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


    I did the non-powered up test to be on the safe side. No tubes, 100 ohm R pin 3 to ground, 50 ohm dummy load just to check things out, my mfj-259c analyzer, and manually keying the relay. Analyzer was connected to the amp input.

    I found that on the 10m setting the best SWR is 1.2:1 at 23.9mHz with a 68pf and 5pf cap and the new toroid: T50-6 with 6 turns of #20 magnet wire. This looks like a 12 meter mod, but I still get an off the scale SWR and about 140 watts out max with 60-70 watts in with my radio’s tuner on, so the amp doesn’t tune well on 12 meters.

    In the test scenario, the best SWR on the 10m setting in the 10M band was 1.5:1 at 28.5mHz, although the SWR is still off the scale when connected to my radio. I can get about 200 watts or so out with my radio’s tuner on at 60-70 watts in.

    Before I did the above testing I did pull the tuned input board this AM and reflowed the solder joints just in case. The board ohm’d out fine.

    Maybe something after the tuned input board?

    Thanks again for all the help! I hope I’m nearing the problem...
    W1TRY and KD2ACO like this.
  2. KC5DFP

    KC5DFP Ham Member QRZ Page

    Hi All.

    I finally got the 10 m input board SWR where it should be, it was a matter of the right capacitance. What was needed was a 150 & 35 pF caps, and now my radio sees a flat SWR.

    Also, After doing some research I decided to look at RFC-7, a 2.5mhy choke, which measured 40.7 ohms out of the circuit using an ohm meter to measure it. I think it should measure only a few ohms. Let me know if this is a problem.

    Thanks again.
    Last edited: Oct 20, 2019
  3. W1QJ

    W1QJ Ham Member QRZ Page

    The 1 mh choke used in SB-200/SB-220 amps measure 24 ohms
  4. KC5DFP

    KC5DFP Ham Member QRZ Page

    Thanks Louis. Will dig a bit further into the amp this weekend.
  5. KC5DFP

    KC5DFP Ham Member QRZ Page

    Hi All.

    Been tinkering with the amp and haven’t made much progress on the plate current issue; it still shows drawing roughly 150mA on receive. I did change D1 and C7 today but no change. Also I changed C21 C22 C23 and R4 R5 R6 on the power supply board hoping for improved voltage which is up now from 1,00 volts to roughly 1050 volts or so. The supply now seems stiffer too and the amp seems to have a little bit more output, maybe 20-25 watts.

    Any insight on next steps in troubleshooting the current draw issue is greatly appreciated.
  6. KE0ZU

    KE0ZU Ham Member QRZ Page

    I haven't read through all the posts, however, until you lift the Cathodes off the zener and let them "float" in "Receive/Standby" you're not going to change the situation. Don't know if the stock relay is a two or three pole unit but either a relay with one more pole, or a second relay for the Cathode switching, is needed.

    Last edited: Nov 3, 2019
  7. KC5DFP

    KC5DFP Ham Member QRZ Page

    Thanks for the reply.

    What current rating should the relay be? In thinking about adding a new one to do the mod. Current relay is a 2-pole.

    Thanks Again!
  8. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    The relay contacts for switching cathode bias only need to be rated for the cathode current, which shouldn't exceed 1A.

    But 3PDT "amplifier relays" are very available, including the one from Ameritron they use in all their's a few bucks and they have them in stock. 12Vdc relay coil, and 3 sets of contacts that can handle about 10A per contact set.

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