Split Cathode on 5f6a question..

[lenniepickit]

Hey gang - I'm new here but a pal recommended it so I thought I'd give it a shot!

So I came across some JTM-y layout that had a .68uf/2.7k split cathode cap/resistor on the preamp so I hooked it up on my Bassman build - sounds mighty fine with that voxy .0022 mallory on V2b (no bright cap btw) but the normal channel wants some love now...

It occured me though that I was no longer sharing the cathode cap/resistor the way the 5f6a normally does and now my second channel actually is independent with it's .68/2.7 and the first channel with the stock 250/820...

So I just wanted to check that this assumption was correct - cause maybe I want to now try a swap with the .0022 to the stock 250/820 channel and go with the the .022 on the .68/2.7 channel and see how that tastes lol
: )

here's that layout just in case btw...

Thanks!

[lenniepickit]

K - so I thought that jpeg posted but here's a link just in case..

http://img840.imageshack.us/img840/3135 ... escopy.jpg

[martin manning]

The input with the original 250uF and 820R is indeed independent now, but since it has that 820R all to itself its bias point has shifted hotter. To put it back where it was you'll have to double the 820 to 1640, and then reduce the cap by (roughly) half to get the low-end frequency response back. That cap would still be so big that it hardly matters, though.

A smaller coupling cap at the output will trim back the bass, but you can also do some of that by reducing the cathode bypass cap down to 5uF or lower too. No reason not to play around and find something you like for each input.

[ToneMerc]

Hey gang - I'm new here but a pal recommended it so I thought I'd give it a shot!

So I came across some JTM-y layout that had a .68uf/2.7k split cathode cap/resistor on the preamp so I hooked it up on my Bassman build - sounds mighty fine with that voxy .0022 mallory on V2b (no bright cap btw) but the normal channel wants some love now...

It occured me though that I was no longer sharing the cathode cap/resistor the way the 5f6a normally does and now my second channel actually is independent with it's .68/2.7 and the first channel with the stock 250/820...

So I just wanted to check that this assumption was correct - cause maybe I want to now try a swap with the .0022 to the stock 250/820 channel and go with the the .022 on the .68/2.7 channel and see how that tastes lol
: )

here's that layout just in case btw...

Thanks!

That's 67ish split cathode 50W Plexi layout, here's a stock 68' without the onboard cap.

TM

[lenniepickit]

I forget how much of this is math at some level but I guess the important thing is it sounding pretty darn good and doesn't smell funny yet. And the darn thing still has tons and tons of bass - maybe too much still in the first channel and I' starting to wonder if part of it is simply that I've built this into an old Hot Rod D 1x12 cab I found in the alley and the old 4x10 just handled it defferently..

Thanks for the great shot of that amp btw - I'm still a bit of a newb so everything kinda looks like a bassman or jtm circuit to me - mostly because it kind of is I imagine lol...

[ToneMerc]

I'm still a bit of a newb so everything kinda looks like a bassman or jtm circuit to me - mostly because it kind of is I imagine lol...

True dat...isn't it funny that no matter what's new, some of the best tones are still basic circuits that are 50-60 years old.

TM

[lenniepickit]

This 5f6a and my first Baby Will 18 watt were truly revelations in tone - I can hear the whole tube amp lineage in these two from tweed to more modern tones in these amps...not to mention how gratifying it is tpo be playing through your own builds

Ended up with a Mallory .0022 on the 820/250 and a .022 on the 2.7/.68 btw and there is nooo shortage of bass to be had yet..may even go back to the other .0022 cause it still seems to have that bassman magic...

Also put Mallorys in the PI coupling caps instead of the Orange drops I started with - there's just something so warm and musical about those caps : )