Need help with mercury magnetics mod on a valveking head

[xxx128]

I need help with the mercury magnetics valveking head mod.
Fist, which resistor do i need to swap out for the choke on the pcb?

And secondly mercury magnetics color coding for the output transformer confuses me.

This is from the instructions. Note it has brown, white and red on the left side.

...my valveking has brown, red and blue. And for the other four wires, orange, white, green and black.

Original chuang meei OT wiring above.

Could someone kindly clarify which wire goes where please?

Here is the vk 100 circuit pdf.
http://mitglied.lycos.de/sadako/peav...ng_100_212.pdf

Thanks so much.

[defaced]

R201 gets swapped for the choke. It's 400 ohm, 10 watt according to the schematic. If I remember some stuff Enzo has said, this value might shift slightly (390 ohm maybe) based on what they had on hand. It's value isn't super duper uber critical, so if you see something that's just slightly different than 400 ohms, don't sweat it.

As for the colors, stop thinking about them and trying to match them up; you're just going to hurt your brain. You're better off playing match the picture with the schematic.

The left side of the MM diagram is the primary of the transformer, that goes to your power tube board. Play match-up between the schematic and the diagram and you'll see what wire matches up to what wire.

The right side of the MM diagram is the secondary of the transformer, this goes to the small vertical board with the impedance selector on it. You'll have to look at the schem and the switch to see what matches up. It looks like it'll be 1 for 1, but the colors are going to be different.

Post up what you come up with and someone can verify.

[tedmich]

remember to always have load (speaker) connected to secondary before start up, and squealing usually means the polarity on the primary is wrong (NFB->PFB!)

[xxx128]

R201 is 400ohm. Alright.
Since both wires from the choke are black i suppose that it doesnt make any
difference which way i solder it onto the r201, right?

[xxx128]

I did the mod and the amp sounds great now. Just as expected if there wasnt this nasty problem.

When i have a patch cable in the effects loop and i turn presence to about five o clock(counter clockwise) i get a very high pitched squeeking. When i turn presence past four i get a very(!) loud boom no matter how low the volume is. I almost jumped out of my shoes when i first heard it.

Without the patch cable i only need to move the texture knob on the backside clockwise and i get the boom.

Here is my wiring.


Whats wrong? Can someone help ?

[defaced]

Does it do the same with the patch cable removed? It sounds like a phasing issue with the NFB, which just means you need to swap the red and brown wires on the power tube board, but the path cable is throwing me off. This is the NFB ->PFB tedmich was talking about.

You are correct, the choke doesn't have a polarity, it just gets wired up.

[xxx128]

It does funny stuff as soon as i play around with "presence" or "texture".
Both directly relate to the power section of the amp.
I didnt dare to crank volume up past 1. Neighbors would kill me, lol.

I try to swap the white and red on the primary tomorrow to see if thats it.
Gosh i really wish mercury would provide better instructions with their stuff.

[defaced]

NO! Not red and white.

If you swap red and white you have moved the center tap of the transformer which is no good. You just want to swap the phase of the OT, so you swap the red and brown, keep the center tap (white) where it is.

[xxx128]

...ooops..yeah i meant that...lol
I l;et you know tomorrow

[defaced]

I figured, but I didn't want to be answering an "I fried my OT" post tomorrow. Have fun and yea, let us know how it goes.

[Steve Conner]

Hey guys

I reviewed the Valveking schematic and came up with the following:

Old OPT wire colour -> New OPT wire colour

Brown -> Brown (or red, phasing)
Red -> White
Blue -> Red (or brown, phasing)


Orange -> Green
White -> Yellow
Green -> Black
Black -> Brown

Like defaced said, either you need to swap the brown and red wires, or some of the wires are dangling too close to the effects loop and preamp boards and need rerouted.

[xxx128]

sooooooooooooooooooooooo...i finally swapped the brown and red wires today.
And everything works like a charm now. Thanks so much to everyone who posted in this thread. I love you guys long time <3

[defaced]

I feel all warm and fuzzy now. Group hug