Oldschool tubes

What happens if you put a portable hole inside a portable hole?

Not sure how they were hyped, but we used them all the time in the 70s to l ocate an open tube(s) in series sets. We kept one in our road tube caddy; it even used the same "cheater" cord as the TV did. You'd be surprised how many low end TVs used a series string back then and how often a dead TV wa s an open filament.

ct

a red dot, useful

locate an open tube(s) in series sets. We kept one in our road tube caddy ; it even used the same "cheater" cord as the TV did. You'd be surprised h ow many low end TVs used a series string back then and how often a dead TV was an open filament.

I thought almost all valve tvs used series heaters. Mine doesn't but it's a n unusual design, Ekco tmb272.

NT

That would be a hole in one.

On tube testers - they are very useful for go/no-go decisions, and if capab le of testing for shorts and gas, even useful for limited quality tests. Bu t there are very few OTC tube testers capable of matching. I happen to have one of those few - and it requires additional instrumentation to do this.

As to microphonics - yes the meter will jiggle if a badly (repeat *BADLY* m icrophonic tube is being tested. And yes, I can leave a KT88 on it for an h our and the power-supply will not heat up, so long-term tests are also poss ible. Hickok 539B.

Peter Wieck Melrose Park, PA

A black hole.

For a brief period transformers were cheaper than a set of tubes with weird custom filament voltages, but that didn't last long.

You're not wrong there...

No surprise at all, since I worked in a radio & TV shop at the time. DIY types would see ads for them, and bug the shop to buy one for them, even after telling them that it only looked for open filaments.

Zenith, GE and other name brands continued to build high end sets with power transformers. Some of the later Zenith TVS had a self resonant CVT that sold for about 1/3 the price of the set.

Their cheap sets were all series filament, with a voltage doubler for the B+.

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One reason would be that TV valves were made locally in the same factories that supplied radio and audio valves which also used transformers - so there was no local manufacture of series heater types.

The few sets that had series strings were imported from the UK or the USA and so were the needed valves. Same goes for the few compactron sets that were sold here.

.... Phil

Those have been on back order since 1963, along with their set of tunnel paints. :(

The 1954 TMB272 used parallel valve heaters for an entirely different reason. It was a dual voltage set, 12v & 240v. From either power it had to derive both filament volts and anode volts. It uses the same transformer on both voltages.

NT

I remember a late zenith with swinging choke supply. Why they did that I don't know, must have cost more than regulating properly with silicon.

NT

For amusement here's a representative list of some of the _retail_ prices on the parts list for the 1935 Kadette 52 I'm working on:

Tube socket: $0.10

incredibly expensive by today's standards

NT

On the plus side, you can get roller skis now. Instant water available soon.

Cheers

Phil Hobbs

Yep. Compared to the 1970s, those parts are at least 4X as expensive. The power XFR seems to be the best deal of the group, less than twice the cost of the IFs.. Strange.

In 2017 money:

Is there any law of Physics, that Acme can't break? :)