Dave's Homemade Radio Paragon RD-5 Project
Paragon RD-5 Regenerative Receiver
Paragon RD-5 Top View
Paragon RD-5 Back View
Paragon Receiver – Side View
Paragon Receiver – End View
Close-Up Of The Tube.
Paragon Regenerative Receiver Nameplate.
Bottom Paper (Larger View)
Introduction & History
Welcome to my second radio restoration page. Most of the activity on makearadio.com centers around homemade radio projects. But once in a while an old radio comes by and I decide to give it a little TLC. In the case of my old Paragon radio, it was more of a matter of clean up and electrical restoration to get it running again.
The Paragon RD-5 was made by the Adams-Morgan Company located at 16 Alvin Place, Upper Montclair, NJ. Their products go back to the days of wireless, around 1916 with a tuner. It appears that before the mid 20's they were selling parts rather than completed sets. But the competition was fierce back then. Everyone wanted to be in the radio business.
Here it is, a pic of the former Adams & Morgan Co. home of the Paragon Radio. I talked with a real-estate agent and tax assessor to confirm the address. To the right of the building is the RR tracks. Now a playhouse. – George K2XL
The RD-5 was offered for sale in 1922, at the beginning of the broadcasting boom. It is a one tube radio, originally using a UV200 detector tube. More information can be found at the radiomuseum.org website. There was a cabinet surrounding this radio, but that got lost over the years. I may see if I can have a new cabinet made.
I really can't say that there is anything really that wonderful about this radio. Just a one tube regenerative radio. But I like these old and simple radios. I sure like those old variometer adjusted regeneration. I felt it very worthwhile to fix this old radio.
It was suggested that I use the parts in this radio to make one of my little homemade sets. But the condition of this radio really didn't warrant turning it into parts. The main problem was the base board was split all the way through. That caused a couple of broken connections on the front panel. The tube was also broken. By looking at the base of the tube, it was probably one of those with the nice tipped top glass envelope.
Other than that, the radio was just dirty. Cleaning with a damp paper towel took off the dirt, and after that I applied a bit of Liquid Gold to improve the wood appearance.
Fixing it up.
Once I assessed that nothing was broken and only the tube was missing, it was time to start working on the Paragon. The capacitor plates were rubbing, so a little adjustment was needed to fix that.
I had to solder a couple of the connections back on the front panel as they were ripped off because of the split wood. To fix the wood, I used some Elmer's Glue and just poured some in the crack and then forced the wood back together. So far it's holding fine.
I didn't have any UX200's or any UX tubes. I ended making an adaptor using a bayonet 4 pin plug I found in my box. I also needed a 4 pin tube socket. I soldered wires to the socket and then soldered the pins on the bayonet plug and I was set.
I used a type 30 tube as I like the filament power requirements better than the original tube. I did use a #30 tube at first. I think it may have been a tired tube as the performance was weak. The set didn't go into regeneration. I used a new VT-67 tube which is a #30 but with a 120mA filament (@ 2Vdc). The higher current filament allowed better operation of the filament rheostat. I can adjust the filament voltage between 1.5 and 2.0 volts. I used my rechargeable battery box project for the power.
The only modification was to add a 3.3 meg ohm resistor across the grid capacitor. Originally, this radio used a "soft tube" detector. This tube didn't need the grid leak resistor. But since I am using a "hard vacuum" type tube, the resistor was necessary to prevent hearing popping caused by grid blocking. The resistor doesn't allow the capacitor to stay charged causing this grid block problem.
The circuit starts at the antenna and ground terminals with a switch tapped fixed coil. The RF energy is transferred to a rotating coil which, with the variable capacitor, is responsible for selecting the stations. The rotating coil adjusts the amount of signal coming in to the tuned circuit. The tapped switch also adjusts the number of turns that the antenna and ground connect to. This also adjusts the RF going to the rest of the radio
The grid leak circuit and tube provide the detection and amplification in this radio. Grid rectification is how this works. Please check my regen radio notes page for further details.
The variometer is used to control the regeneration levels of the receiver. This is an original regeneration control method, but is hardly used anymore. That is because variometer's aren't used much anymore. Later receivers used different regenerative designs, also shown on my regen notes page.
I want to take a moment to expand on this variometer regeneration control circuit as the question had come up on the The RadioBoard forum. The regeneration can occur because the inductance of the variometer works with the grid-plate capacitance of the tube, thus providing the RF feedback. This is how Armstrong achieved regeneration in his original 1912 regenerative receiver. I would suspect that if one were to try this with a pentode, the radio wouldn't regenerate.
When the filament rheostat is rotated fully counter-clockwise, a dead spot is hit. This is the on-off switch for the radio. There is no need to switch off the B+ supply.
Finally the detected signal audio arrives at the headphones terminal. As always in these old sets, high impedance headphones are required. This radio did have an accessory two-step audio amplifier available. It was placed to the right of the receiver and metal straps connected the two boxes together. This allowed for loud speaker operation.
Paragon RD-5 Schematic
That's about it for this project. It didn't take me very long to fix up this radio. I listened to Jack Benny on it last night from a Canadian station. It is very cool when the radio is older than the program that comes out the headphones.
73, Dave - N2DS
One More Thing …
Full Page Paragon RD5 Advertisement (click for large view)
I found this ad for the Paragon RD5 in Radio Broadcast Magazine from 1923. These magazines are available in PDF form from archive.org. Do a search and you will fine these great old, and nearly forgotten magazines.
And Another Thing …
This is sweet! Tom Kipgen in Oklahoma made me this cabinet. I sent him the measurements of what it would take for a cabinet for this old radio. Luckily we both had Made In U.S.A. rulers and Tom was able to build a cabinet that fit PERFECT!
This cabinet is not an accurate rebuild of the original, it is better! I especially like the way Tom made the tube access door. I wouldn't have expected any less than this fine job as Tom is an expert guitar builder too. Thanks Tom!