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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.
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Steve
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vintageradio.co.nz
Posts: 724
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Post by Steve on May 9, 2020 9:37:31 GMT 12
The construction looks quite tidy at first glance, certainly compared to some manufacturers at that time - I look forward to seeing whats next...
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Post by Philconut on May 9, 2020 20:08:39 GMT 12
Some progress. I have tested all coils & IF transformers and dipped them in bee's wax. Now they look like new. I have made a mistake with the paint colour for the chassis so will have to sort that out next week. I have successfully restuffed the old wet electros. Some more photos: A closeup of the quite sophisticated wave change switch, the very rough holes for the electrolytic caps and a circuit.
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Steve
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vintageradio.co.nz
Posts: 724
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Post by Steve on May 10, 2020 0:59:17 GMT 12
looks like a very badly chattering drill bit made that hole... erk!
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Post by Philconut on May 17, 2020 19:34:13 GMT 12
The restoration has progressed well and after a respray of the chassis to the correct colour, Silver, I have assembled all the transformers, coils, valve sockets, power transformer, tuning condenser and repacked power supply electrolytics onto it. It certainly looks much better. The original wiring is in excellent condition so I have reused as much as possible. The tuning condenser required a serious cleanup with grit blasting then a complete realignment and lube. As usual, the old rubber mountings were completely rotten and were replaced with new grommets. All the components on the 3 tag boards have been replaced and these have been returned to the chassis and wired in. Next is to replace the wave change switch and complete the wiring. I have found a mistake in the circuit I posted so will post the corrected one soon with more photos.
Next to restore the wave change switch.
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Post by Philconut on May 19, 2020 20:23:50 GMT 12
Some more photos. The turret has all the coils for the HF bands. It is very tidy. What I can't get to grips with is the dial. It is simply a linear scale 0-100 for a 4 band radio! Very primitive.
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Steve
Society Members
vintageradio.co.nz
Posts: 724
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Post by Steve on May 19, 2020 20:39:01 GMT 12
Given the complexity and elegance of the band change assembly, you'd think the dial would be just a little more 'flash'... its looking good though, nice work.
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Post by Philconut on May 19, 2020 21:45:27 GMT 12
Here is the result of the repack of one of the old wet electrolytics.
Ready now for the refit of the dial which was filthy. Fortunately warm water & gentle soap did the trick. The reduction mechanism is simple & works well.
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Post by Philconut on Jun 25, 2021 22:09:31 GMT 12
Finally finished! It actually looks quite grand. It sounds really good but there is still an instability in the IF, I think. Will get on to that in the next day or so. Otherwise a satisfactory conclusion. The cabinet was in excellent mechanical order. All it needed was a complete re-finish and it really does look good with all the fine walnut veneer. The valves are all Arcturus blue. Unfortunately the 59 has an intermittent internal short but it does work sometimes.
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Post by Philconut on Jun 25, 2021 22:11:13 GMT 12
One more photo. Can't seem to get the orientation to change?
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