6CD6GA sweep tube testing:
After I reported on the 6AV5 and the success that I had operating some of them far in excess of the ratings. A thread appeared on the diyAudio forums:
That number sounded familiar, so I looked in the warehouse and I have about 50 NOS 6CD6 and 25CD6 tubes. I also had a lot of used ones in the assorted sweep tubes collection. I brought a few of each kind home for experimentation. I brought home 6 used 6CD6GA's each one with a different internal construction. I have a Tung Sol that has a monstrous plate assembly that looks like they borrowed it from the 6550.
The setup was still on my bench
from the 6AV5 and 6LW6 testing, so I rewired the sockets to accept 6CD6's
and plugged them in. The whole thing is connected up to a variable power
supply so that I could test at any voltage up to 400 volts. I used the same
Edcor transformer so I could use the UL tap.
Was there any way to use this tube in
triode or UL mode?
This could definitely be considered UNSAFE. Don't even think about this type of prototyping unless everyone in the room understands the hazard and the risks involved!
Check out the massive plate in this tube, It wouldn't glow even with 40 watts of dissipation. With the right circuit this tube could ROCK! Here is the very hastily constructed 6CD6 SE in UL mode with an 0A2 wired in series with the screen grid. This idea has enough merit to warrant further investigation. There are a few (very few) output transformers with a separate screen winding, that allows operating G2 from a separate (lower) screen supply. For those of us who don't have one, I am working on a circuit that shifts the screen voltage with a mosfet, but I haven't had time to experiment.
I will try these tubes in my screen driven P-P test amp in the near
future, but I need to find two that are the same. I have a bunch of NOS
Dumonts (Sylvanias) in the warehouse, I won't be over there until next