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Author Topic: Replacement tube in stock, or wait for an issue?  (Read 1767 times)
AE6RF
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« on: January 22, 2007, 09:49:01 AM »

Greetings,

Potentially stupid question here:

If you own a tube amp, do you have a spare tube (tubes) in stock at your house or do you wait for an issue to crop up?

TIA,

-Donald
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NI0C
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« Reply #1 on: January 22, 2007, 10:17:29 AM »

My amplifier (AL-80B) uses a very reliable tube, the 3-500Z.  I've only had one fail in the past ten years, and that one was replaced free by Ameritron.  

Since the 3-500's are so reliable (and expensive) I see no reason to keep spares on hand.  If I had an amplifier that used cheaper and less reliable tubes (such as the 811A's), I would probably stock up.

73,
Chuck  NI0C
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K0BG
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« Reply #2 on: January 22, 2007, 11:07:25 AM »

I sort of look at this from another angle.

If one looks back over the last 20 years, the number of power amplifiers tubes (suitable for amateur service) has waned to the point, that you can almost count them on one hand. As venerable as the 3-500Z is, and as popular as the 811As are, they too have a short (future) life in the overall scheme of things. The same can be said of some early solid state devices too, perhaps more so in some respects. Nonetheless, the hand writing is on the wall, and all so called "liquid state" devices will soon be gone.

The question was, should you have a spare(s) on hand? If it is a 3-500Zs, 811As, 572Bs, or 6146s, maybe not. Any of the Russian types, most of the Chinese types, and anything with sweep tube finals, I think I'd have a spares on hand.

Alan, KØBG
www.k0bg.com
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N6PSE
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« Reply #3 on: January 22, 2007, 11:27:13 AM »

How about an Eimac 8877?   I see new old stock for sale from $600 to $900!

I have a new Amp on order that uses a 8877 and I am considering buying a spare 8877 if I can get a good (new) one at a good price. This would greatly extend the life of this AMP which I am hoping will be my last Amp purchase (Alpha 9500)

Paul N6PSE
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WB2WIK
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« Reply #4 on: January 22, 2007, 11:27:39 AM »

Many tubes don't age well when "stocked," and need to be used in order to maintain good service life.  The 3-500Z is one example.  Almost nobody who knows anything about power grid tubes would want a "new old stock" 3-500Z that's "new, in box, stored for 10 years."  It's almost guaranteed to NOT work when powered up.

I'd rather have a 10 year-old 3-500Z that's actually been used for the ten years.  Almost guaranteed it WILL work when powered up.

However, one thing to drive this decision should be uniqueness or rarity of the tube(s) in question.  If I were buying an older Alpha that used 3CX400A7/8874 tubes, for example, since those are no longer manufactured and haven't been for several years, if I could get "new" spares at the same time as buying the amplifier, I'd want to do just that.  (Those ceramic-metal tubes actually have a very long shelf life.)

WB2WIK/6
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WB2WIK
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« Reply #5 on: January 22, 2007, 11:30:10 AM »

8877s have long shelf life, too.

I wouldn't pay $600 to $900 for a "NOS" 8877, at all.

Especially considering I can get used "pulls" for $150 each from reliable sources and they always work.

My 6m 8877 amp has had a used "pull" in it since I built it in 1985 and now, 22 years later, it works the same as it did back then: 1500W out with 65W drive.  That "pull" cost me $100 back in '85.

WB2WIK/6
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KB9CRY
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« Reply #6 on: January 22, 2007, 12:40:18 PM »

I have a spare for everything.  Now, I purchased both my SB-220 and my SB-1000 (both use 3-500s) used.  My 1000 still cranks out full power (I only use it on 160M).  I purchased the 220 15 years ago, used.  I'm still using the same old tubes that came with it way back then.  Yes I'm only getting about 700 watts on 10M but full KW on 20 and lower.  So anytime now (like maybe when I'm ready to pass on) it'll be time to change the tubes.

Phil  KB9CRY
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KI4NX
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« Reply #7 on: January 23, 2007, 04:48:21 AM »

Nope.  I use a SB-200 amp and have had those same original tubes working for over 25 years. I thought I had a problem with one of them about 10 years ago. But, when I replaced the power supply caps and diodes, everything was fine again.  I guess I'll get concerned in about another 10 years or so.  And, until then, I'll keep warming the bands.
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N3JBH
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« Reply #8 on: January 23, 2007, 07:57:54 AM »

 "WB2WIK  
8877s have long shelf life, too.
I wouldn't pay $600 to $900 for a "NOS" 8877, at all.
Especially considering I can get used "pulls" for $150 each from reliable sources and they always work. "

Steve i heard you make this statement many times. and i know your a good and caring kind of fellow. so why dont you do the rest these gentleman a huge favor and tell them where they can get these great deals.

please dont take this wrong as i am being a smart _ss i really ain't. i just think it be very nice if you help other's by passing along where they could find these deals.   jeff/ n3jbh
 
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KD5NCO
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« Reply #9 on: January 24, 2007, 09:11:51 AM »

I have a first run of 2007 AL 572 coming this week from Ameritron

My local Elmer's are a mixed bag on this question relating to the 572 tube

I have a few questions but here is my intent:

I bought this Amp as best bang for the buck vs any of the solid state offerings I would prefer. I have no serious interest in the near term to chase DX or spend a LOT of time in HF because I have ten more years to full retirement and my occupation has me working 50~60 hours per week since 9/11 and is not likely to let up for years.

I think this Amp should satisfy my needs very well over the next 20~30 years. The majority of use will be 160M 80M SSB for round table Chit chat and I know my good antennas and radios will work 100W just fine 60% of the time so the AL-572 Amp will fill in on the funky propagation days. Based on my Elmer's success at 400W to 600W with a Dentron 1500 I suspect this one should never see a Kilowatt except for the few times I max it out to see if it works as advertised.

Sorry, I know this is long winded but I respect the opinions of a few folks in here and want to paint the complete picture.

I have been advised to get a second matched quad set of 572 and rotate them into the amp every 6 to 12 months or some recurring schedule to prevent them from getting "gassy" from long term storage.

I see by web searches there is a broad range of these tubes under different suppliers and a fairly broad variance of prices.

Opinions on getting spare tubes, the rotating them "into use" scheme, and ideas on quality of the various sources.

Is this tube likely to be found 20--30 years from now
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