Help With Modulator

[N0WVA]

 Hey guys,

I just scored this thing for 20 bucks, I dont know what its out of, but it looks like an audio amp. Id like to use it to make my SG modulated pair of 807's plate modulated.

I was wondering if the output transformer looks familiar to anyone, and will it feed the plates of two 807's directly? It has multiple taps and I havent a clue as to how they should be wired.

Thanks, Doug N0WVA

[Steve - WB3HUZ]

That mod transformer is a Stancor A-3894. It's a multi-impedance unit rated for 125 watts. You can find the connection info at the link below.


http://www.amwindow.org/tech/htm/modtran/stancor/stancor.htm

Hey guys,

I just scored this thing for 20 bucks, I dont know what its out of, but it looks like an audio amp. Id like to use it to make my SG modulated pair of 807's plate modulated.

I was wondering if the output transformer looks familiar to anyone, and will it feed the plates of two 807's directly? It has multiple taps and I havent a clue as to how they should be wired.

Thanks, Doug N0WVA

[KE6DF]

And here are some pages from an old Stancor catalog describing the A-3894

(sorry I couldn't get the attachment to work)

I can send you the catalog by email if you want. It's too big to attach.

[KI4YAN]

And here is a likely circuit for that modulator:

http://viewoftheblue.com/misc/807_1.png
http://viewoftheblue.com/misc/807_2.png

I have nearly the same thing, found it in a scrap heap. I'm planning to modulate an 812A with it.

[w1vtp]

And here is a likely circuit for that modulator:

Which is out of a 1954 ARRL handbook for those of us who have a collection.  Nice.  I have similar plans down the road.

Al, "Violet Toilet Paper"

[w8khk]

The 53 and 54 ARRL HB cover the PP 807 mod using 6SJ7, 6J5, and 6K6 in the speech amp, as in the links provided by 'YAN above.

Doug, your photos show a 12AX7 and 6C4 in the speech amp.  The 55 HB pp 243-245, the 56 HB pp 254-256, and 57 HB pp 261-263 all have a closer match to your speech amp driving the PP 807 modders. 

Layout is different, using hollow state rectifier bridge, while yours apparently has SS diodes below chassis. 

Also yours has VR tubes, likely to regulate the 807 screens, which the HB versions listed don't have. 

Playing with various plate and screen voltages, with appropriate mod tranny primary impedance, can yield anywhere from 40 to around 100 watts AF.

Hope these references help with your resoration efforts.

[Steve - WB3HUZ]

Cleaned up the schematic some.

[N0WVA]

Thanks for the help guys! Thats the info I needed...

Doug

[Opcom]

Hey guys,

I just scored this thing for 20 bucks

You got a real bargain there! nice to see regulated (screen?) voltages on it.