[AMRadio] Modulator design needed


W5OMR/Geoff w5omr at satx.rr.com
Sun Mar 26 13:38:07 EST 2006


W1EOF wrote:

>I've been gifted a nice mod transformer so I can build a modulator for my
>Johnson 6N2. I don't have a driver transformer so I'm looking for a design
>which doesn't need one. I'm sure the schematics are out there, but I keep
>finding ones with the driver transformer. Same with all my old radio books
>that I've looked at so far. Can someone point me in the direction of a good
>design that is online, or one that you can share with me via email? Thanks!
>  
>

http://www.qsl.net/wa5bxo/driver1.html

Granted, the devices are a bit large for driving something with smaller 
requirements, like whatever modulator tubes are in a Johnson 6N2, but 
you can reduce the solid state device to something that still has 
high-gain, but doesn't require as much Vcc.  Perhaps an ECG198?  
John/WA5BXO (the guy who designed this circuit) uses it/has used the 
circuit with ECG198's in it to drive his push-pull paralle 813 
modulator.  I use this design with the ECG164's to drive the grids of my 
250TH modulator.  The 250TH's will take upwards of 500v pk-pk.  I think 
the 813's only require *maybe* 100?  807's, I believe, are in the same 
range.  Perhaps 811's could be driven with the smaller devices, as well.


>In case anyone is  wondering: I don't want to mod my Johnson Viking to drive
>the 6N2 so I'm building a separate power supply and modulator for it. The
>power supply will server several radios (I also have a Johnson Viking Mobile
>I'd like to fire-up) and I may want to use the modulator on a different rig
>sometime. Considering that this is for a 6M/2M AM rig, all the more reason
>to go this way. So that's why I'm going this route of "separates."
>

I can't think of a better application, than the solid-state audio driver 
for your needs.  For that matter, the modulator, powersupply and driver 
circuit could all be built on the same chassis, with the same microphone 
plugged into it.

Where you might have problems, is figuring out what modulation 
transformer to use.  Different finals, are going to present a differet 
load to the modulator.  Something (more) to think about.

--
73 = Best Regards,
-Geoff/W5OMR

A: Yes.
 > Q: Are you sure?
 >> A: Because it reverses the logical flow of conversation.
 >>> Q: Why is top posting annoying in email?






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