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Author Topic: 811A Anode Cap Cooler/Heatsinks?  (Read 8503 times)
AC2RY
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Posts: 755




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« Reply #15 on: February 05, 2018, 02:12:06 PM »



A 572B in Class C plate modulated service with 2500 volts supply and 100% modulation would see the plate volts go up to 5000, and the RF peak out probably around 9000, and I don't know just how much it can really stand.


Plate modulated class C circuit is anything but linear amplifier. Are we talking about CB stations here?

We are talking about maximum plate voltage ratings for popular glass tubes.  Do "we" understand the dynamics of high level plate modulation??? 

I can imagine 9 kV on plate with 2500 volts supply and low load (mis-tuned) only when tube is biased deep into cutoff (that is class C). But this should never happen in LINEAR amplifier.
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W1BR
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Posts: 4195




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« Reply #16 on: February 05, 2018, 03:18:37 PM »

The question asked maximum plate voltage ratings.  The question was answered.  I'd rather run a tube that will high pot test several times above operating voltage rather than a marginal tube that may age and fail sooner than later.
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G3RZP
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Posts: 1313




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« Reply #17 on: February 06, 2018, 01:44:01 AM »

It does seem a bit strange that the 572B came out in the late 50's or early 60s and yet had 1930s type construction. Had it been really designed for RF, it could have had 'pinchless' construction and a base like a 5894 or 7094, with much shorter grid and cathode leads. It's almost as if it was originally intended as Class B modulator for a small broadcast transmitter and didn't find a market. Scientific Instrument pushed it as an 811A replacement, but how many ham amplifiers of that era used 811As? The only one I can think of is the venerable 30L1. Far more of those were sold to the military than to amateur radio, and I've never heard of the military fitting them with 572Bs.
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W8JX
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Posts: 13268




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« Reply #18 on: February 06, 2018, 04:28:29 AM »

It does seem a bit strange that the 572B came out in the late 50's or early 60s and yet had 1930s type construction. Had it been really designed for RF, it could have had 'pinchless' construction and a base like a 5894 or 7094, with much shorter grid and cathode leads. It's almost as if it was originally intended as Class B modulator for a small broadcast transmitter and didn't find a market. Scientific Instrument pushed it as an 811A replacement, but how many ham amplifiers of that era used 811As? The only one I can think of is the venerable 30L1. Far more of those were sold to the military than to amateur radio, and I've never heard of the military fitting them with 572Bs.

They started life as T160L's not 572's. Then they were T160L/572's for a while then just 572's.
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Ham since 1969....  Old School 20wpm REAL Extra Class..
G3RZP
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Posts: 1313




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« Reply #19 on: February 06, 2018, 03:09:21 PM »

I guess we are left with a riddle wrapped inside a myth inside an enigma... The one solid fact that we seem to have is that today's Chinese 572Bs do not have apparently all have the same quality level as the Cetron ones did......
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N3QE
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Posts: 5593




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« Reply #20 on: February 07, 2018, 06:20:26 AM »

It does seem a bit strange that the 572B came out in the late 50's or early 60s and yet had 1930s type construction. Had it been really designed for RF, it could have had 'pinchless' construction and a base like a 5894 or 7094, with much shorter grid and cathode leads. It's almost as if it was originally intended as Class B modulator for a small broadcast transmitter and didn't find a market. Scientific Instrument pushed it as an 811A replacement, but how many ham amplifiers of that era used 811As? The only one I can think of is the venerable 30L1. Far more of those were sold to the military than to amateur radio, and I've never heard of the military fitting them with 572Bs.

They started life as T160L's not 572's. Then they were T160L/572's for a while then just 572's.

No, they started as 572B's. The T160L was a "back-numbering to Eimac style numbers" that came when Cetron started making them shortly afterwards. Eimac never made a 572B.

The only "vintage", non-Svetlana data sheet I have ever seen for the 572B was by a company called "Scientific Instrument R&D Co" and at best they were a distributor, not a manufacturer. Their address is 525 Lehigh St Union NJ, currently home to a landscaping company, but never ever in the past connected with any other tube. This spec sheet says 225W dissipation in one place and 195W dissipation in another, which might be "optimistic" but seems to clash with the Eimac-style T160L number that implies 160W dissipation (could be ICAS vs CCS but of course the terms appear nowhere on the datasheet.)
« Last Edit: February 07, 2018, 06:25:35 AM by N3QE » Logged
W8JX
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Posts: 13268




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« Reply #21 on: February 07, 2018, 03:44:34 PM »

The only "vintage", non-Svetlana data sheet I have ever seen for the 572B was by a company called "Scientific Instrument R&D Co" and at best they were a distributor, not a manufacturer. Their address is 525 Lehigh St Union NJ, currently home to a landscaping company, but never ever in the past connected with any other tube. This spec sheet says 225W dissipation in one place and 195W dissipation in another, which might be "optimistic" but seems to clash with the Eimac-style T160L number that implies 160W dissipation (could be ICAS vs CCS but of course the terms appear nowhere on the datasheet.)

Never seen a ICAS rating for that tube. Back in 60's and 70's specs I saw said 175 watts for a 572b. Only in last few decades have I seen the 160 watt rating
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Ham since 1969....  Old School 20wpm REAL Extra Class..
K8BYP
Member

Posts: 256




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« Reply #22 on: February 16, 2018, 10:11:23 AM »

Not useful or necessary

These often had ceramic caps-insulators

The thin wire from plate to cap wont allow much heat transfer

Look at the 4-400 - a heavy copper rod from plate to cap- that can transfer heat and the 4-400 must hav eplate cap cooling (mostly for the plate cap seal)
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N4MQ
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Posts: 348




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« Reply #23 on: February 16, 2018, 05:13:18 PM »

If you can improve the ducting of the air to maximize its motion across the tube youll get the most benefit.  Im restoring a thunderbolt and plan on helping focus the airflow off the fan to direct it around the tubes .   Thunderbolts have a socket fan that does a tiny bit of cooling and you can not use chimneys as most of the air is from the horizontal fan.

Tube cooling is beneficial and a couple of air baffles are worth the effort for all power tubes.  Woody Grin
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G3RZP
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Posts: 1313




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« Reply #24 on: February 25, 2018, 08:17:30 AM »

Things I didn't know about 811s and 811As..

The 811 was pumped and sealed off on a 'SEALEX' machine, which one every two minutes. The envelope was heated by an external gas flame to drive off air, the electrodes by RF heating to incandescence, and there were 7 separate pumping stages before finally gettering.
RCA HAM Tips Vol3 No. 2, March April 1940.

The 811A was announced in the HAM Tips Vol 9 No, 4, Sept - Oct 1949 at $4.05 each.....Strangely, the 812A was announced Vol.8 No. 2 for May August 1948 at $3.75 each....

I always had a feeling that the A versions were out towards the end of the war, but apparently not.....
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N2EY
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Posts: 5093




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« Reply #25 on: February 28, 2018, 02:16:44 PM »

It does seem a bit strange that the 572B came out in the late 50's or early 60s and yet had 1930s type construction. Had it been really designed for RF, it could have had 'pinchless' construction and a base like a 5894 or 7094, with much shorter grid and cathode leads. It's almost as if it was originally intended as Class B modulator for a small broadcast transmitter and didn't find a market.

I think that's the case.

Scientific Instrument pushed it as an 811A replacement, but how many ham amplifiers of that era used 811As? The only one I can think of is the venerable 30L1. Far more of those were sold to the military than to amateur radio, and I've never heard of the military fitting them with 572Bs.

In that era, there was also the Heathkit HA-10, which used four 811As.

The US amateur literature of the time had several designs for 811A amplifiers, some with 2 tubes, some with 4 tubes. They were popular because:

- 811As were a common tube with a proven track record, and not expensive.
- 811As used a common, inexpensive 4 pin socket and had the most common filament voltage.
- 811As would give serious power at low plate voltages. A quad would run the old 1000 watt DC input limit on CW with just 1500 volts on the plate. This meant less tuning-capacitor spacing, less expensive bypasses, etc.
- The drive needed for a pair of 811As in grounded grid was well within what a single 6146 could put out.
- No bias supply, no screen supply, no input circuit (or a very simple one).

- A common setup in the AM days was a pair of 812As modulated by a pair of 811As, often with a single common power supply. With the coming of SSB and TV, the power supply could be reused for a pair or even a quad of 811As.

73 de Jim, N2EY

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