[AMRadio] Modulator question

John Lyles jtml at losalamos.com
Mon Feb 1 02:21:28 EST 2016

In modulator service in class AB1, the screen should be run at about 300 
volts DC and no more. It will run very hot above this. It should be 
regulated if possible. I built a replacement screen modulator for the 
1625s in a DX100, using EL34s. I made a simple regulator for the screen 
run off a divider from the 6146 plate voltage. The connection seen in 
some old audio amplifiers shows ultra-linear transformer connection 
where the screen is connected to a tap on the output transformer which 
does put the plate voltage DC level on the screen but it also has a 
percentage of the output AC voltage on it. I wouldn't recommend this 
unless you have the Acrosound ulta-linear transformer.


Message: 6
Date: Sun, 31 Jan 2016 07:38:46 -0800
From: Paul Baldock <paul at paulbaldock.com>
To: Jim Tonne <Tonne at Comcast.net>,amradio at mailman.qth.net

The screen is not tapped on the mod tranny. It is pure DC. at about
half the plate voltage.

I think however the issue may be related to the screen, because in a
typical EL34 output the screen is run at the same voltage as the
plate. I did not do this because my plate voltage is about 660V.  I
will try upping the screen voltage (and readjusting the bias of course)


- Paul

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