HW 16 Audio

[Kenneth G. Gordon]

On 8 Aug 2006 at 7:42, DavidGriffin wrote:

> Just bought an HW 16 and have been testing it and looking it over. 
> Quite low receiver audio output, such that I have to connect the
> speaker output to an external audio amp to hear anything.

That is NOT normal.

>   Transmits
> fine  (but my crystals don't fit...1/2 inch between prongs OK, but my
> crystal prongs seem too big?)

There should be two crystal sockets, one above the other. One of those 
will fit FT-243 crystals and HC-6 crystals with fat pins added.

> Tubes "seem" to check out, but most,
> including the audio amp 6HF8 have to be pproximately checked on my old
> Heathkit tube tester.   Schematic appears to show the speaker and
> headphones jacks in parallel, but the text indicates logic for a
> series connection, i.e.,  "speaker left connected at all times.....hi
> Z of headphones causes an effective mute of the speaker..... a shorted
> phono plug must be inserted into the speaker jackf or headphones only
> operation."

Yes. That is correct.

>   Observing these points does not improve the audio.   On
> this rig, one end of the neon in the cathode  of one stage of the
> audio amp (is this for sidetone?) is disconnected, but there appears
> to be sidetone nonetheless, although dimininshed (over and above the
> low audio.)

With one side of the neon bulb disconnected, you should get NO 
sidetone at all. Perhaps you are hearing your own transmitter signal.

>   Saw an earlier post about low transmit audio from
> 6EA8's, and in fact these are used in the mixer and het oscillator of
> the HW 16.

No, that would not effect the HW-16. The problem was low gain in only 
the mic amp of the SB/HW transceivers.

On your audio problem: first, you should check the values of the 
cathode bias resistor for the output stage of the audio amp. That should 
be 470 ohms. Then you should check the cathode bypass cap for that 
same stage.

Feed an audio signal into the grid of the output section of the audio 
amp tube, and see if you don't get plenty of volume.

I think you will.

Since you are hearing a "sidetone" even with the sidetone oscillator 
disconnected, it seems to me that you are hearing the transmitter itself.

If that is the case, I would immediately suspect the switching transistor. 
That transistor switches bias to the receiver to mute it with the key 
down. If that transistor is shot, the receiver will not un-mute, and will 
appear to have very weak audio.

Ken W7EKB

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