WRL Globe 65 Transmitter modifications

Discussion in 'Amplitude Modulation' started by N8FVJ, Mar 29, 2020.

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  1. W2VW

    W2VW XML Subscriber QRZ Page

    If you follow the online prescription for 6146 grid current which applies to applications other than plate modulated AM the rig will not modulate 100%.
  2. WA5VGO

    WA5VGO Ham Member QRZ Page

    I can’t speak to all of these mods, but I’ve owned a couple of unmodified Scouts. They both delivered about 35 watts output on every band except 10 and 6 meters. Both of them delivered very close to 100% modulation. The fidelity wasn’t hi-fi, but was certainly acceptable communications audio.

    In 1968, as a newly licensed general class licensee I literally worked the world on 10 meters AM with my Globe Scout, Knight R-100A and Hy-Gain 18V.
  3. W1BR

    W1BR Premium Subscriber QRZ Page

    Arcing in a 5U4 during warmup either suggests over sized filter capacitors or too low value bleeders.
  4. AC0OB

    AC0OB Platinum Subscriber Platinum Subscriber QRZ Page

    or an unverified, unproven, unnecessary cap placed here:

    ... a .01uF or better yet a .02uF on the rectifier tube output removes that spike. The .02uF capacitor draws about 8ma thus I would use a poly type capacitor vs a ceramic unless that ceramic capacitor is transmitter output rated. I would also use a 4000 volt rated capacitor.

    My simulation shows the following:

    First determine cap reactance; Xc = 265.4k for a reoccurring waveform of 8.3 ms.

    600VX1.4 = 840Vpeak. Assumed current draw = 0.145A;

    Tube resistance Rp = ~ 200 ohms;

    Drop across Tube resistance Rp = 200X0.145A = ~ 30V. 840-30V = 810V at left side of choke,

    IC = 810V/265.4k = 3.05 mA cap current.

    Bleeder draws about 12 ma.

    Last edited: Apr 8, 2020
  5. K9STH

    K9STH Platinum Subscriber Volunteer Moderator Platinum Subscriber QRZ Page

    The last RCA data sheet for the 6146 does show a maximum grid current of 4.0 mA ICAS for plate modulated AM and 3.5 mA for CCS plate modulated AM. However, running either maximum will reduce the life of the tube by a significant amount. For everything else, the absolute maxim grid current is 3.0 mA and for considerably longer tube life the grid current really needs to be kept to no more than 2.5 mA.

    Glen, K9STH
  6. W1BR

    W1BR Premium Subscriber QRZ Page

    Moot point... it is already up for sale on QTH.COM.
  7. N8FVJ

    N8FVJ Ham Member QRZ Page

    Nothing is a mute point as others may want info on the transmitter beside me. Yes it is for sale. Do you track everything I do? It does not make the power output and 100% modulation I wanted. If it did I would not sell it. Ok? I wanted a 25 to 30 watt carrier with 100% modulation so a 40 watt carrier Johnson Ranger slightly de-tuned or lower 6146 voltage with a resistor should work. Why did not post here my want ad for a Johnson Ranger also posted at QTH?
    Last edited: Apr 9, 2020
  8. W1BR

    W1BR Premium Subscriber QRZ Page

    It is hard to avoid everything you do.. telling folks to measure plate voltage in a Class C transmitter with no drive and then comparing plate redness between two 6146 tubes is NOT something I'd want to admit doing. W8JI and others have already beaten the subject to death.
    The use of a voltage divider off of the high B plus to run a VF-1 was discouraged by several knowledgeable posters... why ask if you're not going to follow advice that is given? Plate
    voltage regulation is also important.
    Last edited: Apr 9, 2020
    W7UUU, WA5VGO and AC0OB like this.
  9. N8FVJ

    N8FVJ Ham Member QRZ Page

    I do not profess to know everything. If I did, I would not post questions or ask for info here. But, it is apparent you follow everything I post on the internet. Is not that kind of odd? Are you an internet stalker if there is such a thing? Have you done a background check on me? I did drive speeding a little a few times. No jail time to help you with info.
    Last edited: Apr 9, 2020
  10. AC0OB

    AC0OB Platinum Subscriber Platinum Subscriber QRZ Page

    But that's not what you have done. Let's step back.

    In your first post you purported to tell everyone everything about the Globe Scout 65, and then your expertise on VF-1's, and then gave what appeared to be discordant testing data results on 6DC6's.

    Then after a few more posts in which people attempted to help you it became apparent you lacked much knowledge in tube theory and tube transmitters. I even gave you some references to expand your vacuum tube knowledge.

    For example, no experienced tube gear user here would conscientiously Keydown a 6146 Final with no RF drive; and for what purpose - just to see the plate cherry-up?

    Furthermore, you said you had somehow simulated the rectifier circuit in what was assumed to be a Spice simulator but never posted your .Subcircuit listing, Then you said the Spice simulation required a capacitor at the filament end. You were asked if you had scoped that point to verify that this transient actually existed but never offered any response.

    So why should we take you seriously?

    Last edited: Apr 9, 2020
    W1BR and WA5VGO like this.
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