Diodes - cross referencing?

ID: 344281
? Diodes - cross referencing? 
21.Mar.14 16:55
14

Craig Curry (USA)
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Count of Thanks: 19

This is a tough nut to crack, and when I left the question on the diyaudio tube forum, I did not get the answers I needed. Days of asking and searching left me with more questions that answers. That is why I know I am not alone. Diodes go bad and finding an exact part number replacement is hard to impossible. Furthermore, the cross references are old, and even those list obsolete part numbers. The toughest thing for me is that the many manufacturers list different electrical specifications, so matching them based on specs is next to impossible for the novice. I have learned that diodes are used for more than one function, and selecting a diode depends on the intended use.

I will give my specific problem for you to digest: I have a Fisher 90-T which needs a set of diodes on the muting circuit. They are M5 and M6 in the Sam's photofact (date 12-58, Set 425, folder 7) link: (fisher_90t_part2), which is listed in circuit on this schematic page of the photofact: (usa_fisher_90t_sch1c). There are other diodes in this unit, so if I do find a source for 1N295 replacements, I will buy enough to replace all six unless they turn out to be costly. 

All help will be very much apreciated, as I am overwelmed by this.

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 2
Alternative Diodes. Very few needed! 
21.Mar.14 18:01
14 from 24050

Michael Watterson (IRL)
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For signal diodes the PIV is main thing. Only TV flywheel sync likely to exceed 1N4148

If it really needs Germanium (low signals, high sensitivity) I use modern 1N60   (0.15V drop). They are more sensitive than best Schottky or regular Silicon up to about 30MHz anyway. Above 20MHz to 35MHz the Schottky such as HP 5082-2800 may be best. But I can't think of any vintage applications using other than tube/valve rectifiers except waveguide based microwave detectors*.

If Silicon will do (0.6 to 0.7V) then 1N4148. Most situations except a bias diode will work with these. 100V PIV roughly.

Sometimes (rarely) a Shottky diode such as HP 5082-2800 could be used. But I can't think of any vintage signal application where 1N60 (Ge) or 1N4149 (Si) doesn't do.

For 20Hz to 400Hz  power 1N4007 LT or HT up to 1000V and 1A. Add a series resistor to simulate resistance of original metal Rectifier. i.e. Mains Transformer LT, HT or Vibrator packs. High voltage SMPSU/Inverters need UFnnnn or MURnnn series equivalents. Schottky power rectifiers only up to about  about 25V.

Oddly an 1N4007 but not so well an 1N4006 or less can be used as a cheap and poor Varicap or PIN  (variable RF attenuator by forward Current). The 1N4007 works as PIN above 1MHz as it's so slow due to high PIV rating that it won't rectiify RF, thus several volts of RF can be variably attenuated by 0.01mA to 10mA forward  current. A 1N4148 will rectify the RF.

* Replacing vintage UHF/Microwave detector or mixer diodes needs more thought and specialist devices.

The 1946 1N60 is quite different package style to "modern" 1N60 which also likely isn't made the same way.

Semiconductor diodes have existed since 19th C. But from late 1920s valves (tubes) better and cheaper. Valve (Tube) signal diodes used till 1960s as cheap. Also a diode in a Triode or Pentode envelope was cheaper than semiconductor diode. Before Germanium (1938? domestic from 1946) and Silicon (1940s?) diodes Copper Oxide was the most common signal diode, even used in 1930s ring diode mixers for cable telephony SSB. Selenium more used for power rectifiers. With some care you can make Copper Oxide diodes and rectifiers at home.

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 3
Need a USA source for 1N60 diodes 
21.Mar.14 19:29
28 from 24050

Craig Curry (USA)
Articles: 5
Count of Thanks: 15

This is very useful information. You certainly know your diodes!

I am not 100% certain that I will absolutely need germanium diodes; however, I feel it is the safest bet given my lack of understanding of the functions of each of the diodes in my tuner. I usually order from mouser when it comes to things like this, but they don't carry modern 1n60's. 

Does anybody have a reliable source for modern germanium 1N60's un the USA?

 

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 4
1N60 
21.Mar.14 19:53
32 from 24050

Michael Watterson (IRL)
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Searching eBay for 1N60

Chinese eBay sellers describe them as Schottky, some sell Silicon diodes described as like 1N60

Buy ones described as Germanium. About $5 to $10 for 100, possibly including postage. China, Thailand, Turkey and other countries selling them.

It's unlikely any domestic radio earlier than 1965 is silicon signal diode, 1946 to 1960s is Germanium. Earlier on domestic radio is usually something else that can be replace with Germanium for signal. Power rectifiers (Metal or Selenium) best only replaced by 1N4007 with series resistor.

 

Searching eBay for Germanium Diode

Gives a lot of 1N34A, which in most cases are also OK replacement, but the 1N60 is maybe better voltage rating and speed (shortwave). 

1N914 is listed by some as Germanium, which is nonsense. It's Silicon like 1N4148 and much the same.

See Links

The 1N914 & 1N4148 are small glass package. The "real" 1N60 and 1N34A (see link) are nearly twice size and similar to each other.

Any of these will probably do for Germanium. Main difference are maximum current and voltage, which is usually not important on Radio Detectors or Mute circuits. Though FM Discriminators can have higher voltage than AM detectors.

The AA119 is similar to 1N60, the 1N60A, 1N60B, 1N60C, 1N60P etc are all just later "better" versions.

1K34A 1T23 1T26 2AP3 AA110 GW20 MD60 OA70
Different maximum ratings:
 1N60A; 1N60C

Also suitable Germanium OA90 AA138 AA112 AA116 AA121 AA123 AA143 OA160

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 5
Small signal Schottky and Germanium. 
21.Mar.14 20:47
41 from 24050

Michael Watterson (IRL)
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I don't see HP 5082-2800 Schottky signal diode here.

Equivalents (approximate)
1N5711, 1N6263, 1SS101, 2800(DIODE), 5082-2800, BAR28, ECG583, HP2301, HP2302, HP2303, HP2305, HP2800, HP2800-28, NTE583, HSCH-1001, HSCH1001, NTE583, SD101A, SD101B, SD101C

In any case, it's generally only a general purpose replacement if original signal diode was Schottky. The 1N914 or 1N4148 will do most signal diodes and 1N34A / 1N60 germanium etc where silicon isn't so good (very small RF signals). For Bias of Germanium complementary Push Pull Totem Pole layout transistors you need Germanium transistor as a diode or Germanium diode and resistors may need adjusted.

About 2007 I did a lot of tests in my job looking at Germanium, Schottky signal diode and Silicon diode for RF level detector for adaptive radio link. We tried even various slight bias on Schottky HP 5082-2800, 1N5711, SD101, Silicon 1N4148, Germanium OA47 and Germanium 1N60 (not sure which suffix).  With a slight bias the 1N4148 was nearly same as Schottky for sensitivity. The Schottky I think works to higher frequency.  But the lower junction voltage meant at the lower end of signal levels the OA47 and 1N60 far better than either.

So for a very sensitive RF meter, SWR meter or "Crystal Radio" the Germanium is still best. The Schottky is best as high speed switch. The 1N4148 best if the most sensitive RF detector isn't needed. It will work as rectifier for SMPSU up to 100V and 100mA or as discriminator diodes for FM detector or AM detector in a Superhet. A single stage TRF though will be better with Germanium diode. The 1N4148 has lowest leakage of these 3 as an RF switch. PIN diodes only needed for a variable attenuator or if RF voltage is more than DC switch voltage. 

 

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 6
Many thanks... problem solved 
21.Mar.14 22:02
51 from 24050

Craig Curry (USA)
Articles: 5
Count of Thanks: 14

Thanks again Michael! I am sure these responses will be of great help to people like me who run across bad diodes in older units. There just doesn't seem to be a good source for this information. As I stated before, there is a lot of information available, but it is sporadic, and hard to digest. Information overload!

The 1N295 I started looking for has a PIV of 40V, so all of the 1N60 series will be sufficient, as they are all equal or higher PIV's.

One last question. Are NOS 1N295's as good? Do shelved diodes go bad?

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 7
Semiconductors going bad? 
21.Mar.14 22:25
55 from 24050

Michael Watterson (IRL)
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The AF117 and some similar type Germanium transistor are known for going bad. This is due to Tin Whiskers growing inside the "goo" inside the can. Obviously the symptom is high leakage or a short. I had two radio sets with this problem. Because the bais involved Emitter Resistors and they where MW/LW mixer/Osc and AM IF, I found that Silicon 2N3906 worked fine without changing bias. However I then fitted NOS Russian ex Military Germanium (60MHz rated) signal types off eBay from Ukraine. No difference :-)

"Lockfit" transistors such as BC148 are known for being open circuit. I believe this is only on PCB and due to manufacturing time stress cracking wire bond, not unused parts. All Lockfit parts have similar TO92 equivalents easily obtained. though pin order may differ. Replace 1 with 5, i,e BC147 replaced by BC547 etc.

I never heard of any other semiconductors going bad in storage.

I'd not even bother looking for 1N295, I usually have 200+ 1N60, OA47, 1N4148 etc as they are very cheap. I've never had a problem using either 1N60 or 1N4148 for replacing signal / switching diodes etc.

Diodes are very easy to test. I use a capacitor leakage tester (600V with 2M Ohm in series) and 10M input impedance DMM to measure PIV of Diodes and VCBo or VCEo of transistors. But the Diode test on most modern cheap DMM displays forward mV at a small current. You can use Ohms on 1M range to see if reverse leakage is high. Note on most analogue meters the Black lead on Ohms range is + volts.

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