I had built a Doerle Shortwave Receiver that employed two vintage Type 30 vacuum tubes. This receiver, and its pristine Emerson Type 30 vacuum tubes, was the crown jewel of my "home-brew" radio collection. I proudly displayed it, with the rest of my home-brew radio collection, in a shelving unit in my basement. One fateful evening I came downstairs and discovered that the shelf above it gave way, smashing the the two Type 30 vacuum tubes in my Doerle Shortwave. This receiver was of open breadboard design and didn't have an enclosure around it that would protect the vacuum tubes from physical damage.
Type 30 vacuum tubes are relatively expensive, typically between $15 and $20 a piece on most websites, catering to "Tube Amp" enthusiasts. You could also try your luck on an auction site like eBay. I wanted to make my Doerle Shortwave Receiver operational again, but didn't want to drop between $30 to $40 to make it happen!
Pictured below is my Doerle Shortwave Receiver, before the accident.
"Old Time Radios! Restoration and Repair" book on Amazon
I consult this book often during radio restoration. I grew up in the transistor, diode, and integrated circuit era and this book taught me a lot about vacuum tube and selium rectifier technology.
Like most antique radio enthusiasts, a have a cache of vacuum tubes and other miscellaneous vintage parts. For some reason I had acquired an unusually large number of 1T4 miniature vacuum tubes. Then an idea formed. Create a tube base adapter that would allow me to substitute a 1T4 for a Type 30 vacuum tube. I liked this idea as it allowed me to get my Doerle Shortwave Receiver up and running at very little cost and without modification. This also allows me to convert back to the Type 30 vacuum tubes should I come across an inexpensive set.
Here are the design challenges and specifications I set for the Type 30 to 1T4 Vacuum Tube Converter project:
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I bent two solder lugs at right angles, then soldered them to a 7 pin miniature tube socket. This will hold the tube socket to the 4 pin tube base. Sorry about the blurry picture.
I drilled then tapped two holes on the opposite sides of the 4 pin tube base. 4-40 screws will hold the 7 pin miniature tube socket to the 4 pin tube base.
Three small holes were drilled into the side of the 4 pin tube base. These holes will be used for the connections to the 50K potentiometer that will adjust the Screen Grid Voltage.
The 50K potentiometer is held to the side of the 4 pin tube base by bending the three leads once mounted. A dab of Superglue under the potentiometer keeps it firmly in place.
I then connect all the wires, the 10 Ohm resistor, and the .05uF capacitor to the 7 pin miniature tube socket. It is much easier to solder with the tube socket out of the 4 pin tube base.
I drilled another hole in the 4 pin tube base then I threaded a test lead with alligator clip through it. This will be used to connect to B+, needed for the screen grid.
The other end of the test lead is connected to an end terminal of the 50K potentiometer.
A black wire is soldered between the other end terminal of the 50K potentiometer and one of the filament pins of the 4 pin tube base. A dab of solder at the end of the hollow tube base pin holds the wire securely in place.
The 4 pin Bakelite tube sockets I had on hand have a built in pin on the side, I will use this as a test point. I soldered a white wire to it.
The white wire from the test point is soldered to the wiper of the 50K potentiometer. A second white wire is soldered to the potentiometer and will eventually connect to pin 3 of the 7 pin miniature tube socket.
Time to wire the 7 pin miniature tube socket to the 4 pin tube base.
Two 4-40 screws, on opposite sides, hold the 7 pin miniature tube socket to the 4 pin tube base.
Here is a side view of one assembled Type 30 to 1T4 Vacuum Tube Converter. Two converters are required for my project.
Here is a top view of an assembled Type 30 to 1T4 Vacuum Tube Converter.
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Believe it or not, Amazon sells a variety of vacuum tubes.
Continuity and Resistance Checks
I always like to take continuity and resistance checks with my Multimeter before putting a piece of newly built equipment into production. I want to make sure that I wired it correctly. I built two Type 30 to 1T4 Vacuum Tube Converters, you can see the second one in the background.
Once the Type 30 to 1T4 Vacuum Tube Converters passed continuity and resistance checks, it was time to put them into a live circuit. You can see them mounted in the white porcelain tube sockets in the picture below. As you can see, the yellow leads from each Type 30 to 1T4 Vacuum Tube Converters are connected by alligator clips to the B+ (90V and 45V) terminals of my Doerle Shortwave Receiver.
The next step was to install the 1T4 vacuum tubes into the Type 30 to 1T4 Vacuum Tube Converters.
Time to power up my Doerle Shortwave Receiver, equipped with the Type 30 to 1T4 Vacuum Tube Converters and 1T4 vacuum tubes installed, to see if they work. The wood cabinet sitting below my Doerle Shortwave Receiver is a "Battery Box". The Battery Box contains Two D batteries, wired in series and tapped, used to provide 1.5 and 3 Volt A+ Filament. In addition, it contains Ten 9 Volt batteries, wired in series and tapped, to provide 22.5, 45, and 90 Volt B+ Anode. The 9 Volt batteries in the Battery Box are getting weak so I had to a connect extra ones externally to achieve the 90 and 45 Volts B+ required for the Doerle Shortwave Receiver.
Success! I could immediately hear atmospheric "hiss", once my Doerle Shortwave Receiver, equipped with Type 30 to 1T4 Vacuum Tube Converters, was powered on and a suitable antenna and ground were connected. I could pickup several AM an CW (Morse Code) transmissions after I fiddled with the Tuner and Regenerative controls. I use a "home-brew" amplifier to amplify the audio output instead of high impedance headphones. My amplifier is housed in the black project case in the the picture below.
Screen Grid Voltage Adjustment
If you recall, each Type 30 to 1T4 Vacuum Tube Converter had a 50K potentiometer installed so that the Screen Grid Voltage could be adjusted for maximum amplification. In order to adjust the Screen Grid Voltage, I tuned my Doerle Shortwave Receiver to a fairly week AM broadcast transmission then adjusted the potentiometer on each converter for maximum station loudness. Measuring the Screen Grid Voltage to ground with my Multimeter, I found the following to be the optimal Voltages:
Type 30 to 1T4 Vacuum Tube Converter used in the RF (Radio Frequency) Section: 37.5 Volts
Type 30 to 1T4 Vacuum Tube Converter used in the (Audio Frequency) Section: 45.6 Volts
My fabricated Type 30 to 1T4 Vacuum Tube Converters were a complete success, making my Doerle Shortwave Receiver once again operational. I had all the parts on hand so there was no expense. The best part is that at any time I can remove the Type 30 to 1T4 Vacuum Tube Converters an replace with an actual Type 30 vacuum tubes.
Here is a before and after picture of my vintage RCA Victor 15X Radio. I think you'll agree that the makeover was a complete success!
About my RCA Victor 15X Radio
I paid $10 plus shipping for this radio at on online auction. I don't think any other "vintage radio enthusiast" wanted to touch it because:
1. There was physical damage to the Bakelite cabinet:
2. The tone switch knob was missing. Most collectors know how hard it is to find matching knobs.
3. The dial indicator, circular and unique to this radio, was missing.
4. The dial cord was either broken or missing.
5. The back panel was missing, exposing the built in antenna.
"Old Time Radios! Restoration and Repair" book on Amazon
I consult this book often during radio restoration. I grew up in the transistor and rectifier era and this book taught me a lot about vacuum tube and selium rectifier technology.
Step 1 Remove Chassis from Cabinet
The RCA Victor 15X uses only two screws to hold the chassis in the cabinet. One on each side of the chassis. The Volume, Tone, and Tuning knobs must be removed first. They just pull off. As mentioned, my RCA Victor 15X is missing the Tone switch knob. Once the screws are removed, the chassis slides straight out of the back of the cabinet.
The Tuning Dial Window is also held in place by two screws, one on each side. You can remove the Tuning Dial Window from the back once the screws are removed. Handle the Tuning Dial Window with care as it is made of glass. I removed the Tuning Dial Window both to clean it and to prep the cabinet for paint.
Step 2 Chassis Cleaning and Lubrication
I use compressed air to remove any loose dirt, then Windex moistened paper towels to remove any remaining dirt and grime from the top of the chassis. Windex moistened Q-Tips work great for getting into hard to reach areas. I only clean the tops of the vacuum tubes as I don't want to remove the markings from the sides of them.
I use Labelle 107 oil to lubricate all of the pulleys for the tuning dial indicator. This oil is safe for plastics. I have this oil on hand for my model train hobby.
I also use Labelle 107 oil to lubricate the shafts of the vintage Volume potentiometer and Tone switch.
I use Labelle 106 Grease to lubricate the bearings of the Tuning capacitor. The red arrows indicate the location of the bearings.
Contact cleaner is used on all electrical contacts, like where the potentiometer wiper contacts the resistive element in the Volume control. I then rotate the Volume control back and forth several times.
Labelle lubricants on Amazon
I use Labelle oil and grease for my radio restoration projects. I already have these products around as I am also a model railroad enthusiast. These products will not harm plastic.
Step 3 Test Vacuum Tubes
Unlike semiconductor transistors that have a near infinite lifespan, vacuum tubes age and become less efficient. In addition, their filaments burn out rendering them inoperable. It is always a good idea to test all vacuum tubes in a radio you are servicing before doing any more troubleshooting.
In addition, make sure that that the right tube is in the right socket. This will save you troubleshooting time later.
Pictured below is my Eico Model 635 Vacuum Tube Tester testing a tube from the RCA Victor 15X radio:
Step 4 Rewiring and Capacitor Replacement
As electrolytic capacitors age, their electrolyte dries up, causing their electrical capacity to drop and leakage current to increase. Circled below is one of two electrolytic capacitors used in this radio.
Electrolytic capacitors should be replaced with one of similar capacitance and equal or above voltage rating.
It is definitely a good idea to replace all electrolytic capacitors in a 74 year radio, such as this RCA Victor 15X.
Molded paper capacitors, like the one circled below, become very unreliable with age and should be replaced with one of similar capacitance and equal or above voltage rating. Molded paper capacitors are not polarized although they may have a black band on one side indicating which lead is connected to the outside foil. I replace molded paper capacitors with new Polypropylene type.
The chassis wiring was complete mess in this radio. Some components weren't even soldered in place!
At some point the electrolytic capacitors were replaced. Their leads were just twisted to a wire and covered in electrical tape.
Some component leads were twisted around tube sockets pins. It looks like several "novice" repairmen tried to fix this radio with little success. See the carnage below:
I couldn't trust any of the wiring in the chassis of this radio. I double checked and corrected all wiring during the process of replacing electrolytic and molded paper capacitors. I am rather pleased with the results. See the picture below:
Step 5 Trimmer Cap Replacement
There are two compression-type trimmer capacitors built into the Multi-section Tuning Capacitor. They are adjusted by screws, circled below. The top screw adjusts the LO (Local Oscillator) Frequency, the bottom screw is the Antenna Trimmer. The screw holes were badly stripped out an neither setting could be properly adjusted.
I replaced the built in trimmer caps with two external trimmers of the of same capacitance range (3 to 25pf) See new trimmer capacitors circled below:
Step 6 Tone Switch Repair
The RCA Victor 15X incorporated a Tone on/off switch instead of a potentiometer. The wiper contact of the switch was missing.
I fashioned a new wiper contact out of a spade lug soldered to the end of the shaft. I also drilled small holes and installed a terminal pin, bent into a U-shape, to limit the travel of the switch. The U-shaped terminal pin was held in place by a dab of Superglue. The red arrow is pointing to the travel stop in the below picture.
Finally, I painted my repair with silver enamel hobby paint to make it less noticeable. I did not paint where electrical contact is made.
Step 7 IF Transformer Resistance Checks
Circled below is one of two IF (Intermediate Frequency) transformers used in the RCA Victor 15X.
As part of my restoration steps, I perform resistance checks using my Multimeter on the primary and secondary windings of all IF transformers. This can be done with the IF Transformer still wired into the radio circuit. The resistance accross the primary or secondary windings should be 50 Ohms or less. I noticed that the a winding of the 2nd IF Transformer had an open. Click on the link button below to see my blog on how I repaired it.
Step 8 Dealing with Chassis Rust
My RCA Victor 15X radio had a fair amount of rust on the chassis.
The first step to chassis rust repair is to give yourself some room to work. I removed the vacuum tubes in the near proximity. I also to unsoldered the wires that connects to the pilot light and then pulled the wires through the feed-through hole.
I started with a Dremel with a grinding wheel installed to remove as much of rust as possible. I then sanded the rusted area starting with coarse sandpaper finally finishing with a fine sandpaper.
It is important to perform paint prep before applying spray paint. I masked off the area to be painted. I used denatured alcohol to degrease the area before paint.
I use silver Dupli-Color automotive rim paint as it is the closet color I can find that matches the natural color of most chassis. Apply in light coats and feather it out so as to make a natural transition from the newly painted area to the chassis color.
Repair job complete! Time to install a new grommet in the hole then thread the pilot lamp wires through the grommet and solder to the proper rectifier tube socket terminals. The final step is to install the vacuum tubes into their respective sockets.
Duplicolor Rim Paint on Amazon
I use this paint to touch up places on the chassis that have rusted.
Step 9 Tuning Dial Back Plate Refinishing
The Tuning Dial Backplate, circled in the picture below, was in need of refinishing.
I removed the Tuning Dial Backplate assembly from the chassis and then sanded the area to be painted with a fine grit sandpaper. I then masked off the area to be painted and wiped it down with de-natured alcohol to remove any residual grease.
The next steps were to apply automotive primer and then lightly wet sand, once the primer is dry.
Finally, a leather brown top coat was applied. Once dry, the Tuning Dial Backplate assembly was re-attached to the Chassis.
Step 10 Dial Cord Replacement
The Dial Cord, Tension Spring, and Dial Pointer were missing from my RCA Victor 15X Radio. I fashioned a new Dial Pointer from a Terminal Pin and Solder Lug I found in my junk box.
I painted the newly fashioned pointer red using Enamel hobby paint.
Most radio schematics include a diagram on how to string the Dial Cord.
I used a spring from a battery holder as the Tension Spring.
Finally, the Dial Cord replacement is complete. I will not attach the Dial Pointer to the Dial Cord until reassembly, so that I can properly align it in the Tuning Dial Window.
Step 11 Cabinet Repair
I do not like to apply paint to a Bakelite cabinet as I feel it covers its natural beauty, but feel I didn't have a choice in the matter due to the large jagged crack, with small pieces missing, on the side.
Click on the link button below to see my blog on Bakelite Cabinet Repair.
Below is a picture of the newly repaired RCA Victor 15X Cabinet.
As finishing touch, I spray the paint that I used on the radio cabinet into the lid. I then use a fine paint brush dripped in the paint and apply it along the back edge.
Step 12 Assembly
The first step in the assembly process is to reinstall the Tuning Dial Window. A screw on each side holds it in place.
Then the chassis is carefully slid into the back of the cabinet. It is held in place by two screws, one on each side of the chassis.
At this point I install the knobs, then I rotate the Tuning knob counter-clockwise until I see that the Tuning Capacitor's plates are fully meshed. The next step is to move the Dial Pointer along the top of the Dial Backplate until it shows the lowest point on the Tuning Dial Window. I then affix the Dial Pointer to the Dial Cord with a dab of Superglue.
Next, its time to consult the schematic and solder the wires to the built in antenna. There are also two connections that go to an RCA Jack that allow you to use the radio as an audio amplifier.
The internal antenna is attached to the Chassis with two screws, circled below. I sprayed painted the fiberboard piece that the internal antenna attaches to a matt black.
Finally, a picture of the finished product! I still need to find a replacement knob for the Tone control.
I spent many hours restoring this vintage RCA Victor 15X Radio. It was satisfying bringing it back to life. Watch the video below to see my newly restored radio in action.
My Baofeng UV-3R+ Dual Band UHF/VHF Transceiver has served me well during the year of ownership.
I use mainly the 2M band fucntion in order to communiate with other Amatuer Radio Enthusiests on a local repeater.
One day I went to charge my UV-3R+ and noticed that the LED (Light Emitting Diode) on the Charger Base did not rapidily flash between red and green when plugged in. The LED on the Charger Base was off yet the LED on the AC Adapter was lit. In addition, the LED on the Charger Base did not change to a solid red indicating that the UV-3R+ installed was charging.
This led me to believe the issue was with the Charger Base itself.
Step 1 Disassembly
The bottom of the UV-3R+ Charger Base just snaps in place with the top. All you need to do is take a Jewel's screwdriver and pry where the two halves meet to separate. Do not be fooled by the screw heads on the Charger Base bottom, they are molded in the plastic and serve no purpose.
The next step is to remove the screw that holds the Charger Base printed circuit board in place. See area circled in the picture below.
What puzzles me is the center terminal, circled below, does not have any internal connection. Yet, there is a mating contact on the back of the UV-3R+ battery. Looking on the Internet I have found references of the a "third pin" used to monitor the internal temperature of a Lithium ION battery or to balance a charge between cells. There is the letter "T" over the center contact of the UV-3R+ battery, making me believe this was for a temperature sensor. It is a mystery why this function was never implemented.
Step 2 Diagnosing the problem
I could measure 5 Volts with my Multimeter on the coax male connector that plugs into the Charger Base. It was a mystery why the Charger Base was not being powered. Upon further investigation, I determine that the coax female connector, soldered to the Charger Base printed circuit board, was the culplit. I removed the coax female connector from the Charger Base printed circuit board in order to take a closer look at it.
I immediatley determined the issue once I looked down the barrel of the coax female connector. The center pin had broken free and was pushed back in the connector. This prevented it from making contact with the center contact of the coax male connector. See below picture.
Step 3 Fixing the Problem
The lead that holds the center pin of the female coax connector was very flimsy. I soldered a much thinker terminal pin to it. This will give it added physical strength that will prevent it from being pushed back into the connector in the future.
I had to drill an extra hole in the printed circuit board in order to accommodate the supporting thicker terminal pin. You can see the end of the terminal pin protruding from the printed circuit board, circled below. This is before I cut the terminal pin flush with the printed circuit board.
Step 5 Reassembly
Putting the charger back together is just the opposite of taking it apart. The printed circuit board is attached to the top section of the Charger Base with a single screw (circled below). The bottom of the Charger Base just snaps in place with the top.
Step 6 Testing
Testing is pretty straight forward, plug the AC Adapter into the wall and connect the AC Adapter cable to the Charger Base. The LED on the Charger Base should rapidly flash between red and green. See area circled in the picture below.
Install the UV-3R+ into the Charger Base, the LED should change to a constant red when charging. The Charge Base LED will change to a constant green once the UV-3R+ is fully charged.
The LED on the AC Adapter is green when:
- It is not connected to the Charger Base
- It is connected to the Charger Base and without the UV-3R+ installed.
- It is connected to the Charger Base with the UV-3R+ installed and fully charged.
The LED on the AC Adapter is red when the UV-3R+ is installed on the Charger Base and it is charging.
Repairing a UV-3R+ Charger Base is a pretty simple task, requiring a minimum of tools. I recommend disassembling a broken UV-3R+ Charger Base, determine the root failure, and fixing it, before purchasing a new one.
I came across this great book from 1938 on how to build four different short wave receivers. What was even cooler is that someone took the time to format it in Kindle EBook format! One click and a Kindle version of the vintage "HOW TO BUILD 4 DOERLE SHORT WAVE SETS" book was mine!
"HOW TO BUILD 4 DOERLE SHORT WAVE SETS" Kindle book on Amazon!
What is a Doerle Short Wave Set?
Doerle "sets" were a popular home built regenerative shortwave receivers of the 1930s. Designed by amateur radio enthusiast Walter C. Doerle of Oakland, California. Doerle's regenerative radio designs were published in many amateur radio magazines in the 1930s. Doerle's Short Wave Set designs were so popular in the 1930s because of the ease of construction and use of inexpensive parts in their design.
Not much is know about Walter C. Doerle or if he was even compensated for the designs featured in the book "How to build 4 Doerle Short Wave Sets" and other vintage publications.
The Doerle name lives on as his shortwave set designs are still popular with "Glowbug", amateur radio enthusiasts that enjoy building simple tube radios, of today.
Can I still purchase vacuum tubes?
Absolutely, there are many vendors that sell vacuum tubes and high voltage electronic components required for vacuum tube circuits. Many musicians and audiophiles even today love the sound of vacuum tube audio amplifiers as they believe they produce a warmer more natural sound. As such, there are many vendors that cater to their vacuum tube needs.
The type 30 and 32 vacuum tubes, and other components used in this shortwave receiver, are available from the two vendors below.
Source of Vacuum Tubes and related components
Who Writes This Blog?
John is an IT professional from Cleveland, OH who enjoys amateur radio, ham radio, metal detecting,
Copyright © 2017
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