Condenser fan motor sustitute

Umm. Capacitor dielectrics have gotten way better over the years.

Just buy the next highest voltage rating. This kind of derating is standard practice. For film capacitors, a common rule is that operating voltage be one half the rated steady-state voltage.

Joe Gwinn

Reply to
Joe Gwinn
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But most HVAC caps are dual caps, fan/pump. I haven't seen replacements rated higher voltage of the same values. Can one use two discrete caps?

Reply to
Tom Gardner

Tom Gardner fired this volley in news:mqufgp$qs1$2 @speranza.aioe.org:

Indeed. "Dual caps" are just a packaging convenience. They're fundamentally a service problem, because if half fails, you must replace both.

Most discrete-component television sets of the late 60s and early 70s that ended up on a service bench could be seen to have had at least one dual cap replaced with single-capacitor equivalents.

Lloyd

Reply to
Lloyd E. Sponenburgh

A lot of TVs at that time used three or four section 'Twistlock' electrolytics. The most common failure was the 160 uF 250 VDC electrolytic used in the power supply of TVs without a power transformer. They handled a lot of ripple current, and often swelled up, blew the vent or exploded and filled the cabinet with shredded paper and aluminum foil.

Reply to
Michael A. Terrell

"Michael A. Terrell" fired this volley in news: snipped-for-privacy@earthlink.com:

Yeah... My Dad and I had the local Sears & Roebuck contract for about five years in the late 60's. Their "Silvertone" line of TVs were just junk. They combined EVERYthing they could into multi-component bundles, without regard to performance. Dad would say, "They don't have enough parts in 'em to make a decent radio!"

They pretty much all had those quad-caps, and some of the multi-section tubes with two to four discrete tube 'sections' in one envelope (like those damnable 6AG11s).

Lloyd

Reply to
Lloyd E. Sponenburgh

At least the OEM was smart enough to use fusible resistors to prevent fires. I forget who was the main TV supplier to Sears at the time, but I met one of their engineers on a flight to a new assignment. He complained about what they had to do to meet the Sears demands, and price.

When Motorola quit building consumer electronics and sold it off as Quasar, their TVs had over 100% failure rate off the production line. Matsushita closed the plant, replaced all the test equipment and put every production worker through classes to improve their skills. Motorola had run the facility into the ground, and no one gave a damn. It was apparent in their products.

I don't have any 6AG11s, but I do have a few new 6AF11 & 6AL11 if you need them ;-)

I bought the 6GH8A by the case of 100 at a time, in the '70s.

Reply to
Michael A. Terrell

Certainly, you can. You just need another wire to connect the common terminal of the two caps together. But you might not find it easy to get capacitors of those values with voltage ratings much higher than the 440V of the ones you have now. And yes, it does need to be that high even for a 240V supply. I measure 425V across the run cap for my compressor. I'm sure it spikes higher than that during power "events".

Reply to
Robert Nichols

Gizmag had an article yesterday which might interest you. It seems that DARPA is hot for vacuum tubes.

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Reply to
Larry Jaques

Larry Jaques fired this volley in news: snipped-for-privacy@4ax.com:

Without even reading it, I can understand why. Tubes are VERY immune to EMF damage, while semiconductors seem to just belly-up and die at the least excuse.

Lloyd

Reply to
Lloyd E. Sponenburgh

Sure you can. They have a common point to which one side of both caps are connected, and then the free end of each goes off to the appropriate load. (The larger one to the compressor, the smaller to the fan.)

For that matter -- the caps in my unit were replaced by a special "replacement" cap which was in reality six caps of different values, all connected to the one common, and the free end brought out to a number of terminals. In practice, one was the right value to run the fan, and all the rest in parallel added up to the value needed for the compressor. (For those who don't know, capacitors in parallel add, resistors in parallel produce a lower value. If only two, and both are the same value, the result is half the value. If different values, or a number in parallel, the math is a little more complex. Divide each value into 1, add the results together, and then divide that value into

1 to get the result. Something similar is done for caps in series.

Enjoy, DoN.

Reply to
DoN. Nichols

And, depending on the failure mode, it can make diagnosis a bit more complex. Mine, when it failed, had the connection of the common of the two caps to the common output terminal open, so in effect there was a smaller value cap between the two load points. That was enough to start the fan (with the compressor acting as a virtual ground), but far too small to start the compressor, so it kept cycling, with the current limit opening and then re-closing a few minutes later, resulting in a repeated dimming of lights. And, when it tried to check it, it appeared that the cap was good. :-)

Those would be the electrolytic caps, no doubt. (Mostly power filter after rectifiers.) They had the common ground in the metal case, and could benefit from the lowered cost of manufacture -- and the lowered cost of mounting components.

Enjoy, DoN.

Reply to
DoN. Nichols

As many others have said, yes you can, and it's often a good idea.

Also, capacitor makers differ in how much safety margin they build in, so buy only from the better brands.

Joe Gwinn

Reply to
Joe Gwinn

The failure mode in mine has always been that the compressor cap blows and causes the lid to dome upward, breaking the internal connection to the fan cap. What makes it interesting is that I have a "hard start kit" installed, and that's enough to get the compressor started. The fan won't start without it's cap, so the compressor cycles on the high pressure limit switch. I wish it would just lock itself out instead of cycling that way repeatedly.

Reply to
Robert Nichols

Good point. I hadn't thought about it from that aspect. Some muzzy moron is surely going to set off an EMP bomb around the world somewhere soon, so the quicker we find ways around it, the better. "We live in 800AD, and so should you."

Reply to
Larry Jaques

I was looking at some kits for making small pre-amps or amps for MP3 players that use very small tubes. I don't know much about how tubes work. I know the basics but I don't know how the actual size of the tube internals and their proximity to the other elements inside the tube affects the operation of the tube. I imagine that today with modern automation equipment that tubes could be made very small indeed. Whether the tubes would operate the same as larger ones I have no idea about but would like to know. I have seen pictures of devices made and used in WWII that contained very small tubes that were used in anti-aircraft shells to iniate the explosion when the shell was close enough to an airplane. These tubes were essentially hand made and even though tubes seem to me to be delicate these had to be made to survive the acceleration of the anti-aircraft shell when fired from a cannon. Eric

Reply to
etpm

second son has built himself what ammounts to a "jumbotron" of 22" monitors, simply by replacing caps in the power supply of out of warranty units. He designed a replacement set of caps then bought in bulk quantity.

Reply to
geraldrmiller

Cool. Got a list of those caps?

Reply to
Larry Jaques

This was one place where the Russian military aircraft had an advantage over ours. But must have at least a backup tube based radio if EMP takes out everything else.

Well ... the distance of the grid from the cathode adjusts the gain (assuming full emission from a fresh cathode), but the main thing is that the smaller tubes can't handle as high a voltage for operation

-- though they could likely survive the EMP induced spikes.

Same principles, but less maximum voltage.

Note that in the 1970s and around then there were some very small metal-cased tubes called "Nuvistors" -- about the same diameter as a TO-5 transistor case, and three times as tall.

There were pencil tubes, mostly made by Raytheon, which had numbers starting with "CK" like the early transistors from the same company, such as the CK-722. I worked with those at the hobby level when I was in high school. The pencil tubes had an end-on profile like "()" and one end was squished flat with a number of evenly-spaced leads coming out the seal. The other end was a little nipple where the vacuum was pulled and them melted closed. I first saw one of these when I took apart an old Radiosonde (a device sent up under a balloon to transmit back the temperature, the humidity, and the barometric pressure/altitude. (They knew how fast it should rise, so they could determine the barometric pressure at the various altitudes. They were launched from the local small-town airport, among other places, and were powered by a weird battery which had several sections for different voltages, and was activated by pouring water in through a hole in the lid. A few minutes and it was producing full voltage. These were not meant to be re-used, apparently.

Anyway -- aside from the pencil tube (and before the days of practical transistors), there was another very specialized tube. about

2" long, with most of the length about 1/4" diameter, with a glass seal in the middle where there was a disc of metal coming out to perhaps 1" diameter which was the grid connection for that tube. Two pins on one end for the filament. The cathode and plate connections were the 1/4" cylindrical sections. Based on the length of the antenna (and things which I learned later in life) it was probably operating in the range of 400-500 MHz.

And -- there were also what were called "Acorn tubes" (about the size of an acorn), a little larger in diameter than the Nuvistors , with the seal between a top and a bottom cap, and the leads coming out radially. Those were used in walkie-talkies and the like in WW-II.

The major disadvantage of almost all tubes was that the emissivity of the cathode would decrease with hours of use, so you had to be able to re-adjust for the differing gain -- or design more complex circuits which would automatically compensate for such drift. Transistors tend to keep the same gain until they are over-voltaged or over-currented at which point they stop working. :-) But in a well-designed circuit, they are unlikely to be exposed to the excess voltage or current.

Enjoy, DoN.

Reply to
DoN. Nichols

Small tubes were popular in Hand Transceivers and all sorts of stuff. Battery radios had them. Typically they drew lower current on the filaments (heaters) and had them on one battery. B+ was on another battery.

Tubes are on the upswing and there are a number of makers for high end audio and high end power amps for transmitters.

I have a number of various tubes here. Some monsters that Iggy would use or Gunner.

Mart> >

Reply to
Martin Eastburn

I got rid of my 1T4's just a few years ago. That was 1.5V filament, and the B+ was 45V, IIRC, which was an Eveready about the size of a pack of cigarettes. My first shortwave radio used them -- a one-tube regen that would run for a long time on the 45V and a D-cell.

The US military was developing a new "vacuum tube" configuration, for the sake of their higher (but not total) EMP resistance, around 15 years ago. They were ganged in groups, with the "tubes" being cavities cut in blocks of some kind of ceramic.

Reply to
Ed Huntress

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