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Author Topic: GE 102 AMBC radio tube problems  (Read 23947 times)
AC5UP
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« Reply #30 on: August 17, 2011, 08:16:36 AM »

Note to N4NYY:

It you really want to learn the legend & lore of the electron tube, download an RCA receiving tube manual: http://www.tubebooks.org/tube_data.htm

Not only do you get the theory of operation and guides for choosing grid bias and screen voltages that put a signal in the linear portion of the curve, but there are also practical circuits for your building pleasure and analysis... Including the AA5 with a circuit description. If you ever want to give your GE a sex change, look at page 215 (15-4) of the 1948 RC-15 manual and you'll find the RCA equivalent. Plenty of other receivers in that section, too.

Scroll through the URL given above and you'll see similar goodies from Mullard, Westinghouse, GE, Tung-Sol, Raytheon, etc...................... Shocked
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W8JI
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« Reply #31 on: August 17, 2011, 08:26:13 AM »

The beam forming plate has often been considered a form of suppressor grid. They are called many thing including beam power tetrodes, beam pentodes, or whatever strikes the particular writer's fancy. I see many beam power tubes represented as pentodes in symbol.

The important thing is how they behave. :-)

The earliest metal tube envelope patent I found is one by one of the partners who formed Eimac. There are many court arguments about who was first. :-)

73 Tom
« Last Edit: August 17, 2011, 08:28:39 AM by W8JI » Logged
N4NYY
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« Reply #32 on: August 17, 2011, 02:48:14 PM »

Quote
It you really want to learn the legend & lore of the electron tube, download an RCA receiving tube manual: http://www.tubebooks.org/tube_data.htm

Nice! We spent about 1 day on tubes when I went to electronics school 25 years ago. I am 44 years old, but only 15 years old if I were to rate myself in ham years.
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W8JI
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« Reply #33 on: August 17, 2011, 04:35:34 PM »

Quote
It you really want to learn the legend & lore of the electron tube, download an RCA receiving tube manual: http://www.tubebooks.org/tube_data.htm

Nice! We spent about 1 day on tubes when I went to electronics school 25 years ago. I am 44 years old, but only 15 years old if I were to rate myself in ham years.

I was lucky to get in on the tail end of tubes Vinny. I had two years of almost 50/50 transistors and tubes. The lab had 400 volt power supplies on each bench. Heathkits. They had bias variable, fixed filament, and HV variable. Saw one on eBay a year or two back and bought it. Works great. 6L6 in the regulator I think.
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N4NYY
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« Reply #34 on: August 17, 2011, 06:54:59 PM »

Quote
I was lucky to get in on the tail end of tubes Vinny. I had two years of almost 50/50 transistors and tubes.

I only wish. Granted, this is 1985, and we were on the cusp of the PC. I did find my original school notebooks and textbooks about communications. I have to go over them again. It was so much easier back then. I did this every night for 2 years. Now, I can only give it 1 night per week. I have to dedicate more time.
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AC5UP
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« Reply #35 on: August 17, 2011, 08:36:23 PM »

I had one college level electronics class and I can't recall if I ever told this story, so here goes:

This is 1971 and the class is about half & half vacuum and sand. I was not strong in math and flunked Calculus in my freshman year which put me at a distinct disadvantage as math is the language of science and physics in particular. But, curiously enough, I was the only one in class who had ever refurbed or troubleshot a radio. My lab partner had no idea what a resistor or condenser looked like prior to that class and I taught him how to solder. The dude was good at math and even though he wasn't always sure why he was using a specific formula, he could usually remember enough of it to come up with the correct answer on an exam. My methods often relied on tea leaves, chicken bones and intuition.

So... Lesson for the day is the resistance coupled amplifier and how to determine component values for a given plate voltage. Instructor draws the circuit on the board, points to one of the resistors and asks me specifically what I think the value will be. I paused for a moment, then said "Ten Thousand Ohms". Instructor gives me a distressed look and I figure I missed it by a few miles. Fifteen minutes and a fair amount of chalk dust later the answer calculates to something like 9,580 Ohms... Apparently the instructor wished I had missed it by a mile because the point of the class was to teach the value of working a formula instead of guessing a part value.

Which is why I was given the opportunity to humiliate myself 'cuz by that time I had been ID'd as Mister Intuitive....

But, the instructor was cool enough to say that in practice the nearest standard part value would be 9,700 Ohms so that's what would show on the schematic. And that 10,000 is within 5% of the calculated value so it <cough!> would work Ohhhhhhhhh Kayyyyyyyyyyy.

Nothing magic, BTW, just a lucky guess on my part because 10k seemed about right for that place in that circuit..............  Grin
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N4NYY
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« Reply #36 on: August 20, 2011, 11:52:35 AM »

Need you guys took at this below. The radio speaker has a hole punched thru it, but is sound fine. In any case, I looked for a replacement and found one below. But it does not make sense. It says that it is a 6" speaker with mounting holes center at 4 3/8". How is that possible, or am I very bad at math?

(SPK) P6W3 Communications speaker. 3.2 ohm impedance, 5 watts. 6" diameter x 2-3/4" deep. 4-3/8" centers on mounting holes. 50-14,000 Hz. New in the box.

http://www.surplussales.com/microphones-audio/MicroAudio-8.html
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AC5UP
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« Reply #37 on: August 20, 2011, 02:22:53 PM »

You didn't take a close look at your old speaker? Didn't measure the hole-to-hole mounting dimension?

Tsk!

Anyway, I have two objects in front of me........................

One is a Utah 6" 'Micro Gap' permanent magnet speaker, model SP6FC. The other is a 6" machinist's pocket rule made by the L.S. Starrett company of Athol, MA. The pocket rule tells me this Utah speaker cone is very slightly over 6" (frame basket inside dimension) with slightly elongated mounting holes that are 4 3/8" on center. An ohmmeter placed across the terminal strip reads 3.4 Ohms. There are three holes opposite the terminal strip that offer two possible ways to mount a low wattage tube type output transformer.

(Betcha' you didn't know you can measure a speaker voice coil with an ohmmeter and ballpark the impedance. Emphasis on 'ballpark')

No, you can't have the speaker 'cuz I plan to throw it out when I do my fall cleaning. For now, look at your old speaker: The speaker diameter is measured across the center while the mounting holes are on a square with their centers measured hole-to-hole "short path". If I measured the hole spacing on the diagonal they would be the same as the diameter, but on a square with equally spaced holes it doesn't matter how the speaker is mounted... It's always 4 3/8" between centers.

The pocket rule is trying to have sex with the magnet so it's time to put them away............ I think it's a case of natural attraction.  Grin
« Last Edit: August 20, 2011, 02:35:57 PM by AC5UP » Logged

N4NYY
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« Reply #38 on: August 20, 2011, 02:29:22 PM »

Quote
No, you can't have the speaker 'cuz I plan to throw it out when I do my fall cleaning.

That is not the right answer. The right answer is that your threw it our last month! LOL  Grin Grin Grin Grin
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