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RF Amplifier Tubes- whats left & affordable for a RF Amp

Discussion in 'Amateur Radio Amplifiers' started by N8FVJ, May 4, 2019.

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  1. KD5OEI

    KD5OEI Ham Member QRZ Page

    Cheap Seats:
    3-500 tubes can be had for $169 from ESRC1 Three will run CCS duty on FSK or AM.
    These are Chinese. "Warranty: Tubes are guaranteed for 90 days, except for breakage, open filaments, or when not operated within manufacturer’s specified ratings."
    These are the cheap grade of Chinese tubes. The RF Parts one for $375-400 are the better grade. It was my experience that unlike USA manufacturers did, China sells what are almost 'seconds' for cheaper prices. The first rate ones are more.

    I have been running a pair of ESRC1 Chinese tubes in a class AB2 modulator for years. Sometimes with 3500VDC and 800mA on voice peaks. In spare time I am working on the transmitter. It's an old homebrew, and is unstable at high power and modulation - so I will run a tone through the modulator (orange plates, 3000-3300V @ 500-600mA) while tuning the Class C stage. I mean to say, a 600-700W carrier, and 100% or sometimes a little more positive modulation and this goes on for 5-10 minutes at a time.. The $169 tubes have held up just fine. They were $135 when I bought them maybe 15 years ago.
    I do not offer the above as an advertisement, but as a statement of my experience and today's cost. and to say don't be afraid of the Chinese tubes at cheap prices. Try them, and you got 90 days, run them CCS for a few hours on and off, (if your amp has the nuts and bolts to do that) and you'll know quick if you need the warranty.

    So what tubes? OF COURSE!! The glorious Chinese Buffet of 3-500C tubes, and any amp that will take them.
    Two will run SSB and CW all day and night.

    Two not enough? AM cariers and FSK? CCS? Three will give 1500W dissipation, lots of margin on the tubes, and so cheap compared to amps with expensive tubes. If one wants three tubes but can not build from scratch, obtain two inexpensive type of identical linear amps that use 3-500Zs in pairs (SB-220 anyone?). Move the power supplies into one chassis and add a third tube to the other chassis. Not technically complicated to do the job, or a cooling upgrade the amp needs anyway.

    Good seats:
    The 3CX3000 is the only tube I would spend 'big' money on. 275W grid, 4KW anode, 1500W out at 100W drive. $799 rebuilt at RFParts. Amazingly cheap Watts per dollar. It should last a lifetime in ham radio use.

    I have been running one in a SSB-rated amp for several years. 100W exciter is perfect. The amp would to AM/FSK but the power supply is at its KVA limit for 'legal limit'. OK by me but I like overkill. So there's a beastly amp being put together that is CCS all the way with extremely generous ratings on all components. OK so space and power comsumption are of no consequence here. Only durability. Overbuild everything. Just don't spend lots of crazy money on little tubes when normal money will get a big tube. Happiness.
    Last edited: May 9, 2019
    AH7I, K6LPM and K2XT like this.
  2. N8FVJ

    N8FVJ Ham Member QRZ Page

    Amp Supply LK-550 is only three tube 3-500Z I know of.
    1 person likes this.
  3. KD5OEI

    KD5OEI Ham Member QRZ Page

    Thank you, I was not aware of that model. Lots of good reviews on it.
    First impressions are the rectangular arrangement of 4 fans with two of them sunk partly below the socket chassis might get some more air under the sockets than the SB-220. *
    Also saw there is a no-tune version, the LK-550NT. There was a comment on the web that it trades some efficiency for the broadbanding.
    Nice separate power supply with PWD iron. I'd have it.

    *I believe in blowers and chimneys but what manufacturers do -hopefully is well considered.
  4. N8FVJ

    N8FVJ Ham Member QRZ Page

    Only desk top HF amplifiers that uses chimneys I know of is the Drake L4B and Henry 2KD series..
  5. N8FVJ

    N8FVJ Ham Member QRZ Page

    After some further thought the Chinese 572B do not last more than a few years. The Cetron 572B lasts 25+ years, but are very hard to find now in NOS. Over a period of 10 years the Chinese 572B replacements can cost $800 or as much or more than your HF amplifier cost. On the other hand, the Chinese 3-500Z does last at least 10 years per ham reports.

    The conclusion is the only true economical tube left is the 3-500Z. Best amps are Ameritron L-80A or AL80B, Heathkit SB-220, Amp Supply LK450 or LK-500 and Drake L4B is it for an overall low cost amp that holds up well. All cost around $800-$900 used. The L4B does have a more heavy duty 29lb transformer vs the 23lb SB-220 transformer so I would chose the Drake. Al80A is 23lbs (AL80B 26lbs), but only one 3-500Z tube and the Amp Supply LK-500 uses a Peter Dahl hypersil type that is 23lbs, but hypersil efficiency performs like a 30lb standard IE lamination transformer. I will pass on the very heavy duty 90lb Henry 2KD due to weight & high shipping costs. If you can find a local Henry and lift 90lbs, go for it.

    I would look for rebuilt Heathkit, Henry 2KD or Drake L4B due to age. The newer Amp Supply LK-450 or LK-500 and Ameritron AL80B do not need a rebuild yet.
  6. W2WDX

    W2WDX Premium Subscriber QRZ Page

    When I purchased my Alpha 8410 a number of years ago, I also ordered a spare set of tubes at that time (they cost much much less then). It just seemed expedient at the time, given the the fact tubes seemed to be going away. I don't think I will need tubes for this amp anytime within my lifetime. The original tubes show no sign of weakness after many hours of use. If you are buying a amp that uses 811 or 572 or even the 8877, it just makes sense to make sure you have the cash to also purchase spare tubes outright. You could otherwise be in a position where no tubes are available anymore once the time comes to replace yours. So instead of just replacing tubes, you end up replacing and paying for an entirely new amplifier. At that time it could only be something solid state; and there we all know that output devices come and go like the wind. Hindsight can suck, forethought just makes sense (even if it hurts the pocket in the short term).

    Years ago (late 80's and thru the 90's), when I saw what was happening with tubes, I started buying lots of common quality-domestic NOS tubes. 6146, 12AX7, 12AU7, etc. I just made an inventory of what the most common tubes used in amateur and pro-audio gear and began buying. They were still cheap then. I even purchased odd tubes like 7094, 6293, 6386, 7378 (QE08-200) and especially a bunch of Telefunken VF14 since I owned a number of original U47 microphones. I also bought "hardened" versions of the common tube types, like 5814 and 7025 based on what was in my R-390a and SP-600 receivers. I just didn't want to be left in cold in the future, either with my ham gear or my audio stuff. Like I said ... hindsight sucks.
    Last edited: May 25, 2019
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  7. W5LZ

    W5LZ Ham Member QRZ Page

    This has been covered but I think it can stand to be repeated. What is the -availability- of the tubes used in an amplifier? The 811 an 572B are getting scarcer all the time. Not impossible to get...yet. But they are getting there.
  8. W2WDX

    W2WDX Premium Subscriber QRZ Page

    Availability is not an issue for new 811, 572B & 3-500G. since they are still manufactured. Cost and lifespan are what has changed. The former has gone up and the latter has shortened.

    As far as upgrades for the SB-220 types, there is a heavy duty Peter Dahl upgrade for the transformer, which runs for about the same as replacing the tubes. (Maybe a little more). The current rating is almost double versus the original Heath transformer. I purchased one from Dahl (Hammond) just this past fall for my HL-2200 (same as SB-220). So I know they can be had newly manufactured. This brings the amp into a realm of being very clean due to the added "stiffness" this transformer provides for the supply. It also runs cooler. I use this amp for 200W carrier service on my AM operations. I do have spare NOS 3-500Z Eimac tubes as well. Thinking of purchasing new Chinese 3-500G's just to see how they hold up in a worst case scenario.
    Last edited: May 25, 2019
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  9. KM4HGU

    KM4HGU Ham Member QRZ Page

    I'm glad mine uses 813. The NOS is available for about $65 each. :D
    W1BR likes this.
  10. W1QJ

    W1QJ Ham Member QRZ Page

    Even in today's money one can buy a used pull 8877 or a pulse YC-257 or 3cpx1500a7 that will drop right in as well for the same money as a set of new 3-500zg Chinese tubes. For my personal amps I have moved on from 3-500's to either 8877 amps or 3cx800 amps. Getting an amp with these tubes that are good and a spare tube(s) should last a life time to other than an avid contester who may require one additional set of spares. Seeking out a reasonably priced tube may take a little time but surely before you will need it you should be able to find one. Typical $350-400 for a full output 8877 or P type tube is very possible. The 8877 or pair of 3cx800's easily do legal limit and any amp using them will loaf at that level. keeping it that way, they should last a long time. There is no reason to ever have to pay $2K for an 8877. There are numerous NOS 8877 tubes in sealed boxes you can buy for around $700 or less. At this very moment there is a glut of 3cx800 based amps for sale at bargain prices. Many of the contesters are dumping their 3cx800 amps for solid state amps. There are numerous Commanders, Titans and 87a's on the market right now with prices slashed from just 6 months ago. Caution: you may want to think twice on the 87a's however. The Titan's and Commanders may be a better choice.
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