My favorite style was the Collins 75a series
I use a 75A4, which is often bashed by the AM folks, but I find it to be
about the best receiver I have ever tried. If I find a truly superior
receiver to the A4, I'll retire mine and change over to that.
The main deficiency of the A4 is the audio. I use an outboard AF amp (an
old 50's vintage 10w hi-fi amplifier using a pair of 6V6's in pushpull). I
changed the .01 mfd coupling caps in the low level audio stages of the
receiver to 0.1. Actually, I just bridged the .1's across the originals, to
minimise melted plastic insulation on the wiring in the receiver. I pulled
out the original 6AQ5 to save unnecessary drain on the power supply and to
reduce heat generation. I also clipped out a couple of 510 pf mica caps
that were added in later models to attenuate the high frequency response.
From the diode detector to the audio output, the frequncy response is now
almost flat from 30~ to about 5000~.
On one of my A4's I added an outboard box with additional mechanical
filters. The stock 3 selectivities is not enough if you want cw, ssb plus
optimum AM under a variety of band condx.
Don K4KYV
_________________________________________________________________
Want to check if your PC is virus-infected? Get a FREE computer virus scan
online from McAfee.
http://clinic.mcafee.com/clinic/ibuy/campaign.asp?cid=3963
