HW/SB Questions..

[Kenneth G. Gordon]

On 12 Jun 2006 at 20:24, Jim Flanagan wrote:

> Question 1:
> I have a unit where the main frequency dial (0 - 500) has become
> yellow with either age and/or heat.  Is it possible to remove this
> yellow tinge with polishing or some other means?

I don't know of any way to fix that. However, there is a fellow on the net 
who sells a multicolored dial for the HW-101 that has different colors for 
each band and segment. It is rather nice, and the cost is reasonable.

> Question 2:
> I've asked this in this forum back in 2000 and didn't get many 
> responses, so I thought I would
> ask again.  In two different rigs, both HW-101s, I notice that there
> is an objectionable 'pop' or more like someone tapping a drum or
> bongo.  I've always referred to this as a thump.

Do you mean when switching from receive to transmit? If so, my rig has 
that.

> If there is anyone with an SB/HW rig who has experienced what I have
> described and has found a fix, I would appreciate corresponding with
> you.

I believe my HW-101 exhibits this, but I will have to get more 
information from you about exactly what you mean. Mine exhibits a pop 
when it goes from receive to transmit. I know in my case, part of that is 
caused by my microphone, a Turner Plus 3, not switching cleanly.

> I have examined the schematics and I understand the principle of
> operation regarding the T/R switching. In a nutshell, a negative pulse
> is generated when the relays are being actuated.  This neg pulse is
> filtered and applied to the grid of the audio preamp.  The purpose is
> to 'squelch' the audio amp until the relay contacts have a chance
> (about 10mSec) to actually close.  Once the relays have finished
> switching, a fixed neg bias is applied to the preamp to insure it is
> hard cutoff.

Yes.

> 
> In my unit, this is happening as described, as I have used a scope to
> monitor the preamp stage.  The problem appears that when the preamp
> (triode of 6GW8) is cutoff, a positive pulse is generated on the input
> grid of the pentode section which causes a transient. This transient
> pulse  is heard in the speaker/phones.  I am not that comfortable with
> tube circuits, however, but from what I see (and hear) the radio
> SHOULD have this pop/thump when switching. So WHY does everyone not
> seem to experience this?

Maybe they just don't notice it. How loud is your noise? When does it 
occur? Going from receive to transmit? What mode(s)? Does it happen 
when in CW? Or just SSB? Or both?

Ken W7EKB

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