[AMRadio] stock or mod

Todd, KA1KAQ ka1kaq at gmail.com
Tue May 30 15:03:05 EDT 2006

On 5/30/06, W5OMR/Geoff <w5omr at satx.rr.com> wrote:
> VJB wrote:
> >Funny it should come up on here about certain members of the Collins crowd and the horrible, sacriligious view they may take of making unintrusive mods that improve the enjoyment of a piece of equipment.
> >
> The one rig that -needs- the most modifications to better the enjoyment
> of this particular peice of equipment, is the 75A series of recievers.
> In particular, the 75A-4, and I'm not sure that enough can be done to
> that reciever to bring it to be nearly as good as a properly aligned
> phase-shift receiver.

That's probably true, Geoff. But we need to keep in mind that the
75A-4 is the 'last in the A-Line' and as I understand it, was
primarily designed for SSB use with AM being secondary. I'm using one
and it 'works fine' for my current AM situation. Limited somewhat by
the 6khz filter and other issues, it has the benefit of being very
adaptable to noise or QRM appearing in a QSO. It's also very stable.
That said, it's not the best choice as an AM-only receiver, but
strikes me as a pretty good compromise considering what is was really
built for (SSB, to mate up with the KWS-1). The 75A-1 is a LOT better
receiver for AM, and even it has its issues. Rather than trying to
re-design or rebuild the 75A-4 into something it was never meant to
be, I prefer the other alternative: get another cool radio! Of course,
I paid a fraction of the going epay-high price for mine or I wouldn't
even be able to comment from experience. Seems like a lot of folks
have paid big bucks for them because someone said they should.

> >Most of those who would criticise changes in the audio of later serial number KW-1s fail to realize the changes actually may correct the transmitter back to an earlier set of factory values that sounded better than the value of components installed in later production examples.
> Another 'good' mod (at least one that's acceptable by the 'in' crowd,
> for a KW-1, would be to change out the 4-400's in the final, for
> 4-250's.  The 810's would work better into those jugs, I think, as
> opposed to the 4-400's.
> These, of course, are my personal opinions.

I looked into this many years ago and even picked up some 4-400Cs just
for that reason. Electrically I believe they work a lot better,
loafing along. The downside is: virtually no purty-red glow.

I also swapped out the 872As for 4B32s (instead of the SS sticks).
Makes a HUGE difference, haven't had an arc over or blown a fuse
since. Still have that nice purple glow, just not as brilliant.

Paul does bring up an interesting point, too: roughly halfway through
production the engineers (supposedly on Art's orders, but who knows
now?) restricted the audio response further to give the transmitter
more punch. Which design is correct or better? That's a matter of
taste and opinion. I changed one resistor and one or two caps in mine
when I first got it on the air back in August of 1990. Also bypassed
the clipper, splatter choke, and changed the taps on the mod iron.
Simple stuff that made a very noticable difference, and I sleep just
fine at night.

> >We, as the Providers of Good Homes when these transmitters reach private hands then have to decide whether to "restore" an already modified transmitter back to original, or functionally bring it up to the application where it can best be used.
> >
> I prefer the latter.  Just because it 'could' be a museum peice, doesn't
> mean it 'has' to.  It was designed to 'work', by golly, WORK IT!


> the idea of 'buying' a show-peice of equipment, and then not using it
> because you don't want to damnage it is counter-productive to the
> activity of Ham Radio, in general, and not just the Boat-anchor crowd.
> I'm agreeing with you, Paul :-)

Yep, it makes good sense. Use it, have fun. If it breaks, fix it.
Whenever someone asks me if I collect old radios, I qualify it by
saying "I collect stuff to use". And I like a clean, unhacked piece of
equipment as well as most any 'pure collector' type. But if the
utility can be enhanced with some simple component changes, or the
safety to self and components is improved by adding a 3-wire power
cord or changing an old cap to protect expensive mechanical filters,
I'm there. Trying to make an old AM/CW receiver into an SSB receiver
("I added a product detector, changed the AGC, added digital readout,
and solid-stated everything with a tube") strikes me as being about as
silly as trying to make a 75A-4 into a Super Pro. Easier to just
trade/buy/otherwise acquire a different rig.

~ Todd,  KA1KAQ

More information about the AMRadio mailing list

This page last updated 23 Feb 2018.