Tom

The?Panasonic RF-2200 is a mid 1970's era transistorized receiver that is not synthesized, that is it is a traditionally L/C oscillator tuned receiver.? Doing a search on the 'net, it seems to have a cult following much like the GE super-radio.? There are several YouTube videos documenting the repair/ restoration of these sets.? Perhaps a common problem in most portable radios is battery leakage which tends to attack PCB conductors.? A good reason to remove the batteries before storage.? .

If the intent is to reform capacitors or to prevent damage form the catastrophic failure of components, then a VARIAC is useless.? A dim bulb tester is what is needed.? The amount of current supplied to the test subject can be easily controlled by selecting the wattage of the incandescent light bulb used in the tester.? It has to be an incandescent bulb, modern compact florescent or LED bulbs do not behave in the same manner to manage current.

Since the?Panasonic RF-2200 is a modern battery / AC powered transistor radio, the troubleshooting technique is different then what is used for a tubed radio.? From the videos it seems that a critical eye checking over the printed circuit board is the first step.? Any corrosion seen is suspect and should be investigated; any damage found should be cleaned and repaired.? Getting rid of any dust, dirt and such along the way is a plus.? Use your favorite contact cleaner to clean / lubricate the various switches and pots is the next step.? I use the dollar store spray can of penetrating oil with great success but you may prefer the much more expensive Caig products.

Once the above has been completed, battery up the radio and turn it on.? Let us know what you find.

Regards,

Jim

Logic: Method used to arrive at the wrong conclusion, with confidence.? Murphy

On Thursday, May 16, 2024 at 02:39:00 AM CDT, Richard Knoppow <1oldlens1@...> wrote:

Now beware these are my opinions, I think they are right but others
may disagree.
A Variac is useful especially if it has meters showing the current
being drawn. A volt meter is also useful but less so.
The main purpose of bringing up a unit on a variable transformer is
to catch sudden shorts and be able to turn it off quickly. The idea of
starting at a low voltage and bringing it up over a long period of time
is really misleading. The idea is to catch anything that is going to
short quickly and turn it off. A filter capacitor that is going to short
usually does so quickly. Otherwise, electrolytic caps that have not been
used for a long time may need to "reform" but will do this in a few
minutes at full rated voltage. Just letting them run for a while will
usually reform them if they are going to reform. Lots of mis-information
about this.
Watch the ampmeter while bringing up the voltage. Usually, vacuum
tube rectifiers begin to conduct pretty well at quite low voltages so
any shorts will show up fairly quickly.
Sensitivity: for the most part a receiver like the SX-42 has pretty
good sensitivity. We must differentiate between sensitivity and noise
level. The biggest difference in modern receivers is noise level. Most
vacuum tube receivers with typical phone bandwidth will have a gain
sufficient to produce about half a watt or a watt of audio power from an
input signal of around a micro-volt. Now, signal to noise is another
thing. A decent receiver with a vacuum tube RF and mixer will have a SNR
of around 2.5 uV for something like 6 to 10 db noise ratio. Some modern
receivers, tube or solid state may be ten times better than this. The
requirement is that the noise contribution of the receiver be small
compared to the noise from the atmosphere. Up to maybe 10Mhz even rather
noisy tubes will do. For higher frequencies the quality of the tubes but
also the quality of the input circuits will make a large difference. The
later tubes, like 6SG7 or 6BA6, will be reasonably good to around 50Mhz
earlier tubes like the 6K7 or 6SK7, may become a bit deaf above about 20
Mhz. Some miniature tubes have considerably better signal to noise
ratio. One measure is the transconductance or Gm. The higher it is the
quieter the tube.
The tubes used in the S-20R are fairly old. The noise level is
higher than in later receivers like the SX-42, which was designed to
work at FM frequencies above 50Mhz. My S-20R has good sensitivity to
perhaps 15Mhz but gets a bit deaf above that. The quality of the coils,
etc, makes a difference so that a receiver like the RCA AR-88, which has
very low loss coils, has excellent sensitivity and low noise right up to
30Mhz.
There two ways of specifying "sensitivity" An old method, which one
finds in the specs of early receivers, is really a measure of gain. It
states that for an input of some given level, often 1 microvolt, the
audio output will be of some value, often 1 Watt. This is sometimes
useful to determine if a set is working correctly but is not really much
of a measure of performance. Another method, which has more valididity,
is a statement of signal to noise ratio for a given input level. In both
cases the input is modulated, usually 30% at some medium frequency,
typically 400Hz. The second kind of measurement is stated as some
sensitivity for a signal to noise ratio of, say 10db, but often some
other value. Typical sensitivity for older receivers is around 2
microvolts. Neither of these measurements can be used to compare designs
because both depend on the bandwidth. For a CW signal using a narrow
bandwidth, the sensitivity may be much lower than for AM with a, say
6Khz bandwidth.
There is a better method but its usually used for VHF or microwave.
That is a measure of equivalent noise input, also stated as noise figure
or noise factor. This is measured by applying a calibrated noise
generator to the receiver (or amplifier) and measuring the level
compared to the calculated noise from thermal agitation, i.e. the output
of a perfect, noise free, receiver. It is usually stated in db. A
typical high quality communication receiver has a noise factor of around
6 to 10 db, much less for low noise microwave amplifiers. The advantage
of this method of measurement is that it is independent of bandwidth and
band shape of the set. That allows comparisons of different designs. It
is not a difficult measurement to make but is not often stated for HF
communications receivers. Again, this depends on the transconductance of
the amplifier and mixer stages and the quality and loss factors of the
tuned circuits.
There are other qualities or properties that depend on the quality
of the components, such as the bandwidth of the RF stages and their
ability to reject images and the gain possible from the RF amplfiers
which depends on the Q and losses of (mostly) the coils.
Older text books on receiver design go into these factors fairly
thoroughly but are usually simple enough to be understandable to the
non-specialist. The higher the frequency the more complicated all this
gets, but up to communications frequencies (say 30 to 100 Mhz) its not
too bad.
I am giving you a long answer to your question. In fact, one can
expect pretty good performance from even older receivers if they are of
good quality.
I should also point out that up to around 15 or 20 Mhz the
atmospheric noise dominates things, far outweighing the electronic noise
of the receiver circuits. This outside noise diminishes generally to
where receiver noise becomes of considerable importance above about
20Mhz and dominates in the FM band above about 50Mhx. All this is
discussed in general text books. I find the older ones (say 1950s) are
easier to understand than later ones. They also have the advantage of
being available at no cost via the web. See <tubebooks.org> for instance.
Enough already, I will shut up now.

On 5/15/2024 8:09 PM, Thomas Latimer wrote:

(I know this is a little off topic but I hope someone out there can answer)

I have had two Panasonic RF-2200 radios for a lot of years and want to
get them back on-line again,? so I have a couple of questions for those
of you who are knowledgeable:

1.?? Should I start them gently on a variac or similar equipment (do you
run the same risk with the capacitors)

2.?? If they need repair, is there anyone that works on these

3.?? How does this model compare in sensitivity and selectability to
something like one of the main-line Hallicrafters stuff? (I have an
S-20R and three SX-42's)

Thanks in advance, any and all advice is appreciated

Tom Latimer
Okemos, Michigan

--
Richard Knoppow
Los Angeles
WB6KBL
SKCC 19998

(I know this is a little off topic but I hope someone out there can answer)

I have had two Panasonic RF-2200 radios for a lot of years and want to
get them back on-line again,? so I have a couple of questions for those
of you who are knowledgeable:

1.?? Should I start them gently on a variac or similar equipment (do you
run the same risk with the capacitors)

2.?? If they need repair, is there anyone that works on these

3.?? How does this model compare in sensitivity and selectability to
something like one of the main-line Hallicrafters stuff? (I have an
S-20R and three SX-42's)

Thanks in advance, any and all advice is appreciated

Tom Latimer
Okemos, Michigan

(I know this is a little off topic but I hope someone out there can answer)

I have had two Panasonic RF-2200 radios for a lot of years and want to
get them back on-line again,? so I have a couple of questions for those
of you who are knowledgeable:

1.?? Should I start them gently on a variac or similar equipment (do you
run the same risk with the capacitors)

2.?? If they need repair, is there anyone that works on these

3.?? How does this model compare in sensitivity and selectability to
something like one of the main-line Hallicrafters stuff? (I have an
S-20R and three SX-42's)

Thanks in advance, any and all advice is appreciated

Tom Latimer
Okemos, Michigan

?

A majority of acceptance is not proof of correctness.