[TenTec] Comments on 1254 receiver

[Stuart Rohre]

Oh the 1254 is a dandy short wave receiver.  I put it together easily, 
and aligned it with CHU before they moved frequency.  It then was right 
on on 40m and all other bands.  WWV could be used as well, but CHU fell 
near the ham band then.  I did not rush it, and think it was something 
over 24 hours spread out over a month or more, to assemble it.
I would only work on it when I was not tired, and my eyes were seeing 
"well", (for tri focals).

There is the suggestion you use a coax fed antenna.  Because, there is 
some hash leakage from the display, but several folks have come up with 
fixes.  With a dipole fed by coax, you don't notice any hash.  There 
might be some shielding one could add, but I have not seriously pursued it.

The tone of the receiver is very good even with the internal speaker, or 
especially with its own speaker.  Having some coverage below the AM band 
is interesting.  I easily got the nearby airport (10 miles) VLF beacon.

If ever you want to disassemble the 1254 to work on it, watch out for 
the fact that the display board is soldered to the mother board.  The 
vaious control pots are soldered to the board below them, and bolted to 
the case.  Don't just undo the knobs and lock nuts and try to pull the 
front panel off.  You will break pot leads.  REVIEW the assembly manual 
before servicing.  A good rule for any equipment, but one can forget, or 
think a disassembly is intuitive but it isn't always so.

There is one other thing to watch out for.  The output of the power 
audio IC that drives the speaker, has a high frequency (out of audible 
band) RC network from speaker line to ground.   It is the usual for 
IC's, a resistor in series with a capacitor.  If that capacitor fails, 
you would pull excess current through the audio IC, overheating it.
It can happen to any power audio IC stage that has this standard series 
RC circuit.  I was leery of the voltage rating of the factory part, and 
there are two ways to insure you don't end up with a low value resistor 
loading your audio stage.  One, use a high quality, higher voltage 
rating cap.  Two, use two caps of twice the desired value, in series. 
You will have a net value of the original, with twice the voltage 
rating, and the chances of both shorting being slim, you have increased 
the reliability.

The receiver worked right out of assembly.  Everything had a good fit, 
directions were clear, and the receiver assembly process was a good, 
simpler, practice before I assembled a K2 transceiver.  Both use a front 
board on a mother board idea.

-Stuart Rohre
K5KVH