Dentron GLA-1000B... a few things I need help with

Discussion in 'Amateur Radio Amplifiers' started by KC5DFP, Sep 26, 2019.

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  1. KC5DFP

    KC5DFP Ham Member QRZ Page

    Hello Everyone, and thank you for reading my post.

    I just picked up a GLA-1000B recently and have a few strange things going on with it as follows and hoping you can help.

    1) With the amp turned on and the function switch set to current, the meter reads just over 100 mA. This is with the transceiver in receive, so the amp is not keyed. I have a GLA-1000 (first gen) which shows no current draw when in the same condition. Diodes? Tubes? Other...

    2) On 10M the tuned input board doesn’t seem quite right as I get a very high SWR, greater than my radio can measure, between the amp and the radio that cannot be corrected without using my radios internal antenna tuner (IC-7300). All other bands show a good/flat match without my radios internal tuner. I don’t know if there’s a problem with the 10 m components on the tuned input board, or perhaps something else. I haven’t checked/cleaned the contacts yet but will tonight.

    Also, on 10M the amp puts out 250 watts and this is with my radios antenna tuner engaged and the radio driving the amp at 80 watts or so, but on the other bands the amp puts out roughly 500 watts. Not sure if these are related, or something completely different.

    3) A resistor was been added to the tube section for what I don't know and can’t seem to find anything on it. I’ve posted a pick of the for your viewing pleasure, in hopes you might now.

    Any insight is greatly appreciated. This is a cool little amp that I’m hoping to get back to working order. Thanks Again!


    Attached Files:

  2. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    First, someone must have added the 10m modification kit, since the base model covered only 80m - 15m. But I know Dentron did offer such a kit. Possibly there are wrong (or failed) components in the 10m section.

    The power resistor in your photo appears to not connect to anything on one end, and I have no guess why it's there.

    It also appears someone changed the output coupling capacitor C11 as there's a splice in that wire that's not normally there and the original capacitor was a doorknob type that doesn't seem to be showing in your amp. Should look more like this;

    If the amp is drawing current in standby, either D1 is shorted or the wrong value, or you have a bad tube (or tubes).
  3. KC5DFP

    KC5DFP Ham Member QRZ Page

    Hi Steven.

    Thanks for the reply, and direction on the current draw issue. I’ll definitely check those out tonight.

    As for the resistor both ends do terminate into the wound inductor, the picture doesn’t show it well. I to question what it’s there for and would like to understand it.

    As for the C11 cap, the original one probable failed and the previous owner installed the replacement. I thinks it’s fine, and attached a pic for your comment.

    Thanks Again.

    Attached Files:

  4. KA0HCP

    KA0HCP XML Subscriber QRZ Page

    These amps are almost 40 years old. Have you gone through it checking the values on all the resistors?
  5. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Wow, in your picture it really looks like a piece of yellow insulated wire is soldered to one end of the resistor and the other end of that wire is just stripped and laying there, connected to nothing. Where does that end actually "attach?"

    The little insulator block at the other end of the resistor isn't original, either. I'd remove all of that.

    The capacitor you showed isn't as good as the one originally used, but might handle the job for a while. The real issue isn't the voltage rating, it's the RF current rating and dissipation factor, based on the dielectric.
  6. W1QJ

    W1QJ Ham Member QRZ Page

    What I see is the Dale type resistor is being used as a glitch resistor and it is in turn connected to a "hair" of a single wire strand being used as a fuse. That is what I see.
    NQ1B, W1TRY and KK4RSV like this.
  7. KC5DFP

    KC5DFP Ham Member QRZ Page


    D1 checks out fine; reading an open in reverse bias and .83V in forward bias co diction. When I removed one tube at a time, following HV practices of course, the current meter readings dropped with each tube removed down to a slight movement of the meter with 1 tube in. Given this I think another set of tubes is needed, luckily I have a set!

    As for the resistor, further examination reviewed the plate choke wire at the bottom of the choke that goes into the PCBA was cut and onnected to the resistor, and from the other end of the resistor back to the plate choke at the bottom where it was cut, basically putting the resistor in series with the plate choke. The wire you thought was lose is actually the segment going back into the PCBA. Any ideas?

    Also I did clear the band switch contacts but no luck on the 10M SWR reading. I noticed there are only 4 turns of wire on the 10M toroid core and I think it should be 5.... not sure but I recall reading this somewhere.

    If anyone have this amp with the tuned input board perhaps you can check this for me.

    @KH0HCP, I haven’t check the various components but will start to...

    Anyway, thank you all again.


    Attached Files:

  8. KC5DFP

    KC5DFP Ham Member QRZ Page


    That’s exactly what it’s configured. What’s the purpose for having this?

  9. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    A glitch resistor on a 900V power supply is really a bit unusual. Placing a metal resistor like that against the chassis with 900V from terminals to ground is not only unusual, but a bit stupid.

    I'd get rid of it.

    "Glitch" resistors are to protect tubes (and maybe power supply components) from an ion arc internal to the tube(s). Usually found in high voltage systems (2-3-4-5kV) powering tubes known to occasionally have ion arcs from gas. 6LQ6s and such are not known for this.
  10. KE0ZU

    KE0ZU Ham Member QRZ Page

    For the 10 meter problem, you might check the relay and the PCB soldering. The filter board on my Clipperton "L", was 2 sided, but the holes were NOT plated through, and there were no crimped eyelets, to connecting traces on the two sides of the board together. Yeah, I know, different amp, but the filter board, and problem may the same.


    Steve is right, although well intentioned, the glitch circuitry is very poorly implimented, and unnecessary.
    WA7PRC likes this.

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