Robertson-Davis Melocouplers

     The Melo-Heald Eleven and the Hot Spot Fourteen superheterodyne transformers were introduced in 1927 by the Robertson-Davis Company. A construction article for the Melo-Heald Eleven was in the March, 1927, Citizens Radio Call Book and a construction article for the Hot Spot Fourteen followed in the September issue. Unfortunately, I have not had access to either issue. I do have an original brochure for the Melo-Heald Eleven and that’s where most of the information for this section comes from.

Merwyn Heald

Merwyn Heald

     Close up view of the left-side (oscillator) tuning control. This is a National Type E “Velvet Vernier” dial. A search of National advertisements from QST indicates that the Type E dial was introduced sometime between late 1927 and March 1928. The Type E dial is the latest part on this Melo-Heald Eleven and it dates the set to early 1928.

National Type E dial

     Here is a close up view of the oscillator Melocoupler. I always thought that Robertson-Davis Melocouplers and Meloformers were kind of an olive-green color. The transformers actually have a coal black background and they have acquired the olive-green tint from the aging plastic sleeves surrounding the transformers. The paper sleeve around this transformer is also starting to come off.

Melo-Heald Eleven Oscillator Coupler

     This is a view of the second detector area. This set was modified sometime shortly after it was made with an Arcturus UX-222 screen grid tube. The tube was still in the socket when I acquired the set (second socket from the left). If I restore the set I will probably remove the UX-222 and replace it with a UX-201-A (how the set was originally designed).

Melo-Heald Eleven Second Detector
Melo-Heald Eleven top chassis angle view

Side angle view of the entire chassis.

Melo-Heald Eleven audio amplifier

     The audio amplifier. Most of the plastic sleeves on the transformers were loose throughout the set but they were totally missing on the last two Meloformers. I don’t think it will be too difficult to restore all eleven transformers.
     It looks like there was once a mud dobbers nest on top of the second tube socket from the right.

A portion of the IF amplifier.

Melo-Heald Eleven IF Amplifier
Melo-Heald Eleven Oscillator and First Detector

The RF front end.

     Top chassis view of the Melo-Heald Eleven. This is quite a large set, the baseboard measuring 29” by 12”. It’s awesome looking though with those eleven tube sockets all in one row. The long line of transformers is equally impressive. There are several different types of transformers but they are all designed to look alike. The transformers, going from right to left, include the oscillator Melocoupler  (type 160 R.F.), the mixing Melocoupler (type 120 R.F.), the six long wave (IF) Melocouplers (type 135 R.F.), and the three audio frequency Meloformers. Though not exact, the parts and front panel on my set are laid out quite similar to the construction article in the March, 1927, Citizens Radio Call Book. Most of the radio looks like it dates to about 1927.

Melo-Heald Eleven top chassis view

     The above photo is a front view of my newly acquired Melo-Heald Eleven superheterodyne. Chances of finding a rare set like this are fairly slim. This particular example needs a lot of work. The 30” by 7” hard rubber front panel is warped in a few places but there are no cracks or breaks (somewhat of a miracle). I’m hoping that a little concentrated heat from a heat gun will be able to straighten it out.
     When I obtained the set it did not have a lid. I suspect that it did have a lid at one time, but there are no signs of where the hinges were located. It may have just had a lid that sat on top of the cabinet and was not attached in any way.
     That light spot on the left rear of the cabinet is where a mud daubers nest was once located. There are a couple of similar marks on the inside right panel. There are some funny marks above each main dial, and I suspect that they are from the mud daubers also. The set is kind of a basket case. Fortunately, the only part missing from the entire set (excluding the tubes) appears to be the far right knob for an adjustable resistance.

Melo-Heald Eleven front fiew

June 8, 2012 update:

     I would consider building the Hot Spot Fourteen from scratch using original 1920s parts if I could find the remaining Robertson-Davis transformers that I am missing. Here is a list of what I need:

     462 H.F.
     468 H.F.
     469 H.F.
     Meloformer (need 2 each)

     Check your extra parts and contact me if you want to sell any of the above transformers. The transformers need not be good because I can fix them if there is something wrong.

     Rear angle view of the Hot Spot Fourteen receiver, from the September, 1927, Citizens Radio Call Book.

Hot Spot Fourteen Rear Angle View

     This is the schematic diagram for the Hot Spot Fourteen receiver, from the September, 1927, Citizens Radio Call Book.

Hot Spot Fourteen Schematic

Internal view of the spare Robertson-Davis 465 H.F. transformer

Melo Heald HF 465 IF Transformer


Peak Freq.

Lower 3 dB

Upper 3 dB


Relative gain

Pri. ohms

Sec. ohms

463 H.F.

406.5 KC

395.8 KC

415.8 KC

20.0 KC




464 H.F.

418.1 KC

407.1 KC

428.3 KC

21.2 KC




466 H.F.

424.5 KC

413.6 KC

434.6 KC

21.0 KC




     I was able to purchase four more Robertson-Davis IF transformers for the Hot Spot Fourteen receiver, a 463 H.F., a 464 H.F., a 465 H.F., and a 466 H.F. I also found a Robertson-Davis audio transformer, what they call a “meloformer.” The 465 H.F. transformer was damaged, but that’s OK because I already had one of them. The table below shows the bandpass and resistance measurements of the new transformers.

March 4, 2011 update:

     Robertson-Davis advertisement for the Melo-Heald Eleven and Hot Spot Fourteen receivers, from the November, 1927, Citizens Radio Call Book.

Robertson-Davis ad CRCB November 1927

     Published data lists the IF frequency of the Melo-Heald Eleven at 125 KC; I measured 129 KC. The IF frequency of the Melo-Heald Hot Spot Fourteen appears to be about 410 KC. However, the Hot Spot Fourteen was designed to use 199 tubes for the IF amplifier instead of 201-As, so the true IF frequency may be a little bit higher than what I measured. The very name of the Hot Spot Fourteen was derived from the fact that it was a one spot superhet (similar to the Madison-Moore One-Spot).
     The 400 series IF transformers have relatively low gain (due to the limitations of the period tubes at higher frequencies; inter-electrode capacitance, etc.), and that’s probably why the Hot Spot Fourteen required fourteen tubes. The screen grid tube with higher gain at high frequencies was introduced shortly after the Hot Spot Fourteen was introduced, making superhets like the Hot Spot Fourteen obsolete.


Peak Freq.

Lower 3 dB

Upper 3 dB


Relative gain

Pri. ohms

Sec. ohms

135 H.F.

129.0 KC

111.1 KC

144.8 KC

33.7 KC




420 R.F.

no peak, no signal output







460 R.F.

no peak, no signal output







461 H.F.

410.5 KC

398.8 KC

410.5 KC

22.4 KC




465 H.F.

396.4 KC

386.3 KC

407.0 KC

20.7 KC




467 H.F.

422.0 KC

410.4 KC

433.7 KC

23.3 KC




     Here is a list of the Melocouplers that I have:

     Richard T. Ammon identified the 400 series transformers as belonging to the Hot Spot Fourteen: The 420 R.F was the mixer melocoupler, the 460 R.F. was the oscillator melocoupler, and the 461 H.F, the 465 H.F., and the 467 H.F. were IF transformer melocouplers. When I did the bandpass measurements on the transformers I treated them all as IF transformers. The table below gives the results.

     Schematic diagram of the Melo-Heald Eleven from the factory brochure. The oscillator Melocoupler  (type 160 R.F.) is identified at 1, the mixing Melocoupler (type 120 R.F.) is identified at 2, and the long wave (IF) Melocouplers (type 135 R.F.) are identified at 3, 4, 5, 6, 7, and 8. Meloformers (audio transformers) are identified 9, 10, and 11.

Melo-Heald 11 Blueprints

     Photo of the Melo-Heald Eleven from the factory brochure. Note that the connection terminals are on top of the transformers. The connection terminals on my transformers are at the bottom.

Melo-Heald 11 from Factory Brochure

January 19, 2015 update:

Melo-Heald Eleven 2 front panel

     I found another Melo-Heald Eleven to add to the collection. It needs some work, but maybe between the two units that I have I can make one complete unit in good condition. This new set is in much better condition than my first set, but it has a few problems also. I suspect that the cabinet was with the set for most of its existence because the electronics is in excellent condition. It was missing the cabinet when I acquired it. Here are some particulars to the new set:

Melo-Heald Eleven 2 rear chassis

     Melo-Heald Eleven (number two) rear chassis view. The chassis is in excellent condition. Sometime back in the 1920s one of the owners modified the set by removing three of the Robertson-Davis audio transformers and replacing them with two Silver-Marshall audio transformers. One tube was also removed in the process. I don’t think it will be very difficult to restore the set back to the original configuration.

Melo-Heald Eleven 2 audio section

     Close-up view of the modified audio section.

Melo-Heald Eleven 2 IF section

     Close-up view of the IF transformers.


McLaughlin<     HOME     >Pressley

February 8, 2015 update:

     I just finished restoring the Melo-Heald Eleven (#2) to its original configuration. The radio still needs some restoration work but it is complete and it is restored to the way that it was first made.

Melo-Heald Eleven schematic March 1927 CRCB

     This is the schematic diagram of the Melo-Heald Eleven as copied from the March, 1927, Citizen’s Radio Call Book. The Melo-Heald Eleven #2 is wired the same as this schematic (except for the two panel meters).

Melo-Heald Eleven 2 rear chassis restored