8935 tube - good for anything?

<< < (2/5) > >>

K1JJ:
Just fantasizing now...

Your original idea of running it as a class A modulator or series modulated class C screen or grid modulated final would be an interesting idea and could work. Though, not very well for linear amplifier service.

A linear amplifier is probably the best use for a tube of that size, but here's the problem...

That tube will put out 28KW pep with the proper power supply.  It's designed more for class C or modulator service, not high quality linear service. The 4CX-15000(J)  is better for linears, but are almost impossible to find cheap.

The problem is that running as a standard tetrode in grid driven linear RF service will give about -32db 3rd order IMD numbers at best. This is a normal ham amplifier cleanliness figure.  28kw is about 13db stronger than a 1500w amplifier. The result is ON THE AIR, the relative side crud products  will sound like a 1500W amplifier with a -19db 3rd order IMD.  Your ham neighbors will come over and lynch anyone with a signal that nasty... :-)

To clean it up, a tube like this would require a hard-to-tame RF negative feedback system or a feed forward system that is even more complex.

To run QRO, stick with a power grid triode designed for grounded grid linear service. An 8877, 3CX3000A7 and it's relatives are the best choice for cleanest linear amp results.


73,

Tom, K1JJ

WA1GFZ:
That 4CX15000 thing looks like a regulated HV power supply. That bottom assembly looks like it could be a nice RF amp. You could ground all the grids and drive the cathode.

W3SLK:
Or...... you could sell it to one of those CB keydown phanatics for some ungodly sum of money and get yourself something along the lines of a 3CX5000(F???) for a nice tidy little linear ;)

W3RSW:
Man would you look at the blower on that thing ...  Must be one of Dayton's biggest!  ;D

And it comes with an emongus fil. transformer.

Hey, if nothing else it'd be a well regulated screen supply for RKW's 813 amp.
(put a bunch of 813's in series and pick off from a divider for all the screens...   why? dunno, maybe because you can?)

Opcom:
It's a nice piece of equipment, but with what Tom said about the IMD on the tube I would hate to go to the expense and trouble of building an amplifier only to operate on several bands at once. The advice to turn it for the $ for a 3CX3000 is good but them CB nuts are cheaper than hams.

I admit no experience GG-ing this tube family but I have been told by one guy who GG-d a 4CX5000 that great care has to be taken during operation that the loading is enough, or the grids will fry before the operator knows it.

I had thought of getting around this by grid-driving it in the same way as the "triode" connection is used with the 807, where the control grid is driven through a resistor and the screen is where most of the business happens. Much less power would be needed for drive of only the grids.

If anyone has experience with GG-ing and driving the 4CX5000-15000 I would certainly welcome some comments.

Maybe a good use would be to sell it or for a tesla coil; I will refer this to my apprentice but he probably can't afford it.

Navigation

[0] Message Index

[#] Next page

[*] Previous page