Grebe Synchrophase

Grebe Synchrophase MU-1

This 5-tube, battery-powered TRF, c. 1925, has very appealing and attractive styling. The front of the cabinet has gold-plated escutcheons for tuning and filament voltage controls. (If you try to polish the escutcheons, the gold plating will come off—which is the way this set is often found.) There are actually two tuning controls for each of three variable capacitors, one serving as a vernier.

The actual electronics are pretty standard, but an interesting feature is the chains than mechanically connect the three tuning caps, thus achieving the “holy grail” for early TRFs—one-handed tuning. (Some ads of the day, I can’t recall whether Grebe’s or not, promoted one-handed tuning by picturing a man with his arm around a gal and tuning a radio with his free hand.)

The MU-1 seems to have been one of the first sets to have a tone control. Actually, it has two filament rheostats—one for the detector tube and the other for all the tubes; the detector rheostat is labeled “tone color,” and it does affect tone, after a fashion. The radio also has another advanced feature: an ON-OFF switch as part of the volume control (the right-hand filament rheostat). Most early sets had stand-alone power switches.

This set also has “binocular” RF transformer coils. Each of the three RF transformers comprises two coil forms, wired 180° out of phase, to help prevent feedback or strong RF signals jumping into the circuit. Other TRFs of this vintage typically employed a single coil form for each RF transformer, and then pointed them in different directions. Grebe’s arrangement is effective, looks nice, and is a nice marketing feature.

Another interesting feature is a dial lamp, which seems to be a bit of an extravagance for a battery-powered set. I suppose that listeners may have used their early radios in dark or dimly lighted rooms, so a dial lamp would have been helpful.

Like other early radio industry moguls, Alfred H. Grebe (pronounced GREE-bee) was something of a character. Getting his start as a radio officer on a tramp steamer to the orient, he supposedly became infatuated with oriental culture, later creating a fictitious Fu Manchu, named Dr. Mu, to tout in Grebe’s ads the technical virtues of his radios. (Dr. Mu presumably was the namesake of this model’s designation, MU-1). The story is that Mr. Grebe got the idea for Dr. Mu from China, but I’ve never heard of Mu as a Chinese surname. My theory, unsupported by any evidence, is that Dr. Mu was a pun; the Greek letter μ, was used then as now as the mathematical symbol for the amplification factor of a vacuum tube.

The horn speaker shown in the photo is an Atwater Kent Model L. The original reproducer in the horn was burned out, so I replaced it with a modern, low-impedance, 2-inch speaker and a suitable audio transformer, all hidden in the base.