Post by Philconut on May 3, 2020 19:29:42 GMT 12
I have finally started on the restoration of this Ultimate 9LAW tombstone radio from 1933, that has been in the wings for a long time. As there is little information about it, I am taking the circuit from it as I go. It has revealed a few interesting things. The first is the use of a 59 in the output stage. I know of only one other radio, a Radiola, that uses this valve. The detector is a type 56 with the plate and cathode connected to ground, so that it becomes a diode, with the IF transformer connected to the grid. Philco did a similar detector in their model 91 using a 37 triode, & maybe in other models. This was done even though the 55 double diode triode valve was introduced in 1931. The really interesting part is the wave change switch & front end circuitry. On broadcast, the set is a reasonably standard 7 valve superhet with the mixer stage being an autodyne circuit using a 57 sharp cutoff pentode. For the short wave bands, the BC receiver frequency is fixed at the top of the band by disconnecting the 3 sections of the tuning condenser leaving just the trimmers in circuit, and a 2 valve front end, oscillator & mixer, tacked on to the front of the 58 RF amp tube. The aerial & osc coils are mounted on the switch shaft like a turret tuner. The osc tuning is the 4th section of the 4 gang tuning condenser & the mixer has a separate variable tuning control on the front panel. It is all apart now and I am quite surprised at the amateurish work in places. Most of the wiring that passes thru the chassis is through small, un-bushed holes, the coil & IF can fixings are crudely soldered in with some verdigris showing where flux has not been cleaned off properly. The holes for the can electros are extremely rough. On the other side of the coin, the screws holding the valve sockets in are all brass & all the coil & IF cans are copper plated on the inside. The tone control is mounted at the top of one side panel of the cabinet.
Most of the components are mounted on three tag boards which are attached to the sides & back under the chassis. It certainly gives an uncluttered view.
Next is a repaint of the chassis & coil cans. While this is drying & hardening I will check all the coils and dip them in bee's wax to reseal them.
More to come.