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If anyone has a physically intact 7A26 of unknown or bad operational status they are willing to part with, please let me know.? I need some knobs and mechanical parts.? Thanks,? Bruce KA2IVY


On 8/10/19 5:17 PM, Dennis Tillman W7PF wrote:

Hi John,
With that serial number it sounds like it was a much later one. It is even
possible it is among the last production run. If you look at the date codes
on the ICs you may be able to tell what year it was made. I suspect you will
find it was made in 1988 or 1989 just before Tek terminated the product
line.

An early serial number would be one like this - B010100 - which is what Tek
usually used as the first serial number for a production instrument.

Dennis Tillman W7PF

-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of John
Griessen
Sent: Thursday, August 08, 2019 5:36 PM
To: [email protected]
Subject: [TekScopes] Is an early 7A26 a keeper?

I was getting some extra 7A26's ready to sell, and came across 7A26 B154366,
which is an early one with the familiar aluminum isothermal clamp blocks for
transistors in cans.

Is that just as good as a late model if it has mostly metal film resistors?
Is it worth keeping for repairability?

I see little failure in 7A26's... tear drop tantalums, scratchy knobs, stiff
knobs, and dust under the attenuator contacts.

Keep or sell/toss?

P.S.

I've got an attic that needs to be cleaned out in preparation for moving to
Albuquerque, and a server that can show you pictures of it's box contents.
Email me if interested in browsing that web server.

Hi John,
With that serial number it sounds like it was a much later one. It is even
possible it is among the last production run. If you look at the date codes
on the ICs you may be able to tell what year it was made. I suspect you will
find it was made in 1988 or 1989 just before Tek terminated the product
line.

An early serial number would be one like this - B010100 - which is what Tek
usually used as the first serial number for a production instrument.

Dennis Tillman W7PF

-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of John
Griessen
Sent: Thursday, August 08, 2019 5:36 PM
To: [email protected]
Subject: [TekScopes] Is an early 7A26 a keeper?

I was getting some extra 7A26's ready to sell, and came across 7A26 B154366,
which is an early one with the familiar aluminum isothermal clamp blocks for
transistors in cans.

Is that just as good as a late model if it has mostly metal film resistors?
Is it worth keeping for repairability?

I see little failure in 7A26's... tear drop tantalums, scratchy knobs, stiff
knobs, and dust under the attenuator contacts.

Keep or sell/toss?

P.S.

I've got an attic that needs to be cleaned out in preparation for moving to
Albuquerque, and a server that can show you pictures of it's box contents.
Email me if interested in browsing that web server.

On Sat, Aug 10, 2019 at 11:41 AM, Chuck Harris wrote:

I would think that a better way would be to properly align
the resistor so that it is away from the chassis. It got
bumped.

-Chuck Harris

I did. The electrical tape is just to stop it from happening again if it loosens.

Sean

Hi all,

Scored a very nice condition 7104 and plugins at auction for a great
price. Long story short it was working during the item viewing hours the
day before the auction. Got it home this morning and it's
clicking...anyway...

I believe the issue lies in either the +5V rail or the +/-15 V rails.
However, specifically, the manual says the typical resistance for the +5V
rail when everything is connected up is 0.005 Kohm. I'm measuring 3 ohms.
Is there any chance that is a typo and it should be 0.050 Kohm and not
0.005 Kohm? It's the former for 7904 mainframes.

Here's my readings:

With the mainframe circuits connected:

+50 is at 1.82 kohm
+15 is at 73 ohm
+5 is at 3 ohm
-15 is at 84 ohm
-50 is at 4.494 kohm

With the mainframe circuits disconnected:

+50 is 9.28 kohm
+15 is 154 ohm
+5 is 7.53 kohm
-15 is 8.55 kohm
-50 is 30.2 kohm

Thanks,

Sean

On Sat, Aug 10, 2019 at 09:19 AM, Gary Robert Bosworth wrote:

Please explain the solution. How does a fan interfere with the switching
power supply?
Hide quoted text ( #quoted-71154881 )

On Fri, Aug 9, 2019 at 9:49 PM <[email protected]> wrote:

Happy ending: the problem was the fan wiring all along. I rearranged it
before I inserted the SMPS for the last time, and we have life.

The best way to explain it is probably a picture: /

Note that little tab? It was intermittently touching the chassis. This morning I made a neat sandwich of electrical tape to put underneath it and now the problem is solved.

Sean

Happy ending: the problem was the fan wiring all along. I rearranged it
before I inserted the SMPS for the last time, and we have life.