interesting amplifier

[WA1GFZ]

Just spent the last few hours field stripping our IFI 406 amplifier  6 4CX250s in twa driving 24- 4XC250s in TWA all to make 1KW 10 KHz to 250 MHz.

Very interesting design for a clean amplifier. It runs about 7 KW to make 1.

Bad bias bypass cap shorted the bias to almost zero tripping the over current interlock.
Anybody ever have a problem I r an espert now.
Of course it crapped out with about two minutes testing to go about 3 hours ago.

[W2VW]

For hammy service, tetrodes make good doorstops to block the door while bringing in parts for triode R.F. power amps.

[WA1GFZ]

Dave this is an untuned broad band amplifier 10 KHz to 250 MHz and quite clean.
The output Z of 24 tubes is very close to 50 ohms. A TWA amp is a number of tubes sitting on 2 tapped delay lines one on the grids and one on the plates. One end of each delay line is loaded with a resistor. The input of this amp has a 50 ohm 50 watt and the output is 100 ohms 270 watts. The other ends are input and output cap coupled. A RF choke isolates the B+ 1 KV 7+ amps and grid bias is the bottom of the 50 ohm 50 watt. Each screen has a resistor in series with a reverse diode across it. 
KISS. Imagine a string of big tubes. The resting current with no drive is 2 amps.

[W2VW]

Quite the bandwidth requirement!
Looks like the design goal included output Z based on available cable impedance.
Simple output network is cheaper than a few more parts elsewhere.
 

[WA1GFZ]

Well after fixing our amp attention falls on the PW one in the back room.
This one is a bit sicker. about a dozen screen reisitors blown.
BUT.......everyone said I can modify this one for more strappage.
It took an act of the boss to let me drill a hole for a ground lug to install the right caps. I would have mounted door knobs if it was my amp.

Man it would be cool to take a dozen 813s and build a twa