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[W8JX]

I doubt the AL811 is as overrated (not, you understand, that I'm saying it isn't) as the Yaesu/Sommerkamp FL1000. Four 6JS6 rated at 1 kW PEP input........a tiny little fan and enough spread on 6JS6s that one or two could be doing all the work. In about the same size box, the KW1000 used two 572Bs for the same power input, and came out about the same time and pretty well the same price in the UK....

In old days sweep tubes lived a life of a abuse in a TV and they were very rugged and frequently over rated in amps but on the KW1000 is not really overrated  because 1000 watts PEP input is about 600 to 650 watts output and with a 320 watts of continuous dissipation that rating is not out of line. Now a AL811 would have to be "rated" at 1000 watts PEP input for 600 watts out but it only has 135 watts of safe continuous dissipation on 3ea 811's. Some use ICAS rating of 195 watts total but that is only a intermittent rating with equal time off with no current (not idle current) for cooling and even using that tubes are way over loaded/taxed. If you do the math you can clearly see which is truly overated and which is not. BTW as I recall the SB200 was rated at 1200 watts PEP input and many of those amps still work today and some with original tubes too. If it was over rated like AL811 series they would have died long ago, had a history of eating tubes and reliability problems too but such is not the case.

[KM1H]

When did the AL811 come out? Were reliable 572Bs available at that time?

Cetron was still in production in the early 90's and the 572B was available from at least 3 Chinese manufacturers. Two were better quality than the Shuguang which started off with the anodes oriented any which way. The other companies werent making sufficient quantities and wen whole hog into audiophool tubes.
The real St Petersburg Russia Svetlana had their own version back then (actually made by another company) which had a smaller anode of maybe 100-120W but they worked fine if not pushed to hard. They quit making those as hams were too stupid to learn how to tune quickly and went to a very low amplification factor 572B-3 and -10 for Audiophools.

[VK3BL]

Cetron was still in production in the early 90's and the 572B was available from at least 3 Chinese manufacturers. Two were better quality than the Shuguang which started off with the anodes oriented any which way. The other companies werent making sufficient quantities and wen whole hog into audiophool tubes.
The real St Petersburg Russia Svetlana had their own version back then (actually made by another company) which had a smaller anode of maybe 100-120W but they worked fine if not pushed to hard. They quit making those as hams were too stupid to learn how to tune quickly and went to a very low amplification factor 572B-3 and -10 for Audiophools.

Carl, do you know what the Svetlana "572B" really was?  Because it sure isn't a 572B by anyones measure; a substitute maybe but it doesn't deserve the same designation / name.

I'd be very curious to know what it actually was and what it was designed for.  It would seem that it was never intended to be used at the same anode voltages of the Cetron version, anyway.

[G3RZP]

I wonder what the 572 was originally intended for. It doesn't appear in the tube section of the ARRL handbook until 1961, and there it has operating conditions for push pull Class B, so was apparently intended for modulators in AM service. Yet the number suggests a tube that has been around for a long time. If it was 'new' in the early 1960s, it would appear it was meant for modulators for transmitters in the 1/2 to 1kW input range - probably broadcast. Further, if one was introducing a tube for GG RF service in 1960 or so, one would surely go for a more RF friendly construction, with say an envelope like a taller 829 and shorter grid and filament leads? Or a high mu triode version of a 4-125? Penta did it with tubes like the PL6580..

The 572 construction was probably cheaper and suitable for audio.......but even so, it seems rather late in the day to introduce a tube with a 1930s structure.

[W3RSW]

Yes, perhaps in upgrading the 811A to a 572B, room was found for larger anode by incorporating the envelope of the 814 but all the connections were still long, 1930's style as you've mentioned.

So where did an "all the way to a 'B' model" come from for that matter?
Hmm.

The last RCA Transmitting Tube manual that I have (TT-5, Oct. 1962) skips right over any 572 listing.  Of course if RCA didn't manufacture a 572 that may be reason it wasn't listed.

I'm Still looking.  
-Interesting question.

[W1VT]

The July 1930 QST announced the 572 by DeForest.  The press release suggests that it wasn't designed to meet a need.  Instead, they adapted the structure of the just invented 566 and put it in the envelope of the UX-872.

[W8JX]

I remember when they were called 572B/T160L's

[N3QE]

I wonder what the 572 was originally intended for.

Oldest actual data sheet I can find, is the "572B Zero Bias Power Triode By O'Malley", referencing the "Scientific Instrument R&D" company of Union NJ, February 1965. It is pushed on the datasheet as a "Type 811A Replacment". See https://frank.pocnet.net/sheets/084/5/572B.pdf

July 1966 73 magazine talks with great interest in the 572 saying "several manufacturers produced a replacement for the 811 capable of greater plate dissipation".

The DeForest 572 mentioned in the July 1930 QST, page 24, I'm pretty sure from context that was a Mercury-Vapor Rectifier.

[1HAMWANNAB]

What was done about neutralization ?

It looks like somebody tried it:
https://www.youtube.com/watch?v=04G0-BMUYcM

Note the placement of the 4th tube due to the smaller chassis.

[N4MPM]

I have a Hammarlund HXL-1 amplifier made in the late 60's which is made for a pair of 572's.  It had the original tubes in it when I acquired it. The tubes were 572-A's and were so labled.  The difference was the anode which was the metal one resembeling an 811-A.  Output was about 50 watts less per tube than the graphite anode 572-B.  The operator manual specified the tube as the factory supply,  and an update later specified the B version.

[G3RZP]

IF the original was out in the 1930's, it would seem highly doubtful that it was meant for much other than a modulator tube for an AM tx. But IF it really was out then, how come it hadn't been used by amateurs and didn't appear in the tube section of the ARRL Handbook until 1961? Plus how come nobody else made it?

I suspect we will never know......

[W8JX]

IF the original was out in the 1930's, it would seem highly doubtful that it was meant for much other than a modulator tube for an AM tx. But IF it really was out then, how come it hadn't been used by amateurs and didn't appear in the tube section of the ARRL Handbook until 1961? Plus how come nobody else made it?

I suspect we will never know......

I think MPM has a interesting explanation with 572A with a metal anode being "born" as a 811 replacement and later becoming a 572B with a graphite anode. I remember Heathkit ads for late 60's mentioning  572/T160L tubes for SB200 and not B's.

[KM1H]

Carl, do you know what the Svetlana "572B" really was?  Because it sure isn't a 572B by anyones measure; a substitute maybe but it doesn't deserve the same designation / name.

I'd be very curious to know what it actually was and what it was designed for.  It would seem that it was never intended to be used at the same anode voltages of the Cetron version, anyway.

I no longer remember the actual manufacturer (Svetlana bought glass tubes from other manufacturers in Russia and Ukraine snd private labeled them. but Ive run them in the SB-200 and Clipperton L at 2400VDC with no problems as long as the 125W PD and NOT 160W of the Cetrons was observed. They even work fine on 6M.
AFIK all the Chinese versions were also 125W and running 4 of them at 1000W PEP didnt bother them at all one the beast was neutralized, and with new suppressors.

Carl

[KM1H]

I wonder what the 572 was originally intended for. It doesn't appear in the tube section of the ARRL handbook until 1961, and there it has operating conditions for push pull Class B, so was apparently intended for modulators in AM service. Yet the number suggests a tube that has been around for a long time. If it was 'new' in the early 1960s, it would appear it was meant for modulators for transmitters in the 1/2 to 1kW input range - probably broadcast. Further, if one was introducing a tube for GG RF service in 1960 or so, one would surely go for a more RF friendly construction, with say an envelope like a taller 829 and shorter grid and filament leads? Or a high mu triode version of a 4-125? Penta did it with tubes like the PL6580..

The 572 construction was probably cheaper and suitable for audio.......but even so, it seems rather late in the day to introduce a tube with a 1930s structure.

It was originally a Taylor T160L designed for AM modulator service in 1959 but with AM dropping rapidly in ham and commercial usage they couldnt find an OEM buyer. The BCB TX's werent Taylor users and stuck with RCA, Eimac, Westinghouse, Amperex which were well known and reliable.

United Electronics in NJ bought the design in 60-61 and called it the 572, not to be confused with the 1930's DeForest version where the 5 identified the manufacturer and the 72 was the actual type.

UE  could not produce them fast enough and partnered with Cetron in IL and the 572A was UE with the round top and 572B was the shouldered glass Cetron.
You will also find some round top Cetrons which were actually built by UE when Cetron was overloaded with orders. Both private labeled for others such as GE, Raytheon, Waters, Amperex, RCA, Dentron, and maybe others.
Eventually UE concentrated on their core business of thyratrons and rectifiers before folding and Cetron was the last one standing in the US.

O'Malley was a wet dream AFIK and Ive never seen or heard of a real one

I have a Cetron spec sheet but no date is listed but it has to be 63 or later as it had a ZIP code.
It lists 2750V MAX for Class B AF and Modulator service and only 2000V for Class C CW. No SSB mentioned but they were in the SB-200 by 63-64.

They also list it as a direct replacement for the 811A but not the reverse of course altho several reported using them in the Clipperton L in the CW position.

Carl

[G3RZP]

In my professional designing career - which involved putting around 12,000 tubes into production radios - for some reason RCA always seemed to fit the bill best. But I never quite got up to the level of going to Eimac. Back 40 to 50 years ago, at the 1kW and below level, glass tubes were the cheapest approach...I could never get convinced that sweep tubes in a radio that had to be used in an emergency were really a good idea. Several of the transmitters of models that I designed WERE used in emergency.....and saved lives. In at least one case, if they had left the booze alone, they would not have hit the rock that made the MAYDAY that got them rescued necessary....