Hacker AF117 best alternatives?

[yesnaby]

Hello,

Is it only AF*** that have this problem, are other types (e.g. AC***) immune from it?

This is just so I can decide whether to get some spares in!

Michael

[davidgem1406]

Yes, just the AF11x's that have the problem of tin whiskers growing.

Dave

[mhennessy]

Sorry - that's sadly not the case. AC128s, etc, can get them. Much less common, for whatever reason, and of course, not noticed unless the device is on an earthed heatsink or two electrodes have been reached. They respond to the zapping treatment though.

Mark

[Philips210]

Hi

The OC170 and OC171 have the same case as the AF11x series so these are also prone to tin whisker growth.

I think there is an OC169 as well, though I've not personally seen one in commercial equipment.

Symon

[crackle]

Originally Posted by mhennessy

So how does a capacitor affect this?

Mark

Hi Mark
The capacitor charge may be depleted on the first connection by having to zap more than one whisker, turning the transistor round into different planes and tapping it in all directions may cause another wisker to momentarily short and be zapped, if the capacitor is already part discharged by this time then additional whiskers which momentarily short may not be zapped.
Having a constant supply eliminates the problem with the capacitor discharging and not being effective if and when another whisker momentarily shorts.
Just a theory, but that is the way I do it now, and it has worked for me, the turning round and tapping is just a bit of belt and braces to try and catch additional whiskers "about" to short.

Mike

['LIVEWIRE?']

For what it's worth, I never try to 'cure' AF117s or similar, but always adopt a 'replace on sight' policy, using AF12x series devices, which I know are getting harder to obtain(and more expensive!)now

[mhennessy]

Originally Posted by crackle

Hi Mark
The capacitor charge may be depleted on the first connection by having to zap more than one whisker, turning the transistor round into different planes and tapping it in all directions may cause another wisker to momentarily short and be zapped, if the capacitor is already part discharged by this time then additional whiskers which momentarily short may not be zapped.
Having a constant supply eliminates the problem with the capacitor discharging and not being effective if and when another whisker momentarily shorts.
Just a theory, but that is the way I do it now, and it has worked for me, the turning round and tapping is just a bit of belt and braces to try and catch additional whiskers "about" to short.

Mike

Ah - perhaps I didn't make this clear: the capacitor remains connected to the bench PSU, and any charge that might be lost is quickly topped up. That said, I don't think I've ever seen the voltmeter or current meter on the PSU (Thurlby PL320) respond - even with the "big" ones that light up via the glass base

The advantage of having the capacitor at the transistor is that it eliminates any losses in the connecting cables - a bit like why the ICE crowd often put large super-caps or a second battery in the boot next to the amplifiers. Perhaps it's only a theoretical advantage, but the capacitor leads also give me a convenient point to clip the croc-clips from the PSU leads.

All the best,

Mark

[mhennessy]

Originally Posted by 'LIVEWIRE?'

For what it's worth, I never try to 'cure' AF117s or similar, but always adopt a 'replace on sight' policy, using AF12x series devices, which I know are getting harder to obtain(and more expensive!)now

I must admit that if I had access to large stocks of these, I'd do the same. I live in hope of a "windfall" - a few months back I was given about 30 NOS AC128s - but until then I consider myself priced out of the market

Mark

[crackle]

Hi Mark
OK understand now.
Cheers
mike