McMurdo Silver's Masterpiece Receivers 1933-1937
Masterpiece II
With the demise of Silver-Marshall in late 1932, McMurdo Silver (the "Silver" of the Silver-Marshall name) began anew with McMurdo Silver, Inc. By mid-1933 he introduced his top-of-the-line receiver, the Masterpiece. Advertised in the December 1933 issue of Radio Craft, it was called the Masterpiece II. This writer has no information on Masterpiece I, if there was such a model.
MASTERPIECE II
Masterpiece II was a four-band, twelve-tube receiver covering the range from 13 to 570 meters. It had one r.f. stage using a 58 tube, a mixer-oscillator using a 2A7, three i.f. stages using 58's, three 56's used as a diode detector, AVC rectifier, and first audio, a 58 beat oscillator for C.W. reception, two 2A3's audio output, and a 5Z3 rectifier.
The circuit was more or less conventional for the time but with a few interesting features. It had two tuning dials; one for the three-gang variable condenser which tuned the RF, mixer, and oscillator coils. The second dial controlled a smaller condenser which tuned the oscillator only and was connected in parallel with the oscillator section of the main tuning condenser. This was called the band-spread dial, making short-wave reception easier to tune. The RF and mixer coils did not have small capacitors to allow adjustment. The idea was that the tuning of these was so broad that there was no need to fine-tune them.
The set used a separate 56 tube (used as a diode) for AVC, the signal for which was obtained from the plate of the third i.f. amplifier. The volume control was tapped for a tone-compensating network, a feature used on many later receivers of all brands. The power supply and audio output was a separate chassis.
Schematic of the McMurdo Silver Masterpiece II
MASTERPIECE III
In the summer of 1934 a new but similar model appeared. Basically the same circuit as the Masterpiece II, it now used a 2A5 first audio which fed two 2A5's audio output. The tapped volume control was discontinued and a separate "tone" control was added.
The separate tuning dial was gone with the main tuning gang controlled by a vernier-drive "airplane-dial" system. Small capacitors were added to the tuning gang to allow r.f. alignment. Strangely, one could only align one of the bands, generally the broadcast, leaving the rest to "fend for themselves" since these condensers were in the circuit regardless of the band selected.
The McMurdo Silver Masterpiece III
Interestingly, Silver introduced an economy model, the All-Wave Nine, using a similar circuit but with just two i.f. stages but which had trimming capacitors on all the tuning ranges.
The Masterpiece III continued until mid-1935 when the Masterpiece IV appeared.
Schematic of the Silver
Masterpiece III
MASTERPIECE IV
A major step forward was made with the introduction of the Masterpiece IV in 1935. There were two r.f. stages and a mixer using 6D6's, a separate oscillator using a 76, three i.f stages using 6D6's, an 85 second detector, a 6B7 AVC amplifier and rectifier, a 76 beat oscillator, a 76 first audio, two 42's second audio in push-pull driving four more 42's in push-pull-parallel, and two 5Z3 rectifiers.
All coils in the r.f. section had trimming condensers, a vast improve-ment over the previous design.
High fidelity was now the rage but Silver's approach to the i.f. bandwidth problem was much different from the usual practice. Instead of varying the response curve by adjusting the coupling, adding tertiary windings, or other means, the Masterpiece IV switched out two of the stages of i.f. leaving just the final stage which was tuned for greater bandwidth. The AVC system made up for the difference in amplification between the three versus one stages. Not a bad idea, either, since the usual mixer-stage noise was also reduced in the one-stage mode.
The audio system was now designed to feed two separate speakers, one for the bass and the other for the treble. The 42's were all connected as triodes (screen tied to the plate). The output stage used fixed bias derived from the negative side of the power supply. The "airplane" dial of the previous model was retained, along with the tuning meter. As in the previous models, the chassis and shield cans were chrome-plated.
Schematic of the Silver
Masterpiece IV
Masterpiece V
In later 1936 another new model appeared, the Masterpiece V. A complete re-design was obvious. In addition to the use of metal tubes, the set now had a larger and more impressive dial and front panel. The much-refined circuit used two 6K7's in the r.f. stages, a 6L7 mixer, a 6J7 oscillator, three 6K7's in the i.f., a 6Q7 second detector and first audio, a 6K7 and 6H6 as AVC amplifier and rectifier, two 6C5's in push-pull driving two 6L6's in the output, and two 5Z3 rectifiers. In addition, the receiver had a volume-expander using a 6L7, 6C5 and a 6H6. A 6G5 Tuning-eye tube replaced the meter used in previous models.
The i.f. bandwidth control retained the system used in the previous model; three stages for maximum selectivity, and just one for high-fidelity local reception.
Bass and treble controls were used, along with the new volume expander control. The audio system was now resistance-coupled, eliminating the interstage transformer which was a feature of earlier designs.
A phono jack was provided so that the audio signal from the radio and phono inputs could be fed to a separate amplifier, perhaps for earphone or public address use. Plugging into this jack disabled the output amplifiers.
This was McMurdo Silver's first major attempt to capture some of Scott's high-end market.
The Masterpiece IV. The
Masterpiece V looked similar
MASTERPIECE VI
In the summer of 1937 a revised Masterpiece VI appeared. Outwardly it looked the same as the Masterpiece V but there were numerous design changes. The tube lineup was about the same as in the Masterpiece V except for the addition of the microphone pre-amplifier and the substitution of 6J5's for the 6C5's used in the V.
The i.f. amplifier now allowed switching between one, two or three stages, giving a three-step bandwidth control. Not only were the number of stages selected, but alternate i.f. transformers were also a part of the system. The audio system was revised by dropping the push-pull drivers of the V and replacing them with a single 6J5 which fed a returned input transformer feeding two 6L6's. The output stage now had inverse feedback for lower distortion. A microphone stage using a 6J7 was added. Just what use this would have been is an open question but it certainly was a feature Scott didn't have.
The Masterpiece VI had a different power supply chassis. The previous model had the two 6C5's and the 6L6's on the chassis along with the 5Z3 rectifiers. The VI had the 6C5 second audio on the main chassis and just the 6L6's and rectifiers on the power supply chassis.
The beat oscillator, using a 6J5, for code reception continued, as did the earphone jack.
Schematic of the radio section
of the Masterpiece VI
This was Silver's final Masterpiece, at least in the radio receiver field. The company folded in 1938 and the last of these interesting receivers were purchased and offered at reduced prices by other suppliers.
Under-chassis view of the
Masterpiece VI chassis
Schematic of the power
supply and audio output section of the Masterpiece VI
Silver also offered economy versions of the Masterpiece in 1937 called the "15-17" and the "14." These sets used the same dial as the larger set but had just one r.f. stage and i.f. stages which used tertiary windings for bandwidth control. The "15-17" used fifteen tubes, two of which were dual function, hence the 15-17 name. Even though Scott had introduced his Philharmonic in 1937, the era of these elaborate and expensive home radios had come to an end. Scott, of course, continued the Philharmonic until WW-II, but with few exceptions most manufacturers began featuring convenience items like push button tuning and built-in antennas after 1938. AM radios have never been as good since. Even today, people marvel at the sound and features of these magnificent sets.