YBA-2 modded schematic

This is the modded schematic Everything in blue or green is either a new value or a circuit redesign. Note the colour coded grounds - this is for the "star grounding" sceme which helps eliminate hum. So here's all the info i have regarding the modification. Unfortunately i didn't do a sound check at each stage... so time consuming and sometimes i got on a roll with the soldering pencil so i just kept going :) Initially (stock): - volume control was really dirty and scratchy - hum was pretty bad - not much sparkle, pretty dead sounding - ok grind turned up but a bit lifeless - i could definitely tell there was a LOT of potential, but since it was so old, it needed new tubes and caps and generally a solid tuneup. My goal was to guitar orient it a bit more, add some sparkle and get the hum way down. I didn't want to overly modify the amp into something new - it was important to me to keep the spirit of the original design and not do anything crazy like drill holes. It's a great amp! let's just make it greater... :) Modification was done in 3 stages: Stage 1 - new volume and tone pots (audio taper, higher value) - updated tone circuit design (more guitar suited) - add the 1m resistor to one of the input jacks to make it a high sensitivity one - new tubes all around - experiment with some hotter preamp tubes (the more i use it the more i like the 12AT7 over the 12AU7 - a bit dirtier) Result: better tone, more useful tone control, much clearer and better drive with the hotter preamp tube. Still hums, still a bit dead, still not great. better, but still room for improvement. Stage 2 - pretty much the rest of the circuit, i got on a roll Result: Waaaaaay better. So much brighter now! Almost too bright! Actually it is a bit bright so i got a few more caps in different volumes to experiment. Putting some higher values in C1, C5, C6 and C10 will give more bottom end. I was planning to start with C1 and go from there. Then i got an idea.... the stock speaker... it's, well, OLD. After some research i decided on the Eminence "Big Ben". I've heard great things about their new Patriot and Red Coat lines, so why not give it a try. The amp breaks up so easily anyway, which should alleviate the speaker-being-a-part-of-the-distortion thing. The sensitivity is much higher so that should make it louder (i jam with a band sometimes and 18 watts is JUST BARELY enough... a little headroom would be a fine thing). $110 later (canadian) and it was at my door in 4 days. no point in changing caps if you're just going to get a new speaker, so i held off any further mods until the speaker was in and broken in. Stage 3 - Big Ben All i did here was install the speaker. Wow. Louder, cleaner, way tighter bottom end. WAY clearer, super crisp, detailed, the most amazing clean sounds i've heard. At full volume it's loud - the speaker doesn't bag out - it can easily handle the power (it's rated for like 200 watts or something) so every nuance of the amp is preserved. The speaker reportedly handled 'small' amps well and i can attest to that being true. It rocks with only 18 watts Normally i like lower power speakers due to the nice distortion they give, but with the YBA-2, the amp is so gritty itself (especially with the 12AT7 pre tube) the Big Ben is actually an interesting option. It basically lets the amp shine through with little colouring. I think it's 'almost done' as i want to play it some more and let the speaker break in a bit and settle down. I might still tweak a few caps in the pre and tone section to sculpt it to match the speaker once everything settles. Overall i think this is one of the nicest sounding amps i've heard, and it is incredible even at low volume. This is just a guess, but i think that Pete Traynor would have built the YBA-2 something like this - had money not been an object. I know it's a rare and collectible amp, and everything i did is reversible. Some people freak when old rare amps like this are modified. Perhaps, this is what the amp wanted to be all along, i just put the extra time and expense into making it that way. Thanks for all the help Evan! Your support and circuit designs worked out really really well.