Paralleled Triodes ala Mojave Coyote...

[tarzanalog]

Sounds (literally) like an interesting alternative to an EF86 channel... thoughts?

[rjgtr]

Is it any different than the parallel triodes of the 1974 18watt's normal channel?

I still think one of the coolest Plexi styled amps used one set of input jacks feeding the normal and bright channels for paralleled operation with the two volume controls for mixing.

[tarzanalog]

I still think one of the coolest Plexi styled amps used one set of input jacks feeding the normal and bright channels for paralleled operation with the two volume controls for mixing.

AFAIK, that's pretty much how the Coyote works. Has anyone implemented this in an 18W/36W amp?

[rjgtr]

I'm sure it's been done. I've done a couple more JCM-800ish amps, but haven't done a complete plexi preamp in front of the 18watt power section. It is essentially mating a standard Plexi front end like Mark Huss's Pexi6V6 with an 18watt power section. Of course, Mark's amp uses 6V6s, but you can get really good results with EL84s.

[zaphod_phil]

Some of the guys on AX84 have been recently trying parallel triode stages, with the two triodes biased differently - ie with split cathodes. So one might have a low cathode resistor value, say 680 ohms, and the other 1.5k or 2.2k, or maybe even a red LED instead. The result is a shimmery effect in the tone. If you take a typical Plexi first preamp stage, with split cathodes, and jumper the two sides together, you are probably getting the same kind of effect. You could also do something like this with a Lite preamp, by splitting the cathodes and using different value cathode resistors. When I get a moment, I might try out this trick myself.

[tarzanalog]

That's the info. I was looking for... thanks!

[rjgtr]

I should add there's a couple modern production amps that use parallel triodes for their inputs. Certain smaller Mesa combos do this, and most Rivera amps (R series, Fandango, Quianna, etc) also do this.

If you jumper a Marshall JTM-45 or early Lead (1987) or Bass (1982) amps, then you essentially have the same thing as the Normal channel Hi input on the 1974. If you jumper a 1970ish on 1987, you have a split cathode version.

I think it makes the amp sound fuller, probably due to slight increase in gain and slightly shifted phase of each triode from the other.

[zaphod_phil]

I should add there's a couple modern production amps that use parallel triodes for their inputs. Certain smaller Mesa combos do this, and most Rivera amps (R series, Fandango, Quianna, etc) also do this.

As do many Matchless and Top Hat amps....

[tarzanalog]

... I think it makes the amp sound fuller, probably due to slight increase in gain and...

You had me at:

... If you jumper a Marshall JTM-45...

[billv]

Some of the guys on AX84 have been recently trying parallel triode stages, with the two triodes biased differently - ie with split cathodes. So one might have a low cathode resistor value, say 680 ohms, and the other 1.5k or 2.2k, or maybe even a red LED instead.

Could one get the same effect with a common cathode resistor, but different plate resistor values?

[zaphod_phil]

Yes. And each side would have a different gain level. That may be good or bad, depending on your outlook.....

[rjgtr]

Then there's using completely separate cathode and plate resitors, like jumpering a '70 SLP. You could also put all this on a switch to allow shared cathodes or split cathodes.

As an aside, I recently did the switchable one wire (cascade) mod on my 1987x reissue that I converted to a turretboard with a Heyboer OT. I also wired the input jacks to allow me to parallel the channels.

I beginning to think a one channel TMB with a parallel triode into a gain stage and cathode follower would be a very cool 18watt.

[zaphod_phil]

I beginning to think a one channel TMB with a parallel triode into a gain stage and cathode follower would be a very cool 18watt.

If you look at the Matchless Lightning that's kind of along similar lines, although done with a Voxish-voiced preamp, rather than a Marshall one. I think I would also do the trick with the separate cathode resistors of different values, knowing what I do now. The tube guitar amp thing is an ongoing learning experience for me....

[johnny5]

if you have the realstate, do an input like the 18watt lite IIb and use a plexi style input stage;
separate plate R's (100k)
separate cathode R's (680 & 2k7)
separate cathode caps (320 & .068 respectively)
separate coupling caps (.002 & .02)
mixing R's after the volumes, one with a peaking cap on it.

Mix the two and have fun. It's a really cool design cuz the 2k7 / .002 side is bright and the low end never gets mushy and the 680 / .02 side fills it out - adjusted to taste.

[rjgtr]

The tube guitar amp thing is an ongoing learning experience for me....

For all of us!

You know the new Marshall Vintage Marshall is setup like an already bridged two input amp, so you have a real similar thing from Marshall.

[briane]

The tube guitar amp thing is an ongoing learning experience for me....

boy phil, just when I started saying to myself I wish I knew as much as that guy........I guess thats whats so great about this...so few components, and so many tonal options....its a journey, not a destination.

Now your going to tell me santa claus aint real. ;-(

[tarzanalog]

Now your going to tell me santa claus aint real. ;-(

WHAT!?!?!?!