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Author Topic: 811A Anode Cap Cooler/Heatsinks?  (Read 8504 times)
MM0IMC
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Posts: 254




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« on: February 02, 2018, 11:53:56 AM »

Just curious, if there were anode cap cooler/heatsinks available for the 811A valves (tubes), would it make any difference to the cooling of them? Huh
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W1BR
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« Reply #1 on: February 02, 2018, 12:02:52 PM »

Due to the small diameter of the internal leads, I doubt they would do anything practical except look pretty.  Yes, they have sizes that will find almost any tube plate cap. The 3-500 plate structure is supported by the anode lead,which is necessarily heavy enough to also be a conduit for heat transfer.  The metal heat sink would help with the glass seal temps.
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MM0IMC
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« Reply #2 on: February 04, 2018, 12:22:12 AM »

Thanks for the reply. I guess the same could also apply to the 572B's to a degree, although from memory they have a larger diameter anode lead (not by much). Still, most of the heat would be radiated through the glass envelop and the graphite plates are more robust than the skinny 811A ones...
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W8JX
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« Reply #3 on: February 04, 2018, 04:13:27 AM »

Thanks for the reply. I guess the same could also apply to the 572B's to a degree, although from memory they have a larger diameter anode lead (not by much). Still, most of the heat would be radiated through the glass envelop and the graphite plates are more robust than the skinny 811A ones...

Robust is a understatement as a 572 has about 3 times the dissipation rating of a 811. Only thing they share is socket and pinout.
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Ham since 1969....  Old School 20wpm REAL Extra Class..
W1BR
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« Reply #4 on: February 04, 2018, 07:36:01 AM »

Thanks for the reply. I guess the same could also apply to the 572B's to a degree, although from memory they have a larger diameter anode lead (not by much). Still, most of the heat would be radiated through the glass envelop and the graphite plates are more robust than the skinny 811A ones...

Robust is a understatement as a 572 has about 3 times the dissipation rating of a 811. Only thing they share is socket and pinout.


Too a degree,  the 572 like the 811 has internal insulators providing support for the plate.  It is not supported by the anode lead.
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W8JX
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« Reply #5 on: February 04, 2018, 07:40:43 AM »

Thanks for the reply. I guess the same could also apply to the 572B's to a degree, although from memory they have a larger diameter anode lead (not by much). Still, most of the heat would be radiated through the glass envelop and the graphite plates are more robust than the skinny 811A ones...

Robust is a understatement as a 572 has about 3 times the dissipation rating of a 811. Only thing they share is socket and pinout.

Too a degree,  the 572 like the 811 has internal insulators providing support for the plate.  It is not supported by the anode lead.

It theory but insulators and internal spacing in 572 is rated to work are nearly twice the plate voltage of a 811 tube
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Ham since 1969....  Old School 20wpm REAL Extra Class..
G3RZP
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Posts: 1315




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« Reply #6 on: February 04, 2018, 08:44:03 AM »


Quote
It theory but insulators and internal spacing in 572 is rated to work are nearly twice the plate voltage of a 811 tube


I can't find any ratings for the 572 in plate modulated class C. The 811A is rated at 1250 volts in such service, so the plate volts will rise to 2500 with modulation and probably around 4500 with the RF swing. The 572 ratings are 2500 in Class B, so with the RF swing it probably peaks around 4500 too.

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.

In the case of modern Chinese ones, it will likely have flashed over long before it reached 9kV!
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W8JX
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« Reply #7 on: February 04, 2018, 09:20:02 AM »

In the case of modern Chinese ones, it will likely have flashed over long before it reached 9kV!

That flash-over is due to improper vacuum tubes during production, not tube design.
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Ham since 1969....  Old School 20wpm REAL Extra Class..
W1BR
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Posts: 4195




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« Reply #8 on: February 04, 2018, 09:39:03 AM »


Quote
It theory but insulators and internal spacing in 572 is rated to work are nearly twice the plate voltage of a 811 tube


I can't find any ratings for the 572 in plate modulated class C. The 811A is rated at 1250 volts in such service, so the plate volts will rise to 2500 with modulation and probably around 4500 with the RF swing. The 572 ratings are 2500 in Class B, so with the RF swing it probably peaks around 4500 too.

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.

In the case of modern Chinese ones, it will likely have flashed over long before it reached 9kV!

Your estimates seem to be close to what W8JI posted about their ratings when they were US made. 
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W8JX
Member

Posts: 13268




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« Reply #9 on: February 04, 2018, 09:58:12 AM »


Quote
It theory but insulators and internal spacing in 572 is rated to work are nearly twice the plate voltage of a 811 tube


I can't find any ratings for the 572 in plate modulated class C. The 811A is rated at 1250 volts in such service, so the plate volts will rise to 2500 with modulation and probably around 4500 with the RF swing. The 572 ratings are 2500 in Class B, so with the RF swing it probably peaks around 4500 too.

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.

In the case of modern Chinese ones, it will likely have flashed over long before it reached 9kV!

Your estimates seem to be close to what W8JI posted about their ratings when they were US made. 

RF Parts told me a few years ago that their white base 572's are HyPot tested at 7kv
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Ham since 1969....  Old School 20wpm REAL Extra Class..
G3RZP
Member

Posts: 1315




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« Reply #10 on: February 05, 2018, 01:50:28 AM »


Quote
That flash-over is due to improper vacuum tubes during production, not tube design.


I never said it was down to tube design...I wonder if you can accurately describe them as 'Vacuum tubes'!
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W8JX
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Posts: 13268




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« Reply #11 on: February 05, 2018, 05:13:22 AM »


Quote
That flash-over is due to improper vacuum tubes during production, not tube design.

I never said it was down to tube design...I wonder if you can accurately describe them as 'Vacuum tubes'!

The problem is graphite anode. By nature it traps air in it when made. The anode needs to be heated a lot during initial draw down vacuum to help release air trapped in it and should be pumped down for 24 hrs or more.  Failure to do this results in tubes getting gassy over time as heat cycle releases trapped air.
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Ham since 1969....  Old School 20wpm REAL Extra Class..
AC2RY
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Posts: 756




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« Reply #12 on: February 05, 2018, 05:16:02 AM »



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?
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W1BR
Member

Posts: 4195




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« Reply #13 on: February 05, 2018, 06:38:25 AM »



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??? 
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G3RZP
Member

Posts: 1315




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« Reply #14 on: February 05, 2018, 02:01:17 PM »

Quote
The problem is graphite anode.

Very true. They need to be at about red heat while they are pumped, and as John says, the 572B and similar tubes should be pumped for at least 24 hours. It then becomes obvious how corners will get cut to reduce production costs.....Scientific Instrument R & D in Union N. J. claimed a zirconium coated anode, which would absorb gas when hot. They also claimed 'capable of 225 watts plate dissipation'. That was in February 1965.

Presumably a zirconium coated carbon anode is cheaper than a tantalum one, while a plain carbon anode is cheaper still....
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