[Collins] 30L1 on 6m ??

[Gerald]

On Sun, 2006-02-12 at 15:17 -0600, Dan Osborne wrote:
> Anyone ever converted a 30L1 for 6m ??
> I know that the 811a's are not spec'd for 50 mc so
> not real sure how well a converted unit would play.
> Might need to run only two tubes instead of four.
> 
> I would like to add it to my 62S1 even if it made
> only 300 watts out. 
> 
> I have a 30L1 'hulk' with bandswitch issues but a good power
> supply so thought could experiment with it and not sacrifice
> a nice stock unit.
> 
> There are some 50mc mods for the Heath SB-200 out there 
> that work (2 ea 572b's) - but don't see anything for the 30L1.
> 
> 
> Tnx es 73,
> 
> Dan  WB5AFY

Back in the 70s, Bill Hoisington wrote a long series of simple VHF
equipment articles for 73 magazine. He showed using a single 811A,
probably grounded grid for maybe 100 watts out.

The big trouble with the 811A is that its several inches from grid to
socket and so grounding the socket pin doesn't achieve zero voltage on
the grid and so not the expected isolation from input to output, leading
to a squirrelly tube. One thing that can help is to series tune the grid
lead inductance for minimum feed through (or back). Like Eimac
applications notes for the screens of 4-125A and 4-250A at VHF at least
as long ago.

It would be FAR easier to abandon the 811A and drop in a 3CX800 and run
it at the ratings of four 811A to keep the power supply happy. Or maybe
there's a suitable 400 watt triode. Something in those classes would
perform well and no suffer the lead inductance problems of a group of
811A. A 4CX250B or 350 or even a 4CX300A grid driven would need only a
grid resistor to load the 62S-1 and probably give 150 or 200 watts with
1100 volts on the plate. That would make a grid drive circuit as simple
as a cathode driven stage but with the 50 ohm resistor on the grid there
would be pretty good stability.

Or there's a mirage that takes 10 watts to drive and puts out 150 watts.
A pair could be combined to give 300. I have one that I'm about to put
up for sale since I'm replacing the 6m module in my FT-736 with a 1296
module and I have several other 100 watt 6m radios.

-- 
73, Jerry, K0CQ, Technical Advisor to the CRA
All content copyright Dr. Gerald N. Johnson, electrical engineer