Hi,

I need to find replacement parts for a Helitrim 9V trimpot that is
labeled:

72x R1k
8134S

and a BCD transistor (that looks like an lithium battery) that is
labeled

M
4 - 518
8127

where the "M" is italicized.

What would be good replacement parts for these components?

Thanx,
Ed

Sky King (aaron_stansbury@yahoo.com) writes:
> Is there a web site or a book the you can cross referance part
> numbers? I have some older schematics that I cant find parts for. I
> would like to be able to build them just for the fun of it. Thanks in
> advance.

There's the NTE line of replacement semiconductors, I don't have
the URL handy but a web search will bring it up. They have a replacement
guide, it's online though I don't know if they still have a paper version,
that translates a lot of devices to a relative few general parts. It is
a very good method of getting a general idea of specs when you don't have
a good collection of databooks. The prices of the replacement line parts
are generally quite high, the cost of individually packaged parts that
you can get at some local dealer, and I can't think of a time when I've
ever bought them. Some will say that the general nature of the replacement
parts means they won't be as good as the exact part. But I have used
such replacement guides to look up parts and then see if I have any
matches for the same replacement part.

Other parts, you aren't likely to find exact substitutes, and you will
have to find data on the original coils or transformers or whatever (if
such data is not included with the schematics), and then go through the
catalogs to find suitable replacements that match the specs.

With time, you will get a general idea of what is needed for specific
useage, and figure out what times you need exact replacements and when
you can use a more general part. You'll also get an idea of how close
things need to be to "exact".

One thing about a lot of projects. They'll tend to use general type
components precisely so the builder at home can build them. Hence
go through back issues of the hobby electronic magazines and most
will use a very small subset of semiconductors, chosen because they
were either on hand or because they were easy to get. Look at
enough schematics and you will get a feel for this, and when such
common transistors are specified, other general type transistors will
generally work there.

One thing you need to be warned about old schematics, especially with
the internet. The beginner will find something, and the schematic will
give no indication of age. They'll search and search for parts, and
not realize they problem they can't find the parts is that it really is
too old. For a lot of such common things, they just need to look further
to find something a little more recent. There's little sense in using
that phono preamp schematic that dates back forty years when a more
recent schematic will have far more common parts.

It's faded, but there was a time when "where can I get tunnel diodes"
was a reasonably common question here, and for virtually all the posts,
they weren't specifically interested in tunnel diodes, they were interested
in some old schematic that did something they wanted. The reason they
had problems finding tunnel diodes was that they were a blip in time,
and during that blip were more a novelty than real advancement in hobby
circles. The fad faded, the diodes disappeared, and there's no way
you can build such schematics without the tunnel diodes. Hence there
is no reason to pursue that schematic unless one really wants to play
with a tunnel diode for some reason.

Michael

On Fri, 1 Feb 2008 00:59:14 -0800 (PST), fcache@gmail.com wrote:

>Hi,
>
>I need to find replacement parts for a Helitrim 9V trimpot that is
>labeled:
>
> 72x R1k
> 8134S
>
>and a BCD transistor (that looks like an lithium battery) that is
>labeled
>
> M
> 4 - 518
> 8127
>
>where the "M" is italicized.
>
>What would be good replacement parts for these components?
>

The pot is 1K, and all you have to do is find something with the same
form factor and footprint.

What do you mean by BCD transistor, or 'looks like a lithium battery'?

Motorola once marketed germanium transistors in TO36 stud-mounted
cases - is this what you mean?

RL

legg wrote:

> On Fri, 1 Feb 2008 00:59:14 -0800 (PST), fcache@gmail.com wrote:
>
>
>>Hi,
>>
>>I need to find replacement parts for a Helitrim 9V trimpot that is
>>labeled:
>>
>> 72x R1k
>> 8134S
>>
>>and a BCD transistor (that looks like an lithium battery) that is
>>labeled
>>
>> M
>> 4 - 518
>> 8127
>>
>>where the "M" is italicized.
>>
>>What would be good replacement parts for these components?
>>
>
>
> The pot is 1K, and all you have to do is find something with the same
> form factor and footprint.
>
> What do you mean by BCD transistor, or 'looks like a lithium battery'?
>
> Motorola once marketed germanium transistors in TO36 stud-mounted
> cases - is this what you mean?
>
> RL
i think he's talking about a TO-3 type transistor comparing to a
CMOS clock type lithium cell.



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