The Modern Radio Laboratories ® One Tube All Wave Receiver

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MRL 1 Tube Radio
This is a Modern Radio Labs 1 tube regen radio, purchased as a kit from Elmer Osterhoudt in 1985.
Headphones, antenna, ground and battery connections are all are in the back. The front panel measures 4.5" x 5.5"
and is a copper-clad board, though the manual (printed in 1953) suggests using a 4.5" x 6" aluminum panel.
MRL vernier dial
The tuning capacitor has a vernier mechanism that is built into the capacitor shaft. This allows it to be mounted directly to the panel. Elmer added this at no extra charge. This type of vernier wasn't sold in the MRL catalog.

MRL 1 Tube Radio
MRL 1 Tube Radio
  Phone jacks on the left, antenna and ground on the right.   This model is in pristine condition.  

MRL 1 Tube Radio
MRL capacitor switch
  MRL hand-made antenna tune capacitor. MRL-made switch on main tuning capacitor.  

MRL 1 Tube Regen Radio
Radio and instruction manual to assemble it.
The copyright date on the instruction manual is 1953 but MRL had been selling the plans since 1940.

MRL catalog page
This radio was purchased in
1985 from the MRL catalog.
Click for full sized view.
MRL coil socket
It's almost an accident that the radio remained in such fine condition. It was because of the hand made coil socket, which came already mounted on the base by Elmer.

Coil socket
When mounted beneath the base there is a 1/8" gap between the coil and the socket. The coils kept popping out! To listen to the set you had to hold the coil down with your finger. I put the set in a cabinet, intending to modify it the next week. That was 28 years ago.
MRL 1 Tube Radio
The battery is a 22.5 volt Eveready  #505.
MRL Tube Socket
The reasoning behind the handmade coil socket, from "RADIO FLYER No. 1, June, 1982."

New coil socket
In February of 2013 it was time to finish the project. The coil socket and dead battery came out. In went a Chinese made coil socket from ebay. Elmer rolled over in his grave!

MRL 1 Tube Radio
You can still purchase the battery, for around 100 million dollars! I dropped this into the shopping cart and the price remained at $99999999.00. In reality they can be had for about 12 bucks, but I tortured Elmer enough with the Chinese coil socket. He recommended two or three 9 volt batteries in series.

MRL 1 tube DC radio schematic
Drawing by Elmer Osterhoudt.

C1 = Two plate variable capacitor 
C2 = 25 - 280 mmfd variable mica trimmer
C3 = 365 mmfd variable capacitor 
         C2 and C3 are set so the total capacitance is 140 mmfd. See note below.
C4 = .0001 mfd mica capacitor (100 picofarad)
C5 = .00048 mfd mica capacitor (480 picofarad)
R1 = 2.2 megohms
R2 = 0 to 10K - 50K

Elmer's early 1 tube sets used a 140 mmfd variable capacitor. When these became unavailable he used a 365 mmfd cap, with a 280 mica compression cap in series with it (C2 and C3). He set the trimmer at his shop so that when installed, C2 and C3 would equal 140 mmfd.

The photographs above show a later version, where C2 is no longer used. Instead, Elmer found a supply of multi-section variable capacitors. He added a switch to connect the rear section if you wanted more capacitance for the broadcast band.

COIL INFO - Coil forms are 1.5" diameter
20 Meters 4 22 5 26
40 Meters 10 24 6 26
80 Meters 22 24 6 26
160 Meters 65 24 12 28
HF BCB 84 28 14 28
Broadcast 120 32 20 32
LF BCB 170 34 25 32

Rewired MRL 1 tube base
The rewired base. The battery is gone, the coil socket has been replaced, and the binding posts are now brass.
This is a set of MRL coils. Except for the pins and the wire, they were completely hand-made by Mr. Osterhoudt.

MRL 1 Tube Radio
MRL 1 Tube Radio
Crooked pins and sloppy coil cement. Today these coils are treasures.
The ultimate MRL coil would have Elmer's fingerprint on it.

MRL 1 Tube Radio
The complete setup, minus the high impedance headphones.

Modern Radio Labs 1 Tube receiver
In 2023 the radio got a new dial scale. After 38 years the old one started looking ragged. There had always been a mark on it that was made by the oil in the vernier mechanism of the tuning capacitor. The old one had been printed, cut out, and applied by Elmer Osterhoudt himself, so I pulled it off while sobbing bitter tears. (That's "tears" that rhymes with beers, not bears.)

As a concession, the label is a copy of the 1953 label that is printed in the manual, but it had to be enlarged to match the size of the old one. The 1985 knob was also replaced with a more appropriate one. It may have looked cool in 1985, but today the market is saturated with Chinese knock-offs and you see them everywhere. Observing the knob with the silver insert, one would assume the original knob had been replaced, when in fact, it wasn't. Ironically, now it has been.

So how well does it work?

A 1.5 volt D cell powers the filament of the vacuum tube. The set comes on instantly, there is no warm up time.
In pitch dark the tube gives off a faint orange glow.

With a long wire antenna and no ground it had no trouble picking up stations on the broadcast band. My usual "test" of a radio is to tune it to AM 1210, broadcasting from Philadelphia. It is hard to pick up here in Upper Gwynedd, PA because their transmitter is in Moorestown, New Jersey! I was able to find it after some searching on the dial. Various short wave stations came in with no trouble at all.

However, without being grounded the set suffers from hand capacitance on weak stations. There is also a problem with capacitance in the headphone cord. If I took the headphones off and put them back on a few minutes later I had to retune the set. However, with an earth ground connected the set is more sensitive and the hand capacitance isn't such an issue.

I was very pleasantly surprised at how well this little set works. I tried various numbers of 9 volt batteries. The set worked with 9 volts to 45 volts. (It BARELY works at 9 volts and I could have gone higher than 45 volts but Elmer showed 22.5 volts in the schematic.) I settled on 18 volts.

The headphones used were a pair of Superex Deluxe SD, made in USA, with an impedance of 2000 ohms.
I kept Elmer's coil socket, it's a piece of radio history.

After looking through my records I found that the set I got in the mail was intended for Robert W. Lyons of 24th Street in Allentown, PA. We both ordered the same thing.

Here is the strange part: I have the envelope addressed to Robert Lyons with a return address of Modern Radio Labs. In the envelope is the order (from Robert Lyons) for the one tube set, dated December 3, 1984. Also included is the letter Elmer wrote back to Robert explaining that he mounted the vernier dial to the front panel. The stamps are cancelled. The cancel date is March 1985. If the stamps are cancelled, it must have made it to the Lyons residence! So how did the envelope sent from MRL to Robert Lyons end up being sent to me?

Robert ordered the set as a Christmas present. My theory is that three months after Christmas he received the set in the mail, then sent it back to MRL along with the envelope. Elmer got my order in March and sent me the set Lyons sent back to him, with the envelope and order form from Lyons still in the box. The set came with the vernier dial already mounted on the front panel, as stated in the letter to Robert.

Anyone who has ever ordered from the old MRL knows how long it took Elmer to send out the order. The fact that he had to include a personal note with each order didn't speed things up any. For Robert Lyons to send in an order in December of '84 and not receive it till March of '85 was perfectly normal for MRL.

MRL 1 Tube Radio

In January of 2016 I found a phone number for Robert and called it. His wife answered and verified I had the correct name, address and phone number. When I mentioned "radio" she said, "I got rid of all those radios last year. My husband has been passed away for 30 years." I apologized and hung up. He died in September of 1985 at the age of 51.

A brief video is below.
Want to build your own set? The complete handbook written by Elmer Osterhoudt can be found here.