[Heathkit] Looking for Heath Mohawk Articles

Wed May 9 18:16:53 EDT 2007

I came in a bit late on this thread but I agree completely with John as 
to modifications.  I have two Mohawks, one paired with my Apache, SB-10, 
and HA-10 "warrior" and the other paired with a Marauder.  I went 
through and added a three wire line cord, replaced the line bypass caps 
with modern AC rated versions, replaced a few out of spec resistors, 
lubricated the variable capacitors, aligned the set as stated in the 
instructions and that was about it.  I have not noticed any problems 
with drift or distortion; perhaps I am just lucky...  The performance is 
pretty similar to the Hallicrafters SX-101 series which is no surprise 
since I think Heathkit was "inspired" by these radios. 

One place where Mohawk users get into trouble is running the IF gain 
control wide open.  Heathkit provided separate IF and RF gain controls 
and they expect the user to exercise sense (or is that sensitivity) in 
the use of these controls.  Many vintage receivers have an IF or overall 
gain set control but it is not a front panel control and is only changed 
as part of the alignment and should not be set to maximum gain in a 
properly functioning receiver.  In retrospect it was probably a mistake 
to put this on the front panel since the average user probably ran it 
"wide open" and then complained about the high noise level and 
distortion.  Make sure that the basic receiver is working properly 
before even considering modifications.  Johnson had a similar design 
"issue" and had they used a "reversed" pot for the clipper control a lot 
more Valiants would likely still have their original clipper circuit.  
In the Valiant, full counterclockwise setting of the clipper control is 
actually maximum clipping and sounds as bad as you would expect.  
However setting the control full clockwise effectively reduces the 
clipping level to zero.  But this is counterintuitive and I have a 
feeling many users never read that far in the instruction manual before 
deciding "hey, this clipper circuit has to go".  I just got through 
restoring a Viking 500 to its original state (including converting the 
audio chain and clipper back to stock) and I have gotten numerous 
positive reports on its audio.

I will admit I am not a big fan of modifications since it is easy to 
cure one "problem" while creating many others.  Any decent engineer (and 
there must have been a lot of good ones in the 40's and 50's given the 
performance of these vintage radios) engineered the radio as a system.  
Coming back and re-engineering it in little pieces will often result in 
a sub-par radio.  In general, if there is a safety issue I deal with it 
through modification.  I do like the use of inrush current limiting and 
this is easy to add without other modification.  I have gone to solid 
state rectifiers in my HT-32 and HT-37 transmitters to get away from one 
common cause of transformer failure in those radios.  I have also grown 
to hate mercury vapor rectifiers (though they are pretty to watch) so my 
Valiants, Viking 500, Desk KW, Johnson T-bolt, and Heathkit HA-10 have 
plug in replacements for these.

Good luck with your RX-1.

73, Rodger WQ9E

john wrote:
> That's a good cite, Pete, but it involves an awful lot of surgery. 
> I've never really understood to make an old radio like a new radio 
> (we've all got those) and I've never really felt like the RX1s I have 
> don't perform.
>
> Before hacking away at it, I'd use it for awhile, observe how the 
> performance varies with gain settings, etc. You might well find that 
> you'll use it the way Heath made it.
>
> John K5MO
>
>
>
> At 03:11 PM 5/9/2007, Peter Markavage wrote:
>> It's still called RX-1. That's its model number. Check Electric Radio
>> Mag. (check the on line index)  for several great articles on improving
>> the Mohawk, RX-1.
>>
>> Pete, wa2cwa
>>
>> On Wed, 09 May 2007 18:52:30 +0000 "John Hensley" <w5jv at hotmail.com>
>> writes:
>> > Has anyone done a compendium CD on the Mohawk?  I'm looking for
>> > reprints or
>> > emailable files on this large Mohawk receiver, once called the RX-1.
>> >  If you
>> > have ideas on how to improve it so that it is more useable than when
>> > stock,
>> > I'd like to hear from you.  I'm curious how well it can be tamed and
>> > so how
>> > enjoyable it can be made.
>> >
>> > I'm also wondering if there is a preferred freq. counter readout
>> > circuit
>> > which is being used with these.
>> >
>> > Please respond directly to w5jv at hotmail.com.
>> >
>> > Thanks in advance,
>> >
>> > John W5JV
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