[Hammarlund] HQ-170 mods (long)

[Peter A Markavage]

In your original post on 1/2/04, you said this was a HQ-170A VHF
receiver. If so,
then R53, the 10 watt resistor going to the OB2, should be 2K, not 3K. If
you don't have the VHF Addenda manual, you can get it up on BAMA. If its
just the 170A, then 3K is fine.

Pete, WA2CWA

On Mon, 26 Jan 2004 18:50:49 -0500 "Craig Roberts" <crgrbrts@verizon.net>
writes:
> As those of you who have been following my riveting commentaries 
> know, I
> recently acquired an HQ-170A with some odd modifications in the 
> power
> supply. I�ve now restored the circuitry to its original 
> configuration and
> thought I�d share the experience just in case others find a receiver 
> in a
> similar state.  Although most of the modifications performed by a 
> previous
> owner on my radio were apparently not authorized or documented by 
> the
> factory, the circuit changes may have appeared in a magazine article 
> or
> other communication lost to history and, thus, may have been done to 
> other
> HQ-170s.
> 
> When I took delivery of my eBay queen, its power supply circuitry 
> showed
> evidence of considerable and sloppy tampering.
> 
> 1)      the stock OB2 voltage regulator tube had been replaced by an 
> OA2
> 
> 2)      the dropping resistor to the VR tube had been changed from 
> 3K 10W
> (or 4K in very early sets) to 2K (thus yielding the 150 volts needed 
> to
> operate the OA2).
> 
> 3)      one diode had been added in series with each of the original 
> two
> rectifier diodes (CR1 and CR2)
> 
> 4)      an �extra� 82-ohm 10 W power resistor had been added between 
> the
> junction of the diodes and the choke L6
> 
> Since the HQ-180 series receivers use an OA2 regulator, I thought 
> perhaps my
> receiver had been �upgraded�.  Maybe so, but there�s no evidence the 
> factory
> ever thought of it.
> 
> Although my modified receiver worked fine, I decided to return it to 
> its
> original state for three  reasons:
> 
> 1)      The former owner�s workmanship was shameful, featuring big, 
> blobby,
> cold (or at least chilly) solder joints, uncrimped component leads 
> and
> soldering iron-scarred wire insulation.
> 
> 2)      Several of you advised me that leaving the unauthorized mods 
> in
> place would earn me eternal damnation (but � sincerely � thanks for 
> your
> advice and useful information).
> 
> 3)      An OB2 glows prettier than an OA2.
> 
> It turns out that the �extra� 82-ohm power resistor was, indeed, 
> suggested
> by Hammarlund.  So, I left the change intact, though I did replace 
> the
> resistor itself with a new one (the old one looked undersized and 
> was
> scorched).
> 
> I removed all four diodes and put two new 1N4006s in their place.
> 
> I replaced the 2K 10 W dropping resistor with a new 3K unit, thus 
> dropping
> the VR tube�s operating voltage back down to about 105V. This 
> allowed me to
> retire the OA2 in favor of a new OB2.
> 
> Since �unmodifying� the receiver, I�ve noted one major change in its
> performance.  The noise floor has lowered remarkably. Perhaps one or 
> more of
> the added diodes was noisy, or perhaps just plain bad soldering was
> generating electromagnetic junk.  At any rate, if there was any 
> benefit to
> be had by the modifications, I can�t imagine what they would have 
> been. I
> feel better now.
> 
> Thanks again to those who offered their friendly advice. It is much
> appreciated.
> 
> 73,
> 
> Craig
> W3CRR
>