Plexi mods for a vintage Traynor YBA-1 - MOD Details & CLIPS

[Riffraff]

Not new information but I thought I would consolidate it and put this in the MOD section for documentation purposes since the original info is spread out in a few different posts I put in as I was doing this. The info below includes details on several simple changes in an easy to follow format. I figured this would be helpful to anyone looking to go down this path.

This thing pretty much mops the floor with my old Plexi reissue and is my favorite amp ever. First some clips to show you what you get.

MIM Telecaster & SD-1 OD (vol @ 5, Drive @ 2). The amp: channels jumpered Vol I @ 5 Vol II @ 8, pull pot out for the cathode bypass cap secret sauce.

[video]https://www.youtube.com/watch?v=qPIEzNvQgts[/video]

Les Paul straight in, channels jumpered Vol I @ 5 Vol II @ 8, pull pot out. No dirt pedals required.

[video]http://www.youtube.com/watch?v=lQh1gwLCtCA[/video]

How do?



Service related

A) Filter cap replacement, two 2 x 50uf /500V cans replaced the old 2 x 40uf dynamite sticks

Plexi mods

B) Replaced 470k volume controls with 1meg volume controls. Used pull switch pot on the bright channel which lowers the cathode resistor value and adds a bypass cap for a gain bump. For the switch I went with a 2.2k resistor and 25uf cap parallel the existing 1.5k resistor because that's what I had. Using a 1.8k and .68uf cap gets you to the actual Marshall specs but it sounds great so I'll leave what I used in.
C) Replaced 100k mixing resistors with 220k
D) Tone stack shift – replaced .01 & .1 caps with .022 caps
E) Tone stack shift – replace slope resistor with 33K & replace 320pf cap with 500pf silver mica cap
F) Re-purposed the old ground switch to switch the feedback resistor between the stock 100K and 33K which adds some sag. I actually like the stock position best because it has more punch in that position.

Tubes

V1 - I63 Blackburn Mullard
V2 - Short Plate Sylvania
V3 - Long Plate Sylvania
Power - Tested and kept a pair of Mesa labeled Shuguan EL34/6CA7's

I snapped this picture before I added the cathode bypass cap which is installed parallel to the resistor coming off the top right corner of the board.

[TTBull]

Now Thats got some killer tones!

Sounds great

[Tortuga]

Pretty killer, man. Love what you've done, and the clips are rad as fuck

[ajaxlepinski]

Major tone boner!!!

[Riffraff]

You should hear what it's like in the room. Those clips were both recorded with my usual shitty recording method, SM57 into a Jamman pedal. I didn't even make an effort to place the mic well. It was about 2 feet away from the cab.