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Mr.RC-Cam

Vintage R/C Collection: The good old days

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Over the past two decades I've been collecting vintage R/C equipment. It's a modest collection of about 50+ R/C radios. Some of this old stuff was what I dreamed of owning when I was kid.

Just to put a time-line on my R/C adventures, my first system was a used Kraft Single Channel Tone setup with a pair of Royal actuators (rudder & throttle). Its original owner crashed his model and decided to quit the hobby. The $25 price I paid for the broken R/C system was funded by mowing lawns at 50 cents a house. That was top dollar for cutting a lawn in 1966.

Here's a photo that shows part of the collection.

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Some of the radios you see in the photo are fully functional and complete with Rx's & actuators/servos. I realize that this stuff looks like junk to most people. But to ancient tech guys like me these are fascinating electronic devices that evolved at a time our nation was desperately trying to get us on the moon. In fact, many of these early designs came from engineers that were working in the aerospace industry. That's right, enterprising rocket engineers created them in their free time and some quit their jobs to start their own R/C company. We've recently witnessed a variation of that with the emergence of FPV companies that began with a personal hobby project.

Some basic information on radio names & dates is discussed in this old post:

http://www.rc-cam.com/forum/index.php?/topic/901-vintage-rc-equipment/

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The most fascinating radio in my collection is the Sampey 404. I lusted after that system for many years, even after affordable "digital" radios appeared in the late 1960's. I first saw it in a Grid Leaks magazine ad and decided right then that I would own it one day; I still have the magazine.

Here's some examples of their ads that made me want to have it.

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The $548 USD price is about $4250 in 2014 dollars (thanks to inflation). Keep that in mind the next time you complain about the cost of your $200 R/C system.

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I was fortunate to find a Sampey 404 Tx that is in remarkable condition. Although I don't have a complete airborne pack, I was able to get the Tx fully working using a o-scope and RF spectrum analyzer. Listening to the audio tones (from a scanner radio) while it transmits is very cool.

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With batteries it weighs over 4 lbs and it is a bit clumsy to hold due to its size. Pilots back then would cradle their hefty Tx in their arm (like they were holding a baby) while they flew.

The photo below provides a comparison to a modern R/C radio. But in its day it represented the usual ergonomics of these things (which is to say, pilot comfort was ignored). There's not much you can do to make a well balanced Tx when all you have are sheet metal cases and vacuum tube construction. BTW, wide use of molded plastic cases did not hit the R/C scene for another 10 years.

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The 3-axis (yaw/roll/pitch) open gimbal stick has decent quality pots. However the stiff return springs are quite strong compared to modern radios. Here's a drawing that shows the stick & trim controls for the Sampey 404:

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This next photo shows the inside guts to the Sampey 404. There are three vacuum tubes and ten germanium transistors. As a 10 year old kid this technology was beyond my comprehension and it looked impossibly complicated. But I wanted to know everything about how it worked.

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Unlike most other R/C systems in its day, the 404 was a true proportional control system. But because it was analog technology (servo control signals were voltage based, not PWM) there were issues with servo drift. Drift problems, plus complaints about poor receiver performance, quickly earned the Sampey radio the nickname "Swampy."

The transmission scheme was a combination of FDMA and TDMA modulation. Different audio subcarrier frequencies (FDMA) were used for each command channel, but it sent one subcarrier at a time (TDMA). These audio tones were filtered by discriminators in the receiver and converted to four analog voltages for servo position control.

One nice touch was the use of four D-size NiCD batteries to power the Tx. It was common back then to have two 67.5V batteries for vacuum tube B+ voltage and some 1.5V cells for the filaments. But the 404 used a DC-DC inverter supply that converted the 4.8V battery voltage to +135VDC. Total current draw is 1.5A, so the original GE 4.0AH NiCD cells would provide 2 hours flight time. I have modern 10AH (10,000mAH) MiMH cells in mine.

Here's a schematic of the 404 Tx:

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Tone generator commutation is handled by a 4-stage ring counter that uses eight 2N223 transistors that are configured as four flip-flops. They form a cascade of one-shot circuits that rapidly sequences three relays. The relays operate in a round-robin affair that step through the four control pots (motor / pitch / roll / yaw). The chosen pot's wiper voltage would be applied to the VCO (voltage controlled oscillator) circuit. During operation you can hear clicking sounds from the relays. From the clicking noise my best guess is that the switching period is about 15Hz. Or perhaps I should say 15CPS. :)

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It should be noted that when the Tx is first turned on only motor control is operational. That is because the ring counter needs to be kicked-started into action. A push switch (marked START) on the front of the radio must be pressed several times until all four channels begin to function (or until you hear the clicking sound from the Tx's relays).

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The VCO (voltage controlled osc) is handled by a pair of 3V4 vacuum tubes. The VCO produces the four audio tone groups and they can be heard on a ham radio scanner tuned to the 27MHz band. The music it creates will vary as you move the sticks and knobs.

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The 404's RF amp is a single 3A5 vacuum tube. It is crystal controlled in the 27MHz CB band. The RF amp has about 1-Watt going in, so output power would be substantially less than that. I think typical control range was about 1000 feet or so. Loss of signal will neutralize the flight control servos, so failsafe existed even back then.

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The DC-DC power supply is a low frequency inverter and its soft whine sound can be heard during use. It converts the 4.8V battery pack to +135V (for vacuum tube B+ bias). The power supply uses a pair of TO-3 size transistors, several top hat diodes, and a voltage step-up transformer.

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I'm still searching for the airborne components (original cased battery pack, 4 servos, and Rx). My goal is to have a complete & functional Sampey 404. I've been searching for a long time and I'm not about to give up. If you find some Sampey parts in Grandpa's basement then let's talk. ;)

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BTW, if you have an old (1960's and earlier) R/C system and want to share the details, then feel free to add your story to this discussion. Many of today's R/C hobbyist have no idea about how the old systems worked. Over the decades there's been rubber powered escapements, reed control, pulse proportional, Galloping Ghost, and other wild technologies. So come and join me around the camp fire and tell your tale.

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Quality stuff! would be nice to use it in something even if only a boat :)

Terry

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Quality stuff! would be nice to use it in something even if only a boat

I'm all for that -- Unless you mean to use it as a boat anchor. :)

BTW, there are organized gatherings of vintage R/C owners that fly with their old gear. I've seen some conversions where the Tx's electronics were gutted and upgraded to modern 2.4GHz digital control. But of course that ruins the value of a vintage system and it would be insane to do it to something as rare as a Sampey. But I have an old Proline radio with open gimbal sticks that is a prime candidate for a full blown conversion. One day.

I forgot to post details to Sampey's proportional servo. I have a very early servo model (Don Steeb version) that is a virgin. That is to say, it still has bare wire leads and has never been installed in a system. I got it from another collector about 10 years ago. Here are photos:

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This is a "new product" announcement from Model Airplane News magazine (1963):

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Here is a schematic of the servo. Position feedback is provided by a pot geared to the output shaft, just like modern servos.

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Gutting vintage stuff defeats the point. Using them as intended is a challenge but also a buzz. I have restored some old valve radio gear and using it is much more fun than using a modern radio with digital read out. I sold a lot a few years ago but still have my 1155 and 1154 but my AR88 is the best performer :)

Terry

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Those are cool old military radios. But a challenge to fit in a model aircraft. :)

Although not very interesting, here's a photo of my Sampey 404 battery charger.

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Inside the metal box is a transformer, diode, and resistors. This is a much safer design than was used in other chargers back in those days. Some R/C charging circuits eliminated the transformer and directly connected to AC mains!

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It would be cool to fly using an authentic multi-channel system from the early 60's. But if I had spent all winter building a vintage model I think I would prefer using modern electronics. That is to say, retain the clumsy vintage layout (and operation) of the original R/C Radio, but put reliable electronics in it. Cheating would be Ok to me if it meant I'd come home with a cherished model in one-piece; I had a hard time doing that back in the old days. :)

BTW, there's a reed radio emulator discussed in the previous web link. It is an interesting way to re-live the old reed days. Here's an example of a "multi-tone" reed emulated system using 2.4Ghz and modern servos:

The servos are no longer proportional, instead they operate the same as the original reed system. So you get to control your vintage model just like the old days. But with higher reliability & safety than is possible from a 60 year old 27Mhz AM R/C system that used vacuum tubes.

But some brave modelers still fly their old gear. Here's a youtube video that shows a Space Control system being flown.

The Space Control was a analog proporational R/C system that came out about a year before my Sampey 404. It's another system I'd like to add to my collection.

Edited by Mr.RC-Cam
Added reed video.

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My dream of owning a working Sampey 404 system is nearly achieved. That is because I found a guy that had the airborne flight pack parts I've been searching for. The price was fair and so now I have a complete system. The receiver and/or servos will need some repairs to get them working; At the moment the servos just continuously rotate and ignore the sticks.

Here's the last pieces of the puzzle that I now own. Fantastic stuff given its over 50 years old. A modern 9-gram servo provides a size comparison with the old R/C technology.

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Here's an interior view of the receiver that shows the two stacked PC Boards:

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My winter project is to troubleshoot the system and get it working. Fingers are crossed I have success!

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Nothing in there you cant fix :)

I thought the same. But I started repairing the flight pack this week and my efforts have been mostly hair pulling. My goal was to get it fully functional before year end, but now I'm not so sure. 

The Tx appears to be working (everything looks reasonable on my o-scope). However, the Rx is dead and this causes the four servos to spin continuously. But the servos are responding to my analog control test voltage, so I think I will have a working system after the Rx's RF deck is repaired.

My flight pack / Rx is the updated 404B version and the circuit diagram I've been using does not match it. After several hours of editing the schematic I discovered that the 404B Rx is a near copy of the Controlaire SH-20 Rx that was used in multichannel reed R/C systems. I'm surprised that the Sampey and Controlaire have near-identical Rx RF designs (they were competitors); It would be interesting to know how that came about.

Here's the Controlaire schematic that is a near copy of my S404B Superhet receiver's front end. I've made a couple edits that reflect component values in my S404B.

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Now that I have an accurate schematic I am less frustrated. But I'm not having any luck getting the local oscillator to run. I've swapped everything in the L.O. circuit and it refuses to work.

It's a long shot, but I've ordered a replacement transistor. This receiver uses several 155TI germanium transistors and these have not been produced for several decades. But NTE sells a replacement part for $6 USD each (ouch). I needed only one but ordered some spares too.

 

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Wow that circuit looks almost too simple to work! I would think the oscillator level would be critical. Have you tried using a signal generator to inject a signal to see if everything else works? Have you tested the crystal? Will be very satisfying when you get it going :)

 

Terry

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I tested the 27MHz Xtal in a vintage Controlaire R/C Rx and it works. I've replaced the two caps and the resistor in the L.O. circuit with more precise parts. The choke tests Ok on my inductance meter. I also swapped the LO's 155T1 transistor with one from the IF stage. No joy.

My hunch is that something has happened to the 155T1 transistors. They ohm out Ok, but perhaps old age has changed their high-freq characteristics.  I should have new ones in a few days, so I'll soon know if that is the issue. Beyond that I am out of ideas at the moment.

 

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Well to be honest there is not much else left its a fairly basic osc. Having said that I am surprised there is no resistor from the base to positive. 

 

Terry

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Having said that I am surprised there is no resistor from the base to positive. 

Base leakage current in the germanium transistors is the reason it is not needed. But early in my efforts (and out of desperation) I tried re-biasing it with a 100K ohm to the positive rail. The emitter voltage was better (went from 2.4V to 1.5V), but still no joy.

Everything points to poor transistor performance. Hopefully the replacement part gets things moving forward.

 

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