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 Post subject: Re: RCA Audio Chanalyst 170-A Project
PostPosted: Dec Tue 22, 2020 3:30 pm 
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Barky wrote:
[...]If they aren't original I'm sure finding original replacements will be the hard part of the restoration.

These are close if you come up empty:
Chicken head knobs


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 Post subject: Re: RCA Audio Chanalyst 170-A Project
PostPosted: Dec Tue 22, 2020 7:20 pm 
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too-bamp wrote:
Barky wrote:
[...]If they aren't original I'm sure finding original replacements will be the hard part of the restoration.

These are close if you come up empty:
Chicken head knobs


Thanks! I might go ahead and order a couple of those anyways just to see how they match


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 Post subject: Re: RCA Audio Chanalyst 170-A Project
PostPosted: Dec Wed 23, 2020 12:04 am 
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A buck forty each plus shipping, you can't go very wrong.


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 Post subject: Re: RCA Audio Chanalyst 170-A Project
PostPosted: Dec Wed 23, 2020 10:29 pm 
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WoodchuckTN wrote:
Attachment:
A00BE04D-8F5A-450A-97C8-BF9B5B2AFE2B.jpeg


Whereas the RCA Audio Chanalyst Model 170-A seems to be somewhat rare, I am of two minds whether to share the adventure of electronically restoring it.

On the one hand, taking up forum space might not be considered its best use since so few might find it useful.

On the other hand, it might be a useful addition to the meager documentation I’ve been able to find on the 170-A.



hi... you might want to consider - pictures, labeled correctly and not, create more web traffic and is beneficial to the site.

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 Post subject: Re: RCA Audio Chanalyst 170-A Project
PostPosted: Dec Wed 23, 2020 10:45 pm 
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Hi ttx,
If Alan (& ARF) benefit from the traffic, so much the better!

Maybe this thread will be as popular as my previous magnum opus :D

https://antiqueradios.com/forums/viewtopic.php?f=5&t=322029

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 Post subject: Re: RCA Audio Chanalyst 170-A Project
PostPosted: Jan Wed 13, 2021 11:50 pm 
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Excuses
The plan to make the Audio Chanalyst my next project was quickly interrupted by my foolishly agreeing to “look at” a Crosley 9-202M chassis he’d recently recapped (turns out, all but the electrolytics) and was getting ready to power up. This being his first attempt, he was unsure of how to proceed. Things being what they are and my “lab/shop” space being rather confined and it being too cold for fresh air ventilation, I finally told him I’d give it the once-over if he’d drop it off. I’ll shorten what could be a much longer story by just saying that troubleshooting the Crosley and making somewhat extensive repairs to it are my excuse for delaying the Chanalyst project since the last post.

Remind me to be more circumspect about breaking my rule of only working on my own stuff! It did, however, give me a reason to play with my RF Chanalyst and Traceometer.

Back to the Audio Chanalyst

Here’s a look under both of the chassis. As you can see, the engineers who designed this made access quite easy while packing a lot of circuitry into a relatively small space.

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Right above and at the bottom of one photo you’ll see a metal rectifier, used for the filament voltage to the two voltage amplifiers - only. All other tube filaments are fed by the conventional 6.3v winding on T3, except of course the 5Y3 which has its own 5v winding.  The metal rectifier, according to the parts list,  is a copper sulfide (CuS) rectifier. I can’t find any info on this particular model to determine if it indeed CuS or the more common selenium.

It is fed by its own 7v winding on T3.

The VTVM  circuitry (an upgrade of the Voltohmyst circuit according to the manual) as well as the oscillator/sweep circuitry and the power supply for the VTVM are located on the upper chassis, and the four amplifier sections and the power supply for all except the VTVM are on the bottom chassis.

Not wanting to expend a lot of effort on a piece if certain nearly unobtanium items are beyond reasonable repair, like meters and transformers, etc., I usually check these first.

A quick check of the 200 microamp meter movement showed it freely and linearly moving to full scale at 200 microamps.

First, quick resistance checks: the T3 main power transformer secondary measured 438 ohms end to end; the primary measured 12.2 ohms.

T2 primary measured 52 ohms; the secondary measured 560 ohms.

Next, voltage checks using a variac/ammeter combo:
The main power transformer, T3, came up to 514v across the secondary with no load except for filaments, and drawing about 250 ma AC from the Variac. Filament voltages checked OK as well on T2 and T3, except the 7v winding on T3. Suspecting the CuS rectifier, I removed one side of the AC from it and the winding voltage measured normal. Looks like this will get a solid state bridge replacement.

T2 measured 193 volts across its secondary, only loaded by the filaments of the upper chassis tubes.

Finally, a quick check of the oscillator coils and transformers showed they had the expected, and hoped-for continuity.

Calling that good for now.

Next up will be replacement of the electrolytics and I’m trying to decide if I want to re-stuff or just go with under-chassis terminal strip mounting. I hope to do a better job that some of the pictures above show for some previous owner. I don’t think targeteye did any work on this while he had it. He’s smarter than me.

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Last edited by WoodchuckTN on Jan Thu 14, 2021 11:27 pm, edited 1 time in total.

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 Post subject: Re: RCA Audio Chanalyst 170-A Project
PostPosted: Jan Thu 14, 2021 7:07 pm 
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Wow, a hinged double-decker chassis! That's impressive. And lots and lots of adjustment pots. I wonder why? I should find a schematic to look over.

As for the electrolytics, from the photos it looks like you could fairly easily cut off the cans from the top of the chassis, clean up the bases, drill holes for leads, and install radial caps. I find that's the fastest way to deal with can electrolytics. You don't have to disturb the wiring as you just re-use the old terminals. You can clean out the goop from the cans and epoxy them back on if you want the restuffed look.

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 Post subject: Re: RCA Audio Chanalyst 170-A Project
PostPosted: Jan Thu 14, 2021 7:56 pm 
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Steve,

There’s a schematic in the 3-part article linked above, as well as a pretty complete description of the whats and whys of the design.

As you’ll see, the short answer is that most are for calibration purposes as I’m sure you’d have guessed. The purpose of the unit is to be able to not only to troubleshoot audio equipment of all sorts but to be able to fairly accurately determine gain when desired.

The more I dig into it, the more I’m fascinated by its design and implementation, just as I was by the RF Chanalyst. But, then, some of us are easily fascinated. :D

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 Post subject: Re: RCA Audio Chanalyst 170-A Project
PostPosted: Jan Fri 15, 2021 12:42 am 
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WoodchuckTN wrote:
I don’t think targeteye did any work on this while he had it. He’s smarter than me.


On the first note... Nope, I did nothing but open it up once for pics and buttoned her back up.
On the 2nd part. I don't think soo... I have plenty of other "why am i doing this " type projects. :)

i just installed over $100 in rebuilt turrents and idlers in a TT worth no more than $30 :).. so there ya go.. A genius.

Steve


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 Post subject: Re: RCA Audio Chanalyst 170-A Project
PostPosted: Jan Fri 15, 2021 3:34 am 
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Steve, I’m hoping this project is one of those “If you build it, they will come” kind of thing, because right now my main use for the finished product will be as eye candy, as I’m not really an audio guy.

Wait, I can use it as a replacement for the little transistor amp that I use for the output of the RF Chanalyst's audio! :D Let's see, a dozen or so tubes to replace a couple transistors...

Anyway, tomorrow begins the paper cap replacement while I await my electrolytics from Sal.

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 Post subject: Re: RCA Audio Chanalyst 170-A Project
PostPosted: Jan Sat 16, 2021 5:44 pm 
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I think there are a myriad of uses you'll find once its up and running.


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 Post subject: Re: RCA Audio Chanalyst 170-A Project
PostPosted: Jan Thu 21, 2021 10:49 pm 
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While awaiting my order of electrolytics from Sal, which he so kindly got out at the last minute before his hiatus, I have been proceeding with replacing the paper caps and checking resistor values on the main chassis.

I’ve also been removing many of the E-cap cans and gutting them in preparation for re-stuffing. In some cases I’ll just be mounting the new caps under the chassis where ample room exists.

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With several of the paper cap’s, because a former repair (and maybe even the originals) used this type of mounting,

Attachment:
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were much larger, and spanned longer distances, I’m having to add terminal strips like this:

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Further testing of the metal rectifier bridge left me suspicious and I decided to replace it with a solid state bridge. This is the replacement setup waiting to supply nice, filtered (4400mf) DC to the filaments of the two high-gain voltage amp stages:

Attachment:
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Per USPS’s usually-unreliable tracking, the caps from Sal have reached Nashville so they may arrive tomorrow.

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 Post subject: Re: RCA Audio Chanalyst 170-A Project
PostPosted: Jan Fri 22, 2021 12:16 am 
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like your tool holder.. have plenty of empties..


Attachments:
pl_ring.jpg
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 Post subject: Re: RCA Audio Chanalyst 170-A Project
PostPosted: Jan Fri 22, 2021 12:32 am 
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ttx450cap wrote:
like your tool holder.. have plenty of empties..


Thanks. It’s on a lazy susan in case that’s not obvious. I like that arrangement the best of the thousands I’ve tried over 6 decades or so - at least for electronics work. Of course it’s only stocked with the “most-used” tools, the rest occupying many drawers.

And, yes, between my wife and I go thru way too many pill bottles. Having too large of a stash of them already, I now just save some of the tops to use as disposable temporary containers for small amounts of various cleaning solutions during a cleaning session on a unit.

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 Post subject: Re: RCA Audio Chanalyst 170-A Project
PostPosted: Feb Mon 08, 2021 12:24 am 
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170-A update 2/7/21

Just to make you aware that I’m not doing nothing (double negative intended) on this project, I thought I would give a brief update.

All electrolytics, paper cap’s, and out-of-tolerance resistors (a lot) have been replaced on the lower chassis which contains the four amplifier “channels”, two of which are identical high-gain voltage amps, an “intermediate” voltage amp, and a power amplifier stage rated at 1 watt.

Attachment:
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These are the type of resistors I’ve almost always found to need replacing, usually well out of tolerance on the high side:

Attachment:
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Their surface is very rough, not purty and shiny like an Allen-Bradley!

I re-stuffed the two main electrolytic cans which were in more-congested areas, but was able to add terminal strips and under-chassis mounting of the other electrolytics.

With all of the R/R (my repair journal shorthand for removal and replacement) work now completed on the lower chassis, the 10k resistor feeding B+ to the upper chassis tubes fed by the main power supply was disconnected to enable testing just the lower chassis portions before proceeding.

Powering up using a variac while monitoring the AC current draw thankfully revealed good B+. This was not to last however.

After a few minutes of operation the old 5Y3 would slowly fade to very low B+, though the high voltage AC was still present on the plates. A replacement 5Y3 cured the problem. The original had been tested earlier but apparently couldn’t take the greater demands of the actual circuit, a phenomenon often seen.

The good news is that quick checks of all four amplifier sections showed them and their controls to be nominally working. No checks of the attenuator calibration were made at this point, but I suspect, based on the number of resistors I had to replace elsewhere in the chassis, that there will be similar issues in these controls needing attention before we’re done.

They are fairly simple devices, being just wafer switches containing many resistors of the often-bad type.

Attachment:
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The upper chassis R/R is about half completed and I’m looking forward to being able soon to check out the built-in AC VTVM and oscillator and audio sweep circuits. Then it will be on to looking at the two attenuators and calibration of the amplifier sections.

Thanks for coming along on the journey.

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 Post subject: Re: RCA Audio Chanalyst 170-A Project
PostPosted: Feb Mon 08, 2021 3:32 am 
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Oh, man, that attenuator is going to be tedious!

It’s looking good! Nice that you can test the lower chassis independently.

How do you cut your electrolytic cans open? It’s a nice clean cut. When I cut them with a hobby razor saw, I usually end up with something of a ragged edge. Not very pretty, but it does help to get the top back on in the original orientation :-)

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 Post subject: Re: RCA Audio Chanalyst 170-A Project
PostPosted: Feb Mon 08, 2021 5:00 am 
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Thanks, Steve.

I’ve actually tried several different methods on the few I’ve done now.

The four cans I did on this unit were of a small enough diameter that my copper tubing cutter fit around them. That makes for a really clean cut, as long as you don’t get too aggressive with the cutter wheel pressure. Of course one can only use the cutter if the cans are totally removed, which was reasonably easily done in this case.

The remaining cans that I elected not to restuff would have been too large for this method and since there was ample space at those points I chose the easier method of mounting replacements on added terminal strips nearby.

One trick I use in restuffing to aid in holding everything in alignment while applying the aluminum tape is to fashion a stiff cardboard (hoarded for just such a contingency) tube sized to fit tightly against the interior of the can. Otherwise, applying the tape is like nailing jelly to a tree.

I’d thought about documenting the process but others have already done that, with better-looking results. You’ll notice I didn’t post any shots of the finished cans. They are what I’d call adequate, but nothing to brag about. The cans looked pretty good, but I was too worn out with the whole process when it came time to put labels on and wasn’t real happy with how they looked. I may redo the labels later - or let the next caretaker do it. :D

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 Post subject: Re: RCA Audio Chanalyst 170-A Project
PostPosted: Feb Mon 08, 2021 11:29 am 
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Quote:
Otherwise, ........ is like nailing jelly to a tree.

First of all, I'd like to see that done some day. Put it on Youtube. You'll be famous

Why do you suppose the resistors in that attenuator have such long and coiled up leads? I can't offhand figure a reason for that, other than possibly some strain relief on the switch lugs.

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 Post subject: Re: RCA Audio Chanalyst 170-A Project
PostPosted: Feb Mon 08, 2021 4:01 pm 
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Barry H Bennett wrote:
Quote:
Otherwise, ........ is like nailing jelly to a tree.

First of all, I'd like to see that done some day. Put it on Youtube. You'll be famous

Why do you suppose the resistors in that attenuator have such long and coiled up leads? I can't offhand figure a reason for that, other than possibly some strain relief on the switch lugs.


Barry, at least until I dig into the attenuators a little deeper, your theory is as plausible as any.

It just now occurs to me that, unless there’s more buried under those, I’ll be able to do any needed replacements using the quigg method which will save wear and tear on the switch wafer terminals.

Thanks for the synapse stimulus!

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 Post subject: Re: RCA Audio Chanalyst 170-A Project
PostPosted: Feb Fri 26, 2021 7:09 pm 
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The upper chassis, containing the VTVM, Oscillator, Sweeper and Indicator sections is now completed as far as cap and needed resistor replacement (almost all) are concerned.

Upon power-up both B+ supplies came up where they should be with no overheating of dropping resistors or transformers.

A quick check of the VTVM on DC 5V range matched my Fluke 27 and showed the circuit to be at least responsive.

Per the manual, I fed the Oscillator output into the Intermediate Amp section and was able to hear it in the internal speaker, adjust its level from the front panel, and adjust its frequency. However, the frequency control section will need work and calibration.

The sweep section “kind of” works but will also need attention. I hope the problem is NOT the 2050 thyratron tube, as I have no spares and they’re pricey when available.

I’m pretty excited to see basic functionality all the way around. That makes the tedious remaining work more fun.

Stay tuned!

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