EMRFD Message Archive 8101

Message Date From Subject
8101 2013-01-14 11:42:34 George Question about 4CX250Rs
Wondering if anyone is familiar with these tubes. I just got some used ones off ePay. Simply checking with an ohm meter shows all 4 reading 1M Ohm between SCR2 and the plate. I don't know if this is normal or not. I would have expected either open (like all the other interelectrode resistances) or shorted, if bad. Since all 4 measure the same, I wonder if this is normal. Would like to know ahead of applying large voltages ;-)

I actually plan to pick up a new 4CX250B when possible, but got these so cheap, I couldn't pass 'em up.

Aloha, Oregon
8102 2013-01-14 12:42:02 Don Hackler Re: Question about 4CX250Rs
Looking at the data sheets...

The 4CX250R is a ruggedized version of the 4CX250B.
The main difference seems to be the tolerances are a bit looser that the 250B, so there might need to be a larger range of bias and tuning adjustments.

The 250R is rated for class AB1 linear amplifiers, where the 250B is rated for both class C and class AB1 operation.

The 250B was used in a lot of FM broadcast transmitters as a driver; typically a push-pull pair coupled to the grid of a 10 to 20 kW final amp tube.

The data sheets didn't indicate an internal resistor.

8103 2013-01-14 13:01:13 john lawson Re: Question about 4CCX2550B'sX250Rs
Hi George, I ran two 4X250B's in Class AB1, Cathode driven operation......1KW back in my College days.....It was a design of Bill Orr's back in the late 60's and in his Radio Handbook......It is VERY IMPORTANT that you use the correct filament voltage which is 6.0 volts for the 250B. If you run 6.3 volts on the filamant you will shorten it's life noticeable......a voice of a learning experience of mine in my early Amateur Radio Days........Check what the 250R's filament voltage is and  make sure you adhere to it....Same goes for the other voltages also.....Best of luck....John K5IRK

8104 2013-01-15 05:27:46 gareth evans Re: Question about 4CX250Rs
4CX250 ?????

Does that not go against the spirit of our Bible? :-)

73 de Gareth G4SDW (nee G8DXY) GQRP #3339
8105 2013-01-15 06:29:31 Thomas S. Knutsen Re: Question about 4CX250Rs
Why would it?
The spirit of EMRFD is MEASURE, so, if you build an amplifier with tubes,
measure the parameters (IMD, gain) and does some engineering instead of
adhering to lore, then its in the spirit of EMRFD as I understand it:

The choise of tecnology, tubes or semiconductors is not that important, It
may be an option to build an high power amplifier with tubes, from an
termal point of view it may make sence instead of using some of the avaible
semiconductors, its all about the application.

73 de Thomas LA3PNA.

2013/1/15 gareth evans <headstone_255@yahoo.co.uk>

> **
> 4CX250 ?????
> Does that not go against the spirit of our Bible? :-)
> 73 de Gareth G4SDW (nee G8DXY) GQRP #3339


Please avoid sending me Word or PowerPoint attachments.
See <http://www.gnu.org/philosophy/no-word-attachments.html>
PDF is an better alternative and there are always LaTeX!

[Non-text portions of this message have been removed]
8106 2013-01-15 15:23:31 George Re: Question about 4CX250Rs
Thanks to Dave for the solution - holding the clips on the plate, I was measuring the resistance of my arms and torso! 8-)

8107 2013-01-15 15:47:57 William Carver Re: Question about 4CX250Rs
Brings back memories, an RTTY KW on 80m with two 4CX250Bs ca. 1967.

On Tue, 2013-01-15 at 23:23 +0000, George wrote:
> Thanks to Dave for the solution - holding the clips on the plate, I
> was measuring the resistance of my arms and torso! 8-)
> Now
8108 2013-01-15 18:08:39 kb1gmx Re: Question about 4CX250Rs
8109 2013-01-16 07:54:24 Ashhar Farhan Re: Question about 4CX250Rs
I got a couple of these beauties up for adoption. They need a loving
home. Send me a message offline if you want to play with one, global
and shack warming not withstanding.
- f

8110 2013-01-16 16:35:37 Johan H. Bodin Re: Question about 4CX250Rs

Eimac's famous book "Care and Feeding of Power Grid Tubes" is available as PDFs


Johan SM6LKM

kb1gmx wrote:
> The screen supply has to be able to source about 25ma and sink up to 12ma. The control grid is limited to 1W and should never be driven to conduction (no grid current) as that makes the tube highly non linear.
8111 2013-01-17 06:35:27 Todd F. Carney Re: Question about 4CX250Rs

All of the links (on the page you referenced) to the chapters of the book
return page-not-found errors.


K7TFC / Medford, Oregon, USA / CN82ni / UTC-8
QRP (CW & SSB) / EmComm / SOTA / Homebrew / Design

8112 2013-01-17 07:29:50 Alberto I2PHD Re: Question about 4CX250Rs
8117 2013-01-17 22:23:56 Barney Re: Question about 4CX250Rs
The links also worked for me with FireFox Beta 19. However, I
have been having fits opening PDF files here lately. Something has
updated and ruined my ability to download and see the PDF files in
FireFox. And these are no different. Just blank..

The PDF's open ok in Google Chrome. And also SeaMonkey and Opera works
ok. Must be a FireFox issue.



8118 2013-01-17 22:23:56 Todd F. Carney Re: Question about 4CX250Rs