Need help from amp builders

Discussion in 'Amateur Radio Amplifiers' started by KN4CTD, Nov 16, 2018.

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  1. WQ4G

    WQ4G Ham Member QRZ Page

    Perhaps you are having parasitic oscillation problems? Are your parasitic suppressors installed? Or perhaps the ones you have installed are not sufficient. Run away amplification due to parasitic oscillations would cause tubes to draw excessive current as you describe (taking off).

    Just throwing that out there.

    Dan KI4AX
     
  2. KN4CTD

    KN4CTD Ham Member QRZ Page

    Yes, they were installed. I’ll check my design again. Thank you for the suggestion.
     
  3. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    I just took a quick first look and that schematic appears to have a lot of errors.

    Bandswitch common connection is not shown, so I can't tell if you're just switching coil taps or shorting sections of the coil as the switch turns -- switching taps alone is a bad idea.

    Filament transformer appears to have its primary short circuited.

    The tubes appear to short to ground on both filament and bias lines (the "supply" side of those lines).

    It appears to show the relay actually switching the B- connection?

    There appears to be a capacitor directly connecting the RF input to the RF output lines when the relay closes. That can't work.
     
  4. KM3F

    KM3F Ham Member QRZ Page

    He is simply not capable of working at this level at this time.
     
  5. KN4CTD

    KN4CTD Ham Member QRZ Page

    I already stated in an earlier post that I did not actually draw out the bandswitching arrangement correctly......I just threw it in there for reference to the rest of the circuit. It uses the exact same bandswitching arrangement as the Kenwood TL922. Im using the multitech industries TL922 bandswitch. The filament transformer is not shorted to ground on the primary side. Not sure how you arrive at that. The grounding at the tubes was MEANT to show the grids directly grounded to the chassis. The capacitor across the input/output relay, is on the NC contacts (standby). Why doesn’t that work? Yes, the B- connection is brought through the NC contacts to the cathode choke (through the 100k) in standby. The bias board is switched into circuit when keyed through the NO contacts thus shorting the 100k out of circuit.
     
  6. VE7DQ

    VE7DQ Ham Member QRZ Page

    Redacted.
     
  7. KN4CTD

    KN4CTD Ham Member QRZ Page

    Thanks to everyone on this forum who has given me suggestions and guidance. Especially the ones who have done so without being condescending. I got the plate current meter wired and shunted correctly (as per the math) using the schematics on W8JI website. I swapped out the original bias board for one that actually works correctly and was able to set the ZSAC to 100ma for the pair of tubes. The tuned input needs more work which I will address soon as it has extremely high input swr on 40, 15, and 10. With 40 or so watts of drive on 80 meters, I’m seeing close to 1kw pep out. Good clean audio was also reported. I guess it is possible to build something as complicated as an amplifier without first drawing a schematic.
     
    WA7PRC likes this.

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