Master
Construction plans for the Master superheterodyne came out in January 1925. My example of the Master was professionally built and it’s in excellent condition. The beautifully engraved panel and the drilled sub-panel may have been combined with other unique parts and sold as a complete kit. All four IF transformers are enclosed in a single housing. This is one of my favorite sets!
Above is a top inside view of the set.
Here are a few particulars of the set:
1. The set appears to operate on the standard 1920s superhet circuit.
2. The front panel measures 30” long by 7” high by 3/16” thick.
3. Master oscillator coupler and ganged IF transformers.
4. “X” Laboratories tuning capacitors.
5. Yaxley rheostats.
6. The audio transformers are unmarked.
7. Kellogg tube sockets (eight tubes).
.
The last transformer (#4) feeding the second detector was measured with the secondary of the transformer referenced to A+ and the grid leak resistor and capacitor in the circuit. As measured, transformer #4 has a narrower bandwidth than the other transformers. I don’t know if the narrower bandwidth is because that transformer is a filter transformer or if the narrower bandwidth is because of a difference in grid biasing. The resistance measurements of all four transformers were about the same.
|
Type |
Peak Freq. |
Lower 3 dB |
Upper 3 dB |
Bandwidth |
Relative gain |
Pri. ohms |
Sec. ohms |
|
Master, #1 (near 1st det.) |
61.5 KC |
51.4 KC |
72.0 KC |
20.6 KC |
12.7 |
67.0 |
137.8 |
|
Master, #2 |
56.4 KC |
48.1 KC |
65.1 KC |
17 KC |
13.3 |
69.5 |
132.8 |
|
Master, #3 |
61.5 KC |
51.7 KC |
71.9 KC |
20.2 KC |
13.0 |
67.0 |
137.5 |
|
Master, #4 (near 2nd det.) |
54.9 KC |
50.8 KC |
58.1 KC |
7.3 KC |
10.4 |
69.7 |
141.6 |
I was happy to find out that the IF transformer block was in good condition with no open windings in the transformers. Although it would have been a learning experience, I really did not want to tear into the housing. The peak frequencies were slightly different between the various transformers. However, slight staggered frequencies will broaden the overall bandwidth and it may actually improve the audio response. It appears that the target IF frequency was 60 KC. The table below shows the results of the bandpass measurements.
Close up of RF front end.
The Master oscillator coupler.
The ganged IF transformers are housed in a wood box with a bakelite front panel. There is a number 38 written in crayon on the backside of the wood box. This may be serial number 38 of a fairly rare set.
Close up view of the engraved panel.
Close up of the audio transformers.