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 Post subject: Are "dome shaped " transistors any good?
PostPosted: Feb Tue 16, 2021 7:02 pm 
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You've seen those tiny transistors that look like a miniature security camera. I've read where people have said they're junk, so I'd thought I'd ask. If you see those in a radio you're considering buying, are they any worse than a standard germanium transistor?


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 Post subject: Re: Are "dome shaped " transistors any good?
PostPosted: Feb Tue 16, 2021 7:26 pm 
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If you are referring to metal encased bullet shaped Transistors, they would be the best you can buy. Think about it; they wouldn't have spent the $ on a metal housing unless it was for a superior item.

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 Post subject: Re: Are "dome shaped " transistors any good?
PostPosted: Feb Tue 16, 2021 8:37 pm 
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fifties wrote:
If you are referring to metal encased bullet shaped Transistors, they would be the best you can buy. Think about it; they wouldn't have spent the $ on a metal housing unless it was for a superior item.

Image


No, not those, these:
Sometimes they're mixed with the bigger types. Hope the picture is good enough.


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 Post subject: Re: Are "dome shaped " transistors any good?
PostPosted: Feb Tue 16, 2021 10:05 pm 
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TO-106
https://www.vintage-radio.net/forum/sho ... p?t=134212

Greg.


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 Post subject: Re: Are "dome shaped " transistors any good?
PostPosted: Feb Tue 16, 2021 10:30 pm 
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Thanks Greg. The concensus seems to be they were early silicon with ceramic and epoxy. May have been used mainly in cheaper generic name radios but sometimes in name brands as well.


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 Post subject: Re: Are "dome shaped " transistors any good?
PostPosted: Feb Wed 17, 2021 12:41 am 
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That style of silicon transistors were common even in high-end and commercial products at the time---am guessing that the "fallouts" or ones that didn't meet manufacturers' specifications ended up in cheap transistor radios like many germanium parts did in early '60's... Perhaps someone here might know for certain.

John


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 Post subject: Re: Are "dome shaped " transistors any good?
PostPosted: Feb Wed 17, 2021 4:45 am 
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I remember those, Fairchild made those and if you ever had a problem with a set that used those transistors, you checked them first! RCA used them as third IF transistors in their hybrid tv's and they always opened the emitter junction.


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 Post subject: Re: Are "dome shaped " transistors any good?
PostPosted: Feb Wed 17, 2021 8:45 pm 
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Fairchild "Glop-Tops" only lasted for a few years in production... late 60s, early 70s. It was evolution in packaging and lost out to TO-92 and other injection molded epoxy types.

As to the metal cans shown,

Quote:
If you are referring to metal encased bullet shaped Transistors, they would be the best you can buy. Think about it; they wouldn't have spent the $ on a metal housing unless it was for a superior item.


That's pretty optimistic. Transistor technology was primitive back then. Early transistor packaging evolved from the tube business at RCA, GE, Sylvania. They knew about glass-to-metal seals, so they used them. The chip itself was pretty rough technology.

Rich


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 Post subject: Re: Are "dome shaped " transistors any good?
PostPosted: Feb Thu 18, 2021 4:24 am 
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Rich, W3HWJ wrote:
Fairchild "Glop-Tops" only lasted for a few years in production... late 60s, early 70s. It was evolution in packaging and lost out to TO-92 and other injection molded epoxy types.

As to the metal cans shown,

Quote:
If you are referring to metal encased bullet shaped Transistors, they would be the best you can buy. Think about it; they wouldn't have spent the $ on a metal housing unless it was for a superior item.


That's pretty optimistic. Transistor technology was primitive back then. Early transistor packaging evolved from the tube business at RCA, GE, Sylvania. They knew about glass-to-metal seals, so they used them. The chip itself was pretty rough technology.

Rich

Optimism based on experience. My four Transistor Philco sets with the metal encased Transistors could easily match up to six Transistor radios. My Philco six Transistor pocket sets with those same metal Transistors are at another level vs most other Superhets.

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 Post subject: Re: Are "dome shaped " transistors any good?
PostPosted: Feb Fri 19, 2021 5:55 pm 
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I am glad your experience was good, but it was a very small sample.

Metal can transistors lost out to plastic over 40 years ago. The military hung on for a couple of decades more, and maybe still uses them. Metal cans have too many parts, cost too much, and are prone to their own set of problems. Weld leaks, weld splash (weld debris that sprays on to the chip), cracked seals and worst of all, losses due to the inductance of the package. Every glass seal is a "shorted turn" around the connecting wire. At high currents, this heats the package (induction heating) and results in worse efficiency, and slower switching times.

I remember the early days at Westinghouse, when no one would think of using plastic or epoxy. The chips we made had rough edges where they were scribed or sawed out of the wafer and we depended on varnish coating to "passivate" the chip. Later, we learned about glass and nitride passivations that were applied directly to the silicon. Of course, we also made our own Kovar (glass sealing alloy) and Dumet wire (used in light bulbs), so glass-to-metal and ceramic-to-metal, were the gold standards of the time. Today, you won't find a TO-3 or TO-5 in your computer or TV and the reliability today rivals or exceeds what we sold to NASA in 1970.

Rich


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 Post subject: Re: Are "dome shaped " transistors any good?
PostPosted: Feb Fri 19, 2021 7:46 pm 
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Rich, W3HWJ wrote:
I am glad your experience was good, but it was a very small sample.

A matter of perspective; I look at it as a collector and hobbyist, you apparently in more of an industrial fashion involving another level of quantities.

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 Post subject: Re: Are "dome shaped " transistors any good?
PostPosted: Feb Sat 20, 2021 4:09 am 
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Exactly right.

In the early 90s at Siliconix, we had to ship a few hundred thousand parts a month to the ABS brake companies. They all had to be good and had to last as long as the car.. They also had to sell for a few pennies above our cost. It was a tough business. Hard disk drives were better. We shipped over a million a month for head and spindle drives. We did make a few cents, however.

Rich


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 Post subject: Re: Are "dome shaped " transistors any good?
PostPosted: Feb Mon 22, 2021 8:09 pm 
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While many dislike these transistors, I have never had any problems with them. Could just be my luck :mrgreen:

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 Post subject: Re: Are "dome shaped " transistors any good?
PostPosted: Feb Tue 23, 2021 1:16 pm 
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I must agree with Fifties that the early Philco models, with their innovative surface barrier germanium transistors in the domed metal envelopes, are excellent performers.

The Fairchild silicon transistors in the domed epoxy envelopes appeared in the late 1960s. I haven’t noted a high failure rate, though a lot of the radios that had this style of transistor were quite cheaply made.


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 Post subject: Re: Are "dome shaped " transistors any good?
PostPosted: Feb Sun 28, 2021 11:30 pm 
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Generally the common Fairchild type had a dark grey ceramic body and a black resin top. They came in two diameters, the larger one being similar to a TO-5 diameter, examples of these are the 2N3643 and 2N3644 npn & pnp types, wonderful transistors. Typically, all these transistors had gold plated lead wires. There are no modern fakes, the worst you would get is a re-label.The fakers cannot work well with ceramics and they cannot afford gold. So NOS transistors of this type are usually a very safe bet as an ebay buy. 2N3643 & 44 are not just great RF transistors, they turn out to have very low audio spectrum noise.

Some companies make them with white ceramic bodies, I have some white body apparently Signetics 2N3644's. These look pretty with the shiny black top.

I have not noticed an excessive failure rate of these types over 50 years. Although I have seen a few examples of mechanical failure where the lead wires rotated in the ceramic body hole where they pass into package, so that it probably the only thing to watch out for.


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 Post subject: Re: Are "dome shaped " transistors any good?
PostPosted: Mar Mon 01, 2021 1:31 am 
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I've only seen the black dome shaped ones. I think one of my Zenith Royal 10s had those, and it fits the time period of about 1968-70. I believe my other Royal 10 had germanium transistors.


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 Post subject: Re: Are "dome shaped " transistors any good?
PostPosted: Mar Mon 01, 2021 10:55 am 
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Zenith Royal wrote:
I've only seen the black dome shaped ones. I think one of my Zenith Royal 10s had those, and it fits the time period of about 1968-70. I believe my other Royal 10 had germanium transistors.


Here is a photo of the White ceramic version shown next to the typical Fairchild grey ceramic version.


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 Post subject: Re: Are "dome shaped " transistors any good?
PostPosted: Mar Mon 01, 2021 4:32 pm 
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Have several in my transistor drawer---believe they also offered FET's, OP-amps, and other devices in that type package long ago...

John


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 Post subject: Re: Are "dome shaped " transistors any good?
PostPosted: Mar Mon 01, 2021 5:31 pm 
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I used to have a Zenith Chroma Demodulator, made by Fairchild using a "glop top" with a 7-pin arrangement so it could plug into a tube socket. Replacement parts had to be hand-made with a metal can IC and a wafer tube base.

Image

Zenith p/n 221-39

Rich


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