Heathkit SB200

Discussion in 'General Technical Questions and Answers' started by KI5HC, Jul 18, 2005.

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  1. KI5HC

    KI5HC Ham Member QRZ Page

    I have owned a Heathkit SB200 for about 13 or 14 years. The manual says it should do 1000 watts on CW. I have had a friend tell me that his SB200 performed as advertised.

    My wattmeter has never shown more than 650 watts.

    I notice Ameritron builds an amp with 4 572Bs....and they claim 1350 watts.

    Does anyone have an SB200 that really does a KW?
  2. WA4NMS

    WA4NMS Ham Member QRZ Page

    That is a KW input, not output. Mine will do 500W or a little better CW....but I don't talk long.

  3. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    Impossible. The amp can't do it, and neither can the tubes. Completely impossible.

    The SB-200 was rated "1 kW DC input power," not 1 kW output power. Big difference. Amplifiers only started being rated for output power when the rules changed to allow 1500W PEP as the legal limit, in the late seventies. Prior to that, all equipment was rated for input power, as that was the only power reference in Part 97.

    The SB-200 should indeed provide 600W PEP output. Possibly 650W PEP with a good, stiff AC line and new tubes.

  4. KI5HC

    KI5HC Ham Member QRZ Page

    Thanks for the replies. I suspected as much, and nice to know that mine is doing all she can.... [​IMG]
  5. N8CWR

    N8CWR Ham Member QRZ Page

    Hello I have a Yaesu FL-2100F amp and it uses the same as the 200, a pair of 572B tubes. They are only 600 watts total for the pair and I have never got anything over 600 out of it. Hope that helps.
  6. K9STH

    K9STH Ham Member QRZ Page

    If you run the SB-200 on 240 VAC (actually up to 254 VAC in some locations these days) you might get 650 to 675 watts out on 80 meters with good tubes.

    On 10 meters the output is going to drop to around 500 to 550 watts depending on what you have chosen for the line voltage.

    I had an SB-200 back in the early 1970s and it was an excellent linear. Am looking for another one to complete the "re-creation" of my 3rd primary station.

    Glen, K9STH
  7. W2ILP

    W2ILP Ham Member QRZ Page

    The SB-200 which uses 2 572Bs is supposed to be capable of 1kw PEP for sideband. For key down CW it can't quite do 1 KW. Another factor is the ALC and how it works with the transceiver that drives the SB-200. ALC automatically reduces drive during long key downs but may not do it as much when CW is actually keyed. As with PEP, CW power for rapidly keyed CW can not be read reliably on a simple meter because of the balistics of the meter itself. Bird make peak RF power meters that are supposed to read peak power. It is only under fast keyed CW and properly adjusted ALC that the SB-200 can manage to reach 1 KW on CW. The output is lower on 10 meters in any case as STH mentions.

    w2ilp (Intrinsic Low Power)
  8. W2ILP

    W2ILP Ham Member QRZ Page

    Opps I did not remember that the ! KW may have meant input power rather than output power.
    Actually I have a Heathkit HA-14 which is the same as the SB-200 except that it has the power suppy as a seperate unit and also was designed to use a 12 volt operated mobile power suppy. as well as a fixed station supply.
    The HA-14 was discontinued by Heathkit as a mobile amplifier because it was recognized, even in 1967, that it could present an RF hazard. . Heathkit only wrote Maximum in the HA-14 manual specs and that an SSB 50% duty cycle could make 1000 watts PEP with 100 watts drive. There was no spec for CW, since they thought it was not going to be used in a mobile installation. It is interesting that Heathkit did not specify whether the maximum power was input or output power. The FCC regulations at that time were based on input power and the limit for hams was 1 kw.
    I dunno why but now they go by output power which is more difficult to measure reliably and the limit on most bands is now 1.5 kw. The specs also say that the SWR should not exceed 2:1 for proper operation.

    When I used the HA-14 I added a cooling fan and I used the 240 volt line option. When I used 120 volt line power the lamps in the shack flickered when I PTTed. The power supply provides 2000 V DC and the unit draws about 500 ma so the DC Plate power is indeed about a kw.

    w2ilp (Input Legal Power)
  9. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    W2ILP, the "1 kW" rating for the SB-200 is/was a "DC power input" rating, not output. Ratings for amplifiers were revised to "output power" in 1978 when the FCC changed Part 97 to allow 1500W PEP output power, and eliminated the DC input power restriction.

    The SB-200 was already discontinued by then.

    Prior to that time, all amateur RF power amplifiers were rated for DC input power.

    A 572B's maximum rating is 160W plate dissipation (per tube). A pair are rated 320W max dissipation. At 65% efficiency, that would yield 492W output power. For intermittent service like SSB, this can be pushed a bit, but it can never be doubled. The 572B is also rated 275mA maximum anode current per tube, and that should never be exceeded.

  10. K9STH

    K9STH Ham Member QRZ Page


    You did the same thing that I did at first when calculating the power output and that was dividing the 320 by 0.65.

    However, the actual power is considerably more. Remember that the power being dissipated is not 65 percent but is 35 percent of the input power. Therefore, to get the input power that will result in 320 watts of power being dissipated is 320 divided by 0.35. This gives 914.3 watts. You then have to subtract the 320 watts that are being dissipated to get the power being delivered to the load.

    914.3 - 320 = 594.3 watts.

    Or, if the input power is 1000 watts and the plate dissipation is 320 watts then the output power would be 680 watts or 68 percent efficiency. 68 percent efficiency is not unrealistic for the SB-200 with good tubes, "stiff" AC power (i.e. 240 VAC), at 80 meters. By the time you get to 10 meters the efficiency is going to drop to between 50 and 55 percent on average. This will mean at 1000 watts input you are going to get between 500 and 550 watts output. Unfortunately, this means that the dissipation within the 572B tubes is exceeded. But, for SSB and even for CW this "overload" is generally acceptable.

    Glen, K9STH
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