18 watt volume/tone with 1M pots ?

[Madison]

Is it a problem using 1M pots for the volume and tone?
I always forget, does it shift the frequency range up?
If so can I compensate somehow?

[LooseChange]

You want the 500k pots? Just strap a 1M resistor across the outside lugs or the pot.

[darryl]

One of the addenda to the Marshall 18-watt circuit at Schematic Heaven claims that some amplifiers left the factory with 1meg potentiometers installed.

[Dave]

I like 1 meg pots because they can be used generically by doing what Loosechange said. You can strap a resistor in parallel with a 1 meg pot accross the outer legs and customize the resistance to anything you need less than 1 meg.

Dave

[LooseChange]

The smaller volume pot value = less gain.

[jjasilli]

Yes, but the grid leak resistor VOL POT  is also a shunt resistor = high pass filter.  The smaller the value of that resistor, the more hi's will leak to ground.  This can be compensated for by tone scaling -- doubling the value of any associated cap in an RC circuit.  Ultimately, the resulting tone is a matter of taste.

[Madison]

Thanks gents.
The reason I was asking is because I have a "buzzy" 6SL7 only when I add a 22uF cathode bypass cap.Without the BP Cap the gain isn't enough for my taste.
This is a SE Champ style build.
So, I am thinking that lowering the tone pot down to 500k or maybe even lower will reduce the buzz?
Shot in the dark.
I didn't like the 5F2a tone/vol so I went with an 18 watt style.
I have no resistor between the vol and tone pot right now and it seems to works fine.

[darkbluemurder]

Try a cathode bypass cap lower than 22uF. That would shift the corner frequency upwards and reduce the buzzing. The gain in the highs and mids would stay the same. I would try a 1uf - they can be obtained in a non-electrolytic variant as well.

Cheers Stephan

[LooseChange]

Hey Madison,
Put the same bypass cap back and add a grid stop resistor to the grid of the next gain stage. Put the resistor on the tube socket as tight as you can against the pin.  Try something between a 10k and a 33k.

[Madison]

Hi guys.
Thanks for the ideas.
I went ahead and took out the 6SL7, besides being "buzzy" it ended up being microphonic as heck and I couldn't tolerate it.
Still having a tiny bit of buzzing trouble though much better.
Sound strange, but I swear buzz is coming through the plates/B+.
Thanks again.