[Hammarlund] HQ-170A mods?

[Peter A Markavage]

Keep in mind that the regulator circuit (resistor value for one comes to
mind) for the 170A VHF is a bit different that what's stock in the plain
170A. The 170A VHF Addendum manual covers these changes. The stock 170A
manual does not.

Pete, WA2CWA

On Fri, 02 Jan 2004 13:47:30 -0500 Kim Herron <kherron@voyager.net>
writes:
> Hi Craig,
> 
> >While re-tubing my "new" HQ-170 VHF I discovered that it has been 
> equipped 
> >with an OA2 VR tube rather than the OB2 called for in my schematic. 
> The 
> >OA2 tube seems to work okay. So, for that matter, does an OB2 
> (while 
> >glowing a very bright orange).  Underneath, I've noticed what 
> appears to 
> >be a modification to the power supply circuitry (perhaps to 
> accomodate the 
> >OA2 ?). Two additional diodes -- besides the stock pair -- have 
> been 
> >added.  And then there's this gray "thing" down there. It's not the 
> 3K 10W 
> >power resistor but it is near it and resembles a "cement" power 
> resistor, 
> >too. It is small in diameter, somewhat long and cylindrical in 
> shape. This 
> >thing is as mysterious to me as a 1920's grid leak (which looks 
> like a 
> >fuse) was years ago.
> >
> >What is this device?  A choke?  (I don't have the radio with me 
> here at 
> >work so I can't tell you exactly where this thing is in the 
> circuit). The 
> >device is a bit scorched and cracked, which is why I'm worried 
> about 
> >it.  If it need replacement, I have no idea what to replace it with 
> (!).
> 
>     The best way to deal with this type of thing is to put it back 
> stock.  There are people here who will disagree with me on this,
> but I've found that the design that Hammarlund used works well, when 
> all 
> the components are in spec.  So usually the mods
> are covering up something deeper in the circuit that is actually 
> broken/out 
> of spec.  Put the supply back to stock,
> check your voltages and then fix the offending components.  I've 
> found 
> several partially shorted P/S chokes over the years
> that will cause you fits but aren't readily apparent.  Make SURE 
> that you 
> are using the right voltage chart for an A model (and
> schematic).  The P/S values are different because the supply is 
> using the 
> diodes instead of a 5U4GB.  That does make a difference,
> and the wrong service info will lead you down the "garden" path.
> 
> 
> Thanks!!
> 
> Kim Herron
> 1-616-677-3706 
> 
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