HW/SB Questions..

[Jim Flanagan]

Hello..
     I have several questions regarding the HW101:

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?


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.  Everyone that I have
corresponded with have claimed that they do not notice this symptom.  
Some time in the past, I  was
playing with an  SB-102 that did not exhibit what I have described.  The 
only sound present, as I recall,
were the relays switching.  This has had me stumped for some time.  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 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.

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?

Anyway, hopefully someone who is valve 'expert' can help me out figuring 
this out.  Maybe there is nothing to figure out
and this is what I should be expecting, but I doubt it.

Looking forward to your help....
Thanks and 73

-Jim
WB5KYE
Largo, Florida

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