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Dentron GLA 1000 performance

Discussion in 'Amateur Radio Amplifiers' started by N6UH, May 30, 2020.

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  1. N6UH

    N6UH Ham Member QRZ Page

    I have been working on GLA1000, plain vanilla (no suffix).

    It had been unused for at least 15 years and in original unmolested condition apart from the 10m mod.
    There appears to be 1 or 2 versions of the original design. This one had an 8v zener permanently wired from cathode to ground for setting the bias although the relay had a set of unused changeover contacts. I have added a 50k resistor and switched the diode in on tx only using the spare contacts.

    It has 4 Dentron branded D50 tubes which I am assuming are original and just a branded sweep tube? This version has all 3 grids grounded.
    I have recapped it and replaced the equalising resistors which were way long.
    Here's what I get:
    Around 1100v on the meter no load
    Approximately 50ma key down idle current. It's difficult to be accurate as the plate current meter increment is 100ma but it's about half way to 1 division
    If I drive it with 85w of carrier from the HT-44 I get 500w out on 80m and around 450 on 1om when tuned using a dummy load. The plate voltage drops to around 875v and the current is around 1 amp.
    The numbers in the manual are 800v at 1.25 amps for 1kw in.

    Am I in the ballpark here?
  2. KA0HCP

    KA0HCP XML Subscriber QRZ Page

    Sounds pretty good. Key to tube life longevity is NOT running it hard [and keeping tune up short, short, short]! ;) Edited
    Last edited: May 30, 2020
  3. KA0HCP

    KA0HCP XML Subscriber QRZ Page

    Yes, the tubes are just OEM branded 6LQ6 tubes. Standard stuff for the industry.
  4. WB4IUY

    WB4IUY XML Subscriber QRZ Page

    I have one of Denny's later versions, the LA-1000 (Amp Supply), at one of my operating positions. Basically the same amp, but only the screen and buffer grids are grounded, the control grid is tied to the cathode and biased at abt 24vdc with a switched zener. About the same power as your GLA, and no plate heating with 65w drive after long SSB QSOs. The 6MJ6's were a tougher tube, but these 6LQ6's are decades old and still running fine.
  5. N8FVJ

    N8FVJ Ham Member QRZ Page

    With only Chinese making 811A, 572B and 3-500ZG tubes that have many early tube failures, IMO you are better off with a sweep tube amplifier. 500 watts carrier out is above tube specs after a few seconds. However, the amp will produce 500 watts PEP output and maintain long tube life.
    I have lost a few Chinese 811A and a 50 hour old 3-500ZG tube ($230 replacement cost). Sold the 811 and 3-500z amps and now using a Yaesu FL-2500 sweep tube amp with the reliable sweep tubes and replacement NOS tubes are much less than a 3-500Z. I been taking a beating from other hams here and other sites stating I am using a sweep tube amp. Some state sweep tubes amps are CB radio amps- nonsense.
    Cheaper 6ME6 works perfect in your amp replacing the expensive 6LQ6 tubes. Findatube has inexpensive 6ME6 if you ever need replacement tubes.
    BTW- post above states 6LQ6 are decades old. So much for others stating sweep tubes do not last long. So much 'garbage' being posted now-a-days.
    WB4IUY likes this.
  6. KD2ACO

    KD2ACO Platinum Subscriber Platinum Subscriber Life Member QRZ Page

    Sweep tubes can make awesome audio power amps too. You just have to know how to bias and load 'em.

    Emission for days and high trans-conductance too. Little fire-bottles they are.
    W1BR likes this.
  7. N6UH

    N6UH Ham Member QRZ Page

    So it appears to be working to spec. It's uses here are limited because of the absence of tuned input circuits. I may keep it as a backup or just move it on.
  8. ND3L

    ND3L XML Subscriber QRZ Page

    The GLA12000 (n0 suffix) I'm told has no tuned input so power out varies band to band. Use antenna tuner to tune swr and power vwill increase somewhat. Newer GLA1000 (with suffix) has tuned input and doesn't have that problem.
  9. W1BR

    W1BR Premium Subscriber QRZ Page

    I just wish the tube manufacturers gave specs for other than horizontal output service in the manuals. Very hard to find data for Class C, AB1 or AB2 service,
    never mind CCS or ICAS for ham use.

  10. W1QJ

    W1QJ Ham Member QRZ Page

    That’s because it was never an intended use for them.

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