Plexi- 'Hot Rodding' a Traynor YBA-IIA?

[Leo_Gnardo]

So is the amp in question the 1st one in the file Randallp posted, the "YBA 2A"??

I couldn't open Randallp's file but the OP specified MkII version which may be quite different than the YBA2A Bass Mate found on Doug Hoffman's site and Schematic Heaven. The non-MkII shows some resemblance to brown Fender Deluxe with volume, tone, and a pair of 6V6 riding atop a cathode RC combination. Which isn't a bad amp at all, just not so amenable to an easy conversion to a boost-modded plexi screamer. Still waiting to see the MkII version.

Jerry2013, Traynor usually included a schematic page glued to the metal chassis cover. If you're lucky enough to have one there, it would be a treat to flatbed-scan it & post here.

[Jerry2013]

Sorry for being MIA on this topic. I found that there are three versions of the YBA Bassmaster MKII Traynor amp;

http://www.prowessamplifiers.com/schema ... rk_II.html

"VERSION 1";

http://www.prowessamplifiers.com/schema ... ion_1.html

"VERSION II";

http://www.prowessamplifiers.com/schema ... ion_2.html

"VERSION III" ;

http://www.prowessamplifiers.com/schema ... ion_3.html

I don't know which version mine is. I don't have the schematic with my amp. It isn't one of the ones that the top comes off for easy acsess.
I'll have to print out the schematics and have a tech take a gander.

They should be all similar. As you can see, mine is about identical to this amp in this video clip, and its pretty close to the Plexi, with just a couple of resistor and cap changes.;

http://www.youtube.com/watch?v=gHcpOylpp14

Now heres a righteous Plexi conversion. Sounds fantastic, don't you think? I'd be tickled pink if I could get to this point with the amp. My Bassmaster stays way too clean at volume;

http://www.google.com/url?sa=t&rct=j&q= ... 5948,d.aWc

..and in a perfect world, I'd get a hot rod Plexi 'Brown Sound' , like this ( clip plays automatically);

https://soundcloud.com/jeff-fiorentino- ... ic-film-tv

[Smokebreak]

I would verify which one you have, based on looking at your amp, and looking at the 3 schematics you posted. It should be very easy to spot right off. 2 of the schematics are typical Marshallesque CF driven tone stacks, and 1 is plate driven. They all will be easy to convert, but the CF the easiest.
All you need to do is determine whether the treble cap (.001) and the slope resister(47K) are coming off the plate, or the cathode of V2a(or V2b).

Then you would change all values to Marshall spec.(and possibly the CF depending on which amp you have). This schematic is layed out similarly to the Traynors : http://www.drtube.com/schematics/marshall/1987pljp.gif

Looks like some cathode values, mixer resistors, PI

Then you can start to figure out how you'd like to cascade, thus hotrodding.

That's how I'd do it at least.

[Leo_Gnardo]

What smokebreak said ^^^ and I'll add something I wrote the other day but waited to post until you came back. And I'm glad you did. Also good to see those schemos on Prowess' site. You have 4 band EQ thank goodness not just the tone control that was on the early Bassmate. Here goes:

Some of the work is maintenance: Possibly a little power supply redesign and/or rebuild with better filtering. In any case, you'll replace 70's era filter caps in hi-voltage and bias supply. Separate screen grid resistors for each output tube. It's a good thing to lower the screen grid supply voltage too - help your output tubes live a lot longer. Decreasing that screen supply will mean swapping out the first resistor in the power supply for a larger value one thereby increasing filtering to the point where adding a choke wouldn't be necessary.

Replace dodgy potentiometers - I've seen plenty of old dodgy PEC's.

Optional - add 1 ohm bias current sensing resistors, maybe test points & bias adjust pot that can be accessed from outside the chassis.

With a healthy power supply and a set of good working tubes - with clean pins please - now you can massage your EQ stack values. One of my fave quick mods is to jumper the mid control hot-to-wiper, so you can put a scoop "hole" in the midrange. If you're a mid boost nut and never want to go there, you can "stand up" the mid control on a resistor and you'll never be lacking for mids.

Decreasing the cathode bypass value on the "fat" pre will remove flabby bass.

EQ drive tube - you can add a bypass cap on its cathode R to boost highs, midrange on up, or full range depending on the size of the cap you use.