[AMRadio] Tek 535/545 vertical amp calibration question

Larry Szendrei ne1s at securespeed.us
Sun Oct 29 13:19:01 EDT 2017

Thanks for the comments, Jim, and good to hear from you.

Yeah, I've got a 535A and an RM45 (rack-mount version of the 545). 
Unfortunately, they've both had repairs which preclude "just leaving the 
adjustments alone." I received some very helpful feedback from another 
reflector which sent me to this link:


I've got an extra plug-in I can modify to serve the purpose of the 
missing adaptor. It's an extremely simple procedure to do so.

I've never had the HV problem you described in either scope, or with my 
Tek 575 curve tracer. The HV transformer is an open-frame (not the 
potted type) in each; maybe that's why.


On 10/29/17 12:51 PM, Jim Candela wrote:
> Larry,
> Those scopes are great shack heaters in the winter! Running yours 
> might save some coal. I once had a 547 with 1A4 plug in. That was one 
> of the best scopes I've ever owned. That series has a weakness though 
> with the HV CRT flyback circuit. The potted ferrite transformer gets 
> lossy as the potting (epoxy?) ages. As time goes by the closed loop 
> regulator driving the 6AU5 (?) goes open loop, and from there the CRT 
> begins to dim quickly. There was a retired Textronix guy named Dean 
> (?) back 30 years ago selling new transformers.
> As to your question, best I have heard, just leave those adjustments 
> alone if you don't have an EP53A. If you proceed, you might make 
> things worse then they already might be. Still, with enough time, some 
> level of experimentation might produce the results your looking for.
> Good Luck,
> Jim
> Wd5JKO
> ------------------------------------------------------------------------
> *From:* Larry Szendrei <ne1s at securespeed.us>
> *To:* Glowbugs <tetrode at googlegroups.com>; AWAGroup 
> <AWAGroup at yahoogroups.com>; AWA Reflector 
> <antiquewirelessassociation at yahoogroups.com>; Discussion of AM Radio 
> <amradio at mailman.qth.net>
> *Sent:* Saturday, October 28, 2017 8:42 AM
> *Subject:* [AMRadio] Tek 535/545 vertical amp calibration question
> Hi,
> Apologies for the slightly off-topic post.
> I wonder if anyone has any tips for how to calibrate the vertical
> amplifier on a Tektronics 535 and/or 545 oscilloscope without the EP53A
> Gain Set Adaptor called for in the manuals' procedure?
> Thanks,
> -Larry/NE1S

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