[Collins] wider audio for 51J4?

[Dr.Gerald N. Johnson]

Dr. Gerald N. Johnson, Electrical Engineer
----- Original Message -----
From: C E [mailto:catman351 at yahoo.com]
Sent: 6/13/2006 2:17:03 PM
To: ehertz at tcaf.org;collins at mailman.qth.net
Subject: Re: [Collins] wider audio for 51J4?

> I think the 51 J family seems to suffer from
> unreasonably tight audio. Can anyone else confirm?
> Cal, N6KYR/8
> 
> 

Since the 51J family was mostly used for communications, not super hi fi broadcast listening, its highly likely the coupling capacitors in the audio stages roll off below 250 - 300 Hz and there might be a shunt capacitor or two from plates to ground to "build out" the output transformer and to make a relatively sharp cutoff to reduce high audio frequency noise to the speaker. I don't have my 51J-4 manual close (about 360 miles at the moment) so I can't check the schematic. Likely tapping audio off at the detector load to a wider audio amplifier (as is handy in the R390()) would give wider hi - fi audio. Likely taking off the shunt capacitors, increasing the coupling capacitors and adding some feedback from an unbypassed cathode resistor or a shunt feed back network from speaker winding to first audio cathode (taking care to keep the phasing right so its negative feedback) could be another way of increasing the audio bandwidth, but the added bandwidth would probably not improve the receiver as a communications reciever, its primary design.

73, Jerry, K0CQ, Technical Advisor to the CRA