anyone have any practical experience with the 4E27A/5-125?

[N3DRB The Derb]

Seems like these may be not on the radar of many folks and therefore be more affordable. Except for the high screen voltage, the power looks about right for what I wanna do. There used to be lots of these around.

Anyone ever made a rig with em? Look to be great for the peek a boo window factor too - the sing for their supper glow. 

[W3RSW]

Used to use a bunch of them in our 48.4Mcs FM Base Link Xmitters.
I have one left and use for show on my tube shelf.

Nice tube.  A pair modulated by a pair would be just like JJ's 'infamous'  813 rig.

[N3DRB The Derb]

Yes, thats what I was thinking. Not quite as much power, but a lot shorter vertical mounting.

here's the datasheet on it. likes lotsa voltage.

I think a pair of these will make quite the nice RF deck. Not sure about modulators yet. I tend to dig triodes for audio and I need to use JN's 572b's - I dont like AB1 operation for audio.

no demand for them to really speak of that I know. thats what I like to roll with. 

[W3RSW]

"But wait, there's more!"

It's an improved 8001. 4E27.
The 5-125 is the 4E27A.

Uses the same socket as an 813, (7 pin giant)  And almost the same base pin out too.

The plate will show color under load and look mean compared to an 813.

Hmmm,  5-125 Uses 5 volts at 7.5 amp fil's.  Maybe with a center tapped 10v @ 10 to 15 amp fil. xfor. alreadly in an 813 amp,  you might be able to lash up a 'complimentary' filament supply.   I ran an 813 pair from a 18vct control xfor some years ago by using split resistors in the cathode (bypassed for RF, of course.)   The current rating was about 15 amps, so the 813's saw about 9.8 volts and didn't know the difference.   Tron gave me a slight hum report, but what the hay. 

[WA1GFZ]

4-125 better at RF than an 813. 4-125 modulated by 813s sounds very cool.
Use a bigger heater transformer so the whole family fits the rig. 4-125 to 4-400.

[W7TFO]

They can use supressor mod for free as well, no big audio needed.  Not beam pentodes so this works well.

[W3RSW]

And if you run into a nice supply of 5-125's you can always use them as zero bias triodes in a modulator by connecting up the grids, etc.    All grids to plate, one type of mu.  All grids to each other or screen drop of 20k or so to signal grid, another mu.  Great for experimentation, but some bias may be necessary in some cases.

All depends on what you find.  I think a mess of 5-125's is a great idea Derb.
But you may be surprised, a mess of 813's may be easier to come by.   You do have a few friends, ya know. 

[N3DRB The Derb]

well, I found some. look in QSO to see them.

[KM1H]

Its all about trying to upstage the other guy.

H&K started it with the 257 in the mid 30's so naturally RCA replied with the 813 saying graphite was better than tantalum. So then Eimac responded with the 4E27 (and bought H&K along the way) and then RCA responded with the 7094 dog which pretty much ended the war.....and RCA was pretty much washed up as a TX tube leader by then anyway.

Before that Eimac had only triodes on their mind and didnt like the H&K competition in that area either.

Both the 813 and 4E27 and its later improved 4E27A are still fine tubes.

Carl
KM1H

[W3RSW]

257 ?   typo?

http://tubes.mkdw.net/sheets/136/2/257A.pdf

[KM1H]

The H&K 257 is no typo. Just not listed most places and numbers get reused.

Carl
KM1H