Hi, I `m having trouble getting a good clean out of my OTS 50. Even when running the pre low(say 4 and below) and the master at full. I`ve checked out all of the preamp tubes. And I compared it to another OTS 50 at a local store here in St. Paul (Willies Guitars) That one sounded not only louder but extremely clean, even w/ the pre running at 6-7.  I`m running fairly vintage  output humbuckers and mini-hums into the normal channel. Any help would be greatly appreciated, thanks in advance!

How long have you had it? It will improve enormously when you have 30hours plus run time on the tubes with improved brightness and articulation, but break up will not really be affected. If what you describe as a 'good clean' is zero break up, you should get that without a problem, this is a very clean amp even up to 8 on master (not on O/D obviously!). What happens with pre at 8 and master on 3? What about pre on 3 and master on 8? That should tell you whether it is a pre-amp problem or not.

   Could you further elaborate on the master distorting at full volume please. I assumed it worked like a Fender type circuit( pre and master volume). Thanks again in advance!

even with the preamp low your gonna get distortion with the master full. its inevitable, tubes breakup when they're pushed like that

My OTS is biased from the factory with standard JJ tubes. and the clean volume is at about 4 but if i crank the Master up to 10 it gets really dirty

i get that with all my tube amps. after 3 you just get more breakup on the powertubes

This is due to the fact, that the fender preamp/tonecontrol circuit puts out much less volts that a Dumble preamp.
In a typical fender (blackface) preamp circuit with a 10k mid pot or 6,8k fixed resistor, there is much more signal dampening, than in a Dumble-style preamp.

A dumble preamp/tone circuit has a 250k mid pot and puts out 10-20 dB more signal to the poweramp. Its ALMOST like haveing a fender pre with the middle pot up full AND the preamp gain at full power.

There you have it !! ;-)

I don't think the JZ mods will have a great effect on the amount of break up, it didn't with mine when I converted it. One thing that will is the valve type in V1 for the clean channel and V2 for the OD channel. If you want less drive try a 5751 or Ay7 in V2. Also a 5751 in V1 will lower the overall gain for both channels.

PAB ON will drive the clean into break up a lot earlier. Make sure you have it turned off, the switches are counter intuitive (pedal postion is OFF)!. You'll know its ON if the tone controls have no effect.