Mhuss Plexi 6V6 to el34?

[JGk]

Hi all its been awhile since I've posted busy goofing off. Anyway I built a Plexi 6v6 based around the M Huss one online with a tube rectifier. I installed beefier trannies for Allen in it and am currently running 6L6s in it since the OPT had duel impedance's. I was thinking of trying EL34 in in it I know I have to move the resistor off of pin 1 and connect it to 8 to ground. But I was wondering about the grid and screen resistor values 1.5  and 470ohms (5 watt). If I understand correctly the 470ohm should be changed to 1K how about the  1.5k on the control grid. I'd like to keep it flexible enough to swap out power tubes. Any thoughts on the changes? Thanks JK

[shooter]

I put 1k's on G2 and 1.5k on G1 like you figured out, how far down does your bias adjust, you might have to rework that also

[Willabe]

The PT might not have enough heater current for EL34's.

Very nice looking cab, where did you get the faux gator skin?

[DummyLoad]

which allen transformers?


--pete

[JGk]

Thanks I got the Faux Gator from Fabric.com on line. It was felt lined so I experimented with a few adhesives and settled on tite bond type 3 wood glue for and supper glue on the corners. I did do a cascading gain switch on it with a type 3 PPIMV prior to that I also put a Lamar in but didn't like the sound.

Transformers are Allen TP25 and TO26. I will put 1Ks on the G2 and see how that sounds the bias adjust should be fine if not I will tweak it. I find the TP25 is a bit stiff putting out around 420 volts fine with JJ 6v6s although I'm not fond of the sound. I ran some vintage 6V6s in it with a 5Y3 its about 390 or so very sweet sounding. Currently running a pretty matched set of old RCA 6L6s With a 5AR4 at about 420 biased a bit hot. It sound great but I just want to try the EL34s. JGK

[Willabe]

It will, heater current per single EL34 = 1.5A, 3A for 2, that leaves you with 1.5A for 5 @
12 _ _ 7 small bottle tubes.

From the Allen web store;

TP25

........310V-0-310V @ 150ma, 6.3V at 4.5A, 5V at 2A. 50V bias tap, center-tapped heater winding and internal hum shield brought out to a lead for grounding.  ........


TO26

A beefier output transformer with 50% more core steel for Deluxe™, Deluxe Reverb™ and similar 2x6V6 based amps........  7,000 ohm primary to 8 or 16 ohms. Also works great with a 2x6L6 or 2xEL34 amp (with 4 or 8 ohm speaker load) where the intention is to limit the output with core saturation for natural compression and sustain.

[Willabe]

But I was wondering about the grid and screen resistor values 1.5  and 470ohms (5 watt). If I understand correctly the 470ohm should be changed to 1K how about the  1.5k on the control grid. I'd like to keep it flexible enough to swap out power tubes. Any thoughts on the changes?

You can use 1K for a screen R with 6L6's. Some guys like it better than a 470 ohm  screen R.

The 1K5 grid R, as long as you don't have stability problems with the EL34's in there, then you can leave them.   

[sluckey]

It may be worth noting that the original "Plexi" (JMP-1987) did not have any control grid stoppers. Grid stoppers appeared with the JCM-800 series amps. The chosen value was 5.6K.

About that Allen OT (or any OT) it's important to realize that for 6V6s the speaker taps are 8Ω and 16Ω. But when the same transformer is used with EL34s or 6L6s the speaker taps become 4Ω and 8Ω. I would adjust the speaker loads accordingly.

 

[JGk]

Hi all thanks for all the info I post the results of my tinkering as it come together.

[Shack]

About that Allen OT (or any OT) it's important to realize that for 6V6s the speaker taps are 8Ω and 16Ω. But when the same transformer is used with EL34s or 6L6s the speaker taps become 4Ω and 8Ω. I would adjust the speaker loads accordingly.

Do you just change the tap , or the speaker too?

[shooter]

I would adjust the speaker loads accordingly.

speakers are what determine load impedance "seen" reflected back to the tubes

[JGk]

Thanks for all the info, I am starting to grasp a little about speaker impedance and reflective load. Its funny I built this as I love 6V6 amps and they just never jumped out as sounding great in the Plexi. Tried a set of vintage RCAs very closely matched, Vintage Tungsols that were about 8ma off and a set of new JJ very closely matched. Currently running a set of vintage RCA 6L6s which I like allot. JK