Traynor YBA-3A Super Custom Special

[danfrank]

Hi everyone!
Right before new years Guitar Center had one of these for sale so I jumped on it. Price was decent and it came with one 8X10 bass cab, plus shipping was $32 so what the hell… $32 to ship 200lbs across the country, can’t beat that!
There were two versions of this amp, the first one without a master volume and the later version with master volume… The second version has an extra gain stage so it’s definitely a hotter amp than the first version.
The one I got was the first version, and frankly I wasn’t impressed… Kind of dead sounding and pretty tame. So, I converted it to the second version but I didn’t install the master volume control. It was an easy conversion and easily reversible…
Version 2 is the ticket! The extra gain stage really makes this amp come alive, the attack is explosive. I was always impressed with the punch of a properly running SVT, but this amp puts the SVT to shame. I’m not going to even mention how loud this amp gets!
The controls are pretty innovative, the bass and treble expander knobs really add to the tones that this amp can do.
The main reason I bought it was that I had to see the circuit. I’m surprised that more amp companies didn’t use sweep tubes in their amps. The current sweep tubes can swing will make a KT88/6550 look like a 12AX7!
Lol
I also added Speakon connectors for speaker out and put a heavy duty impedance selector switch. The current going to the speakers is 15+ amps and Traynor used a 3 amp slide switch originally! I also installed new filter caps as when I got the amp it had the originals from 1970.

 

[solarburn]

Congratz on the amp!

I've never heard of sweep tubes. Had to look them up:

Sweep tubes" refers to types of tubes that were designed for the horizontal-output circuit of tube-type TVs. They generally have reasonable current ratings, high voltage ratings, good gain, and used to be cheap and widely available. The classic DIY amplifier application was not for audio, but for amateur radio as a linear RF amplifier.

On the downside, they're desinged for high-impedance place circuits, so an output transformer to utilize them in a traditional audio amp would have to have a very high turns ratio, which would compromise performance. Now for a very high-impedance application they can work well, such as the Acoustat direct-coupled electrostatic-speaker amplifiers, which indeed used sweep tubes.

But there's also the reason that since it's been what, 35 years since tube TVs were common? So they're not nearly as cheap and plentiful as they used to be, meaning that there's no longer much of a reason to find uses for them so tangential to their original application.

 

[danfrank]

Thanks!
But actually, all pentodes/beam tubes are high plate resistance so the OT with pentode/beam tubes in the amp is a fraction of the resistance/impedance of the tubes used.
The schematic for this amp is widely available on the internet but the one thing I wanted to know the most about this amp was the primary impedance of the output transformer. I took measurements on it and the primary impedance on the OT is 1050 ohms which is very low for an OT, so the turns ratio is very low for good transfer. Plus we’re talking about bass frequencies here so the core size is more important than turns ratio, but this OT meets both conditions favorably.
A low impedance primary OT is the only way to take advantage if the output current that sweep tubes can swing… A KT88/6550 can swing about 200-250ma average with maybe 500ma peak, sweep tubes can swing around 400ma average with 1100-1400ma peak! That’s over 1amp each tube. Like I said, the attack this amp has is explosive…