[Hammarlund] Fw: Hq170 hum

[Lee Bahr]

Craig:
There was an article in the DECEMBER 2003 Electric Radio magazine showing
you how to use a 70 volt line transformer as an audio output transformer in
a ham receiver.  These transformers sell for $3.00 to $8.00 each and are
readily available.

Here is how you can wire them for a 6AQ5 output tube as is in your HQ170
receiver:
1. The 1.25 watt tap goes to the plate of the 6AQ5
2.  The common "C" end of that winding goes to the B+
3.  The output winding common "C" end goes to ground or one side of the
speaker
4.  The 4 ohm tap of this winding goes to the other side of the speaker
THE ABOVE IS FOR DRIVING A 4 OHM SPEAKER USING A 6AQ5 AUDIO OUTPUT TUBE

HERE IS HOW YOU DRIVE A 500 OHM SPEAKER:  (You are going to wire in a second
70 volt line transformer)
1.  Wire the second transformer's 16 ohm tap to the 16 ohm tap of the first
transformer
2.  Wire that windings common 'C" wire to ground.
3.  Wire the second transformer's 10 watt winding to the 500 ohm output
terminal to drive a 500 ohm speaker.
4.  Wire this windings common "C" wire to ground or the other output
terminal for the 500 ohm speaker.

These transformers are fairly small and as I said very inexpensive.  Doing
the above will give you both 4 ohms and 500 ohms for a very affordable
price.  Radio Shack used to carry these transformers but has recently
discontinued them.  There are a lot of internet sellers selling them.  Just
make a search for "70 volt line transformers" and you will find many
sellers. The above info came from an artical intitled THE SEVEN DOLLAR
WONDER and was written by K6DPZ, Hal Guretzky.

I hope you find this information helpful.  (Good luck with the hum problem).

Lee Bahr, w0vt
Houston


 Message ----- 
From: "Craig Roberts" <crgrbrts@verizon.net>
To: "'Lee Bahr'" <pulsarxp@earthlink.net>; <hammarlund@mailman.qth.net>
Sent: Saturday, February 21, 2004 2:57 PM
Subject: RE: [Hammarlund] Fw: Hq170 hum


> Hello Lee,
>
> I agree with you -- absolutely. The increased audio bandwidth afforded by
my
> new output transformer is quitre possibly at the root of the hum problem.
I,
> however, have no idea of what the factory "normal" passband was, since the
> radio -- as I got it -- had been retrofitted with a low-end universal type
> transformer. The output stage wiring had also been modified and the audio
> was plagued by a limited bandwidth and a lot of noise. I had to do
something
> to remedy this.
>
> I didn't arbitrarily install a "high-fidelity" transformer in dumb 'n
doomed
> attempt to transform a '60's communications receiver into an audiophile
> set -- it's simply what I had available. I must admit, though, that while
> the new transformer seems to pass audible hum, it's also cleaned up the
> sound considerably.  If possible, I'd like to attenuate the hum without
> unduly compromising the new intelligibility.
>
> Barring that, I'd like to find an original output transformer for the
> HQ-170A (the late xfmr with the dual 3.2 and 500 ohnm secondaries), but
> these are understandably scarce. I'd also like to find out how the factory
> leads were routed so I could replicate the original wiring. At least then
> I'd know what the radio USED to sound like. I'd be happy jus tto know
that.
>
> Anyway, thanks again for the wisdom, Lee. And thanks to everyone else
who's
> responded. I'll keep you posted.
>
> 73,
> Craig
> W3CRR
>
>