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Old August 2nd 07, 08:39 PM posted to alt.binaries.pictures.radio,rec.antiques.radio+phono
Don[_5_] Don[_5_] is offline
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First recorded activity by RadioBanter: Aug 2007
Posts: 1
Default Design help: Modulator schematic

Brenda Ann,

There are several ways to go here. First, the specs for the
modulation transformer- impedance, watts, and if it is for push-pull or
single-ended. From that, we can get the right tubes, maybe a pair of 6V6 or
6AQ5. Those tubes are happy with 185 volts. If your modulation transformer
can use the 6L6, you can easily change the power supply circuit to a "Full
Wave Voltage Doubler" and I can e-mail the RCA circuit. Is this circuit
designed so the current for the 6L6 and the current for the transmitter tube
are on separate windings that cancel each other out? The transmitter may be
a bigger headache than the modulator, and this power transformer may limit
the choices, as it is small.
Don

As someone else said, you have a major problem with the power supply.
The output voltage should be much higher.


I think I have kenned out what that problem IS. It's not a 250-0-250..
it's a 125-0-125 on the secondary.. which would output pretty much what
I'm getting.


This is my transformer. From Mouser

http://www.hammondmfg.com/pdf/5c0030.pdf #261G6
261G6 45250V C.T.@ 130 ma 6.3V @ 2A 1 4.00 2.50 2.63 3.56 2.0


What is the modulation transformer you're using?

If it's a mains transformer it could be going into saturation. Proper
modulation transformers are designed to accomodate a d.c. bias through the
windings which normally requires an airgap in the core. In an ungapped
core the dc bias will drive the core somewhere up the BH curve and the
effects will be exactly as you describe - clipping on one of the peaks