[Hallicrafters] Voltage question re SX-71

[Joel R. Hallas]

Well, the line voltage was my first thought too, until he said the B+
voltages were right at the supply.

I think the clue may be the cathode voltages, indicating (and contributing
to) lower or higher tube current. If the tube currents are higher or lower,
that will impact the plate votage significantly. Often times it is a result
of AGC action and/or problems, so I'd start there, especially if the non-AGC
(audio) sections are closer.

Alternately, if you like the performance, just note the "new" readings in
pencil for future reference and go with the flow!

Regards, Joel Hallas, W1ZR

----- Original Message ----- 
From: "Lee Bahr" <pulsarxp at earthlink.net>
To: <rjb at lynden.com>; <hallicrafters at mailman.qth.net>
Sent: Thursday, March 25, 2004 10:21 AM
Subject: Re: [Hallicrafters] Voltage question re SX-71


> Bob:
> Part of the problem is:  line voltages are higher today then when the
manual
> was published. Back then line voltage was around 110 to 115 volts.  Today,
> voltages are running around 120 volts or even slightly higher.  Lower your
> line voltage with a variac and I bet things will look a lot better.
> Lee, w0vt
>
>
>
> > Good morning to all
> >
> > Back with another SX-71 question. I posted a few weeks back about
> re-capping
> > and re-sistoring my ebay SX-71. The radio sounds very hot on the HF
bands
> > and i am very pleased with it. FWIW, i decided to check the tube
voltages
> in
> > the IF strip against the TUBE SOCKET VOLTAGE CHART in the manual. Big
> > mistake :(  I found that the voltages in my radio are nowhere near those
> in
> > the chart. The anode and screen voltages on IF2 and IF3 are 20-30 volts
> too
> > high, and the cathode voltages are either way high or way low.
> > I have all the front panel control settings as indicated in the chart,
the
> > B+ and regulated voltages are correct (250V and 150v resp'ly). All
> resistors
> > are new 1% xicons, and their values match those in the circuit diagram,
> and
> > they test correct. The tubes are NOS and tested ( i have one of those
> bright
> > red Hickocks :) and i have tried several in each IF socket.
> >
> > Here's my question... were Halli radios made with such wide tolerances
> that
> > a 20-30 volt difference is acceptable?
> >
> > By way of comparison, i also recapped and re-sistored an ebay NC183D
> during
> > the same period. It's voltages are all within a few volts of its chart.
> >
> > thanks in advance for any help
> >
> > Bob Bennett, Maple Vly, WA
> >
>
>
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