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Collins 30 L 1 Question

Discussion in 'Amateur Radio Amplifiers' started by N7WR, Aug 15, 2021.

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  1. N7WR

    N7WR Premium Subscriber QRZ Page

    I recently bought a 30 L 1 which has extensive mods. It came with 572 B tubes installed. With 80 watts of drive it outputs 500 watts max. That's really all I need but my questions are: Should it do more like 600-700 watts even though I will keep it at 500; I have a full set of NOS 811A's which is what the amp was originally built around. If I wanted/needed to swap tubes any problem with just replacing the 572's with 811A's? I can't see any mod (and I have all of the mod documentation) that would preclude swapping back
     
  2. N8VIL

    N8VIL Premium Subscriber QRZ Page

    If the 572 tubes are good, I would use those as they have higher dissipation rating than the 811 tubes and are more robust. It would seem that you should be able to get a bit more power for a short duration but I will leave those that are more familiar with this amplifier to answer that question.
     
  3. WA2EIO

    WA2EIO XML Subscriber QRZ Page

    The 572s will take a bit more abuse since they have a higher dissipation rating (helpful if you are new at tuning a tube amp to extend the life of the tubes.) than the 811s but the power supply will not be able to produce the extra current/voltage to take advantage of the higher power capability of the 572s, so either can be used without any modification to the amp. 500-600 Watts is what should be expected from the 30L-1 with about 80Watts of drive. Are you using ALC? Some suggest that it is not necessary.
     
  4. W1QJ

    W1QJ Ham Member QRZ Page

    The power supply in those amps should be rebuilt with a modern kit sold by a few vendors. Once that’s done you are assured that the maximum efficiency will be obtained. The manual tells you to use a special circuit that the amp has to load it up. Unless that circuit has been properly adjusted you may not be getting maximum output. You should use conventional loading procedures first and then compare output to the suggested method to check to see it’s adjusted properly, if not don’t use it or align it properly. Personally o do not use the method suggested as that is a crutch for not knowing the usual method that is foolproof. With a power supply rebuild and on a 240v line and good tubes, these amps should easily deliver 700 watts output with no problem. With today’s line voltage vs the old designed line voltage of this amp, pumps the plate voltage to 2000 volts. The last few 30L1 amps I went through and upgraded with power supply kits, soft key and new tubes all easily did 700 watts with convential tuning.
     
  5. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    That makes sense.

    At 2000V, I'd sure stick with 572Bs -- 811As were never rated for anything close to that.

    Also if used on a modern 120/240V line where the actual voltage might be 125/250V (as it often is here where I am), I'd think either 811A or 572B filament ratings will be exceeded, making for shorter tube life unless something is done internally to reduce the "loaded" filament voltage at the sockets.
     
  6. KJ7MX

    KJ7MX Ham Member QRZ Page

    That was my experience after installing the Harbach board and replacing some of the grid circuit components. With a fresh set of 811s, It will do 700 out. As a side note, it had sat 20+ years before the refurb. Runs better than it did before it was mothballed lol!
     
  7. KA4KOE

    KA4KOE Ham Member QRZ Page

    I never drive my 30L1 with more than 70W, per the manual. 500W outpoot.
     

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