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Vintage threads from the first ten years

Re: Any one ever build a plexi head?

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2/26/2000 6:11 PM
Mark Knapp	Re: Any one ever build a plexi head? Isn't the rectifier tube (well, and the transformers) the biggest difference between a 50W plexi (or a YBA-1 Traynor) and a 5F6-A Fender Bassman?

2/27/2000 4:50 PM

quote:
"Isn't the rectifier tube (well, and the transformers) the biggest difference between a 50W plexi (or a YBA-1 Traynor) and a 5F6-A Fender Bassman?"

That's not the only difference actually. I'm going off from the top of my head here so I may be a little off here and there. I'm not sure with the Traynor as I don't get as many of those in compared to the Fenders and Marshalls.

1.) The Bassman's cathodes were jumped together where the plexi seperated them.

2.) The trannies were different

3.) The filter supplies were different (I think Rick E. also mentioned this in another post and most do not mention this as a relevent difference).

4.) The Plexi used a 500pF (470pF) treble cap and the Bassman used a 250pF.

5.) The mix resistors on the Plexi were 470K's and the Bassmans used 270K's (or 220K's) The Plexi bypasses one of these with a cap (on the treble channel) where as the Bassman doesn not.

6.) The feedback was also different. I believe the Bassman used a 27K and the Marshall used a 47K or 100K (depending on the wattage of the model).

7.) The Plexi used EL34's (this is what they are most known for) and the Bassman used 5881's (6L6's).

8.) The PLexi used .022uF's for the coupling caps between the Phase Inverter to the Power Tubes. The Bassman used .1uF's.

9.) I think the Screen grid resistors were also different. I The Plexi used 5.6K's (some used none at all) and the Bassman used 1.5K's.

That's all I can think of off the top of my head. Speedracer, Richie Hall, or Rick E. could probably hop in and correct what I may have goofed up (ha, ha) Again, this is just from memory so please don't quote me.

Hope it helps;
Trace

2/27/2000 6:30 PM
Steve A.	Trace: Well, other than that the amps are identical- right? Steve Ahola P.S. I think that the trannies might be the biggest factor because you can do all of the other changes to a 5F6A clone and it still sounds more like a Fender than a Marshall...

2/27/2000 8:08 PM

The difference in the sound of a plexi
and bassman,Alot depends on alot of things
,the transformer as Speedracer and others
have found will make a difference. It depends
on what guitar to what speakers are used.
I built some plexis from old sunn amps..
And they use dynaco transformers.And sound great
I have used the generic OT from new Sensor.
2,4,8, ohm taps.. in plexis clones..
and have good results with them.They breakup
a little more when overdriven.But a good sound.
i have used an Ampeg.. well i tried many
different ones.If you build the plexi
it will still have the overall sound of one.
Tubes used will make a difference..
I use EL34.. tubes..The Marshall Jtm 45.
was more a knockoff of the bassman amp.
With little changes that have been posted.
{~}==::: Richie

2/28/2000 5:41 AM

1.) The Bassman's cathodes were jumped together where the plexi seperated them.

Only later Super Leads, the "Plexi's" were more identical to a Bassman, with a shared cathode bias

2.) The trannies were different

BIGGEST difference!!

3.) The filter supplies were different (I think Rick E. also mentioned this in another post and most do not mention this as a relevent difference).

Negligible differences-- although, the Plexi's used SS rectifiers, vs the tube bassman recto

8.) The PLexi used .022uF's for the coupling caps between the Phase Inverter to the Power Tubes. The Bassman used .1uF's.

Plexi's actually used the .1uF's, the grindomatics is where the .022's came in
.

2/28/2000 6:47 AM

3.) The filter supplies were different (I think Rick E. also mentioned this in another post and most do not mention this as a relevent difference).

quote:
"Negligible differences-- although, the Plexi's used SS rectifiers, vs the tube bassman recto"

I hear the difference on the low-end but maybe I'm the only one who does. (ha,ha) The other interesting thing is that there were three models that did have the plexi glass panels so which model do most people refer to as a plexi?

It's about 2:00AM so I'm bushed (ha, ha) Speedracer, Eric, Richie, Randall, Doc, Graywater...what's your opinions?

Trace

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