yba-2b build questions

[mbailey]

quick question I can't find the 64mf 64v bias cap what would you guys suggest i use? thanks

[Chuck H]

It's just a filter. As long as the voltage meets or exceeds the spec it's fine. The uf value can be approximated too, though I wouldn't go lower. Use a 100V/100uf available at any Rat Shack or Frys.

[mbailey]

another question please


I am drawing a board layout from pics I have of the original and from the schematic. I cannot seem to figure out where the Rectifier circuit goes to ground. I do not have the amp I am cloning on hand to go by. any help is appreciated!

[Chuck H]

The rectifier doesn't go to ground, the power transformer HV secondary has a center tap that should go to ground. Yours is a full wave type rectifier. A bridge rectifier also uses four diodes but is wired differently. With a bridge rectifier the 0V reference is on the rectifier.

[mbailey]

so the amp I am copying is apparently different from the schematic I ref. at the beginning of this thread?

[Chuck H]

Yes. It seems. I did look around a little and I found a schem for a YBA 2B that uses a full wave rectifier. The rectifier in your schem above is indeed a bridge type. What type you end up actually employing will depend on your PT secondary voltages and whether or not the HV secondary has a center tap.

[mbailey]

I ordered the hammond xformers you suggested in this thread http://music-electronics-forum.com/t19285/ I am just now getting around to finishing this project. I appreciate all your help.

[Chuck H]

OK... Got it. I have those trannies in my personal practice amp and there was a guy here several years ago that won a psuedo big amp shootout with his 18 watt Marshall clone using the 1608 for his OT. I think you'll be pleased.

You definitely want to use a full wave type rectifier. Not a bridge type. Here's a modified schem clip. I'm not 100% on the pilot lamp wiring but I think it's fine. Note the pot in the bias supply. With modern tubes and different voltages you'll need this to dial the amp in.

[mbailey]

thanks chuck

I am seriously considering going cathode bias with this amp, or maybe switchable? You say You used these Trannys in Your own amp. care to share any details on that amp? You have been a great resource & I'll probably bother You again as I am getting this thing together.

[Chuck H]

My own amp is a fu(k!n@ monster. Unfortunately I can't share it right now because I'm working out of town and all my schem and layout files are at home. I won't be there for about three weeks. I'll work on getting my wife to send me the files. If your interested I'll Email them to you. I can probably get them (my daughter may have to do it as she's much more computer literate).

Just so you can decide if it's your cup o' tea... It's a single channel with FX loop. Bass, mid, treble and presence with a bright switch and a boost switch. With the boost switch off it sounds about like many other vintage tube amps and has about the same amount of gain. It falls between a BF and a Marshall for tonal EQ. Not hard to "approximate" either type of sound but it doesn't nail either one. With the boost switch on the amp is capable of huge amounts of over drive. I have special circuits in place to clean up the ever present crossover distortions that plague EL84 amps and they really do sound like small versions of the bigger bottles with fat smooth over drive. Think TrainWreck for the OD tone and your pretty close but better cleans and more bottom end. This amp was designed to be controlled with the volume pot on my guitar. With a simple bright cap mod to the guitar I can go from sparkley clean to fully saturated high harmonic content over drive with very little change in volume without ever stepping on a pedal.

I presented the final amp (mine is the prototype) under way less than ideal circumstances at the 2009 winter NAMM show. Everyone who played through it wanted one. I've built more than a half dozen for private owners and a couple of custom 4xEL84 models based on the same preamp. Nothing but praise so far.

[mbailey]

I am def. interested! I have been considering a TW type build as my next project but may put off the yba clone and build your design. i like the idea of the boost switch...prob build W/out the fx loop as i am not a big fan. but please send me info asap....you are the man!

[Chuck H]

Well, how far into the Traynor build are you??? This circuit doesn't retrofit into a different layout because the gain could make it unstable. Also, if you need a loudish clean tone the Traynor will put out about 20 watts clean. My design uses a sag resistor that simulates a rectifier tube and reduces plate volts and is biased close to class A and so only puts out about 15 watts clean.

[mbailey]

I have barely started at all really. I started laying out a eyeletboard and gathering parts thats about it. def. not to far in to turn back!
Btw besides the obvious el84 duet whats your tube configuration?

[Chuck H]

Three 12ax7's

I think the layout diagram might be saved in my profile images. If it is I'll PM that to you right now. I've made some changes since I drew it up but just a couple of resistor values. I'll look it over and tell you what they should be now.

EDIT: Ahhh... It's the wrong document. I'll retrieve them from home and Email them to you. Please PM your Email to me.

[mbailey]

pm sent