Saint George

Discussion in 'Amplitude Modulation' started by W7TFO, Mar 9, 2017.

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  1. W7TFO

    W7TFO Platinum Subscriber Platinum Subscriber QRZ Page

    The 'D' series meters I used are safe up to 750V. Their steel cases are directly mounted to the rack panel.

    After that, you get to mount them recessed for safety; Behind glass was very popular for metering HV or RF Amps in transmitters.

    In this case, they are either at less E, or wired after the plate E multiplier, or in the returns for the RF or mod filaments.

    The trick to that is to route your minus side of the B+ separate from the bias returns thru the respective meters so you're not adding the grid current to the readings.

  2. K4KYV

    K4KYV Subscriber QRZ Page

    That's the way I do mine. With the push-pull final I wanted separate grid and plate current meters for each tube so I could readily determine balance, so I had to use separate filament transformers for each.
    N2EY likes this.
  3. W7TFO

    W7TFO Platinum Subscriber Platinum Subscriber QRZ Page

    The HF-300 modulators will have separate windings for the filaments, and the single F-128 final makes it easy.

  4. K4KYV

    K4KYV Subscriber QRZ Page

    What are you planning to use to drive the HF-300 modulators? They take more bias and more grid swing than 810s, so I'm not sure I'd get enough from my quad of 2A3s. Would probably have to go to a pair of 845s to drive them.
  5. W7TFO

    W7TFO Platinum Subscriber Platinum Subscriber QRZ Page

    PP 211's, 'cause I have 'em. And they aren't far off of 845's.

    Plus I finally landed a NOS LS-48, causing unmitigated mirth here.

    N6YW likes this.
  6. K4KYV

    K4KYV Subscriber QRZ Page

    Sweet. And it's easy to change over to 845s if you find a stash. Just re-adjust the bias.
  7. K6BSU

    K6BSU Ham Member QRZ Page

    I guess I missed the real point for powder coating a relay rack. I welded up my own 19" rack for an amplifier. Gave it a coat of auto primer and a spray can coat of enamel. Plenty tough and should last for 100 years!

    The rack is the one on the floor to the left.

    Attached Files:

  8. W7TFO

    W7TFO Platinum Subscriber Platinum Subscriber QRZ Page

    Nice job!

    Building from the bones is a true pleasure.

    N6YW likes this.
  9. KC3EPA

    KC3EPA Ham Member QRZ Page

    Sounds great.
    Why do all commercial AM stations use Pulse Width Modulation.
  10. W7TFO

    W7TFO Platinum Subscriber Platinum Subscriber QRZ Page

    Well, most of them do today, but a few still have vintage gear. Most commercial highpower shortwave stations still run tube gear, using PWM.

    A lot cheaper & simpler to build, especially with sold state for powers up to 50kW.

    Plate modulated finals are a throwback to the Golden Age of analog transmission.

    Excellent audio and livable overall efficiency can be had with tubes using high level modulation.

    Thanks fer the inquiry.


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