EMRFD Message Archive 2169

Message Date From Subject
2169 2008-10-03 09:29:17 Ashhar Farhan can any on er .. running a 4cx250b qrp?
I have received half a dozen 4cx250Bs, 813s and some really monsterous
looking valves. Apart from using them as room heaters (not very
appealing, it is 32 celsius in shade right now), night lamps (xtal
says it reminds her of Frankenstein movies) and paper weights (too
light), i would really want to run this as an amplifier.

Does anyone of us know if this will run on lower voltages? I am going
through the docs. I know that the 12BY7 could run off 12volts.

- farhan
2173 2008-10-03 12:40:30 john lawson Re: can any on er .. running a 4cx250b qrp?
Hi Ashhar....before I became hooked on homebrewing and qrp about 30+ years ago, I built an amplifier with four 4CX250B's in Class AB1  cathode driven  operation from William Orr's Radio Handbook around 1964 give or take a year or so.....Be sure to that you check the necessary voltages carefully and adhere to them. Make surre your  filament voltage of 6 volts, NOT 6.3 volts.....if you use the 6.3 volts you will shorten the life of the tubes as some fellow amateurs I knew found out the hard way..  Good luck with your amplifier...73's John K5IRK

2176 2008-10-03 20:27:15 Allison Parent Re: can any on er .. running a 4cx250b qrp?
2177 2008-10-03 21:34:11 Hari G Re: can any on er .. running a 4cx250b qrp?

Does that mean a regulated 6V DC ?


On 10/4/08, Allis
2181 2008-10-04 07:49:49 Allison Parent Re: can any on er .. running a 4cx250b qrp?
2183 2008-10-04 09:23:17 Don Hackler Re: can any on er .. running a 4cx250b qrp?
4CX250s were used as drivers in FM broadcast transmitters. Typically
20-40 watts in, 1000 watts out running class C in push-pull. The final
amps were 10-25Kw output

813s were used in old AM broadcast transmitters...

2184 2008-10-04 15:17:59 Ashhar Farhan Re: can any on er .. running a 4cx250b qrp?
my question was is there a way to operating them on a low voltage (if
so, how low can we go) and use them in a qrp rig (output below 5
watts). I know that the filaments will probably use up more power than
the RF output.

- farhan

2185 2008-10-04 15:53:17 Allison Parent Re: can any on er .. running a 4cx250b qrp?
I understand.

Not really. Something like a 4cx250 is not worth the effort for less
that 50 or so watts. It can be run with voltages the 500-800V range
and you will get the same or similar power as a pair of 6146s. It's
a tube (valve) designed to deliver serious power. FYI the gain a
4cx250 offers is very high at 6M 2W will drive it to 300+W output!

Same for 813s.

Yes, the heater currents for 4cx250 are in the 2.5A range at 6V.

For qrp power using valves, there are many easier to use parts out
there that can be had. My favorite is 5763 good for at least 5W,
but that list includes hundreds of possible candidates including
a lot of audio and receiving types.


2188 2008-10-06 04:54:06 Hans Summers Re: can any on er .. running a 4cx250b qrp?
Hi Farhan et al

Hihi, why not? Sure, it CAN be done, whether or not it is sensible to
do it is another question entirely, and arguably of less relevance ;-
) after all, what's "sensible"? Sensible is probably just picking up
the telephone - in my house telephone and broadband wireless internet
cost me £5/month ($8 or $9) and the package includes FREE telephone
calls to 100 countries. But what does SENSIBLE have to do with
anything radio related? I gave up completely on the idea of
justifying anything I solder as "sensible" 25 years back.

And anyway, a very similar question to Farhan's raises itself here at
G0UPL headquarters, following the receipt a few weeks back of a
mysterious wedding present from John VK6JY in Albany, WA. In his
email, John noted that according to his observations at least 99.5%
of wedding gifts are somewhat XYL-orientated. When I thought about
the motley collection of mismatching glasses, mugs, kettles,
tablecloths, rugs, etc etc etc the wisdom of this theory was indeed
quite inescapable.

So VK6JY informed that he was determined to break the wedding-gift-
trend, and send something a little "different", via airmail from the
opposite side of the planet. He further advised that the romantic
nature of this gift might not be immediately apparent to the esteemed
new Mrs-G0UPL, and that accordingly it would be highly recommended
that I be present at the parcel-opening ceremony to avoid damage to
the sensitive gift. Which itself was a non-trivial logistical
undertaking, given that Mrs-G0UPL arrives home before the chief
station op.

However, fate was on my side, since the day of delivery arrived and
happened when neither of us was home, and XYL was not inclined to go
down to the recepti
2189 2008-10-06 06:27:23 Dave Re: can any on er .. running a 4cx250b qrp?
2193 2008-10-06 11:05:30 Ashhar Farhan Re: can any on er .. running a 4cx250b qrp?

i get it. if anybody needs 4cx250b's drop me an email. now, lets get
back to the 2sc1969s...

- farhan