Two amps (two 3-500z), different drive input power required

Discussion in 'Amateur Radio Amplifiers' started by K5VV, May 28, 2016.

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  1. K5VV

    K5VV Ham Member QRZ Page

    I have two amps.
    1. Heathkit SB-220 (two 3-500z)
    2. Hammond HL-2000A (two 3-500z)
    The SB-220 requires 55-65W (depending on band) to get 600W out in "CW mode" (2500 V resting plate voltage).
    The HL-2000A requires 80-95W (depending on band) to get 600W out in "CW mode" (2300 V resting plate voltage).

    I swapped the tubes, and the HL-2000A behaved the same (I haven't operated the SB-220 after swapping tubes).

    Does this make sense? Should I be concerned about the additional drive required by the HL-2000A? Does it have something to do with the input circuit?
  2. AF6LJ

    AF6LJ Ham Member QRZ Page

    Don't be concerned;
    Drive levels can depend on many things such as input circuit design, or rather there is an input matching circuit or not.
  3. WA5VGO

    WA5VGO Ham Member QRZ Page

    What's the grid current in each instance? Maybe the tubes in the Hammond have lower emission.
  4. W1QJ

    W1QJ Ham Member QRZ Page

    Although I am not completely familiar with the HL-2000A amplifier, I do have an HL-1000A amplifier which is the single 3-500z version of the HL-2000A . That said, they did not make very many of each amplifier. I highly doubt many on this forum have ever even seen either a HL-2000 or an HL-1000 amp. My HL-1000 amp is a masterpiece of an amplifier as far as the quality of the parts and workmanship. Everything is heavy duty. I recently played around with my amp and found that the input matching circuit is not very good as far as matching the input swr to my radio. On 80 and 40 meters the input swr is respectable but on the rest of the bands it is terrible. It is so bad that the radio cuts way back on power that the amp is useless. Heavens knows what "test radio" they used to set up the input circuits. Obviously with the vintage of this amp, the radios used were tube type finals. Perhaps using the amp with an exciter like that it would be just fine. So, back to your question, if your radio is seeing a poor input swr to this HL-2000 amp you will need increased input power to make the same power as an amp that has a lower input swr. I have not determined the efficiency of the tank circuit of this amp yet. Unfortunately this amp does not have adjustable input circuits for every band. Some bands are adjustable and some are not. That is not a good thing. The reason not many of these amps were sold is obvious to me. The quality of parts and workmanship is far and above anything of it's time. The prices must have been far and above the competition. However, that does not address how well these amps actually worked. All I know is that my amp doesn't work very well with my solid state radio. It looks like my amp is slated for a 6 meter conversion. I am actually excited that you came across one of these very rare amps. The "rareness" of the amp might well make it a collects item. Before I convert mine to 6 meters maybe someone collects these rare amps?
    AF6LJ likes this.
  5. KM3F

    KM3F Ham Member QRZ Page

    There is 200 volts difference in Plate voltage.
    The lower one will require more drive. all other things being equal.
    It's Plate current and Grid current will also be higher for the same output..
    No mystery here.
    Good luck.
    KA9UCN and AF6LJ like this.
  6. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Yes, the plate voltage makes a lot of difference and so does the input circuit.

    I'd run them both at full Ep and see what the difference is. They're probably both a bit low on Ep even in the SSB position.

    Henry amps and the AL-82 run the tubes at higher voltage where they have more gain, and they also have good input circuits so they don't require much drive for full suds.
    K8PG and AF6LJ like this.
  7. W1QJ

    W1QJ Ham Member QRZ Page

    And while we are on the subject of plate voltage variation I have to say once again that all these older vintage amps that have these CW/SSB switches that change the plate voltage are a WASTE by today's standards. These switches were put on these amps for one sole purpose. That purpose had to do with legalities. That goes back and ties into the old power rule of ONE KILOWATT DC INPUT TO THE FINAL STAGE. That would have been the "key down power" read as input power by the meters. At the same time it was allowed to run 2 KW PEP INPUT SSB. The 2KW PEP INPUT SSB is not the same as one kilowatt DC input. It would have been technically illegal for the amplifier manufacturer to tell you to load the amp to 2 KW input in the manual. So what they did was to vary the plate voltage in such a way that "in theory" if you loaded up to 1 KW DC input on CW, that would be the "loading" and plate voltage you would use in a "full carrier" mode like CW. However, if you were to run SSB that was a different story, now it was 2 KW PEP input. Since it would be illegal to load the amp to that level with a full carrier the assumption was that when you flipped the switch to the higher plate voltage, and since the amp should be linear, the amp would "in theory" already be properly loaded for the PEP input value allowed. So you can see that the switch was a "work around" of the rules. BTW... when certifying an amplifier with the FCC to obtain type acceptance, the actual manual writing is scrutinized just as well as the technical part of the amp. Therefore whatever the claims are for the amp to meet certain specifications, the manual must coincide with the specifications when they give loading instructions. Anyhow, back to the plate voltage CW/SSB switch. An older amplifier that has these switches, and to name a few, Heathkit SB-220/1 etc. Kenwood TL-922, Clipperton L, Henry amps, PT-2500 amps, and the list goes on. All these amps can now simply run the full SSB voltage in any mode, can legally be loaded up with a "full carrier" mode at that voltage and operated at full power. This from a legal stand point. Now depending on the nature of the operation one would have to consider if the amp will be up to the duty cycle of that mode of operation. For myself, who was always (and still is) a DXer, I would run my SB-220 at full power on CW and SSB because when calling for DX, the duty cycle is rather low, compared to running voice keyers and "auto CQ contest" keyers during contests. I recommend using the highest plate voltage on all modes and adjusting the drive level, hence the power output to a level that is prudent for the mode of operation I am using.
  8. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    That was a long diatribe, Lou.

    But I agree. No reason to use the 'CW' position in any of these amps today. For those in countries with lower legal output power restrictions than the U.S. has, run them in SSB anyway and reduce drive.

    The 'CW/SSB' switch was a weak link in many amplifiers and destined to fail. First thing I did in many of them is jumper that switch so it was out of circuit and didn't do anything.
    KP2XX and AF6LJ like this.
  9. WA7PRC

    WA7PRC Ham Member QRZ Page

    As long as your rig has enough "steam" to drive whichever amplifier to maximum output, does it matter?
    KP2XX and AF6LJ like this.
  10. K5VV

    K5VV Ham Member QRZ Page

    I have the wrong resting plate voltages in the OP. The HL-2000A is 2500V and the SB-220 is 2300V (thus that doesn't explain the HL-2000A needing more drive).

    The input SWR is okay on both amps on 20m & 40m. On 12m, the input SWR of the HL-2000A is a bit high but I've turned on the internal tuner of the exciter so it can still deliver the full drive.

    Interesting comments on the CW/SSB. I thought the concern was whether or not the amp could handle 100% duty cycle in SSB mode while tuning.

    Nope, just curiosity. When I first noticed it, I assumed one set of tubes was "better" than the other but apparently that's not the case.
    KD2ACO likes this.

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