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[KM1H]

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.

RCA listed ONLY their own designs.

The 814 was a beam pentode and always had a sheetmetal anode and can be considered a half 813
I have a 1940 and 46 version of the Hallicrafters HT-9 that uses one as the final. An easy 120W out and fantastic AM audio with 4 6L6's as modulators.

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.

I believe you are mistaken about the sheet metal anode as there is no way it could handle its rated 160W PD. Even the cheapened post WW2 813 with its sheet metal anode could be easily destroyed during a long tune up and that tube is rated at a 125W PD. Ive run the graphite versions at around 200-225W PD and with 4 in GG at 3000V it was easy to get 1500W with no anode color but a muffin fan was used to keep the seals happy.

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..

RCA initially rated the 811 to 54 mc at full power; its ancestor was the 1923 211 aka VT-4 in WW2. Ive converted hundreds of 2 x 572B amps to 6M with no difficulty and once the lossy stock RF input and output networks are tossed they will easily do a stable 700W+ on 6M with 80W drive.

[VK3BL]

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.

Absolutely nothing.  I can't imagine it would be particularly friendly to neutralize in that arrangement.

[K9AXN]

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.

The 320 watts for sweep tubes is high but you struck a chord regarding ratings.

There is no ICAS rating for sweep tubes only pseudo CAS.  A sweep tube lived in a TV set surrounded by other tubes, stuck in a corner, used as a coat rack,  homework depository, moms jungle plants, left on for noise, and no hope of air movement.  That's TCAS --- terrible continuous commercial service.  A 30 watt sweep tube is simply underrated.  The most likely problem with a sweep tube is operator error --- that's not to say incompetence simply a very different tune up procedure.  The plate current on a pair of 6KD6's will easily soar to well over 1000ma when the plate is tuned off resonance.  That's what provoked the builders to add the 200 watt for 40 second rating to the data sheets and no, it's not once for the life of the tube.  Sylvania built 6KD6's under special contract for the SR-400A.  They were balanced, worked in the second bias quadrant limiting them to 500 watts in and 275 out in AB1 SSB mode.  Hal originally thought it would be fine without a blower but quickly added one.

Sweep tubes are not those wimpy things, just misunderstood.         

[W8JX]

Sweep tubes are not those wimpy things, just misunderstood.         

No argument there. If they were they would of never survived decades of being used in TV's before solid state replaced them

[VK3BL]

Sweep tubes are not those wimpy things, just misunderstood.         

No argument there. If they were they would of never survived decades of being used in TV's before solid state replaced them

The sweep tubes in my FT-101E are the factory original NECs.  It still makes 160 watts PEP on 40M!

That is something that will never happen with an AL-811.  On the other hand, you can still buy 811As unlike 6JS6Cs!

[W8JX]

Sweep tubes are not those wimpy things, just misunderstood.         

No argument there. If they were they would of never survived decades of being used in TV's before solid state replaced them

The sweep tubes in my FT-101E are the factory original NECs.  It still makes 160 watts PEP on 40M!

That is something that will never happen with an AL-811.  On the other hand, you can still buy 811As unlike 6JS6Cs!

Its kinda a shame that they do mot make those tubes any more even in China.

[KM1H]

Sweep tubes are not those wimpy things, just misunderstood.         


No argument there. If they were they would of never survived decades of being used in TV's before solid state replaced them

They were also among the most replaced in TV's as they got bigger and the tubes worked harder leading to frequent design upgrades.

A killer when used in ham gear was they had such a high reserve emission as compared to the 6146 family they were easily driven into thermal runaway and melted down internally....and sometimes softened/melted the glass. This was due to the poor tuning procedures used by those used to more robust real TX tubes' A single or a pair of 813's would never complain at 300-600W input and long tuneups nor would a single 4D32 at 200W+ input.

[W8JX]

They were also among the most replaced in TV's as they got bigger and the tubes worked harder leading to frequent design upgrades.

My dad was a TV repair man in 50's and early 60's and I remember him stocking and replacing sweep tubes.  Most TV's had poor ventilation and those tubes ran really hot. With better cooling failure rate would of been much lower. 

[K9MHZ]

The 4-hole AL-811H has and needs a neutralization circuit that the 3-hole AL-811 does not have or need.

There is literally no room in the AL-811 chassis to add a fourth tube and the neutralization network.

This. ^^^^
Don't do it OM, you're going to be in for a lot of angst, sweat, and tears for just marginal gain if you can even get it to work properly.
 

[K9AXN]

They were also among the most replaced in TV's as they got bigger and the tubes worked harder leading to frequent design upgrades.

A killer when used in ham gear was they had such a high reserve emission as compared to the 6146 family they were easily driven into thermal runaway and melted down internally....and sometimes softened/melted the glass. This was due to the poor tuning procedures used by those used to more robust real TX tubes' A single or a pair of 813's would never complain at 300-600W input and long tuneups nor would a single 4D32 at 200W+ input.

Why would a 4D32 be bothered?  It has to be driven to 200 watts dissipation simply to tune it up is SSB mode.  Same with sweep tubes --- done every day. 

Your point which is valid, sweep tubes simply require more care in tuning as a result of the emissions capabilities.

A sweep tube is simply a 6146 with approximately 90 beam channels whereas the 6146 has 33.  It has 2 to 3 6146’s under the covers.

An amp using a pair of 6KD6's will soar to 350 watts per tube if tuned off resonance with full drive applied.  Will they survive?  Sure, happens every day unless you walk away from the radio to see who's at the front door.

I have a question.  I have never seen the plate in a sweep tube show color!  Anyone out there see it in their radio??       

[W8JX]

I have a question.  I have never seen the plate in a sweep tube show color!  Anyone out there see it in their radio??       

I have seen 6146's show color as a dull red more than once.

[KK4YDR]

I would not waste my time doing it for two reasons. First it will at best gain 1 db of signal which will make no difference down range. Second a far better investment would be to simply install 3ea 572 and they have over twice the continuous safe plat dissipation as 4ea 811's and the HV power supply in a AL811 amp does not have enough guts to really hurt 3 572's  as they can safely handle 125 more ma or current than 4ea 811's. That being said while 4ea 811's look more impressive than 3, 3 ea 572's are far more bullet proof and can safely make more power than 4ea 811's and not even come close to max ratings while all AL811 amps exceed tube rating a good deal for their rated outputs. BTW, 4ea 572's will not make any more power than 3 in that amp because power supply cannot begin to exploit four of them.

They wont make more power in that amp chassis. Simply put they are just safer to use. But expect no more power.

[W8JX]

They wont make more power in that amp chassis. Simply put they are just safer to use. But expect no more power.

Not quite true because you can make more power with 3ea 572's than 4ea 811's and not even exceed 572's ratings while you will have to push 4ea 811's well beyond ratings and into a early grave trying to keep up.

It never fails to amaze me those that defend 811'a as great tubes and near equals of 572's in power output when they have thin metal plates and about 30% of the continuous safe dissipation of a 572.

[K9MOV]

I think we need a new thread for discussion and review of the 572 tube. I see some recent reviews of the NEW 572 tubes that are not very good. It seems they lose emission after 6-8mo. I myself, run an AL-811. My first set of 811's lasted over 15 years running 99% CW. A year and a half ago I put in 3 NOS RCA/JAN 811's and they are very nice. I myself need more info on the 572 tube before switch over to them.

[VK3BL]

I think we need a new thread for discussion and review of the 572 tube. I see some recent reviews of the NEW 572 tubes that are not very good. It seems they lose emission after 6-8mo. I myself, run an AL-811. My first set of 811's lasted over 15 years running 99% CW. A year and a half ago I put in 3 NOS RCA/JAN 811's and they are very nice. I myself need more info on the 572 tube before switch over to them.

Why would you switch? Your current tube life is exceptional; you would literally be throwing money away.

For what its worth, I have already started a thread about the current production OEM / She Guang 572Bs.  At this stage, everything that can be said about them is in that thread.