Given an SX-100. It doesn't work.

Chassis and interior in good shape, no corrosion. Lights fire up when
turned on. Attached Hallicrafters 3.2 ohm speaker (or headphones if
plugged in) hums, and I hear scratchy noises when I change across the
bands or switch to phono. S-meter moves across the dial when I spin the
sensitivity knob.

But, it doesn't actually receive anything, and the S-meter does not
move as I traverse the bands nor does it change as I move within a
band.

Suggestions on priorities for troubleshooting, by tube replacement or
otherwise, appreciated. I feel the detector is the place to start?
Have a multimeter, is all. In Portland (OR) Metro area.

0A2 voltage rectifier $6
5Y3GT rectifier $10
6AU6 1st mixer & crystal cal (1 ea) $10
6BA6 1650 KHz IF amp, 2nd mixer, 50.5KHz IF amp (1 ea) $8
6BJ7 detector/AVC/noise limiter $5
6C4 1st conversion oscillator & KHz IF amp (1 ea) $13
6CB6 RF amp $5
6K6GT audio output $8
6SC7 audio amp/BFO $9
12AT7 2nd conversion oscillator $13

Your Elmering would be appreciated. Thank you in advance.

1 Check power supply voltages
2 Audio output
3 Audio Driver
4 Detector
5 IF amplifiers
6 Make sure oscillator is working
7 RF amp

Sounds like a good candidate for a paper cap replacement party.

You'll need a signal generator to inject a signal into the various stages.

A VTVM or scope can be used to see a positive voltage on the grid of the
oscillator tube to determine its working.

oh yeah, I forgot to ask, is the ANTENNA hooked up ?



"K7AAY" wrote in message
oups.com...
Given an SX-100. It doesn't work.

Chassis and interior in good shape, no corrosion. Lights fire up when
turned on. Attached Hallicrafters 3.2 ohm speaker (or headphones if
plugged in) hums, and I hear scratchy noises when I change across the
bands or switch to phono. S-meter moves across the dial when I spin the
sensitivity knob.

But, it doesn't actually receive anything, and the S-meter does not
move as I traverse the bands nor does it change as I move within a
band.

Suggestions on priorities for troubleshooting, by tube replacement or
otherwise, appreciated. I feel the detector is the place to start?
Have a multimeter, is all. In Portland (OR) Metro area.

0A2 voltage rectifier $6
5Y3GT rectifier $10
6AU6 1st mixer & crystal cal (1 ea) $10
6BA6 1650 KHz IF amp, 2nd mixer, 50.5KHz IF amp (1 ea) $8
6BJ7 detector/AVC/noise limiter $5
6C4 1st conversion oscillator & KHz IF amp (1 ea) $13
6CB6 RF amp $5
6K6GT audio output $8
6SC7 audio amp/BFO $9
12AT7 2nd conversion oscillator $13

Your Elmering would be appreciated. Thank you in advance.

K7AAY wrote:

Suggestions on priorities for troubleshooting, by tube replacement or
otherwise, appreciated. I feel the detector is the place to start?
Have a multimeter, is all. In Portland (OR) Metro area.

Maybe, or something before the detector. You really, really want a scope.

If you don't have a scope, you can make the assumption that what has gone
bad is _probably_ a paper cap somewhere in the IF strip or detector, and
just shotgun all the paper caps out. If it turns out not to be a paper
cap, you haven't wasted your time because sooner or later one of them will
fail.

The second thing you can do is measure grid, plate, and cathode voltages
on each of the tubes on the IF strip and detector stage, and see if any of
them is way out of wack. If you see 200V on a grid, you have a DC blocking
cap issue. If you see 10V on a plate, you have a plate resistor gone open.
If you see 200V on a cathode, you have a cathode resistor gone open.

It's a lot easier with a scope and a signal generator because you can run
signal in and trace it step by step with the scope, so you can identify the
offending stage before you start poking around with the meter. This saves
a lot of time.

It's almost certainly not a tube. Tubes fail sometimes, but resistors and
capacitors fail more often. I would make sure all the filaments are lit
first, of course.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

On 11/29/06 6:37 AM, in article
, "K7AAY"
wrote:

Given an SX-100. It doesn't work.

Chassis and interior in good shape, no corrosion. Lights fire up when
turned on. Attached Hallicrafters 3.2 ohm speaker (or headphones if
plugged in) hums, and I hear scratchy noises when I change across the
bands or switch to phono. S-meter moves across the dial when I spin the
sensitivity knob.

But, it doesn't actually receive anything, and the S-meter does not
move as I traverse the bands nor does it change as I move within a
band.

Suggestions on priorities for troubleshooting, by tube replacement or
otherwise, appreciated. I feel the detector is the place to start?
Have a multimeter, is all. In Portland (OR) Metro area.

0A2 voltage rectifier $6
5Y3GT rectifier $10
6AU6 1st mixer & crystal cal (1 ea) $10
6BA6 1650 KHz IF amp, 2nd mixer, 50.5KHz IF amp (1 ea) $8
6BJ7 detector/AVC/noise limiter $5
6C4 1st conversion oscillator & KHz IF amp (1 ea) $13
6CB6 RF amp $5
6K6GT audio output $8
6SC7 audio amp/BFO $9
12AT7 2nd conversion oscillator $13

Your Elmering would be appreciated. Thank you in advance.


If you don't have the manual, you should download it from the BAMA Mirror
site.

Read through the Test section and set all switches, pots, Band Switch,
frequency, etc to what is directed.

Next, using the page(s) showing the bottom view tube layouts with pin
voltages, measure all the voltages with a VTVM or equivalent and write down
all voltages that are off by more than about 10%. This should provide a
guide to where you have one or more defective components.

Please give a clue about your level of electronics. What town are you in?
I'm in Washougal (East about 15 miles on State 14, from I205 bridge). I
have a sig gen I may loan you, but can't let loose of my scopes. Maybe
later.

Don

I agree with the previous advice. Paper & electrolytic capacitors should be
replaced eventually, so why not start now? This article has basic advice
about recapping.

http://antiqueradio.org/recap.htm

You can download the schematic & service data from the BAMA site:

ftp://bama.sbc.edu/downloads/hallicra/

I don't know offhand if all of the SX-100 tubes are glass, in which case you
can look for duds by simply looking to see whether tube lights up inside. I
believe this set uses a 0A2 regulator tube, which will glow purple rather
than the usual orange-ish. Don't freak out -- that color is normal.

Knowing that a tube lights up doesn't tell the whole story, since the tube
might still be too weak to perform well. On the other hand, if you find a
dud or two, you've learned something useful.

You can also check for duds by measuring the resistance of each tube's
filament with an ohmmeter. You can look up each tube's basing diagram at
Nostalgia Air:

http://www.nostalgiaair.org/

Click on Tubes, then enter the type (for example, 6SN7) of each tube you
want to test.

The tube filament is shown in the diagram as little mountain-peak sort of
symbol. In a 6SN7 tube, for example, the filament pins are 7 and 8. If the
filament is good, you should measure very low resistance between those pins
using an ohmmeter. If you measure infinite resistance, the filament has
burned out and the tube is no good.

When you say that the radio "hums," if that means a loud, low-pitched hum
which doesn't change as you turn the volume up or down, then you have bad
electrolytic capacitors in the power supply. Replace those before doing
anything else. You should do that anyway, to avoid burning up your power
transformer if one of them fails.

If by "hum" you mean just the normal faint background hum from a tube radio,
then don't worry about it.

There is a very simple test to tell you whether your audio amplifier is
working. Turn up the volume, then briefly touch a turned-on soldering iron
to the input terminal of the volume control potentiometer. (That is, the
side that is not connected to ground.) If your audio section is working,
you'll hear a loud growl from the speaker.

Voltage checks are tedious, but can be very informative. When making any
measurements on a powered-up chassis, follow the old-timer's rule of keeping
one hand in your pocket when doing the test. This prevents you from getting
a shock by touching two hands to places they should not touch (Bzzzt!).

Have fun. That should be a great receiver when you get it working properly.

Regards,

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html

"K7AAY" wrote in message
oups.com...
Given an SX-100. It doesn't work.

Chassis and interior in good shape, no corrosion. Lights
fire up when
turned on. Attached Hallicrafters 3.2 ohm speaker (or
headphones if
plugged in) hums, and I hear scratchy noises when I change
across the
bands or switch to phono. S-meter moves across the dial
when I spin the
sensitivity knob.

But, it doesn't actually receive anything, and the S-meter
does not
move as I traverse the bands nor does it change as I move
within a
band.

Suggestions on priorities for troubleshooting, by tube
replacement or
otherwise, appreciated. I feel the detector is the place
to start?
Have a multimeter, is all. In Portland (OR) Metro area.

0A2 voltage rectifier $6
5Y3GT rectifier $10
6AU6 1st mixer & crystal cal (1 ea) $10
6BA6 1650 KHz IF amp, 2nd mixer, 50.5KHz IF amp (1 ea)
$8
6BJ7 detector/AVC/noise limiter $5
6C4 1st conversion oscillator & KHz IF amp (1 ea) $13
6CB6 RF amp $5
6K6GT audio output $8
6SC7 audio amp/BFO $9
12AT7 2nd conversion oscillator $13

Your Elmering would be appreciated. Thank you in advance.

If you hear noise when changing the band switch try
cleaning the switch and the tuning capacitor contacts. Also,
blow out the tuning capacitor to make sure there is nothing
shorting the plates.
If you have not tested the tubes do so but I think a bad
tube is unlikely.
Do you have any service instruments (VOM, scope, etc.)?
Do you have the service manual? If not there may be a
free one on line somewhere. If you have the book you can
check voltages at the tube sockets, this will often find the
problem or give you a pretty good clue as to where it is.
Evidently, the power supply and audio stages are working.
If you have a signal generator try inserting a signal into
the IF strip. You can often do this by wrapping a few turns
of wire around a converter tube. The SX-100 is double
conversion so there are two I.F. frequencies, again, a
handbook will be very helpful.


--
---
Richard Knoppow
Los Angeles, CA, USA

snip
oh yeah, I forgot to ask, is the ANTENNA hooked up ?

Should have mentioned, yes it is.