Recent content by fusedbrain

Should also mention that the max grid resistance for a JJ el84 is 300k in fixed bias, and 1meg in cathode bias, in case you were wondering.....

I thought this was interesting: https://www.aikenamps.com/index.php/what-is-blocking-distortion I think all the likely solutions have been covered. You will have to experiment and see if the issue is in the preamp, power amp, ot both areas. Let us know how it goes!

Just saw the other post. Yeah, blocking distortion for sure, but I think its more likely at the el84. The tone stack is lossy, so there likely is not enough level at the second triode to cause it. You could add a 33k grid stopper between the volume pot and the second triode if you want, but I'd...

I took a look at the schematic. The issue is likely the signal level into the el84. El84's are very easy to drive, and you are hitting the wall on input level. Try a 47k grid stopper in place of the 5.6k and see what happens. If it helps the farting, but changes the tone too much, lower the...

There's a picture in this thread of the output transformer and speaker jacks inside my amp. All you are doing us moving a wire from one jack to another. I don't have any other pictures of the inside of my vh4, and I moved recently and all my gear is still packed up. I won't be taking the amp...

Yes I do! A lot of stuff has come and gone, but I don't expect to ever sell the vh4. Great amp, and yes, it still has the nfb mod : )

I have no knowledge of this guy or his $9k builds with the "musical caps"....but...... In reference to the screenshot you posted, there actually is some merit to what he is saying.... Steel and aluminum have vastly different electrical properties, and most steel chassis have a zinc plating on...

The main issue with the PT supporting an output tube change is the heater current draw of the new tube type. EL34's draw 1.5amps per tube. KT88 / 6550 draw 1.6amps per tube. So an increase of 400ma across a quad. About the same as adding another 12ax7 preamp tube to the amp, which guys have...

Well...if you have the 1987x reissue, its actually pretty simple, given that the circuit in the reissue is a bit of a mash up of lead spec values. Both V1 coupling caps in the reissue are .022uf, and both V1 cathode resistors are 820ohm, so all you would need to do is replace the large...

Stock screen grid resistors are 100 ohms. When replacing large screen drop resistor with choke, change screen grids to 470 ohms, as choke will drop way less voltage than stock 400 ohm dropping resistor. You will have to pull the tube board to swap screen grid resistors. Older amps have tube...

I'm thinking it could be a triode stage configured as a cathode follower inserted between the tone stack and p.i. input, to drive the p.i. with a low impedance signal.....or maybe not.....:scared: Also, I believe the EVH Iconic has a solid state phase inverter.

Ok, so there you go..... :thumbsup:

Looks good to me overall. Changed tone pot is the only "mod" I can see. No big deal. I don't see any 1k screen grid resistors on the power tube sockets, so I would think about adding those. Also, for the other Marshall guys: is that ceramic cap on the mid pot something Marshall put in the...

Had an 83 Canadian 2203, that to this day, was probably the best sounding 800 I've heard. Had an 81 Canadian 2204 that was not great. Both amps were stock and in proper working condition. So typical Marshall.....it depends..... 2 BIG issues for me with the Canadian amps: the fuses on the extra...

Amp sounds decent in the video. If it will only go to 23ma with EL34's, then it will likely bias 6550's properly. I'd try that first, and see what you think with the amp properly biased. Those boards are a bitch to work on, and the traces are really fragile. If you are thinking about swapping...