[Hallicrafters] SR-400A output

[james.liles at comcast.net]

Hello Alexander, Walt,

The SR-400A usually has more than adequate drive in CW mode.  V3 is a 6HL8A rather than 7059 doubling the I.F. amplification.

Couple of suggestions along with Walts.  Check the carrier oscillators for USB and LSB to verify they are where they belong.  The USB carrier which is used for CW, tune, and USB is by specification a bit lower than correct design. This moves the carrier about 120 cycles further into the filter band pass than normal in order to pass through the filter at a higher level (Further up the filter skirt than the –25db point.  

The consequence is the USB audio sounds to favor the high side audio.  

A correctly aligned SR-400A will generate more than enough drive in CW and tune mode to max out the finals enabling you to raise the USB carrier frequency 120 cycles for more pleasant audio. 

You can check the drive by wrapping a strap around the 12BY7A attaching your scope to the strap and measuring the voltage.  Full drive is achieved when 46 volts is read.

Kindest regards Jim K9AXN 


Message: 6
Date: Tue, 9 Sep 2014 15:43:27 -0400
From: "Alexander N. Gerli" <ac1wye at gmail.com>
To: hallicrafters at mailman.qth.net
Subject: [Hallicrafters] SR-400A power output
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<CACs0R207OO0bey=7hk8uYxk5EEchGq=1_HXsxpFku6EsdObPDg at mail.gmail.com>
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Hello, Friends,

I'm starting to think about realigning my SR-400A. Hears just fine, but the
power out isn't where it should be. I have several pairs of 6KD6s I can use
besides the pair in the rig.

First of all, the present PA tubes appear to be balanced OK. I can get them
adjusted to within .425 and .427Vdc on J11 and J12 with the rig tuned for
as near 300mA as I can achieve.

What is strange is that my max PO into my Waters metered DL is about 80W in
CW mode. No way that's right. If I go to LSB for instance, and whistle, I
can get easily 175W. This is using 7250kHz. Can't explain the big
difference, except for a need for realignment of the driver stages? I
haven't used the rig for about six months. And, over the past two days,
I've been on several favorite nets with good signal reports. But the PO
seems to be in the tank. Probably needs to have the neutralization checked
as well?

?73,?
??


?Sandy AC1Y?


Alexander N. Gerli, Sr.
548 Allred Mill Road
Mount Airy, NC 27030-2202

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