I was very impressed with your CC installation picture
and quite blown away by the audio from the SRF-42.
You probably have already read this somewhere, but
I have a SONY SRF-A100. Electrically it works great,
but the front was badly scratched up in a move years
ago. I actually cut up a speaker grill from another radio
and I am trying to put the whole front of the A100
back together so it looks nice again.
As far as the LPB RC-6A is concerned, I have a bunch
of comments and questions that you may be interested
in looking at, but I will probably have to save them until
next week. I do plan to test the transmitter some more
also.
Thanks for all of the really cool information.
Best Wishes,
Bruce, MICRO1690/1700
Ahh the SRF A100..I have one of those as well. It sits in the living room with the home theater setup. 🙂
I used my Sony SRF-42 for the sample because I wanted to have in the sound sample of actually tuning in to the station instead of using the studio monitor's Sony ST-JX220A receiver, which is a digitally tuned unit. (modified to tune the expanded AM band)
This way no one could say "hey that could just be line level recorded audio!" 😀
I will post more pictures of my CC setup, particularly the coupling arrangement so folks can get an idea of how that is configured.
I look forward to the questions and comments about your LPB RC 6A unit. Be happy to help. 🙂
(added links to new LPB auctions)
Here is another auction for an LPB AM25 D transmitter and a separate auction for an LPB TCU-30D coupler.
AM 25D - http://cgi.ebay.com/LPB-AM-25D-Transmitter-/330535117177?pt=LH_DefaultDomain_0&hash=item4cf56da179
Any questions about either of these units just ask. No..I am not the seller I just have extensive experience working with LPB transmitters, but these new auctions are from the same seller of the earlier LPB AM 25D transmitter that sold for $430.00.
Again these things are highly sought after and worth their weight in gold. FCC certified for Part 15.221 Carrier Current operation.
RFB
RFB, I hope there aren't too many questions
here.
I guess the unit's crystal is in a U-17 case. I'm
wondering if the unit is made to work across the
entire AM band, well - 540 to 1600 kHz - when
it was made. I have a small 1590 kHz crystal which
could be soldered in somehow. (1590 here is clear
during the day.) It would be nice to figure out a
way to have the unit send a signal around my house
and yard. But maybe this particular transmitter won't
go that high in frequency. Also, the 1590 kHz crystal
(HC-6U, I think) might not be able to take the strain of
the voltage from the transmitter's oscillator. Also, I
think that the fundamental crystal frequency determines
the frequency of the transmitter, unlike some other
LPB transmitters, where the crystal frequency is a fraction
of the operating frequency. Also, the 1590 crystal may
have the wrong capacitance, but I guess that could be
netted in with some other caps.
The crystal that is in the transmitter right now is on 860 kHz.
This is not a very good channel, although if the signal just
covered my house and yard, I guess it would be OK. I notice
there are 3 tuning adjustment screws that are near the RF
section. They are very chewed up, so they have to be turned
by needle nose pliers. They appear to be almost all the way
down into their holes. Since the transmitter is putting RF out
very well on 860, I am leaving them alone for now. (Besides,
turning the screws a little bit doesn't seem to do anything.)
There is a
neon light near them, which must be a tuning indicator. It
is glowing very brightly, so that seems to confirm that the
RC-6A is well matched to the 50 ohm dummy load.
The power transformer has a layer of brown stuff on top of it. Two
things come to mind. (This brown stuff has not changed in
25 years.) I guess this stuff is either some kind of glue that was
put on top of the transformer for some reason or - (and I hope
it isn't this second idea I have) - once leaking PCB stuff!? I have
never touched it, and it has never changed. Since the
transmitter is working - it seems to me that the power
transformer is OK. So, who knows?
The crystal label says 860 kC, so I guess this RC-6A, or
the crystal, anyway, is pre-1966, or whenever everybody
decided to change kC to kHz. I think it was around that
year.
The two input screws on the back of the unit, which are
made to accept an audio signal - do not work. Instead,
somebody brought out of the back panel holes, 2 wires with alligator
clips on them. If you put an audio signal into those wires,
the transmitter will modulate pretty well. The volume control
on the back of the transmitter (which is screwdriver adjustable)
does work. I have no idea where those two wires actually go.
One of the 6AL11s is different from the other two. This doesn't
surprise me. I think the transmitter went through a great
deal in it's life of service. That may explain why swapping
the tubes around made the transmitter modulate better. That
different tube was made by Raytheon. (Sp?) I can't read
the labels on the other two 6AL11s, but they are made by
another manufacturer. They also look a bit different from
the Raytheon tube.
Sometimes there is a high pitched audio whine that comes
from the RF section. I tapped the chassis near there and
the whine stopped. Something must be a bit unstable,
so therefore it is sometimes oscillating in the audio range.
This noise does not show up on the air signal.
The above are my main observations of the unit. In spite
of it's many problems, I still consider it to be quite a treasure.
Here are a few more comments. RFB, do you know the difference
between the RC-6A and the RC-6B?
Also, just to get a signal around my house, I was thinking of
making an 50 ohm RF attenuator network and feeding the
output to some kind of antenna under the Part 15.209 reg.
Again, I haven't checked, but I think Part 15.209 is the
permitted RF field strength regulation for the AM BCB.
I have a friend who is a great RF guy. He is not a
broadcast engineer, but he is an RF expert (particularly
with tubes) who is wiling to look at the transmitter.
If, after some time, the unit's quirks can be worked out,
and I can get it on a better frequency, I think it would
be great for yardcasting. If a coupler could be found
someday - I could attempt carrier current a second time.
My broadcast engineer friend took the coupler back (I
had borrowed it) but maybe it might become available
again some time. I know some people have attempted
to feed the AC line with just a couple of isolating caps,
instead of a real coupler. I don't see how this could work
well. I had heard that in World War Two, some experimental
college broadcast operations fed transmitters into gas pipes
to get a signal around the campus. (Because broadcasting
was prohibited, I guess.) Somewhere around here I have
a book called, "The Gas Pipe Networks," which tells about
this history of this kind of "broadcasting." It also has pictures
of some of the station set-ups. I would never try to it that
way!
I did connect a 100 mW Part 15 transmitter into a house radiator
about 30 years ago. The signal did get out about 500 feet.
I guess all of the radiator pipes in the house were acting
as a kind of antenna. The transmitter was a Panaxis AM-100 (?)
which is long gone.
Well, RFB, that's all I can think of. If you which to comment
on this message at your convenience, that would be cool.
Well,, I think one of my dogs has to go outside, so I have
to get off of here.
Best Wishes,
Bruce, MICRO1690/1700
I will try to answer in the order of your posted queries. I do not have a schematic on hand to reference to except for one to an LPB 50 unit which if I remember correctly, uses the same design in the oscillator and driver sections prior to the final twin tube power amp and the same series of tubes.
The use of an HC6-U may work if it can handle the circuit currents and if it is a parallel resonant crystal. The cathode of the oscillator tube is of the grounded cathode design and there is a resistor in series with the crystal to G1 (grid). Some feedback is also incorporated here through two capacitors and a diode to G2. Again this is referencing to the LPB 50, there may be variances especially for the particular part of the band being operated.
I would not attempt to use the HC6-U crystal for the very reasons you suspect...it may not handle the currents and simply get ruined. However it should not be too difficult to find a crystal as I have seen a bunch of them recently on ebay for both upper and lower frequencies of the MW band. Yes these used crystals that were fundamental crystals and not multiples like the solid state units.
The neon light is your final plate resonance tuning indicator. At resonance the neon light should give a slight dim glow and not a bright one. This indicates a good plate dip and match to the load. If it is bright, the plate circuit is drawing too much current and not quite tuned. Tune the output for a "dip" in this neon indicators brightness. It works just like tuning for a dip on a meter. Since its putting out about 5.5 watts with the neon light at its present glow, it must not be very far off resonance, or the circuit for the plate tuning indicator has some components that are out of tolerance and giving you a false indication, which can be checked with an external watt meter, or put a small reading lamp light bulb in series with the output connector to the dummy load and that can indicate the output power at resonance..the light will glow upon peak resonance and dim when off resonance.
The brown stuff at the top of the transformer is most likely just assembly adhesives used to help keep the transformers from oscillating as well as insulate them. Those transformers will not contain any PCB oils in them as PCB oils were used as a coolant on high power, high current transformers. Do not worry about the brown stuff. It is normal to see that on small transformers of that era.
Yes it was around 65 or 66 when they started changing the labels over from kC to Khz or mC to Mhz. I cant even remember why or what the big deal was about that...they mean the same thing! 😀
Odd that someone would disconnect the audio input from the supplied screw stock terminals and use a pair of alligator clip wires. Only way to find out for sure is to remove the bottom cover and look inside. Curious.
Some tubes with the same number will have slight differences in appearance from one manufacturer to another. Nothing to worry about. The important thing is to make sure your using the proper tubes with the same number. The variances might have one tube with a little better specs than the other, but should work just fine.
The audio whine is an indication of something in there oscillating either due to loose mounting or perhaps isolation adhesives have become brittle, but strange that it is a whine sound. There is nothing in these units that would make them oscillate at an audio frequency whine like how the old tv's horizontal circuitry would whine at the H frequency (15Khz). Another curious thing to ponder about...but without looking inside to see the condition of the underside components and the age of the unit...anything is possible. If it does not appear to affect the output power level or audio modulation and frequency stability...it should not be an issue unless the whining tends to become excessive and drives you crazy from the whine pitch! It could be saying "Help Meeeeee!!" 😀
Have your friend take a look at the unit and see what he finds. Its good you have someone nearby with experience in tube RF. Tube RF or solid state RF is all the same to me as to me, if its a vacuum or slice of silicon it does the same in the end. The differences is the elements themselves and the voltages/circuits used around them to make them work. 🙂
Coupling to gas pipes is indeed a very dangerous approach to carrier current. You certainly do not want to be feeding RF energy onto a gas pipe that one day develops a slight leak. Even at low RF levels as 5 watts could possibly ignite that leaking gas and BOOM! Not a good thing! The neighbors wont like that and its too cold this time of year to have the entire neighborhood's gas supply go out!!
The use of simple capacitors to couple to the power grid or pipes is not a good idea either. This is not properly coupling and matching the transmitter as the loads such as power lines constantly change their inductance due to loads placed upon the lines. Proper coupling units are designed to compensate for the swings in inductance changes as well as provide isolation between that varying inductance and the transmitter output so as the transmitter always sees a proper load impedance. They also provide a means to effectively "null" out the 60hz induced hum. The early couplers used tuned circuits to accomplish this..a very cumbersome and clustered mess of coils and capacitors and inductors. They were not very effective in eliminating the 60hz induced hum, and constantly had to be tweaked and peaked due to the varying inductance changes on the power lines from one part of the day to the next, especially during evening hours when people were home turning on appliances and lights.
Maybe the coupler you borrowed might be for sale if it is not being used or can be borrowed again. But keep an eye on ebay for those as well as other auction sites. Another good source for those is at ham fests.
You could run a length of RG-8 coax in the areas of the house where you want some coverage, or even out into the yard. Cut at regular intervals slices into the coax but not splice the coax. Move a little bit of the ground braid away from the slice, making each slice about 1 to 2 feet long and spaced about 10 feet apart from each. Terminate the end of the coax with 50 ohms and of wattage at least twice the power rating of the transmitter output. This is a "poor man's" leaky coax setup and you wont need the full 5 watts from the transmitter. You can pad it down to probably a half watt, maybe even less to get the signal where you need it through the home made leaky coax. Also you do not have to cut away the insulation of the center conductor. Leave that intact. The only removal of insulation will be the outer insulation at the slice intervals and only a small portion of it. Do not completely remove the outer insulation at each slice point. You can also wrap the slices after making them with electrical tape to help insulate the copper braid from corroding, or use coax putty.
Ahh the Panaxis AM-100....great little kit, I still have mine with the AM-5000 companion amplifier and power supply. They sit with all my other collected transmitters and still work perfectly. Only problem the AM-100 had was its limitation to frequencies...particularly the upper portion of the band because the divide by N counter chip was limited to 4Mhz input and thus the output could only go as high as 1500 Khz. But the unique part about the AM-100 was the modulation scheme and the fact it could throw out a 300% modulation punch in one mode versus the normal 100% mode. The second drawback was that it had to have a dual rail power supply of + and - 15 volts. For a mere 100mW output, that could have been obtained with 5 volts, even dual rail, but the output circuit utilized the whole +/- 15 volts. It was way too easy to modify that board and replace those transistors with beefier ones to get as much as 500mW right out of the board itself.
Well I hope I have been of some help here. It sounds like the RC-6A unit is not in bad shape considering age and such. A little TLC will get her going to full speed once again.
RFB
I really appreciate all of your information!
The leaky coax idea seems great! I'll probably
do that. I am going to put an equalizer and
audio processor on the transmitter and try to
get an idea of how well the audio circuitry is
functioning.
I also have some stories about the Panaxis AM-100.
I'll have to pass those on when I can.
Thanks again, I really really appreciate it.
Best Wishes,
Bruce, MICRO1690/1700
No problem Bruce. Oh I forgot to add...regarding the RC-6A's frequency range. These particular units were designed to cover the whole band and were meant for low budget CC installations. Most installations that used these operated in the low part of the band as coupling back then was still quite experimental until the good ol TC-8 came out. As you can see inside the unit, there is not a whole lot on the output section except for the plate tuning circuitry. These did put out a nice clean signal even by themselves into a dummy load or long wire. When coupled to the TC-8, they further improved their out of band specs as well as in-band specs.
As we all know, fundamental carriers will have 2nd, 3rd, 4th and so on harmonic emissions. At a frequency of 600 Khz, your 2nd harmonic would fall in-band at 1200 Khz. So when you operate at the low to mid band sections, double check that 2nd!! Building a filter is easy and lots of tips can be found on the web and even here on various threads. Keep in mind though, some of these filter designs are meant for very low power levels and not meant to filter a 5 watt signal, so you will have to beef up the components and swing the values a little + or -.
Fixed filters are great, but I like to work with a tunable filter with variable caps and inductors to peak the filtering. I guess its just from the old days of when we engineers spent more time tweaking and peaking than fixing. Old habits die hard and I hope they never do!!! 😀
RFB
I have never met anybody that has
known so much about these old LPB
tube transmitters.
I may have some more thoughts. Also,
I would like to tell you about my adventures
with the Panaxis AM-100.
Hopefully, that will be coming soon.
Best Wishes,
Bruce, MICRO1690/1700
No problem Bruce! I look forward to the adventure stories! 🙂
RFB
I just wanted to report that the LPB
transmitter sounded good after I
hooked it up to an equalizer and
audio processor. I don't know if it
was 100% modulation, but it wasn't
bad.
Aside from maybe a few other problems,
this rig sure could use some new (NOS)
6AL11s!
The Panaxis stories are pretty long. They
will be coming soon. I also have used some
other Part 15 transmitters that seem to be
completely unknown. I'll have to write
those up as well.
Thanks again, especially for the info about
the RC-6A power transformer!
Best Wishes,
Bruce, MICRO1690/1700
No problem Bruce. For accurate measurement of modulation on any AM rig, Part 15 or 73, you need a modulation monitor with peak detection.
Using any regular radio will only give you somewhat close comparisons because AM radios have AGC circuits that maintain modulation detection while blanking out noises for maximum audio demodulation performance.
They work a lot like audio limiters and compressors, except they are working in the envelope detector circuits and doing a few things at once and not just an audio chain. If you have a receiver that has AGC on/off option, turn off the AGC to make comparisons.
Looking forward to those AM-100 tales! I got a few as well. One real quick I can throw in here is an experience my neighbor encountered while enjoying a BBQ on a nice sunny Sunday. He wanted to place his stereo speakers outside on the back patio for music. He had to run extra length of speaker wire so they would reach the stereo 2 rooms over from the back door. He could not understand why his speakers were making sound when he had not even turned on his stereo yet!
He came over to ask me if I could look at his stereo because he thought there was something wrong with the power button and that the stereo was creating sound while turned off!! I just laughed and explained it all to him. After he too had a good laugh and wondered if there was a way to pull tricks on people like that!
RFB
We have several AM 100 stories already and it will be awesome to add Bruce's experience.
We also have all the AM 100 docs in the library
I was lucky enough to live close to an AM transmitter site for a station with content I really liked. My (high impedance, high efficiency) Speakerlab 8s pulled that station right in over my speaker wires, too, and at a delightful, subtle volume level. Very nice having 24/7 radio you like with no power required.
Total fluke, of course, but nice.
I used a Panaxis AM-100 20 years ago. It
was given to me, built, as a Christmas
present, by a local broadcast engineer
friend.
As many of you know, this transmitter
only transmits on a few frequencies.
These are 600, 750, 1000, 1200, and
1500 kHz. This is because the crystal
oscillator runs at 6 MHz, and there is
some dividing circuitry that permits
choosing the above output frequency you
want. You do this by using DIP switches.
The transmitter also operated on a few
odd split frequencies, but I don't remember
which ones.
I had said my Panaxis is long gone in the
above post, but that was a simplification to make
writing that post easier. It HAS BEEN long
gone, BUT it is still in my house, somewhere,
I think. Along with ANOTHER ONE, that was
given to me many years after the first, from
a college carrier current operation. I do not
have the five watt amp, which is fine. I
wouldn't know what to do with it anyway.
Because of my eye trouble, it is hard for me
to find things (just ask my wife.)
If I ever found them again, I would put them
on the air in a heartbeat. I would just replace
that limited 6 MHz/divide = f with a crystal
oscillator running at whatever channel I wanted.
As far as I'm concerned, who cares if the transmitter
needs plus 15 volts and also negative 15 volts. There
are plenty of power supplies lying around in my house.
About five years ago, I had the pleasure of talking to
the man who designed and built the Panaxis AM transmitters.
He must have sold the design and stock parts to somebody else?????
Or maybe it was just the FM design? (The FMX or whatever?)
He was very nice, and was retired and out of the radio biz.
He was taking up gardening and I sure wish him well.
I don't remember his name, and have since lost the
contact info. But I sure liked him.
The 2 Panaxis transmitters I had were a little bit different
from each other. One transmitter put out a lot more
power on the low end of the AM band. The other
transmitter worked better up on 1200 and 1500. I
believe there is a fixed cap on the final RF board.
Whether it is there or not determines which end of
the band (high end of low end) will give the most
RF power. There are also some other adjustments
that I didn't understand, because of lack of documentation.
I had the first transmitter on the air twice, in about
1989 and 1991. In the first experiment, knowing
NOTHING about how to get it to really radiate
(lacking documentation) I came up with the following
goofy solution. I hooked the RF output to the radiator
in the house. I just got an alligator clip and
hooked the RF out to the little protruding section where
the radiator gets bled. The signal became very strong
all over the house, out in the yard, and about 500 feet
beyond. This was on 1000 kHz, which was pretty empty
in Gardiner, Massachusetts, where I was, at the time.
(1000 kHz was quiet there, at least, during the day.)
In 1991, at an apartment in West Hartford, Connecticut,
I tried a different approach with the same transmitter.
I was on the 3rd floor in this particular house. Again, having
no knowledge, I tried to make a output matching transformer
with a disgarded radio loopstick. For ground, I used the
ground screw on an outlet strip. I kept everything below
the 3 meter length. After fooling around with this setup
for a while, I obtained coverage of about 500 feet from
that house on 750 kHz. Also, the signal would show up on adjacent
streets under power lines and such. I had no programming
of any kind. I was just trying to get the thing to work.
Then I moved. I know the transmitter and it's twin got
to my present house, but WHERE ARE THEY? I have a
very very good hearted sister in law who has helped me and
my family with so many things. Sometimes, when our
kids were younger, she would take up the cleaning chores.
She may have moved the 2 AM-100s. I am sure she didn't
throw them out.
I know the transmitter has adjustments on it for very very
high modulation for very small lengths of time. It was 300%,
right? I could never figure any of that out. So the above
two experiments were all I was able to do. I like this transmitter
very much. It has wonderful audio and is clean. I believe the
output to be around 50 ohms. It just seems like that is the
case. But if you hang a 3 meter wire off the back of it and
expect it to go any distance, you will be disappointed. It
will barely get across the room.
I believe there was a person on the board who had a Panaxis
AM-100 on 1500 kHz, with a good solid half mile range.
That would be good enough for me. Whoever this guy was,
he knew what to do for range.
Well, maybe I'll find them some day...
Best Wishes,
Bruce, MICRO1690/1700
Bruce MICRO1700, loved your Panaxis AM 100 story. The glory of part 15 at its best.
More stories!
More stories!
About a year before the FCC reduced the permitted
field strength on the FM band, Radio Shack had a
cool FM broadcast band wireless mike called the
FM-90. It was shaped like a mike, but it was
more like half of a brick. Sort of a long rectangle.
You talked into one end. Excellent audio. It
also had a phono jack which would take line
audio and a volume control. Nobody seems to
remember this thing. It worked from 88 - 92 MHz
and could easily cover up a local station from 50
feet away. It was very stable and tuned with
a little tuning stick. Radio Shack also had a whole line
of kits that were on red perf boards on one side
of a box. They were called P-box kits and the
FM transmitter P-box kit blasted a signal out
that was unbelievable. Especially if you jacked
up the voltage. This was earlier than the FM-90.
It was about 1970.
Around 1962 Heathkit had a wireless broadcaster
that was on the AM band. Again, it was hand held
and huge and bright Heathkit green. It was powered
by 6 D cells. They lasted for about an hour and then
ran down. It had a huge thick whip antenna. The
frequency range was from 1400 - 1600 kHz. It
went about 30 feet and was super loud and strong.
(Remember, this was a Part 15 AM transmitter you
were holding in your hand, so there was no ground
system.) You would have to see this thing to believe
it. And it was so big you had to hold it with both hands.
(Well, I was 7 years old, so maybe that's why.)
I am interested in the history of when the field strength
was cut down on the FM band (like I said, it was about
1972 or 1973.) I also wonder what the permitted field
strength or permitted power was before the reduction.
Here's a dumb thing. I put the FM-90 transmitter up
on a kite to see how far the signal would go. The kite
and the transmitter crashed in a swamp.
Oh well.
Best Wishes,
Bruce, MICRO1690/1700
And to this day people visiting the swamp at night hear unexplained radio broadcasts from somewhere in the lilly pads.