"SW-05" diodes.

[G6Tanuki]

I'm reworking a Trio 9R-59 communications receiver and it includes a number of strange diodes/rectifiers in the signal and AGC paths.

They're marked "SW-05", black-encapsulated lumps about the same diameter as a Polo-mint.

Strangely, these often form half of a voltage-doubler network with a 1N-60 diode as the other half.

Does anyone know what the charateristics of these boiled-sweet-sized diodes are??

[Nuvistor]

Radio Museum has a little info, silicon power supply diode.
https://www.radiomuseum.org/tubes/tube_sw-05.html

[HamishBoxer]

Possibly similar to 1N4007

[Radio Wrangler]

Just have a look at the circuit diagram and pick something to serve in the actual application.

David

[paulsherwin]

I also thought these were power rectifiers. I've no idea what they're doing in an RF circuit.

[G6Tanuki]

Originally Posted by paulsherwin

I also thought these were power rectifiers. I've no idea what they're doing in an RF circuit.

That's whats confusing me! particularly since I'm having 'issues' wrestling with the receiver's AGC action!

[Station X]

Just had a look at the parts list in the service manual.

The diodes in the PSU are specified as S-05-08, the others as S-1.5-02.

This differs from the block diagram and circuit diagram in the same publication.

I have no idea what's actually fitted or whether the specs differ.

[barrymagrec]

Some power diodes such as 1N400x also work as varicap diodes.

[Radio Wrangler]

Originally Posted by barrymagrec

Some power diodes such as 1N400x also work as varicap diodes.

It's the higher voltage members of that family. They can be used as varicaps or as PIN diodes. They are simply too slow to work as diodes much above 50Hz.

I wouldn't expect to see one used as a diode at RF or IF frequencies.

David

[Radio1950]

Diode D5 is part of the noise limiter, and is a silicon type chosen probably for the slightly higher voltage barrier.
If it works, leave it alone.

If you must test it.
Measure it in circuit for resistance, with rx power OFF.
If the ratio of resistance from one polarity to the other with your meter leads is 10 to 1 or higher, then it is probably OK.
If not, or suspect, lift one leg and repeat, paying attention to leakage, ie back resistance.

Replace with 1N4004 or similar silicon diode, even a 1N918 or 1N4148 should be OK.

In this circuit, these diodes should be virtually indestructible, and last forever.

[Terry_VK5TM]

The NTE equivalent of the SW-05 is listed as NTE5800 (3A 50V), and I suspect if it has 08 tagged to the part number, it would be the NTE5808 (3A 800v)

That should equate to 1N5408.

Datasheet here:
http://www.farnell.com/datasheets/1483202.pdf

[G6Tanuki]

Thanks for the info. I'm not thinking these diodes are faulty, just that I'm trying to track down a low-gain problem in this particular radio and was somewhat surprised to see such diodes used in the detector and AGC circuitry!

It's deeply odd to me that the voltage-doubler for the AGC bias has one of these 'power' diodes and a 1N60 point-contact diode. Why one of each? I could understand two 1N60 being used but there must be a reason why Trio did what they did.

[TrevorG3VLF]

The 1N60 is a germanium detector diode which will have a low voltage drop. The SW-05 are silicon diodes which have a larger voltage drop and may be used for very low voltage Zener diodes.
I have seen a handful of the SW-05 diodes in an electric fencer used for their high voltage ability.

[Nuvistor]

The manual states that a C bias , presume they mean -ve, is fed to the AVC via the aux socket, it can be used to remotely control the radio, presume mute, when transmitting.

Could this silicon diode have to have been used with it having higher reverse breakdown voltage than the 1N60?

[G6Tanuki]

That's something I hadn't thought about!