Traynor YBA-2A Mods

[bobloblaws]

Hi folks, I just picked up a nice little 6V6 powered head, it's a Traynor YBA-2A Bass Mate, circa 1969. It sounds real sweet as it is. I bought it with a set of Mullard 6V6's installed, I wondered if that was why it sounded so good to me, but realistically it's probably just icing on the cake. Anyway, I think it's just begging to be modded since there is an unused half of a 12AX7 waiting to be pressed into service. My 1st thought was some kind of foot-switchable boost stage. I just wondered if anybody had any thoughts/suggestions. What would you do with it?

[Justin Thomas]

I would wire the first tube triodes in parallel, that's it. I am skeptical of adding distortotron stages to amps that weren't designed with it. If I just <HAD> to add a gain stage I'd do it á la the pre-JCM800 Marshalls where you just pick the Hi or Lo input by input jack.

Jusrin

[Leo_Gnardo]

I like Justin's suggestion. BUT before you dive into a mod project, I'd suggest getting the amp into shape - all the usual old amp stuff - and find out what it sounds like that way. Might be the charm! After you're satisfied it's working as well as it can, let that be the decision point for embarking into modification.

[bobloblaws]

I would wire the first tube triodes in parallel, that's it. I am skeptical of adding distortotron stages to amps that weren't designed with it.

Right, I considered that, IIRC there is at least one of the many iterations of this model that does that. what would the result be, more head room?

[bobloblaws]

I like Justin's suggestion. BUT before you dive into a mod project, I'd suggest getting the amp into shape - all the usual old amp stuff - and find out what it sounds like that way. Might be the charm! After you're satisfied it's working as well as it can, let that be the decision point for embarking into modification.

Yes, I'm planning that as well. For example, some one has already put in new electrolytics but they are cheap generic caps, so I reckon I'll probably replace with F+T's or Spragues.

[Chuck H]

I've considered this thread and what "I" might do if it were mine. So...

Adding the unused triode in series for more gain (if that were the eventual goal) probably won't yeild great sounding results with this design because of the paraphase inverter. Putting big drive into a paraphase can make for a wonky imbalance at the power tube grids because the input side of the inverter is now feeding a clipped signal to the re inverting triode. For this same reason even just using a boost pedal up front probably won't be great either. But tone is subjective so YMMV.

The reason Traynor used the paraphase in this design was to get a little more gain since there's only one triode for the preamp. So the overall design seems absolutely intended as a clean amp only. That isn't to say it doesn't clip the power tubes. It will. That's just not what it was designed for.

If I were to make this into a more typical "guitar amp" I would gut it and build an entirely different circuit using the full tube compliment and change the PI to a LTP for sure.

[loudthud]

I remember playing a combo version of this amp back in 69. It had a Marsland 15 in speaker and plenty of overdrive with a Gibson guitar. Don't know if it was the exact same circuit but it did have the Treble and Bass controls unlike the earlier version with just Volume and Tone.

[mozz]

Though i have my YBA1-A modded into a Plexi, i would not mod the smaller YBA2-A. They are sleeper amps. If anything, i would double up the 12ax7 pin connections and leave it at that.

[bobloblaws]

Though i have my YBA1-A modded into a Plexi, i would not mod the smaller YBA2-A. They are sleeper amps. If anything, i would double up the 12ax7 pin connections and leave it at that.

Cool. What do you think the result would be? In post #6 Chuck cautions against boosting the signal into the paraphase PI.

[mozz]

You will probably hardly even notice. I don't think it increases gain, but it may lower output impedance depending on the next stage.

[Helmholtz]

Paralleling the two 12AX7 triodes for V1 will double gm, halve rp but not change µ.
Also the voltage drop across the cathode resistor will increase because both cathode currents add, resulting in colder bias.
Because of the latter, the cathode resistor should be halved.
Then results will be a gain increase of 27% and output impedance lowered by 39%.
A benefit might be lower tube noise.