A true unique TV set: 27" Allocchio Bacchini

[Giulio Maiocco]

Hello everybody,I'm really proud to publish the end of restoration of a quite unique set in Italy: a 27" Allocchio Bacchini from 1954 with wired remote control!

As some of you may remember, quite a few years ago I asked help because of some weirdness of the horizontal output section, and the fact that the original flyback transformer was missing sure didn't help.

The circuit is inusual, at least here in Italy, it's a derivative of a much simpler and common 17 or 21 inch chassis, but with some modifications, in order to accomodate the much larger CRT, a 27RP4 with its different drive requirements. The flyback transformer is of the autotransformer family, but with series linearity coil connected at the damper tube cathodes and 2 taps of the primary itself, an arrangement found only in very few sets, mainly prototypes (for my Italian friends, as an example, the Geloso GTV1001 chassis 952 is one of these).

After a long time, almost 8 years from the purchase of this Allocchio Bacchini, I had the luck to find the correct flyback transformer, that, needless to say, once found it's specs on old catalogs, was only intended for 70° kinescopes up to 20", driven by a single 6AV5GT tube.

I tried to mount this FBT on the 27" chassis, bearing in mind it's original application, and it works perfectly, even with 2 6AV5GT tubes in parallel driving it full strength. As a result, the boosted voltage reached +590V (the original spec was 500V), the EHT is 16.7KV with normal brightness on the screen, the total cathode current for the 2 HOTs is 140mA, but I'm very happy because now the horizontal sync is perfectly stable and the flyback is not even lukewarm after more than 1 hour of operation.

During this resurrection, I had to change the tuner, someone in the past tampered with its adjustments rendering it useless. This fault caused somehow the "drop like a stone" of the horizontal frequency as the fine tuning was adjusted, the yoke made some very nerve-wrecking sounds.

Another strange thing was the backward connection of the video detector diode, connected that way, exactly as drawn on the schematic, negative image and no sync, I simply flipped around the damn diode and everything's A-OK.

I know I already posted some photos of it about 2 months ago on this thread http://www.videokarma.org/showthread.php?t=253838, but I wanted to do some more tweaks to the controls and re-install the rewound original vertical output transformer (6300 turns of #38 magnet wire really tests your patience). At least my friend Telecolor 3007 will see it, after I promised him long time ago some photos.

Best regards

Giulio Maiocco