Fender/Marshall Dual channel build ideas needed

[mmmoser]

So I have a request to build a head that has two channels. One in the vein of a Fender Blackface "clean" style and the other more gain oriented in the Marshall style. Also reverb.
Is there some prior art on this design somewhere already done by someone that is a known good circuit? I think ideally I would like to have the channels relay driven and operated by a footswitch.
So this is NOT an ODS style build- hopefully simpler and under or around 20 watts. Pretty sure its going to have to be dual 6V6 power section.
Any tips, schematics or pointers in the right direction appreciated.

[Stevem]

For starters you can go to the AX84 site and look at the building blocks they offer, which are very good!
For any of the builds that use a EL84 you can exchange it for a 6V6.

Have you built or modded any thing tube before?

[10thTx]

Two relays switch simultaneously to switch between Marshallish vs. Fenderish channels.

On the Marshallish side there is a hotswitch relay to add a gain stage.

IF you have a PT with 300-0-300 or 330-0-330 & at least 150ma capacity, consider that you can make the amp cathode biased.

Once cathode biased, you can switch between 6V6 or 6L6/5881 by just switching the tubes and not needing to rebias anything. I do this with both of my amps. This makes for a very versatile amp.

The original drawing is not mine. I simply added PPIMV and cathode bias. And I changed the post PI coupling caps to .047 from the original .1,

I would not have cathodes share a resistor & cap as the designer drew. I might change the .001 cap into the LTPI to .0047 or .01.

With respect, 10thtx

EDIT: there should be a resistor to ground prior to the hotswitch gain stage grid. Maybe a 220k-1M range there.

[mmmoser]

Thanks so much for the schematic. I will pass this by the customer- I knew somebody must have done one of these over time.
I have built a few amps in my day. Thanks for the concern, I should be OK.

[jaysg]

Circuits like the two channel Rivera Rake and three channel Suhr PT100 are pretty complicated all in all. I think you can find those online...the older CAE OD-100 is the father of the tweaked Suhr model. I think with 6V6's you're in a good place splitting the 6L6 and EL-34 natures with the innate chewiness of 6V6s.

This Knuckelhead schematic contains notes for the Rake/Jake amp.

[gingertube]

Or just take the easy option
http://www.londonpower.com/tube-preamp- ... tar-preamp
I've built a few of these, and have been happy with the results.
Even built one from scratch using 6SL7 instead of 12AX7. That is what I'm currently using.
Cheers,
Ian

[bal704]

Thanks for the schematic. I noticed on your power string you have a 'D' and 'E' voltage, both at 325V. It looks like they feed different sides of the pre-amp.

What's the purpose of that?

[jaysg]

Or just take the easy option
http://www.londonpower.com/tube-preamp- ... tar-preamp
I've built a few of these, and have been happy with the results.

Did he modify it much from the version in TUT? I built that into an amp and was a bit underwhelmed. Just wondering...

CAE

[roberto]

The Bogner Shiva is almost there.

[V2]

Finally there is a demo of the LP Standard (presumably based on TUT).

www.youtube.com/watch?v=2duY5Z5d-3Q

[Luthierwnc]

Some of the old Tophat schematics show cathode-follower TMB tone-stack values built around 6V6's. The inverter bleed resistor and cathode resistors are much larger than the Marshall values. 47k/1k2 versus 10k/470R.

A cautionary note: I've built some two-channel 6V6 amps. The tonal difference only really mattered in the low-to-mid volume settings. Cranked they sounded so similar that it wasn't worth the effort. Even with high volts/SS rectifier and fixed bias, the power-amp distortion is what you hear. And it will get cranked by the second set. YMMV.

Some off the wall ideas: think about 7591s. You get a nice bump in volume, headroom and low end but still have the same Z-out for whatever speaker configuration you had in mind. Bigger trannies -- but not that much bigger.

Try a trimmer or panel pot equal to the sum of the large signal resistors leading to the top PI grid. The middle lug goes to the PI. That way, if one side crushes the other too much, you can preset the relationship instead of hitting the pedal and scrambling to adjust the guitar volume simultaneously.

FWIW, sh

[John_P_WI]

V2, erigm and I used to post back and forth many years ago on the now defunct power scaling forum (gingertube too), I think he has built damn near every high gain amp in that bassman 10 chassis lol.

mmmoser, ironically i built a fender / marshall circuit into a bassman 10 in the mid 90s using separate vibrolux and plexi channels, not the shared circuit of the LP Standard mentioned above.

To really get it right, care must be taken to get the preamp voltages set for each channel and the feedback resistors and the OT tap which the feedback is taken from needs to be switched. Too many people over look the power amp differences.

Set up a few relays for channel switching and feedback....

John

[Smokebreak]

Hey John,
I'd like to hear your ideas on the switching in the power amp you mentioned. I've pondered this , but felt like if I go down that road, I should then address the rest of the PI (including tube choice!).
As for voltages, marshall and fender were both kinda all over the map, so I tend to pick what ends up being "compromise voltages", so to speak. Same with NFB.

[John_P_WI]

Smoke, regarding the PA on that amp I only switched the NFB resistor, using a much larger value for the plexi, alowing the PA to be a little more spongy.

I also used different and additional power supply nodes for the preamp, setting the first fender plate around 220 and the plexi at 160 ish volts to darken and add compression to the plexi. The PI was low 300s IIRC.

The amp was magical with a strat but I ended gutting it due to a ground issue... and like a lot of my projects it never got finished a 2nd time....

[renshen1957]

So I have a request to build a head that has two channels. One in the vein of a Fender Blackface "clean" style and the other more gain oriented in the Marshall style. Also reverb.
Is there some prior art on this design somewhere already done by someone that is a known good circuit? I think ideally I would like to have the channels relay driven and operated by a footswitch.
So this is NOT an ODS style build- hopefully simpler and under or around 20 watts. Pretty sure its going to have to be dual 6V6 power section.
Any tips, schematics or pointers in the right direction appreciated.

Hi,

Kevin O'Connor's The Ultimate Tone vol 5 has just such an amp schematic and layout (full size circuit board drawings, for a Fender Clean Channel, and Marshall gain channel, with reverb on both channels.

This amp contains switching using transistors to mute the channels (but no audio signal goes through the transistors for tube purists) for switching, however the book also contains another schematic and layout which uses relays instead. The amp uses 4 power tubes, (for 50+ Watts) but also has Power Scaling as an option, but its the preamp that is the real gem you are looking for.

Best regards,

Steve