Diodes with coils in old Roband Vareco bench supply?

[MattPadden]

Hi. My first post here, so hello to everyone.

I’m refurbishing a pair of Roband Vareco 33-2 bench supplies. They appear to date from the early 70s or thereabouts. I noticed that the discrete diodes on the board all have a single coil turn in their anode leads, and I wonder if this is to protect against soldering heat, or some inductance technique? I’m doubtful of the latter as the leads aren’t enamelled, so the coils would almost certainly be shorted due to the tightness of the coil. Image hopefully attached so you can see what I’m talking about.

Many thanks,
Matt

[turretslug]

Hi Matt and welcome, this forum is a good place, I'm continually amazed at the repository of amassed knowledge here.

I assume that if it was to guard against heat damage to the diode junction whilst soldering that both leads would have a loop in them. Perhaps it was to give a bit of resilience against thermal expansion/contraction- some power diode packages have thick leads (presumably for junction heatsinking as much as anything) and hard, brittle plastic packages, an unfortunate combination that can cause package cracking or board solder joint failure over time and maybe the loop adds a bit of springiness? It'll also raise the package a bit off the board, some diodes get quite hot in operation and need breathing space. Neither reason/excuse needs two loops, that would keep the time-and-motion folk happy.

Colin

[Radio1950]

Colin is correct.
Thermal protection during assembly, particularly with hand soldering with old style larger irons.
Common practice in 1960s

[M0FYA Andy]

I've always thought that it is good practice to give resilience to thermal expansion, although I suppose the same argument could be applied to resistors which rarely have the coil!

Andy

[Bobdger]

Test points. Makes life easy to clip your large clam type avo leads to test points for adjustment.
Bob.

[joebog1]

It is in fact for thermal protection. The large leads on diodes are for the heatsinking they provide. If one doesnt believe me cut all but 2mm of lead off a 3 amp diode and measure the temperature of the diode with 3 amps running through it. You will have to be quick because the diode will fail in just a few seconds.

Joe

[MattPadden]

Thank you all for your replies. Thermal expansion and test point provision both make sense.

The refurbishment is going well. I fitted new electrolytics throughout. Next steps are to refurbish the Colvern wirewound pots and the very chunky 4PDT DC range switch. Mullard seem to hold some NOS Colvern stock but I’m interested to see if I can recover the originals if possible. That said I’m intending to use this refurbished supply on the bench so if new replacement parts become necessary then so be it.

Best,
Matt

[AC/HL]

Good value engineering. It achieves several things at virtually no cost.

[Herald1360]

Perhaps the leads were also too thick to just use fishspine beads as with the WW resistors?

[Chris55000]

Hi!

I got some "fish–spline" ceramic beads off eBay about 2mm hole diameter that go over 1N5401 leads, etc., but duplicating the method used originally is definitely worth while, both asthetically and to heatsink the replacement diodes!

Chris Williams

[barrymagrec]

This technique was used quite widely on other Roband equipment from the sixties.

Conversely, the Philips PM3370 scope used a large number of BY127s connected on short leads rigidly on the transformer connection panel and they failed frequently, and not because they were being over run.