Monday, June 18, 2018

Problematic Tek 7A26

I have a 7A26 vertical amp unit that is misbehaving. The symptoms are as follows:

(1) The amplitude of a given signal does not remain constant when trace is scrolled from top to bottom on CRT.
(2) Both channels behave as described here.
(3) Occurs with low frequency traces (10 KHz) AND high frequency traces (10 MHz).
(4) A signal that shows 3 div is positioned with the upper peaks at the topmost graticule line.
(5) Its position is lowered using the POSITION pot to the next lowest graticule line and still shows 3 div.
(6) Its position is lowered using the POSITION pot to the next lowest graticule line it shows 2.6 div.
(7) Its position is lowered using the POSITION pot to the next lowest graticule line it shows 3 div.
(8) Its position is lowered using the POSITION pot to the next lowest graticule line it shows 3 div.
(9) Its position is lowered using the POSITION pot to the next lowest graticule line it shows 3 div.

The rapid motion sequence of the positioning is that the trace size diminishes in the upper portion (at approximately the second graticule line down) briefly and then regains its amplitude.

The pictures of this sequence are shown below:

Monday, June 11, 2018

You know me, Al.., of course, a title stolen from Ring lardner's incomparable baseball about a rookie pitcher trying to catch on in the majors in the years before World War I. Of course, this post is for my good friend, W6AAX, who is named Al.

Basically, the crystal checker outputs the oscillator sine wave through the BNC but it also have provisions to an output meter in the form of a plus and minus set of terminals. The voltage (energy level of the crystal) can be measured by using a DMM connected to these terminals. These and some more aspects of the checker operation are depicted in the pictures below.

Note that the meter output terminals are just leftover component leads suitable for alligator clips.

Here are the clip leads in place.

Here's the unit under test,

..and the frequency and voltage output..

..and, finally, the scope output.

Saturday, May 19, 2018

Dancing a jig..

The great thing about the NorCal 40A project is the stack of boards I accumulated through misuse of the PCB house's weird website. Having a passel of 'em, I figured the little rig is a great tutorial on building and electronics in general. Also, being the obsessive person I am, I scored Rutledge's Electronics of Radio, the test that Rutledge uses for his Cal Tech class based on the NorCal 40A.

Anyway, it became apparent to me that if I was going to delve into this and slam together variants of this little beast, a means of testing these without tacking on the controls making each project look like some electronic Medusa.

So, as Tim Allen famously said, "I rewired it!"

So I built a test jig (introduced in the previous pose below) that would support "plug and play" by incorporating headers and plug/connectors to the controls. (Thanks to Tom, N8TPN, for the lowdown on the connectors that led me to Pololu. A few minutes of browsing there yielded a moderately inexpensive method of implementing the re-usable setup.)

Anyway, the pictures below of my step-by-step construction of a 40 meter version are pretty self-explanatory. If you have questions, leave a comment and I will get back to you.

First, the labelled shots..

..and now the rest.

Entire test setup for K7QO's Phase 3 testing.

Add caption

This was one of K7QO's crystal checkers used in generating the 4.915 MHz signal to test the BFO.

And here's a little added bonus. When not in use, the soldering station wand cord used to get in my way and drive me nuts. So, I ran the cord through a used toilet paper tube and use that -- as shown -- as a means of gathering it up neatly.

Tuesday, May 15, 2018

NorCal 80A (80 Meter NorCal 40) and odds and ends..

Did a final checkout on my NorCal 30A the other day and had a chance to preview WB6JDH's 80 meter version shown in the pictures below. The 30 meter version is in my "test jig" that I will be using to check out additional versions being built. These incorporate the header pins and, as such, will be a "plug and play" affair. I still have some bugs to work out but will present a pictorial with construction info in a subsequent post.

Anyway, here are the 30A shots. Top to bottom are the test jig, the rig output, and Dick overseeing the ceremonies.

And here are Dick's 80A shots in no special order.

Monday, May 7, 2018

Offering Tektronix 7D15 Frequency Counter Plug-In..


I have a 7D15 Frequency Counter Plug-In that is spare to my needs and looking for a good home. It is in decent shape with one problem: it requires about 2-3 minutes to warm up and display a frequency. I went through this unit a while ago and could not seem to determine the problem. However, since I have a 7D14 that serves my purposes, I am offering this for $75 plus s&h from 92708 to someone who will make use of it and possibly who may be able to track down the problem.

Typical operation is as follows: I turn on my Tek 7704A and apply a frequency to the appropriate channel and the 7D15 displays "0.00" depending upon the settings. After about three minutes, the frequency will be displayed (accurately) and will change format as the gate time is changed -- per manual spec. Shutting the scope down or removing the unit and replacing it after a 5-10 minute wait will cause the frequency to be displayed correctly. "Cooling down" for about 20-30 minutes will require the aforementioned warm-up period.

Knobs and connectors sound and intact; interior clean; some signs of age but otherwise decent condition (save for the difficulty described). Price includes clean, like-new instruction/service manual with bright pages and no scribbling or underlining as I remember.

Pictures are below.