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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 18th Dec 2018, 1:06 am   #1
Jolly 7
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Default Which semiconductors are useful to have for repairing radios

The huge variety of transistors and diodes out there can be overwhelming for an average hobbyist. There may not be a straightforward answer to my question, but are there any silicon or germanium transistors that are most useful to have in one's parts box ? Particularly ones that can be substituted in most instances where the exact transistor cannot be sourced ? I am aware of the AF11x substitutes.
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Old 18th Dec 2018, 1:21 am   #2
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Default Re: Which semiconductors are useful to have for repairing radios

You should certainly keep a stock of NPN and PNP general purpose Si types - 2N3904/2N3906, 2N2222/2N2907, BC546/BC556 etc. These will sub for most Si transistors in radios apart from output types, even including RF types like BF194s.

If you want to use proper VHF transistors, MPSH10s and 2SC2999s are cheap and versatile.

Ge are trickier. You can often sub silicon even without component changes, but many people buy a quantity of Russian Ge RF types from eBay sellers. These are relatively cheap and can be used for AF applications as well as RF.

For Ge diodes you will find the American 1N34A cheapest and easiest to source. For Si switching diodes use 1N4148s, and for rectifiers use UF4007s.
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Old 18th Dec 2018, 1:36 am   #3
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Default Re: Which semiconductors are useful to have for repairing radios

Thanks Paul. That's really helpful. I have fond memories of using a Germanium OA79 glass diode to build my first radio. The six transistors were all silicon though. I haven't seen any OA79s for a long time now.
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Old 18th Dec 2018, 1:40 am   #4
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Default Re: Which semiconductors are useful to have for repairing radios

I buy these jellybean parts from Chinese eBay sellers and haven't had any problems. I guess they are so cheap that there's no point in faking them. They are made in vast quantities there.
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Old 18th Dec 2018, 7:14 am   #5
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Default Re: Which semiconductors are useful to have for repairing radios

I went to buy the parts to build a solid state replacement for a tube in the Zenith TransOceanic, from a schematic I found on the 'net.

After finding a wholesaler who had the IC needed, I queried him as to the cost of the 10 1N4148 diodes I needed, the 1N4007's etc.
If I bought in quantities of 10 ea, I was informed that the parts would cost 1.00 ea. If I bought them by the 100 lot, the price dropped to 1 and 2 CENTs each!!! I placed my order & in a week, had all the parts. Grade "A" ones too. (They were even cheaper if I bought in lots of 1000 pcs. That was 4 lifetimes of them for me.

By all means, shop around and share your take with your mates. I sure did.
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Old 18th Dec 2018, 7:48 am   #6
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Default Re: Which semiconductors are useful to have for repairing radios

I order mainly from bitsbox. They deliver quickly and I foumd that I readily spotted a list forming of my 'ought to stock myself' items.

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Old 18th Dec 2018, 11:08 am   #7
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Default Re: Which semiconductors are useful to have for repairing radios

I keep BC546, 7, 8 and 9, BC550, BC556, 7, 8, 9 to cover the small silicon ones that one finds in AF, control and logic circuits. BC337, 338 etc for higher power stuff, BD131 / 132 for a bit more, BF240 for RF, TIP41 / 42 range (A, B, C) for TO220 applications, 2N3055H (RCA type) for the big stuff. For diodes, 1N4148, 1N4007 and BY298 are the common ones and cover most things. For TV, BU208A (Toshiba type), BU508A and BU508D take care of most line output / converter applications (Sony aside). Its also worth keeping a few zener diodes in useful increments from 3V9 to around 15V.

The rest come from odds and ends in the box, possibly the most useful semiconductor resource of all. You can get the more obscure ones on eBay in a few days, no need to hold huge stocks of those.
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Old 18th Dec 2018, 11:21 am   #8
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Default Re: Which semiconductors are useful to have for repairing radios

The UF4007s I suggested are just fast recovery 1N4007s. They don't cost much more.

Scrap equipment can be a good source of components, though they will be short leaded. A first generation VHS recorder or a late 70s / early 80s cassette deck will be full of useful transistors and caps.
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Old 18th Dec 2018, 11:33 am   #9
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Default Re: Which semiconductors are useful to have for repairing radios

The UF4007 is a much better part than the 1N4007 and the price difference is small. The 1N4007 has a problem with making RF noise as it switches off. The higher voltage 1N400x parts are worse. Best avoided

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Old 18th Dec 2018, 1:17 pm   #10
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Default Re: Which semiconductors are useful to have for repairing radios

Thanks for the note on the 1N4007. Just curious whether the 1N540x series are similarly affected?

I have successfully used Russian GT322A's in place of AF117's, however I did notice in the Roberts R200/R300, that the value of the AGC resistor needed to be increased as the AGC was throttling down too much. I suspect this may relate to the hFE of the GT322A being higher then the AF117. I have also successfully used a pair of MPSA56 silicon transistors in place of the two OC81 germanium output transistors.
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Old 19th Dec 2018, 5:06 pm   #11
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Default Re: Which semiconductors are useful to have for repairing radios

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Originally Posted by Radio Wrangler View Post
The 1N4007 has a problem with making RF noise as it switches off. The higher voltage 1N400x parts are worse. Best avoided
OEM spec for thousands of models over the years, how bad can it be? I've never had any problems with them, its good to have a component available which has been so thoroughly tested and proven. Where it matters, 1nF (ish) in parallel is the standard answer.
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Old 19th Dec 2018, 5:22 pm   #12
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Default Re: Which semiconductors are useful to have for repairing radios

BC10x and BC14x series [I default to the 'C' gain-grouping ones for everything] for small-signal audio stuff.

BFY51 for things like relay-drivers and voltage regulators.

MJE340 for high-voltage switching and audio amp/driver.

OC35 or NKT404 for germanium audio-amps/inverters/modulators.

2N3771 for high-current regulators/audio-amps (think of it as the 2N3055's successor).

BF115 for receiver RF/IF amps.

AF239 germanium UHF transistor for old TV- and mobile-radio front-ends.

1N914 diode for switching/logic stuff.

2N3819 general-purpose JFET.

BY127 diode for high-voltage rectification.

2N3866/2N5109 for anything needing a bit of power at VHF (transmitter-drivers, high-current RF amps, driver for diode switching mixers)

I also keep a stash of the VN66AF-style FETs for switching and the like.
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Old 19th Dec 2018, 5:40 pm   #13
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Default Re: Which semiconductors are useful to have for repairing radios

Quote:
Originally Posted by Studio263 View Post
Quote:
Originally Posted by Radio Wrangler View Post
The 1N4007 has a problem with making RF noise as it switches off. The higher voltage 1N400x parts are worse. Best avoided
OEM spec for thousands of models over the years, how bad can it be? I've never had any problems with them, its good to have a component available which has been so thoroughly tested and proven. Where it matters, 1nF (ish) in parallel is the standard answer.
In most applications it won't matter, but if you're buying 100 general purpose rectifier diodes then you might as well buy fast recovery parts given that the cost difference is so small. The difference is more significant if you're ordering them in millions.
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Old 20th Dec 2018, 9:35 am   #14
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Default Re: Which semiconductors are useful to have for repairing radios

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how bad can it be?
It's one of the mechanisms whereby cost-sensitive SMPS and lightbulbs are blanketing the LF, MF and HF spectrum in mains-modulated noise. It isn't just the chopper makes the noise, even the rectifier gets to contribute. It can actually be more significant than the chopper's noise in some cases.

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