Type 111 Pretrigger Pulse Generator


Sean Turner
 

Hey all,

I was wondering if anyone knows of any factory mods that were done on the Type 111? I have an example that has a significant divergence from the schematic in the manual, namely around the fixed increment control. It's a little circuit mounted on an aluminum tab with a small ceramic strip on the inside and three socketed transistors on the outside, and there is a pot installed instead of the switch. I can't discern that this control has any effect on anything, and it is definitely not present in any scan of the manual or any pictures of the internals of other Type 111s.

Furthermore, it is factory quality assembly work, so I'm assuming it's either factory or someone who was really careful.

I put three photos of the circuit here (https://groups.io/g/TekScopes/album?id=261991). I annoted one of them to show the four places where the mystery circuit is wired into the main PCB.

Thanks!

Sean

Sean


Tim Phillips
 

From Tim P (UK)
Hi; This is the mod to supply double pulse output. See Hakan's page

http://hakanh.com/dl/kits.htm

I think it was used to set up the loop gain on samplers.

Tim

On Thu, 18 Mar 2021 at 03:16, Sean Turner <sdturne@q.com> wrote:

Hey all,

I was wondering if anyone knows of any factory mods that were done on the
Type 111? I have an example that has a significant divergence from the
schematic in the manual, namely around the fixed increment control. It's a
little circuit mounted on an aluminum tab with a small ceramic strip on the
inside and three socketed transistors on the outside, and there is a pot
installed instead of the switch. I can't discern that this control has any
effect on anything, and it is definitely not present in any scan of the
manual or any pictures of the internals of other Type 111s.

Furthermore, it is factory quality assembly work, so I'm assuming it's
either factory or someone who was really careful.

I put three photos of the circuit here (
https://groups.io/g/TekScopes/album?id=261991). I annoted one of them to
show the four places where the mystery circuit is wired into the main PCB.

Thanks!

Sean

Sean






Sean Turner
 

Aha! Mystery solved. Apparently whoever installed the mod didn't also install the new front panel label (or it fell off). I never occurred to me to try to pull on the knob; sure enough it pulls out!

Thanks!

Sean

On Thu, Mar 18, 2021 at 12:22 AM, Tim Phillips wrote:


From Tim P (UK)
Hi; This is the mod to supply double pulse output. See Hakan's page

http://hakanh.com/dl/kits.htm

I think it was used to set up the loop gain on samplers.

Tim


Sean Turner
 

And it was installed to replace the fixed increment control, instead of the variable control, which explains why fixed increment is inoperative. Very interesting.

On Thu, Mar 18, 2021 at 07:42 AM, Sean Turner wrote:


Aha! Mystery solved. Apparently whoever installed the mod didn't also install
the new front panel label (or it fell off). I never occurred to me to try to
pull on the knob; sure enough it pulls out!

Thanks!

Sean
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