[Heath] HW-16 update and additional question (11 MAR 14)

Tue Mar 11 01:13:45 EDT 2014

Thanks to all who responded and gave comments and suggestions to the questions regarding the HW-16 refurbishment.  Most were very helpful.  I still have a locked slug in the 15M het oscillator coil form in the receiver that I may have to break out and retune with an external capacitor.  Silicone spray was not the answer.  That 15M LO level is a lot lower than 40 and 80 M.  On the transmitter side, I seem to get 50-60 watts out on all three bands so I'm happy, happy, happy about that.  

The comments I have seen previously on the reflector about carbon composition resistors increasing in value on this old equipment is very important to heed.  So far, of those removed or tested, all have been 15-20% high in value.  Some also had very little 'headroom' in their dissipation.  The order to the electronics parts place is already in process.  

Okay, so I won't say this is the last problem I'll post, but it is so far a vexing one.  At even moderate audio levels, a strong station will cause something - I think the audio output tube - to regenerate the received tone.  It sounds like the tube is oscillating in synchronization with the incoming CW and producing a strong keyed tone - sort of like a locked oscillator.  It ends up being a LOT louder than the signal level.  

The troubleshooting instructions in the manual talk about the output transformer plate (blue) lead being too close to the PCB (and hence the grids of the audio amp tube) and causing 'howling'.  I would not characterize this as howling (unrestrained audio feedback) - the oscillation only happens when the strong CW signal is there and ceases between dits and dahs.  It's a keyed audio oscillation.  

Just in case, I moved the blue transformer lead all the way to the edge of the chassis per the troubleshooting hint, and I also shielded it with the braid from of a piece of RG-59 cable.   However, no joy.  Still as bad as ever.  Also tried to replace the audio tube cathode electrolytic capacitor since I wasn't sure I'd changed that recently.  No change.  I performed the tube socket voltage tests and all were within a couple of percent.  

Until this gets fixed, I'm not going to attempt any of the increased gain mods for the IF and RF amps as they would be counterproductive.  But, it needs to be fixed else the radio will be pretty useless.  Anyone seen this before and found a fix for it?  I don't remember this sort of thing happening on the one I assembled and used back in 1968-1970.  

Should I just take a piece of insulated solid #16 buss wire, bring it up absolutely vertically from the PCB plate connection, and then route it over to the vicinity of the transformer before connecting to the blue transformer wire on a terminal strip under the transformer mounting screw?  I can't think of any way of getting it any more quickly away from the PCB and putting space between it an the tube grids.  I could use Teflon coaxial cable to make this a shielded run as well.   Other thoughts?

Thanks and 73       John...   WB4LNM

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