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Marshall Mods / Trace Allen / etc

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9/26/1999 12:44 PM

Marshall Mods / Trace Allen / etc

Hey all.. hooked up with Trace after the AES show yesterday and we hung out at casa speed for some 100W JMP amping.. Couple interesting things:
1 - the amp we worked on is an ex-Brian Adams 100W head that had been **Butchered**, and Trace had put it right. This thing was set up for 6550's and sounded GREAT. A real surprise to me actually. It was using NOS GE's and sounded every bit a Marshall. Blew me clean away. We were going to convert it over to EL34's but canned the conversion because it sounded so good. Really!

2 - using my handy (and dandy) CD cap dub box, we did a little testing. A few weeks back TA got some head scratchin' responses to one of his mods, (to be honest I had to wonder about it as well!) where he put a 330pF cap in || with the PI input cap. Well, I'm here to tell you to toss the calculators down the garbage chute.. it does actualy do something! Weird science.. With the cap in parallel the highs smoothed out and there was a "fatter" midrange. Less detail, but more "beef" to the tone. Good for soloing for sure. Brought out the "Billy Gibbons" kinda vibe. Why it works, who knows. Comb filtering from phase/freq differences between the two caps?(WAG) All I can say is try it (put it on a switch and go back a forth a few times and you'll hear it. For real.) One more reason to "tweak with your ears"..

9/26/1999 3:12 PM
Fj	which # pin on which tube socket does the 330pf cap get attached?...PI tube?...I have a JMP 50 watter

9/27/1999 1:56 AM

quote:
"which # pin on which tube socket does the 330mf cap get attached?...PI tube?...I have a JMP 50 watter "

You can grab a 330pF 1kv ceramic cap and clip it (using test leads..be careful) in parallel across the .022 cap that goes to pin#2 of the phase inverter tube. A 500pF is more noticeable but also alters the frequencies. Again, I have no clue why it works and I wish I could answer that!
After you clip it in there play some lead stuff for a few minutes and then take the cap off and then play the same lead stuff (helps to play the same thing since it's easies to A/B I.M.H.O.) I think you'll hear what it does.

Hollar back;
Trace

9/29/1999 6:06 PM

Re: Marshall Mods...another interesting thing

Hey gang;

I posted this under a different post but I thought I would post it somewhat seperately and see what you guys (and gals) thought.

I was playing about a few days ago and have a 4-input 1983 (year) Marshall. For yucks and grins I put a 300pF mica cap in parallel to the 47pF cap that is across pins #1 & #6 of the Phase Inverter tube. We were talking about the 47pF cap in another post so I tried some experimenting.

There was a slight volume boost (not all that much), the tone was a bit more "round" and rich and the amp was stable. No instability as far as I could see.

I noticed that a few amps use a 120pF cap so I figured "what the heck" and slapped a 330pF in parallel. it sounded pretty cool!

For what it's worth;
Trace

9/26/1999 11:04 PM

Re: Marshall Mods / Trace Allen / etc

I have this mentioned to me in kinda another form. Mixing two types of caps in paralell for really thick tones.

Example: Paralelling two .01 caps of different types to get the .02 value needed. The finding different cap types that can compliment each other for even more fine tuning of the tone. I having played with this yet myself but seems interesting. Guessing that you wouldn't even have to split the value in half, per SR example to achieve some of these benefits.

quote:
""One more reason to "tweak with your ears".."

It always seems to come back to this don't it...

bw

9/27/1999 4:40 PM

quote:
"It always seems to come back to this don't it..."

It sure seems to! (ha, ha) I've been playing around with different caps to get a "not so normal" value and it works great. I think Speedracer was saying that one of the Marshall re-issues was using two caps in parallel..Speed?

Trace

9/27/1999 10:34 PM
SpeedRacer	The 1959 SLP re-issue uses parallel caps on the volume pot as well as the mixer resistor. Interesting bit o'tweaking says I..

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