Mine is working very well. No problem to copy cw. Drift is a bit
noticeable on cw above 20mtrs but not too bad. I replaced all the
caps but the type that rarely go bad. Got my caps from Mouser.
There are several good websites to figure out which ones. And
replaced all the resistors with (mostly 1w and 2w) metal film
resistors. Bought the larger size version of metal film (near the
physical size of the carbons). The others just to tiny to look
right in this receiver IMO. As I got to checking carbon resistors
found out over half were out of tolerance so decided best to do
them all. Some may think that is overkill but in the end it is
your rig to do with as it pleases you. Biggest challenge was the
dog house but not that bad with patience. Redid the coax there
with RG-174. Took lots of pictures at various stages of
restoration. Lubed where appropriate with superlube. Deoxit where
appropriate. Spaghetti where appropriate. Aligned. Those things
took up the most time. Seems like I may have replaced a weak tube
or two, do not remember. Tested them all with my restored Hickok.
Only mod was the sensitivity pot to make the range more pleasing
to me. The chassis was not bad cosmetically. I first considered a
complete strip down, buff down, possible plating of the chassis
until I got to reading about the toxic coating on halli's, so just
give it sort of a sponge bath so to speak after removing easier to
remove items form the top side. A complete strip down would have
taken a boat load of time anyway.
73
Chuck
W4NBO
On 9/14/22 08:57, Mike wrote:
toggle quoted message
Show quoted text
So what I am hearing is replace all the
caps before making any voltage checks.? I do have the Hayseed
Cap kit in hand, so I will go ahead and get to work with that
along with checking resistor values as I go along.? Sounds
like in my excitement that it was actually receiving signals
pre-cap replacement I was getting ahead of myself.? Thank you
all for the advice.
?
As for the replacement resistor for R68, I
have several MEMCOR VL3 390 Ohm 3W wire wound resistors in my
junk box.? Understood it is an odd wattage rating, but they
are out there and I just happen to have several pulls in my
junk box all of which are less than 1% off value.
?
Thank you,
?
Mike
W5CUL
?
?
Check the grid
voltage, if it is too high (+) there will be too much
current drawn across the plate and cathode resistors,
usually caused by a bad coupling cap
The resistor is for grid bias. Check
the plate and screen voltages
?Actually, measure the resistor.
Composition resistors rend to go up in value.? ?That would
cause the drop across the resistor to go up.? It doesn't
hurt to have more dissipation.? 17V ACROSS 390V is about
0.7 watts so a one watt is marginal.? It will run hot
which will make it drift more.? I bet it's way off value.?
The larger resistor should be ok but 3 watts is an odd
value,? usually next size is 2 watts and then five watts.?
Check it's value before using it.? Also? , if there is a
bypass capacitor make sure it's ok.
? ?I think you are overdoing the VRiac
business? Of the filter caps don't short right away they
are probably not going to.? I assume this variac is
metered or you have some other means of watching for a
sudden rise in line current.
--------
Original message --------
Date: 9/13/22
6:51 PM (GMT-08:00)
Subject: Re:
[HallicraftersRadios] Calling all SX-100 Owners
Thank you Jim and All!!!
?
Very good information from everyone.?
This is certainly a haven of Hallicrafters Experts!!
?
Jim, I certainly hope that is the
issue as opposed to a bent shaft as was another
possibility mentioned by another gentleman.? I do not
relish digging the assembly out of its make shift can to
inspect the mechanics.? But if I must, then I must.
?
In the meantime, just for fun, before
any cap replacement, I put the receiver on a variac and
slowly brought it up watching for any of that magical
smoke to escape.? When I say slowly, I am talking about
advancing the variac 10 Vac every 15 minutes or so.? This
also helps in reforming some of those old caps along the
way, although I will be replacing all of them soon.? By
the time I hit roughly 40/50 Vac on the variac I could see
dial lights starting to perk up; so far so good.? When I
hit around 70 Vac or a little more I was hearing good
rushing noise coming out of the speaker; so far even
better.? I stopped at around 100 Vac and let it soak more
on that looking for that magical smoke, none smelt or
seen; just keeps getting better.? At that point, just for
fun once again, I attached an antenna to see if it can
receive on the BC bands.? Low and behold I was able to
tune in strong and some weak stations.? Next was 80M and I
was able to tune in some of the more stronger stations,
although the dials are off a little; wow looking really
good.? So after an hour of playing around, I started
creeping up to 110 Vac and let it sit for a little on
that.? By the time I hit 120 Vac, only 5 Vac from the
incoming line voltage to the house, that is when I could
smell the magical smoke; Houston we have a problem.? So I
let it sit for a while on that setting and let whatever it
was that was baking, although I kept a close eye and hand
on the transformer, finish cooking such that I could see
the magical smoke or at least a crispy component.? So the
culprit turned out to be R68, a 390 Ohm 1W resister in
line with the Cathode/Suppressor Grid of the 6K6GT audio
tube? A quick voltage check showed ~22.4 Vdc at that
point, yet the schematic shows it should be 17 Vdc.? So a
quick calculation indicated that the resistor was actually
dissipating ~1.25W of power with the radio sitting on 120
Vac, a little over what it is rated for.? I replaced it
with another 1W resistor for now and a new electrolytic
cap as well. Now I only move the Vac momentarily from 100
Vac to 125 Vac to check the voltage in the various other
areas to see what is really going on at todays higher
Vac.? In retrospect I will probably replace that resistor
with a 390 Ohm 3W pull I have in my junk box.? But I am
debating on whether to change the value to get closer to
17 Vdc when running the radio with 125 Vac input.? I have
seen a couple of designs showing a 500 Ohm used in the
same situation when faced with the same Plate and
Screening Grid voltages.? After a quick calculation 500
Ohms would drop it back to ~17 Vdc when running on our
normal home Vac voltages.? Decisions decisions.
?
Thank you,
?
Mike
W5CUL
?
?
Greetings to Mike and the Group:
?? As I recall, the SX-100 BFO pitch control is indeed a
variable inductor.?? It is capable of several turns either
way from its ideal position.?? To index the control
properly, there is a stop mechanism which is (again, as I
recall) built into the knob.?? There is a combination of
tang and milled slot that prevents rotation of the control
more than 300 degrees or so.?? The "bump" you are
experiencing is probably this stop mechanism and is due to
the knob not being fully seated on the shaft, i.e. too far
away from the front panel.?? If the "bump" is in the
middle of the BFO range, then there is an alignment issue
as well.?? Perform the BFO alignment as per the manual.??
Then install the knob centered and as close to the panel
as it will go.?? You should now have a rotational limit at
the extremes (+/- 5 on the knob skirt).??? Hopefully, the
repetitive forcing of the knob past the stop has not worn
the mechanism down to the point where it can no longer be
made to function.
73,
--
Jim T.
KB6GM
