8101	2013-01-14 11:42:34	George	Question about 4CX250Rs
Message	Date	From	Subject
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. Thanks, George 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: Measure-Understand-Improve. 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-) Now
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. W7AAZ 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
Hello, Eimac's famous book "Care and Feeding of Power Grid Tubes" is available as PDFs here: http://www.cpii.com/library.cfm/9 73 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
Johan, All of the links (on the page you referenced) to the chapters of the book return page-not-found errors. 73, Todd ------------------------------------------------------------------------------------ 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. 73 Barney
8118	2013-01-17 22:23:56	Todd F. Carney	Re: Question about 4CX250Rs