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 Post subject: Re: RCA Audio Chanalyst 170-A Project
PostPosted: Feb Fri 26, 2021 7:41 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 1530
Location: Auburn, AL
Hi Chuck,

Thanks for documenting your work on this beautiful piece of equipment. and now I also have a good tip on putting electorlytic cans back together with the cardboard tube stuffing method. I imagine toilet paper rolls could easily be cut and slit to any size, taped back together, and inserted in the can before re-closing. I'm going to have to try the pipe cutter method next time I do one of those. in the past I've used hopes and prayers and a dremel with a cut off wheel successfully, though I did need to file/sand the joint square again before re-attaching the two sides.

-Hope you're well, let me know next time you're back this way. maybe I've got my shed/shop ready for visits by then.

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 Post subject: Re: RCA Audio Chanalyst 170-A Project
PostPosted: Feb Fri 26, 2021 8:28 pm 
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Location: Portland, TN, USA
Hi Jon,
I was wondering how/where you were these days. It’s been almost a year since we’ve been there and you can guess why.

I had the same TP roll idea, but found it too flexible to do the job and used some thicker material - think it was the backer cardboard from a tablet or some such. The TP roll idea would likely work if all you wanted was insulation. Or maybe you buy a better grade of TP than I. :D

We hope to get down there in April sometime as we’ll be protected by then. I’ll hope to be able to see you then.

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If talk is cheap, it's because the supply usually exceeds the demand.


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 Post subject: Re: RCA Audio Chanalyst 170-A Project
PostPosted: May Fri 21, 2021 8:51 pm 
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Well, it’s been a busy spring!

Leaving off a page or so of excuses, I’ll give a brief project update before I actually get to work on the final phase of the rebuild. All that remains is replacement of the Range switch resistors for Voltage and Ohms ranges - and whatever surprises I may find during the operational tests and calibration.

I actually completed rebuilding the 3 attenuators back in March but have been procrastinating the documentation (a character flaw first manifested some 60 years ago).

Here’s the before view of S2:

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All of the egg shell finish carbon comp resistors were replaced in this process, as all were found to be out of tolerance as expected.

As mentioned earlier, I used the quigg method to minimize mechanical and heat stress on these ancient switches, though they seemed pretty sturdy.

I took the trouble to remove the switches, both to make access easier and to avoid undue stress on the terminals that might be caused by trying to work on them without removing them.

Almost every range step, as found, was made up of hand-selected ordinary 20% resistors so that is mostly what I used for replacements.

Here’s the after view:

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I’m including a sketch of the switch configuration for those who may follow after.

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With the 3 attenuator (S2, S3, and S4) rebuilds completed, I turned my attention to the terminal board mounted at the rear of the meter. Tracing out the circuits involved loosening the board from its mounting so I could see where the leads terminated in each case. The faded colors on the very brittle insulation made for challenging work.

Here’s a sketch of the board’s component location:

Attachment:
Audio Chanalyst Terminal Bd REV 2.jpg
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Note that each of the resistances for R97, 98, 99, 100 is made up of two resistors in series.

These will be replaced next assuming I can come up with the resistors from my stock.

I recently spent a couple hours hand-selecting resistors for the Range switch (Volts & Ohms). I wasn’t going to bother with this initially since I planned to keep the Audio Chanalyst for myself and would never use the VTVM function and didn’t need it to be more accurate than it appeared to be during the earlier power-up testing. However, I’m now pretty sure I’ll be finding it a new home once it’s done.

Time to stop typing and start replacing resistors!

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73, de Chuck K4CCW

If talk is cheap, it's because the supply usually exceeds the demand.


Last edited by WoodchuckTN on Sep Sat 25, 2021 8:54 pm, edited 5 times in total.

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 Post subject: Re: RCA Audio Chanalyst 170-A Project
PostPosted: May Fri 21, 2021 9:25 pm 
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Nice job on the attenuator. Quiggs were definitely the right choice.

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 Post subject: Re: RCA Audio Chanalyst 170-A Project
PostPosted: May Fri 21, 2021 9:46 pm 
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Thanks, Steve.

I use the quigg method often with the the stuff I mostly work on that, like I am, is old and brittle. :D

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73, de Chuck K4CCW

If talk is cheap, it's because the supply usually exceeds the demand.


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 Post subject: Re: RCA Audio Chanalyst 170-A Project
PostPosted: May Mon 24, 2021 5:11 pm 
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Actually my next step was to finish tracing out the circuitry around the Range switch (S9) and the Function switch (S8).

Since the manual did not supply pictorials for these, I made up drawings for both (see below). In case you're wondering about the inconsistency of my drawings, I'm trying to learn/relearn a couple different 2D CAD methods. These are in ExpressSCH which Mike H. had helped me with some time ago but when I went to use my old library with the latest version of course it wouldn't work. :evil:

Gonna try QCAD as time permits. Anyway, here ya go for S8 and S9:

Attachment:
Audio Chanalyst S8 Rev 2.jpg
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Attachment:
Audio Chanalyst S9 REV 2.jpg
Audio Chanalyst S9 REV 2.jpg [ 438.29 KiB | Viewed 48 times ]

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73, de Chuck K4CCW

If talk is cheap, it's because the supply usually exceeds the demand.


Last edited by WoodchuckTN on Sep Sat 25, 2021 8:47 pm, edited 2 times in total.

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 Post subject: Re: RCA Audio Chanalyst 170-A Project
PostPosted: Jul Tue 27, 2021 2:08 am 
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170-A update 7/26/21

In case anyone is still interested, here’s a project update as of this afternoon:

Having configured the requisite accurate 600 ohm input and output loads a couple days ago, I spent a couple enjoyable hours this afternoon running through the calibration adjustments for the four amplifier sections of the 170-A.

Using an HP 651B generator for a signal source, and Fluke DVMs at the input and output points, I was able to achieve all required signal levels with no issues.

By the time you’re feeding signals into the voltage amp sections, with the Intermediate and Power amp sections set for max gain as instructed, you need to be sure to also follow the instructions to short the non-involved Voltage amp to prevent feedback. Just sayin.

Since last reporting, I also completed the replacement of all resistors in the VTVM range controls for voltage and ohms sections.

The DC and AC calibration went without issue, but I now need to revisit the Ohm range divider string, as the calibration there had some issues.

— To be continued —

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73, de Chuck K4CCW

If talk is cheap, it's because the supply usually exceeds the demand.


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 Post subject: Re: RCA Audio Chanalyst 170-A Project
PostPosted: Jul Tue 27, 2021 4:36 pm 
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WoodchuckTN wrote:
170-A update 7/26/21...

— To be continued —
Thanks Chuck. I will eventually have to go down that path too. I have a Chanalyst sitting "In Queue". Hope I don't die before I get to it.

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 Post subject: Re: RCA Audio Chanalyst 170-A Project
PostPosted: Sep Tue 21, 2021 7:22 pm 
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Still chasing leakage issues in the high-impedance sections of the Function (S8) and Range (S9) wiring areas and have so far had to replace a couple of 77-year old leads which had measurable insulation leakage when laced into their bundles.

My main reason for this post is to note that I’ve temporarily removed several of my drawings for revision and correction. Multi-wafer switches and laced wiring bundles buried beneath them are challenging to say the least.

This thing is turning out to be every bit as much of a challenge as the SX-42 project.

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73, de Chuck K4CCW

If talk is cheap, it's because the supply usually exceeds the demand.


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 Post subject: Re: RCA Audio Chanalyst 170-A Project
PostPosted: Sep Tue 21, 2021 8:11 pm 
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WoodchuckTN wrote:
Still chasing leakage issues in the high-impedance sections of the Function (S8) and Range (S9) wiring areas and have so far had to replace a couple of 77-year old leads which had measurable insulation leakage when laced into their bundles.

Woodchuck, you're going to give me nightmares. Just thinking about that makes me shudder.

I'm glad you found them, it can't have been easy to troubleshoot that problem.

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 Post subject: Re: RCA Audio Chanalyst 170-A Project
PostPosted: Sep Tue 21, 2021 8:28 pm 
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Joined: Dec Sun 21, 2014 6:37 am
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Location: Portland, TN, USA
It’s been interesting because the leakage slowly builds from about 20megs to about 50 or so.

This takes it out of range of my Fluke FM-27 fairly quickly so I had to sidetrack to firing up my Hickok 209A to use its much higher ohms capabilities. I don’t normally keep batteries in it, normally using the DMMs for resistors, so I (in true Sr. Citizen “but first…” fashion) took the opportunity to open the 209A and wire in an external battery box for the ohms functionality. I don’t use that often enough to install a permanent circuit to supply the 3v needed. Plus it’s + to ground and not as easily implemented as some VTVMs.

Anyway, between these sidetracks and my puttering pace I may get ‘er done one day.

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73, de Chuck K4CCW

If talk is cheap, it's because the supply usually exceeds the demand.


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 Post subject: Re: RCA Audio Chanalyst 170-A Project
PostPosted: Sep Sat 25, 2021 8:56 pm 
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All drawings now revised and put back where they were in the saga sequence.

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If talk is cheap, it's because the supply usually exceeds the demand.


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