[Boatanchors] Need Globe King 500C Modulator Question

[Sheldon Daitch]

Guess there are two schools of thought.  I've a schematic for the modulator section of a Continental 419-F 250kW transmitter and the spark gap is shown on the secondary of the modulation transformer.  

Interestingly, this transmitter did not use a modulation reactor, as is typical for higher power Class-B modulation systems.  Guess Continental used a large enough transformer that DC saturation of the transformer from the RF PA plate current wasn't a problem.

I inquired of someone who actually worked with that model transmitter when it still had the Class B push-pull modulator section if he remembered how wide was the spark gap.  Said it was too far back for him to recall.  

IBB is still running the 419 series transmitters, but I believe all of them have been converted to the Solid State Modulator and no more classic tube modulation system.

73

Sheldon 
WA4MZZ

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From: Boatanchors <boatanchors-bounces at mailman.qth.net> on behalf of Dennis DuVall <duvallddennis at gmail.com>
Sent: Saturday, December 5, 2015 9:43 PM
To: boatanchors at mailman.qth.net
Cc: Donald Chester
Subject: Re: [Boatanchors] Need Globe King 500C Modulator Question

In the T-368 (Military) the spark gap is on the secondary side of the mod transformer.  No gaps on the primary.  Anyone have any data on T-368 mod transformer failure rates/modes etc?

Dennis D.  W7QHO
Glendale, CA

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> On Dec 5, 2015, at 10:01 AM, Donald Chester <k4kyv at hotmail.com> wrote (in part):
>
> A common practice for protecting the modulation transformer is to place spark gaps across the windings.  The gaps should be wired across the primary, using two gaps, one from each end of the winding to mid-tap, not just one gap across the entire winding.  No gap should be placed across the secondary.

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