开云体育

Jeff,

Thanks, maybe I'll go with Mouser. I order stuff from them with some regularity, and that's not a horrible price IMO. Amazon is right out...too much counterfeit garbage. Though it might be fun to get some of both and compare their characteristics.

Sean

On Wed, Mar 24, 2021 at 09:56 PM, Jeff Dutky wrote:

Sean,

Or Amazon:

I'm not sure Amazon is really any more reliable than eBay, but just so you
know your options.

I did find 114 count 2N3442 and 951 count 2N3442G in stock at Mouser, both
available in qty 1 for about $6.75 each, so you have an option of a reputable
source, but it comes with a price (the stuff on Amazon is about $2 each, but
you get what you pay for, maybe)

-- Jeff Dutky

Sean,

Or Amazon:

I'm not sure Amazon is really any more reliable than eBay, but just so you
know your options.

I did find 114 count 2N3442 and 951 count 2N3442G in stock at Mouser, both
available in qty 1 for about $6.75 each, so you have an option of a reputable
source, but it comes with a price (the stuff on Amazon is about $2 each, but
you get what you pay for, maybe)

-- Jeff Dutky

Sean,

I've been trying to find what the selection criteria were for Q1197, which is
Tek part number 151-0209-00, if I am not mistaken. The service manual does say
that it is selected from 2N3442, but when I consult the Common Design Parts
Catalog I do not find 151-0209-00 listed under selected transistors. Further,
in the section that discusses (and tries to dissuade engineers from using)
selected parts it sounds like a selected part should have a part number
starting with 153- rather than 151-. It also sounds like there are a
population of 151-****-89 parts that are still considered "selected" in the
sense that while they have failed the selection criteria, they have been
checked to be free of other faults, and so are considered higher quality
parts.

Could it be that Q1197 is from the latter population of selected parts and
that the -89 suffix was not yet in use when the 454 was designed? Maybe any
old 2N3442 would suffice, so long as it was working?

-- Jeff Dutky

Thanks... but I broke the nylon holder, and those diodes are rather prone to destruction (which is how I got the S-1 in the first place). Also they are REALLY tiny and I just don't have the mechanical skill to work with them - in fact I broke a lead, on the remaining good one of course, just removing them from the holder. I decided that more recent diodes could be substituted, and SOT-23 packages are about as small as I'm comfortable handling... and don't forget that they are available from electronic suppliers like Digikey, instead of (50+ year old) dwindling Tek parts stashes.

Anyhow, I finally found the problem... the push-together connectors carrying the trigger from the sampler board pickoff to the preamp board were just barely mating. So when they parted, the center pin(s) were so close that there was enough capacitative coupling to send a fast pulse to the trigger amp, but way too small for the blowby compensation circuit. Verified with scope. On further investigation, the case is supposed to have four "wiggly" long spring strips to make contact with the ground planes on the outside boards, and presumably to also keep a tiny bit of pressure on the connectors at issue! There were only three, and the missing one was on the side where the problem is. I moved one strip to that slot, reassembled and everything's working fine again :)

p.s. to dan: the notorious R18 (36 ohm) was 37.7 so I left it alone :)