[ARC5] Why "Noodling" About Sweep Tubes

[Kenneth G. Gordon]

For one thing, of course, the 211 has a plate dissipation rating of at least 50 
watts in the old versions and 100 watts in the "new" versions, like the VT-4C.

Also, it is "single-ended", which makes adapting to a tube with a top-cap 
somewhat of a problem..

I don't know how much "adaptation" you want to indulge in, but I don't know 
of any sweep-tubes with plate dissipation ratings much above about 30 
watts.

In the 191/375, since output is usually no more than 50 watts, I suppose a 
sweep tube with a PD of even 20 watts would be sufficient.

But why a sweep-tube? Those are getting pretty expensive. Even those with 
"weird" filament voltages, like the 21JS6 for instance. 

One of the 211s is the master oscillator. I don't know how much power output 
is needed from that tube to drive the final amp (another 211), but I would 
think that any decent NON-BEAM tube could be used. I say NON-BEAM 
tube, since beam-tubes make very poor oscillators, although they have been 
used as such for many years. I cannot, at the moment, think of a non-beam 
tube with "high" output capability, but will dig around a bit.

Perhaps an 811, or even a 572B could be used, although either of those 
would be "overkill" and both are over-priced now...when you can find them. 
"New" ones are being made by the Chinese, though.

As for the final amp, another 211 as I said, since we are talking about 50 
watts output, or something like 75 to 90 watts input, a 6146 or others of that 
family should work just fine.

I think the same thing would go for the modulators, the other pair of 211s 
originally. The 6146 family should work well, even triode-connected.

I suppose we could also substitute other tubes for the final amp 211, some 
which would "look" more like a 211, but all that I know of have a plate cap, 
and some have a side grid cap.

Filament current would have to be taken into account.

Replacing the mic amp, a 10 (or is it a 25) should be relatively trivial.

Well, those are my preliminary thoughts on the matter. YMMV.

Ken W7EKB