Cathode Bias Red Plating Discussion

[Zozobra]

I had these lurking in my folder of random schematics. Hope they help elucidate the problem.

[eschertron]

I don't see D3 and D4 on the drawing. At least you have confirmed the two x 500R cathode resistors are stock

[Mr_bibbles]

i had these lurking in my folder of random schematics. Hope they help elucidate the problem.

[ATTACH=CONFIG]49318[/ATTACH]
[ATTACH=CONFIG]49319[/ATTACH]
[ATTACH=CONFIG]49320[/ATTACH]
[ATTACH=CONFIG]49321[/ATTACH]

zozobra! I could fucking kiss you! <3<3<3!

[Mr_bibbles]

Agree.
Only you didnīt notice because bthe redplating tubes problem is way more dangerous and you (and probably an earlier Tech) focused on it only.
Hey, if at the same time a dog is biting your ankle and a mosquito is biting your ear ... what would be the focus of your attention?

I wouldnīt even be surprised that an earlier Tech disconnected the preamp trying to find what was pulling his +V down

Actually the amplifier was passing signal before, while it was red plating. Pre-amp out was OK.... I think I smoked a dropper to the preamp? Now that we have a schematic I can probably manage the rest on my own. I'll be back if I hit any brick walls, but there should be a national "Music Electronics Forum Appreciation Day". You old heads are saints for spending your time here and helping out doofuses like myself.

[Zozobra]

No problem. Hope they're useful.

The krank's are interesting designs to dissect, at least in how they copied something and ended up with a semi-successful product. At their very core they are basically tweaks of the Sovtek Mig-100H with a dual recto-ish poweramp with no NFB and vox presence. This makes a lot of sense as the guy who ran krank used to import them and flip them on with a few modifications. The Mig circuit isn't one that has been copied a great deal as most people probably think they're cheap Russian crap but I rather like them. They aren't terribly subtle though!

The Mig-100H in itself is pretty interesting as all the Mig-100's apparently use the same PCB and they really kludged a conversion from a 3+CF topology of the Mig-100 to the 4 stage plate driven stack of the 100H. Notably the easiest way to achieve this was by referencing the 3rd to 4th stage divider to the cathode of the 3rd stage rather than ground. This has sparked a fair few arguments about feedback and bias shifting and what tonal effects this may have. I was certainly guilty of this until someone pointed out it was just kludge to get it to work on an existing PCB and that the designer probably didn't give a shit about either of those things; they just wanted a 4 stage high gain ripper! The kranks reference to the 4th stage cathode.

Some people find some parts of the krank design a bit questionable as the shift/sweep and presence controls do have HV on them. Both could have been avoided by either changing their placement or adding a cap without any real tonal penalty.