Re: 7623A Storage problem

Colin Herbert

Would you believe that I have a 7CT1N curve-tracer, but of course nit
operates in the 7623A mainframe, which isn't working? I don't have another
7000-series mainframe, sadly.

-----Original Message-----
From: [] On Behalf Of Thomas
Sent: 04 October 2020 22:37
Subject: Re: [TekScopes] 7623A Storage problem

The junctions of that type of counterfeit power transistor will have a
higher forward voltage than a genuine part. Usually they read as much as
.1 to .15 volts higher on a typical DMMs diode test range. They will
also have different junction capacitance. I can't give numbers as I'm
not where I have proper tools. However a data sheet for the McCoy will
provide at least some of that information.

A curve tracer will reveal a lot. Small signal transistors have very
different family of curves than most any power transistor. While the Tek
curve tracers are the tool of choice, I've gotten a lot of good mileage
from the Heathkit variety. The Heathkit curve tracer, which does not
have a display, will work with any DC coupled 'scope and can sometimes
be found on eBay for a low price that belies its usefulness. Even if
broken, they are relatively simple and easy for a moderately
knowledgeable tech to fix.

Thomas Garson
Aural Technology, Ashland, OR
By my calculation, the dynamic range of the universe is roughly 679dB,
which is approximately 225 bits, collected at a rate 1.714287514x10^23 sps.

On 10/4/20 12:59 PM, Tom Lee wrote:
There are also notorious Chinese knock-offs which contain low-power
(2N2222?) dice in what appear to be period-authentic packages. They'll
pass the standard multimeter diode test, but don't survive actual use.
The ft test that Brad T. suggests is a very good way to identify
non-genuine 3055s.


Join to automatically receive all group messages.