6v6 Plexi with Hi and Low Inputs

[steve_p]

So I am considering building something similar to the mhuss 6v6 plexi.
Original schematic can be seen here:
http://mhuss.com/Plexi6V6/Plexi6V6c.gif

I would like to do hi-low input jacks, while keeping the first 2 triodes paralleled.
Is this possible, and if so, how would I implement it?
I did find the attached PDF that shows an example from an 18W that uses 2 inputs paralleled, however it seems that that version removes 1 side of the tube when you pick the low input.

Am I thinking about this too much? Should I just use a standard hi-low input wiring scheme using 68k grid stoppers and a 1M grid reference, then just jumper across the 2 tube grids?
If I go this way, should I use different value grid stoppers, or wouldn't it matter?

I apologize in advance if what I am asking doesn't make sense.

I mostly want to do this build because i just got a new laser engraver at work and want to make some faceplates.... So I figured, might as well build a marshall-style while im at it.

Thanks,
Steve

[statorvane]

Am I thinking about this too much? Should I just use a standard hi-low input wiring scheme using 68k grid stoppers and a 1M grid reference, then just jumper across the 2 tube grids?
If I go this way, should I use different value grid stoppers, or wouldn't it matter.

That should work. You can reduce the value of the grid stoppers if you want. The lower the grid stopper value the lower the noise. The higher the value the less interference from radio stations. Personally I've stuck w/68Kohm myself.

[steve_p]

Cool, thanks for the response.

Gratuitous faceplate CAD drawing attached. I apologize that the drawing looks "fuzzy". The way I drew it with the engraving on the rear, i had to make the front surface transparent so you can see the text. This causes it to look slightly fuzzy for some reason or another.

I need to order some gold reverse-engraving plexi tomorrow to I can cut one to try.
I may have to make one tomorrow from plain clear acrylic just for kicks.

Steve

[Reeltarded]

A thought.. my thought is just to use a lowerish B+ suitable for making an EL34 amp that loves 6V6 and you make up for slack with hotter bias for either pair. I think.

Ya know, like 380 or something.

Versitile and wicked.

[JoeCon]

Miles

So your saying 380V on the plates and run the bias up 80-90% for either tube type EL34 or 6V6?

So what OT cause that 20watt is not gonna work with El34's right?

This sounds interesting....

[Colossal]

Joe, when I built mine, I ran the amp at 440V with 6V6 into a 7k8 20W Marshall OT. Sounded killer and very loud. Biased around 19, maybe 21mA IIRC. But if you wanted to go the route Miles is suggesting, and it would sound great...you could go with a 6k6 OT, same as an Express. That would get you right in the ballpark at the 380-400V. Incidentally, Mark built the original 6V6 Plexi with parts on hand, so a 345-0-345 PT. Screen voltages were reduced by running an additional dropping resistor in series with the choke. The amp had a very Marshally presentation. JJ 6V6S are the tube of choice for this build.

Nice job on your faceplate!

[JoeCon]

Dave

Thanks. I searched on your 6V6 build and that sounds nice. I like the lowered PT too like 280 to 300 should do and reducing the filtering.
Yeah 22 Watts can be blistering loud in a small place but I don't need more than that and like the Plexi sound.

I've got an Express chassis that just might morph into one of those 6V6 Plexi beasts...

Did you need PPIMV too??

[Reeltarded]

Marshalls need all kinds of stuff,but not really.

You could just use the normal 50w scheme in an express style thing. The option of being able to tube it bigger isn't like a huge expense and it makes the amp competitive with a little headroom compared to a drummer.

[Colossal]

Dave

Thanks. I searched on your 6V6 build and that sounds nice.

If that god-awful sound clip is still posted somewhere on PPwatt.com, that's a pretty bad representation of it, but you can hear the compression and squish. The 6V6s at that voltage have a bit of a hard bark but I attribute that to the diodic effect of the tetrode knee as opposed to the soft knee of an EL34 or EL84.

I like the lowered PT too like 280 to 300 should do and reducing the filtering.

Yes, I think the reduced voltage would be good and the slight reduction in output welcome. Yes, definitely stay lower on the filtering. I used 47/choke+R/47/22/22/22uF and it was perfect. Bumping the reservoir cap up to 47||47u for 96u just took the life out of the amp; way too stiff.

Yeah 22 Watts can be blistering loud in a small place but I don't need more than that and like the Plexi sound.

Totally. That thing was almost as loud as a 50watter It did have some plexi flavor though and that could really be tweaked further. I had a cascade switch on it as well as a bunch of other mods, mostly to satisfy curiosity. The straight up plexi mode was very good though and you could get a convincing Zeppelin or Rush tone. Cascading the bright channel into the normal channel and it took on more of a Def Leppard sound. Watch the lead dress if you do that mod and keep wire runs very short. I would stay away from shielded wire and just lay your board out with ample breathing room. I made my board way too dense. These days I can get 4 or 5 cascaded gain stages to coexist peacefully and dead quietly, but that 6V6P board was a bit too tight for all the crap I packed on it. Might want to give yourself at least 0.375" on center for your turrets or eyelets.

I've got an Express chassis that just might morph into one of those 6V6 Plexi beasts...

Cool! Have fun. I used conventional yellow flavored Sozos (the so-called hand wound ones had not been released yet) and they sounded great; very clear but had the midrange smear that smoothed things up nicely. I did use teflon coated silver-over-copper wire on that amp and I wouldn't do that again. The amp "went away" after a time.

Did you need PPIMV too??

I did incorporate one yes. It was useful. The amp had a VVR as well.

[JoeCon]

Miles and Dave,

This is excellent. Now I wanna do both or rather "one" that incorpoarates both.

Being a weekened warrior at best a 22 watter would be all I'd ever need. But having the EL34 option for the rare bigger venue is valuable too.

I'm gonna have to do more thinking and researching about this one.

Thanks guys!!

[Reeltarded]

You might look at other 6v6 amps that you like and pay attention to what the B+ is and start there. I like the JJ things running kinda scary but they aren't really 6v6s. I have a buddy running a quad of RCAs in a Carr that rips.

[steve_p]

Thanks everyone for the replies.
I think at the moment, i am going to stick with a 6v6 amp only. I probably will use the GDS 18W transformer set, so my secondary HT will be about 290 VAC. Under load, using a SS rectifier, i would probably guess about 360ish B+.... Unless someone here can talk me out of the lower voltage..
I think i like the idea of a slightly quieter, lower headroom amp.
I hadn't planned on PPIMV in the amp, but I may leave the hole on the back of the chassis....just in case I want to add it.

Colossal, what did you use for a choke in your build? Did you use the hammond part that Mark specified in the schematic, or something else?

[Colossal]

Thanks everyone for the replies.
I think at the moment, i am going to stick with a 6v6 amp only. I probably will use the GDS 18W transformer set, so my secondary HT will be about 290 VAC. Under load, using a SS rectifier, i would probably guess about 360ish B+.... Unless someone here can talk me out of the lower voltage..
I think i like the idea of a slightly quieter, lower headroom amp.
I hadn't planned on PPIMV in the amp, but I may leave the hole on the back of the chassis....just in case I want to add it.

Colossal, what did you use for a choke in your build? Did you use the hammond part that Mark specified in the schematic, or something else?

Sounds good Steve! I used a Mercury 10H choke.

[ToneMerc]

I gathered up parts do one these based on both 6v6 and 6cm6. Had a couple of upright 290 and 280 trannies, sans rectifer tap with a low current 6.3v relay tap made up. For output iron I'm using of Dave's 18w trannies for the 6v6 and for the 6CM6, a clone of a Partridge 15w model. If I can ever get a chassis and faceplate made, I might get these done.


TM

[10thTx]

I built the Texas Raptor for my son. He liked the amp really well and the one tube reverb sounded great.

Just another Marshallish topology option with paralleled V1 and cathode biased.

Thing I liked about this amp design is that you could change between 6V6 to 5881's without having to re-bias anything.

The ExpressSCH schematic and layout are here:

http://www.el34world.com/Forum/index.php?topic=2442.0

With respect, 10thtx