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   Home   Help Search  
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Author Topic: Indirectly Heated Valve (Tube) Longevity Question.  (Read 17291 times)
MM0IMC
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Posts: 255




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« Reply #60 on: December 25, 2017, 02:40:43 AM »

But you get a nicer glow from a glass valve. Grin
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W8JX
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Posts: 13268




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« Reply #61 on: December 25, 2017, 05:41:44 AM »


So let me get this straight; you're suggesting that a tube with:
A more compact design
More rugged in handling
Better cooling
And a list that goes on

Is going to have worse filament life than a poor QC control 811A.  Have you even seen the photos of the Shu Guang plant and the complete lack of cleanliness?


Exactly where did I say a ceramic power tube has worse filament life than tube you mention?
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Ham since 1969....  Old School 20wpm REAL Extra Class..
KM1H
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Posts: 5529




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« Reply #62 on: December 25, 2017, 09:54:02 AM »

Quote
Just ask Carl (or any other amp repairer) how many ceramic tubes he's replaced over the years compared to glass envelop tubes.  There simply is no lifetime comparison.

Very few and after the RCA 8122 fiasco was fixed. All were owner admitted faults to the 8873/74/75 family, 8877, and 3CX800A7's without any or adequate fault tolerance circuits. I will not work on amps with Russian tubes which are run well out of design and have a short emission life or short first.

Carl
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KM1H
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Posts: 5529




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« Reply #63 on: December 25, 2017, 03:16:13 PM »

Quote
But you get a nicer glow from a glass valve.

Not when it is in a cabinet and whatever airholes there are are not situated for easy viewing; exceptions are when chimneys are used such as the L4/4B and AL-82 and other amps with easy viewing holes.

Because of the way they are setup here I see nothing glowing and have to lift the top cover of vintage RX, and TX (most are all screwed together cabinets) to see anything.....even a 807!

Carl
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N2EY
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« Reply #64 on: December 26, 2017, 08:22:54 AM »

I have little doubt that reason they use the ceramic valves is because of higher power output, more compact design, more rugged in handling/replacing, ducted cooling that allows tube heat to be discharged outside of unit without heating chassis, frequency range of tube and list goes on. I seriously doubt that filament life is part of choice logic because in medical use they swap them long before they get close to rated life. Operating parameters are the determining factor here.

One of which is heater/filament life!

An MRI machine costs big bucks; tube cost is a drop in the bucket. For many hams, tube cost is a considerable factor. Preventive-maintenance replacement of tubes is just common sense when a failure in-service can be much more costly than the replacement cost.

Also remember: Warmup time. Many ceramic-metal tubes have indirectly heated cathodes and strict warmup-time rules. Eimac data sheet says 3 MINUTES for the 3CX800A7 and 60 seconds for the 8873 family. RCA says 60 seconds for the 8122 family. More time is better, too.

The NCL-2000 and the SR-2000 used a pair of 8122s - and both had time-delay circuits built in to prevent too-early application of B+ and/or drive. A different situation from the "instant on" directly-heated bottles.

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KM1H
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Posts: 5529




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« Reply #65 on: December 26, 2017, 03:09:33 PM »

The MRI developed YC-156 is 5 minutes and most ham users of those pulls suggest 6 minutes.
Even so they seem to loose emission rapidly even run within specs.

OTOH it is an extremely easy tube to use, no socket required and a low power filament transformer is used.

Carl
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VK3BL
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« Reply #66 on: December 28, 2017, 05:29:21 AM »

The MRI developed YC-156 is 5 minutes and most ham users of those pulls suggest 6 minutes.
Even so they seem to loose emission rapidly even run within specs.

OTOH it is an extremely easy tube to use, no socket required and a low power filament transformer is used.

Carl

I didn't realise the YC-156 / 3CX5000A7 lost emission quickly... perhaps its because the pulls have reached their useful life?  Thoughts?
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J.D. Mitchell BA  - VK3BL / XU7AGA - https://www.youtube.com/ratemyradio - Honesty & Integrity
N9AOP
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Posts: 1174




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« Reply #67 on: December 28, 2017, 08:54:43 AM »

0IMC, Roger on the 'glow of the glass'.  But if your ceramic glows you may have a problem.
Art
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AA2UK
Member

Posts: 923




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« Reply #68 on: December 28, 2017, 09:06:50 AM »

Quote
Just ask Carl (or any other amp repairer) how many ceramic tubes he's replaced over the years compared to glass envelop tubes.  There simply is no lifetime comparison.

Very few and after the RCA 8122 fiasco was fixed. All were owner admitted faults to the 8873/74/75 family, 8877, and 3CX800A7's without any or adequate fault tolerance circuits. I will not work on amps with Russian tubes which are run well out of design and have a short emission life or short first.

Carl
Is there a Russian replacement for the 8874?
Bill, AA2UK
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W8JX
Member

Posts: 13268




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« Reply #69 on: December 28, 2017, 09:15:59 AM »

Is there a Russian replacement for the 8874?
Bill, AA2UK

http://www.g8wrb.org/data/Svetlana/pdf/3CX400A7.pdf
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Ham since 1969....  Old School 20wpm REAL Extra Class..
MM0IMC
Member

Posts: 255




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« Reply #70 on: December 28, 2017, 09:24:41 AM »

0IMC, Roger on the 'glow of the glass'.  But if your ceramic glows you may have a problem.
Art

I hope it doesn't glow!  Shocked  Here's a GS31B Russian triode with just the heater voltage applied. Wink



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KM1H
Member

Posts: 5529




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« Reply #71 on: December 28, 2017, 09:42:04 AM »

Quote
I didn't realise the YC-156 / 3CX5000A7 lost emission quickly... perhaps its because the pulls have reached their useful life?  Thoughts?

Since most were in MRI's those are pulled on an filament on basis and were still full power.

I suspect hams were running out of tolerance filament voltage, exceeding grid current or some other parameter. Another reason was buying already beat up tubes from other sources or hams and CBers.

The YC-156 has a 3CX5000A7 anode and 3CX15000B7 internals
http://www.wv7u.com/yc156amp/qa/qa.html

Carl
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