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Viking ranger attenuator 4-400a grounded grid amplifier help

Discussion in 'Amateur Radio Amplifiers' started by KC0VVB, Nov 23, 2019.

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  1. KC0VVB

    KC0VVB QRZ Member

    Well, I just hooked up the sb-610 monitoring scope to the ranger last night.
    Without the attenuator I was able to get a really good looking signal it took more drive than I would have expected the knob was cranked to the 3:00 position.
    The audio pot was turned to the 12:00 position but any increase after that had no effect. 40 Watts carrier filled up the first two grid lines above and below the center. With modulation voice peaks reached the 3rd grid line above and below the center grid. The watt meter shows 80 Watts peak.

    With the linear in line the sb-610 showed the exact same wave form. 400w carrier modulated produced 800w peak. I believe the linear is perfectly linear. Faithfully reproducing the signal from the ranger to quote an old computer saying garbage in garbage out. I may need to investigate the audio pot to figure out why there is no response above the half way point.
    Erik kcovvb
  2. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    A "good looking signal" doesn't say anything about % modulation.

    Did it look like the "100% modulation" waveform below? Or did the RF envelope not "close" between modulation crests (positive peaks)? Did it look closer to the "50%" waveform shown?

    Ideally, you'd want it to look much like the "100%" waveform, with both negative and positive cycles resembling a sine wave, or at least smoothly following your voice waveform.
  3. KC0VVB

    KC0VVB QRZ Member

    The rf envelope did not close it looked close to the 50% modulated wave form symmetrical sine wave smoothly following my voice. More like 40%.
    The ranger is responsive to audio control the peaks extend upwards as the valleys drop toward the centerline.

    I am having thoughts of replacing the mini coax that runs from the mike jack to the modulator section. I also remember a couple of resistors being buried in the coax braid near the tube sockets that would be out of spec by now. I could try another d104
    microphone that i have lying around the shack. I think I am having an audio input issue.
    Erik Kc0vvb
  4. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    You'll never achieve PEP of 4x carrier power unless the envelope looks about like the "100% modulation" envelopes shown in the images I posted.

    I don't know if the Ranger was actually capable of 100% modulation or not, although I had one a very long time ago and it sounded okay on AM. That was in about 1966 and it was third-hand at the time but in good condition.

    My homebrewed 4-250A rig with P-P 811A modulators hits 100%, and since I still have it, I've checked it lots of times. It can run a 100W carrier fully modulated, about 400W PEP indicated on everything. It only has a 2000V B+ supply which sinks down to about 1850V key-down.

    I'd use AM more if the "rag chews" didn't go on forever. I like rag chews but not when each transmission is 10 mins long...I can't be entertaining for more than about two minutes at a time.:p
    KD2ACO likes this.
  5. KD2ACO

    KD2ACO Platinum Subscriber Platinum Subscriber Life Member QRZ Page

    You beat me by about a minute! :p
  6. KC0VVB

    KC0VVB QRZ Member

    Yea me either, I switched the ranger to a surge protector by itself rather than sharing with the hallicrafters sx- 100, both amplifier fans, the watt meter, and the scope. I was able to get 120w peak with 40w carrier. The wave wave form looks like 75%. Thanks for all your help Steve.

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