View Single Post
  #16   Report Post  
Old August 3rd 07, 06:03 AM posted to alt.binaries.pictures.radio,rec.antiques.radio+phono
Jim Mueller Jim Mueller is offline
external usenet poster
 
First recorded activity by RadioBanter: Apr 2007
Posts: 91
Default Design help: Modulator schematic

You're right about the power transformer. 250VCT means 125 - 0 - 125. You
could use it with a full wave bridge if your load current isn't too high.

Measuring the inductance of the modulation transformer won't help much.
What you need to measure is the turns ratio. Then you need the load
impedance which is determined by the operating conditions of the RF
amplifier you are modulating.

If you want to keep the power supply as it is, a better output tube would be
a 6Y6. You will need to use a resistor to drop the screen voltage though.

--
Jim Mueller

To get my real email address, replace wrongname with eportiz. Then replace
nospam with sacbeemail.

"Jim" wrote in message
...

"Brenda Ann" wrote

As others in the other group have mentioned, you're pushing your luck
with 600V diodes. They have over 700V on them (or they would have if
things were working right). Replace them with 1000V diodes. This also
means you need to replace those capacitors with 1000V capacitors,
preferably AC rated.

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