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. KD2ACO

    KD2ACO Platinum Subscriber Platinum Subscriber Life Member QRZ Page

    It was beautiful on the water and I still have 2 kids so we didn’t flip the boat upside down. Rock star friends here and the studio repair took about 40 minutes because I did my homework. The rest is all fun. :p
     
    Last edited: Sep 30, 2019
  2. KC5DFP

    KC5DFP Ham Member QRZ Page

    All,

    Finally got a moment to post.

    I order the two tuned input caps as well as the c11 door knob cap. Should have all of them by the W/E, so I’m excited to get the amp on the air soon.

    I’ll post accordingly.

    Thanks again.
     
  3. KC5DFP

    KC5DFP Ham Member QRZ Page

    Hello everybody.

    Wanted to let y’all know I did get my components in today and I installed them in the amp: two caps on the tuned input board and C11 door knob cap.

    No luck on the 10 m tuned input as there’s still an off the scale SWR reading. I’ll have to dig into it more over the next couple days.

    I’m hoping that someone has the same a.m. and can look at the actual values of the two capacitors just to verify I do have the correct values as well as how many turns on the toroid core for the 10 m tuned input.

    Again any help is greatly appreciated.
     
  4. KC5DFP

    KC5DFP Ham Member QRZ Page

    Hello everybody.

    Wanted to let y’all know I did get my components in today and I installed them in the amp: two caps on the tuned input board and C11. No luck on the 10 m tuned input as there’s still an off the scale SWR reading. I’ll have to dig into it more over the next couple days.

    I’m hoping that someone has the same a.m. and can look at the actual values of the two capacitors just to verify I do have the correct values As well as how many windings on the torrid core for the 10 m tuned input.
     
  5. KC5DFP

    KC5DFP Ham Member QRZ Page

    Also, I suspect the 10m toroid on the tuned input board may have been tampered with as the wire isn’t as tightly wound as the other toroids.

    I have an MFJ antenna analyzer and am wondering if I can connect it to the amp input, switch the amp on and sweep the band to see where it’s resonant, but I’m concerned I’d fry my analyzer. Would this be the case or is it safe to do this?

    Thanks again.
     
  6. W1QJ

    W1QJ Ham Member QRZ Page

    Those amps had 10/11 meter filters installed in them from the factory. This was to satisfy the FCC so it would not make power on 11 meters. I have seen these filters all the time on the "no input network" models. I haven't actually seen one with the input network board like yours so therefore they may have done some other method of deleting 10 meters on the input board itself. There could be an unseen grounded jumper on the 10 meter input switch connection on the board that needs to be removed. The problem is you probably wouldn't know what they did to delete 10/11 meters even if you were looking at it. The amps that had the filter trap for 10/11 meters WAS NOT SHOWN on the schematic and countless times over the years someone would come to a group and ask what that trap was because they did not see it on the schematic. They knew they were looking at "something" that was not shown but had no idea what it was. First time I encountered one I was puzzled as well but for about 2 minutes until I figured it out. Removing it or shorting across it would then enable 10 meters. Seeing that that one was a later model or a "special" they may have used a different method or a combination of methods of disabling 10/11 meters. In the past Dentron/Amp Supply used different methods of accomplishing this. The ones I saw over the years were the following, some had any combination of them all.
    1. Band switch did not advance to 10 meter position......Required a switch modification on the stop
    2. No connection from the band switch to the 10 meter tank coil location on the coil........Supply your own connection was needed
    3. No parts supplied on the input board for 10 meters..........had to know, find, install, the correct parts to enable
    4. 10/11 meter trap filter on the input to the cathode........remove and replace with single coax or short around the filter.

    Those were the Dentron/Amp Supply techniques, a similar technique was used by Kenwood on the 922a, they used the non-advancing of the band switch to the 10 meter location, missing the input caps on the 10 meter input coil and required a jumper on the band switch contacts to enab;e the connection to the tank coil. Heathkit SB-221/201 amps.....Both these amps would not advance the band switch to 10 meters, they were void of any input circuit for 10 whatsoever, neither the input or band switch had any contacts on the wafers for 10 meters even if you wanted to install the parts, you would still require additional contacts on the switches. Probably the most radical of all amps to get 10 meters on.

    So as far as your amp goes, a full exam of your amp is needed to see what is going one there with what is needed to restore 10 meters. Perhaps more photos of the inside of the amp and the input board and maybe even the back of it is needed for further analysis.
     
  7. KC5DFP

    KC5DFP Ham Member QRZ Page

    Hi Louis.

    Thanks for the responSe.

    I did go through the 10 m mod instructions and it appears that the 27/28 MHz blocking circuitry has been removed, the coax is routed properly, and all components on the tuned input board and connections are made to enable transmit on 10 m including the band switch moving over to the 10 m position.

    I suspect that the 10 m portion of the tuned input board might have been modified for another frequency, perhaps the CB band. Not sure if this is the case but the 10 m components look to have been previously re-soldered which leads me to believe that those components might have been changed. I see pictures on the net of the same amp having different cap values for 10m so I’m hoping someone with the same amp can tell me what those values are. Also I ran across a schematic last night that showed different cap values, so I’m leaning towards the amp was nodded at some point.

    I’ll do a detailed review tonight and will take and post pictures accordingly.

    Thanks again for all the help
     
  8. W1QJ

    W1QJ Ham Member QRZ Page

    What kind of swr does your radio see on 10 meters with what you’ve constructed for a 10 meter input circuit? Even if you had a high swr a couple of watts getting in would show some amplification. Do you see any sign of output at all?
     
  9. KC5DFP

    KC5DFP Ham Member QRZ Page

    Louis,

    My radio with its tuner turned off sees a pegged SWR reading (full scale so infinity I guess) and power folds back to somewhere around 10 watts (my guess). Although, the amp puts out about 50-75 watts or so.

    If I put the radios tuner in line, which barely tunes it, but can’t hold the tune, so the radio folds back power a bit to about 30 watts and the amp puts out about 150 watts out or so.

    All the other bands. 15, 20, 40, & 80 work fine and my radio shows a flat SWR.
     
  10. KC5DFP

    KC5DFP Ham Member QRZ Page

    All,

    Was looking over the 10m toroid and saw this. Looks like it’s seen better days but not sure if this is a problem.

    I’ve not heard of a core going bad, but maybe, but I’m thinking the wire insulation might be gone and it’s touching the core.

    Any thoughts??

    I plan to take it out tomorrow and do a closer inspection, but let me know.

    Heres a pic. You can see the new caps added too.
     

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