EEVblog Electronics Community Forum
EEVblog => Other Blogs => Topic started by: Radio Tech on May 29, 2018, 12:50:35 am
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I wanted to tear this old unit down and see what it will take to get it back to standards of the day.
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#166 Clough Brengle Model 110 Signal Gen Tear Down
https://www.youtube.com/watch?v=lqKBpUuBmvI (https://www.youtube.com/watch?v=lqKBpUuBmvI)
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I fell in love with that band switch.
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Mr. Radio Tech, were you using an isolation transformer/variac/dim bulb chain to power that lovely DUT?
If not, I cordially suggest to please source something asap,
lest unwanted zaps ruin your day and test gear big time :o
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Mr. Radio Tech, were you using an isolation transformer/variac/dim bulb chain to power that lovely DUT? I
If not, I cordially suggest to please source something asap,
lest unwanted zaps ruin your day and test gear big time :o
Maybe a variac or dim bulb, but there should be no need for an isolation transformer.
Pre WW2 US made equipment, especially test gear, did not use transformerless construction.
That sort of thing was used for the postwar "All American Five" receivers as a cost cutting measure.
If you look closely at the quite quick view of the schematic, you will see a power transformer with
centre tapped secondary feeding a rectifier tube in a classic full wave rectifier circuit.
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I fell in love with that band switch.
Yes it is a thing of beauty. Very clever design. Sure beats a wafer switch that could fail.
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Mr. Radio Tech, were you using an isolation transformer/variac/dim bulb chain to power that lovely DUT?
If not, I cordially suggest to please source something asap,
lest unwanted zaps ruin your day and test gear big time :o
The unit was brought to life on a current limiting isolation device at first power up.
I did not use an isolation transformer for this test. I wanted the viewers to see the full effect of faulty equipment so they would know the dangers. So hopefully if they watch this video they will see the hazards with this older gear.
As mentioned already (Thanks vk6zgo) this unit have a real transformer unlike the proceeding "All American Five" units types.
The chassis is hot due to failing capacitors that is leaking AC to the chassis.
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Mr. Radio Tech, were you using an isolation transformer/variac/dim bulb chain to power that lovely DUT? I
If not, I cordially suggest to please source something asap,
lest unwanted zaps ruin your day and test gear big time :o
Maybe a variac or dim bulb, but there should be no need for an isolation transformer.
Pre WW2 US made equipment, especially test gear, did not use transformerless construction.
That sort of thing was used for the postwar "All American Five" receivers as a cost cutting measure.
If you look closely at the quite quick view of the schematic, you will see a power transformer with
centre tapped secondary feeding a rectifier tube in a classic full wave rectifier circuit.
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Spot on
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I finally understand why that special band switch. I was studying these old-time signal generators and stumbled upon people trying to design and build them. One of the major complaints about this technology has to do with those coils. In less expensive signal generators, the coils are mounted in close proximity on a two-pole rotary switch. All their center taps are connected together like in the picture below (a). However, they tend to interact with each other and produce undesirable effects.
(https://www.eevblog.com/forum/other-blog-specific/tear-down-of-a-clough-brengle-signal-gen-from-1937/?action=dlattach;attach=630913;image)
One solution is to mount them apart from each other. But you have to use long wires to connect them to the band switch, and that has problems too. So the solution taken by Clough Brengle (b) solves both problems: you have them apart from each other and connect them to the variable capacitor with a very short extension.
This piece of equipment must have cost a fortune back then.
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Old Zenith TV sets had a similar solution, the tuning coils (and caps) were built on tag boards. A bunch of those boards mounted on a turret, which indexed by channel. A reasonable solution given how fragmented the US TV spectrum at least was (and not a bad approach for international sales, assuming other differences between standards were resolvable with similarly minor changes, which, I have no idea).
Tim