PROBLEM W/6 POSITION TONE CONTROL

[zozoe]

Hi all well, I just got my BOGEN HE-10 back & it's running great, but on the 6cwa6 control knob pictured, is out of control. The first 5 positions from L to R, offer different degrees of mids & bass, and TOTALLY fill w/no high end string definition. But the 'Brilliant' is especially cool, but incredibly bright. Comparing all 6 preset tone options, the Brilliant is the only real true usable position, and if I could somehow tweak it, and tame high end ever so slightly, while injecting some low end that, and give me the best of both spectrums. So, looking at the schematic, could someone suggest kindly where some simple component value changes would round out that 6th position, since the other 5 are useless?
Thanks & be well~
Kenny.

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[Phil_S]

There are probably a few problems here. One is that the amp is not intended to be a guitar amp. Another is that the tone control isn't really what we'd use in a guitar amp as a tone control. That switch doesn't control a typical guitar amp tone stack. There are other things about the whole circuit -- if you were starting from scratch, you wouldn't build this for a guitar amp.

The tone switch is tied to the cathode of the first triode of the 6SL7. The switch changes the r/c (resistor/capacitance) value between the cathode and ground. I'm not surprised to hear the options are mud, more mud, extra muddy, etc. The one clean option is probably the position on the switch that grounds that part of the circuit, making it inactive. So, I think we have the answer. The selections on that switch offer nothing of value when used as a guitar amp, except for what amounts to an "off" position.

It might be better to remove what's on that switch, replace it with a pot, and build a "regular" tone stack that gets inserted into the circuit in a traditional location, not on the cathode.

Based on all the postings you've made, I suggest this work is not yet within your grasp. Take it to an experienced tech. He should be able to advise you on the options and build out whatever you choose, provided there is adequate physical space for it.

If you don't have the scratch for it, use it with that one setting that works for your ears and move on. While, in theory, there are infinite possibilities for modifying an amp, there are considerations that create practical limits. Sometimes, the juice just isn't worth the squeeze.

[martin manning]

The tone selector is switching different networks into the feedback loop, along the lines of a presence/resonance control. Since the switch positions are not marked on the schematic, it's not obvious which one is "brilliant."

[zozoe]

You got that right Phil_S,,, this not in my limited wheelhouse. Is there an effective,suitable tone stack & out I could propose to him? Perhaps a diagram, or part of a known schematic that he could read from & do it? Unfortunately he's not a guitar player, but really knows his stuff. I told him to get them running & safe, & that I'd go home, assess things, then return with desired 'guitar amp' tweaks... Are you able to kindly steer me, and/or offer a diagram?
Thnks!!

[thetragichero]

I'd start with a simple one knob tone control (6g3, tilt/supro/big muff, etc) and see what you like and don't like

[zozoe]

Interesting,,, For my own edification, can someone kindly circle on my diagram the essential components of the 6G3 Tone Stack?
Many thanks.

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[Phil_S]

To locate the tone stack(s), look between the 7025 and 12AX7 below the big horizontal wire that exits from the pair of 220K resistors. There are two tone controls, one for each channel. The upper one consists of a 1MA pot, .005 cap, and .01 cap. The lower one consists of a 1MA pot, .005 cap, and .02 cap. Choose one. Any tech worth his salt can install this. The pot replaces the switch on the panel. The parts are attached to the pot. Working room inside the chassis shouldn't be an issue.

[zozoe]

PHIL_S, You're dead on about the mudfest at this switch,,, and is it safe to assume that the 'Brilliant' position, which has everything BUT mud & may even have less low end, is more of where I'd be starting tone wise w/a pot (1MA?) in its place?
Best regards
Kenny

[thetragichero]

simple tone control one the 6g3 is basically just an rc low pass filter cutting the high frequencies. about as simple as you can get. if it ends up too woofy but you like the action of the tone pot you could always decrease coupling caps to "tighten up" the bass

[zozoe]

Silly question, but what is 1MA,,, I know 1M is 1 meg, but 1MA? Is that referring to a pot?

[thetragichero]

Audio/log taper. except in some areas of the world but pay no mind to it

[zozoe]

Aha! I know audio vs. linear from my guitar projects, but never have deal w/pots in the amp arena. Thnx, Kenny