12 Traditional Recto cab, go for it, its a perfect match with the Mark IV !!!

I built my own shock-mount rack case and installed my Mark IV amp in a rackmount adapter. http://pages.videotron.com/heliweb/MarkIV.htm The Mesa 4 x 12 "Traditional" Recto Cab gives me plenty of headroom and bottom with a very focused and defined sound, much more tonal possibilities than using...

For the price vs effects quality, the G-Major rules !

The knobs on my Mark IV stick out in front of about 1-3/8" from the rack adapter ears.

Boogiebabies When you say "remove three filter caps", could you provide more details on the location of these caps on the Mark IV (model A) schematic and what is their effect on the tone of the amp. Thanks

Here what I found on the TC Electronic support page : Channel switching with newer MESA BOOGIE amps Question What kind of cable should I use to connect the G-Major / G-System with my Mesa Boogie Amp in order to switch its channels. Answer This answer is valid for all these...

Forgot to mention that FCB-1010 is used as a midi controller for the G-MAJOR.

******* CAUTION, I'M ONLY SEEKING ADVISE HERE, I NEVER USED THIS SETUP SO I DON'T KNOW IF IT CAN CAUSE ANY HARM TO THE SWITCHING CIRCUIT OF THE MARK IV *************** I'm wondering if this configuration may be used to switch the 3 channels of the Mark IV using the FCB-1010 and G-Major without...

I had similar problems with my 1991 Mark IV, sterile distortion, low amount of sustain. I installed a new set of preamp tubes, replaced the 6L6 in the outer socket for EL-34 and I changed all the filter caps and voila, I now get a fuller distortion with more sustain !!! The tone is what it...

Mark, Are you connecting both the amp speaker (8 ohm) and the 1 x 12 Rectifier cab (8 ohm) in the two 4 ohms jack of the Mark IV ? Or you leave the amp speaker in the 8 ohm and connect the cab in one of the 4 ohm jack ? I'm not sure if I understand the Mark IV manual correctly, but it seem...

Is there any advantage of using a matched triodes tube (two halves of the tube with equal electrical performance characteristics) in the V5 phase inverter position of a Mark amp ? My Mark IV use a 12AX7 in that position. Some says that using un-matched triodes would produce a harsh sounds...

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