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Planning to overhaul my 1973 SB200 Amp.......

Discussion in 'Amateur Radio Amplifiers' started by K3RU, Oct 12, 2017.

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  1. K3RU

    K3RU Ham Member QRZ Page

    Did I really build this old amp way back in 1973 ? Unfortunately the answer is YES. So 44 years later it still works but I'm sure it needs a "going over".

    So.... ordered from HARBACH a power supply and soft start combo kit, and a keying interface so I can retire the external Ameritron ARB-704 which currently keys the amp. So good.

    Next step get a set of tubes. Now it's getting "dicey". Over the years I have followed the trials and tribulations of the various available 572B's always being "scared-off" by the quality of the made in CHINA "copies". The now 44 year old CETRONs in my amp still produce over 400 watts on most bands, but I want to re-tube the amp and hope for the best.

    I find DX Engineering has 572B's for $82~. DXE claims these tubes are so good that "matched sets are no longer needed", and these tubes can be mounted - to paraphrase - AT ANY ANGLE. I like that because the SB200 mounts the tubes HORIZONTALLY which was a BIG no-no over the years for non-CETRON brand 572Bs. I'd get free shipping for a pair and the warranty seems good too.

    Then I download the DXE spec sheet for their branded 572B and noticed the "Limit Rating for Anode Voltage" is ONLY 1250V. Last time I looked my SB200 put over 2200V on the tube anodes. The SB200 manual mentions "approximately 2400V". My hope is that the DXE spec sheet is wrong and the 1250V should actually be 2250V or more.

    I might ask them about this discrepancy as not that I expect their tubes will fail but if there is a failure are they going to deny warranty coverage because I "misused or abused" the tubes ?

    For what-it's-worth the original CETRON 572B was rated at 2750V Class B Audio service, and 2000V Class C Telegraphy.

    Maybe RF Parts or Ameriton is a better source for 572B's. I doubt it but we shall see.
    Last edited: Oct 12, 2017
  2. N7WR

    N7WR Subscriber QRZ Page

    I would go with RF Parts
    KD2ACO likes this.
  3. KD2ACO

    KD2ACO Platinum Subscriber Life Member Platinum Subscriber QRZ Page

    I agree with Gerald. My SB-200 had a new pair of Taylor 572bs put in last year and they perform pretty much the same as a pair of "not worn out" Cetrons that were in the amp. We'll see how long they last but the tubes seem great.

    Avoid the Svetlana 572s. They were designed for audio amp use and are not right for a linear amp.

    I got the Taylors to check out new production tubes out of curiosity, and the Cetrons were brought to Tokyo for a ham with a Yaesu FL-2100 that really works better with Cetrons than what he could get his hands on over there at the time. I suspect that the new Taylors would work fine in his amp, but he's more careful about duty cycle now and won't need new tubes for a while. :p
    Last edited: Oct 13, 2017
  4. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    I'd go with RF Parts, also.

    Merit says they have new 572Bs that are built exactly like Cetrons, to the Cetron specifications (but in China) and he has a good warranty on them...and in my experience, he honors his warranties just fine.

    Not only SB-200s used them horizontally, so did Yaesu in their FL-2100s and a few other smaller "brands."

    Go with RF Parts.
  5. N7WR

    N7WR Subscriber QRZ Page

    The venerable Collins 30L1 had tubes mounted horizontally. Tons of them were used by the military in very demanding conditions, not to mention the number used and still in use by hams today. I have never heard of a failure in those amps due to the horizontal mounting
  6. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    Those used RCA JAN-CRC 811As.

    I did see them fail, in Vietnam. However, the failures weren't related to the tubes, they were from the unbelievable humidity.
  7. K3RU

    K3RU Ham Member QRZ Page

    Thanks to all for your comments. I'm going to order the 572Bs from RF Parts.

    I purchased a Chinese TAYLOR 8877 from RF Parts about a year ago for my then "broken" AL1500 and so-far-so-good. The AL1500 issue turned out to not be a defective tube but I installed the TAYLOR 8877 as it is/was under warranty. The TAYLOR 8877 CW and SSB idling currents were about THREE times higher than the original EIMAC 8877 which came in the amp so adjusted the tube bias to bring the TAYLOR 8877 idling currents down to approximate the original EIMAC, which is now my spare tube.

    Speaking of EIMAC 8877's - DX Engineering no longer sells them. DXE charged $1500 for a "genuine EIMAC", which makes RF Parts Chinese 8877 at around $750 look like a good deal. I'm keeping my fingers crossed.
    Last edited: Oct 13, 2017
    KD2ACO likes this.
  8. KD2ACO

    KD2ACO Platinum Subscriber Life Member Platinum Subscriber QRZ Page

    Good info, James!
    The idling current stayed the same with the new 572s in my amp. The Cetrons were mid 90's and in great shape. The amp doesn't seem to notice any difference.

    A few years back, there was a lot of speculation here about having to retire thousands of 572-packing amps. It seems like Merrit really came through on this one! 600 watts for 160 bucks is a bargain.
  9. W1QJ

    W1QJ Ham Member QRZ Page

    Help me out here. I don't see the RF parts 572b tube that had a white base and gold colored pins on the website. Some time ago those were reported to be their Cetron knock offs. The ones on the site that claim to be the Cetron quality aren't these white base gold pin units from before. So what gives?
  10. KD2ACO

    KD2ACO Platinum Subscriber Life Member Platinum Subscriber QRZ Page

    Here's the Money Shot, Lou!


    (click on the photo for the big picture)

    As far as I know, the white base and gold pins would be the Svetlana tubes made for 572b audio amps (mostly single ended triode). Audio geeks (of which I'm a professional one who knows the difference between reality and BS) like shiny gold pins apparently... :p

    This tube in the picture is dated 20th week of 2016. I bought them in November. I mostly operate SSB at about 600 watts PEP. The new tubes seem really nice and sturdy.

    The ink is a bit discolored. I've pushed them in initial tests but take it easy on them now for the long haul. The getters are clean. No chunks rattling inside!
    Last edited: Oct 13, 2017

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