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I finally found an older radio that I can build from a kit
It's made by Knight and is dated October, 1969. The way I see it, it's been sitting in someone's closet for over 50 years waiting for me to work on it!
I consider this a repair too because some of the boards were pre-built by Knight but they used carbon composite resistors that may now be out of tolerance. I'm going to take the time to bring this radio into perfect shape with the best of parts from Digi-Key.
I can hear my neighbors now, "what's that tower for?"
I'll post pictures as I un-box it and scan the schematic tomorrow.
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That's totally cool, I'd love to build an old kit like that. I'm sure some people will freak out that you're "ruining" an unbuilt kit by building it but what else is an unbuilt kit good for? Just do a good job, your other work that I've seen has been pretty meticulous. I'm pretty sure my uncle has exactly that same radio, he found it at a garage sale about 30 years ago when it was already old. I remember playing with it sometimes when I was a kid.
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...and the Nippon Chemi Con caps are dated '69 too:
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The gold cad plating on the metal is near perfect. The kit also includes plastic tuning tools!
The boards are in the same shape, but I plan to replace the resistors and electrolytic capacitors. I have a nice selection of Vishay Dale CMF resistors that should work good.
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That's the shiniest tuning capacitor I've ever seen. I've never encountered a new one before.
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Shiny it is. I would say it's because they put the parts in plastic bags
Here are the scans of the schematic and parts list:
Schematic
Parts
And while searching the internet about this radio, I found this schematic by Bill Meacham. He went through his radio and found some differences from what he seen on his schematic compared to how his radio was built.
He annotated some voltages and values that he discovered didn't match.
I'll keep an eye out for what I measure too.
As for all of these images, they are large, so right-click to see them in full size.
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So far, the only thing that doesn't look good are the packets of wires. Something in them turned to goo and now everything is stuck together. I ordered new 22 AWG stranded silver-plated Teflon wire but it looks like the tuning line cord is screwed. The line cord measures .03" in diameter so I'll be searching for some fresh stuff:
The resistors measured as expected too. 60 new resistors coming up
As for the rectifier diodes CR4-9 on the schematic (DS-16C's), they appear to be in good condition but I couldn't find a data sheet for them:
I read an article by Mark Johnson where he tested and ranked 48 semiconductor diodes based on the smallest dI/dt at switch-off. The Vishay SBYV28 type came out on top so I'm going to buy a few of the 100v version:
...and a fresh batch of Mil-spec wire and cable has arrived too
The pages of instructions are laid-out pretty well. On this page, the instructions say to cut the bare spool of 24 AWG tin-plated copper wire to size and slip it into the decomposing sleeving. I'll better that by using some 22 AWG silver-plated PTFE stranded stuff:
I bought these Vishay/Sprague Atom axial capacitors to replace the new/old Nippon Chemi Con electrolytics that came with the kit. I read that these Spragues were just a hollow can with a smaller "cheap" cap inside so I tested the 1000uf/50v Atoms against the Nichicon UHE 1000uf/50v's on my Sencore LC53. Btw, the Atom's are described on their datasheet as "low-leakage" caps, and sure enough, the results proved it. The Atoms dropped to zero leakage but not the UHE's. Anyway, they'll fit the point-to-point wiring area better while looking "retro" too:
Since the majority of the parts that I need are now sitting on the bench, I started to rebuild the audio board. The original caps were tested for leakage and capacitance. All of them tested high:
The resistors also read high. Here's R49 (4.7K):
I'm going to use 1%, .5%, and .1% Dale CMF60's and Vishay SFR25 resistors in this radio:
I also made one change on the audio board. I replaced C52, a 1uf/25v electrolytic, with a 1uf/50v PPS capacitor:
Whoa! So I'm going through and replacing resistors on the audio board and I find this:
It's a short of the base and collector of transistor TR10, a 2SC838.
This is a factory-built board from the kit. Sure enough, after I cleaned the pad with solder-wick, you can see how the stencil for the conformal coating wasn't laid over the pads correctly. I'm going to go through these boards with a fine-tooth comb:
Dodged a bullet
The audio board is now finished
...and now onto the I.F. board.
Before:
After:
Here's what I'm finding on the boards assembled by Knight. I imagine a few of these kits were returned due to issues caused by cracked solder joints, shorts, and dirty boards (solder balls in resin).
Soon I'll be turning to page 1 of the "assembly" instructions
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I'm moving along with the radio pretty good but I have a question about these coils and transformers:
On the schematic, it shows that within the dotted lines of T3 (I.F. transformer), T4 (BFO Coil), and T5 (I.F. Transformer) are unmarked capacitors.
I watched a video where Mr. Carlson says that they are, on average, 100pf capacitors. He also stated that in these types of coils, the capacitor isn't soldered-in. It's a press-fit sandwich with a piece of Mica spacer that has a layer of conductive metal applied to it or something like that, and over time, tarnish sets-in and disrupts the signal path and causing noise to be created. He shows how to bypass the capacitor with new ones but he doesn't mention any sort of test that I can do first to see if there is a problem.
looking at these two types of schematics within this radio, is there a test that you can help me set up to test these 50 year old/new coils for degradation/noise?
I.F transformer
BFO Coil
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Why test the coils? Do you have reason to suspect they're bad? I don't think I've ever seen a coil like that which had failed. The best test is probably the radio itself.
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Thanks James.
I've no reason to believe that they're bad. It's just that I'm beginning to realize why that small Leader oscilloscope repair attempt I made a year ago was so difficult. The Japanese way was to populate all of the boards with components first, then add a gazillion jumper wires to the boards. Then after installing the boards, connect the gazillion jumper wires to all of the switches and other boards in the chassis.
This radio is just like that.
And now after watching Paul Carlson's video on these coils, I thought, why not be proactive and save myself some future pain and suffering
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Do a basic ohm test to confirm that they are not open circuit and that windings are not shorted to one another and that will catch the vast majority of things that could reasonably go wrong.
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"a new modular concept where most parts are already soldered in and all critical adjustments have been made at the factory so that the builder merely interconnects the boards"
The transformers are fragile and irreplaceable so I would not do much with them. The Litz wire may corrode and break inside so a continuity test is good enough. Inside I usually see tubular capacitors that don't fail, Mr. Carlson might be talking about older, higher impedance (tube) radios where those caps go bad? I did not agree with his tuning technique because of the loading error of his spectrum analyzer.
You have to have the right alignment tool and if the slugs are too stiff they tend to crack apart. A little graphite might work. Most important is to not put the transformers in backwards or mix them up T-4, T-5 but I think the factory has them already in?
Knight-Kit R-195 priced at $89.95 in new products Ham Radio magazine June 1970 pg. 74 is $624 in today's dollars.
Small text mentioned in Popular Electronics magazine June, August, Oct. 1970 but Knight did not take out ads.
It looks like an era where Japanese radios and kits, i.e. Radio Shack DX-150 were prevalent and Heathkit was the most expensive. -
When I was in college in the 60s I helped a number of guys that had built audio Knight Kits coming to me for help. From >50 year old memory I remember replacing a lot of power supply electrolytic capacitors in order to fix problems with excessive hum.
These were recently completed kits. So either the supplied capacitors were faulty, or they were under specified. Given how often it happened, probably the latter.
So watch out for excessive power supply ripple. -
Yes FloobyDust, the transformers were installed by Knight. I tell you, the copper on and in them shine like new and they look really good.
I may try just a drop of dry Teflon lube into each core since I don't have any graphite. Blaster Dry Lube w/Teflon that I have is also safe for plastics.
I imagine that I'll be needing to align this radio when it's done since the resistor values are probably no where near where they were in 1969? I need to find a copy of that Popular Electronics magazine too
Anywho, I measured the pots and the 2K one measured around 1.7KOhms. The 5K pots measured 4.71KOhm and 4.83KOhm. I put a small shot of DeoxIT D5 into them and their movements are smooth and the numbers were fluid while looking at the DMM. They're brand new pretty much:
What I like the most so far about this radio is that it's all metal. From the brass standoffs and bushings to the metal case. Most of the holes in the metal are tapped and spaced very accurately too. Parts fit perfectly. Kits like this would probably cost quite a bit if made today:
One change I did was to upgrade the tie strips to these NOS Sprague ones. They're much beefier:
Tom45, thanks for letting me know about the capacitors. Maybe I should set up the rectifier circuit on the small breadboard that I have and do some experiments before the final install? I could set it up with the original parts/values first then modify it for the best result. I wouldn't know how much of a load to put on it though.
Also while looking through the paperwork I found this modification from Knight. It has two wires stapled to it. So, I imagine, this change isn't present on the schematic? or, maybe, it's just an error in the instructions and the schematic is correct. I haven't gotten to that page in the instructions yet. I do know this, the parts list is more accurate than the schematic when it comes to resistor values:
So far, so good but I'm not even 2/3rds of my way through page 1 yet! and there are 25 more pages to go
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I may try just a drop of dry Teflon lube into each core since I don't have any graphite. Blaster Dry Lube w/Teflon that I have is also safe for plastics.
Uh, don’t do that. The inductor cores are the equivalent of a waxed paper drinking straw. The ferrite core should have a light wax coating on it. Any blaster products would likely do irreparable harm.
Stop with the “improvements” and just build the thing. -
For what it's worth, the one my uncle has works just fine, it's never had any work done on it at all, at least not in the ~30 years he's owned it. I would not expect to have to make any adjustments and would not mess with the coils at all. Monkeying with the coils is a good way to make sure it never works right.
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That wire with the green goo is because the original formulations of PVC wire from the 1960's used PCB oil in the pvc as a plasticiser, to make it flexible. However with time the oil reacts chemically with the copper wire ,forming the green goop you got. Yes replacement wire is in order, and if you got the proper MIL spec cable it will be either tinned or silver plated, so will not react with the PVC and PCB oil to form that kind of reaction. Common in older buildings to open a switch or socket and see the drips of green goo on the wire and metalwork, if it has not gotten to the point of dripping down the wall already.
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Thanks for the warning about the coils. I had no plans of touching them and nothing has been squirted inside of them either. The boards were restored, cleaned, and put back in their boxes.
SeanB, the wire is M22759/11. I believe it's silver-plated copper. I buy it from an Ebay seller going by the name of EmpireDon. He claims to have over 40 years of experience in aerospace assembly. He sells some nice cable
I've installed one of the variable capacitors on the front panel and I'm using RG-316 shielded cable. The original stuff was going bad (sheath was stiff) and the conductors and shielding is bare copper. My magnet stuck to the center conductor so it was steel based and I thought RG-316 would be a good substitute. I slipped some fiberglass/silicone sleeving over it too since the metal edges were sharp. As for solder, I'm using Kester 62/36/2 leaded silver solder (24-7150-0018):
As for the "improvements" that I do, well, I like doing them. I have between 9pm and 1am to fiddle with electronics and since it took 50 years for someone to open this box, I'm going to take my good, sweet time putting it together
I like using these NOS Sprague tie strips. They sit higher above the chassis than most other strips and it allows me to use the holes below the eyelets. I populate the tie-strip as much as I can before it's installed. As for this one, there are still four components and four transformer wires yet to be attached to it! I've done this several times before in other projects and it saved me from some frustrating soldering inside of the chassis, especially if it's deep:
On another strip, I drilled a small .04" hole in the ground post for a jumper. The "open" eyelets can now be used for the big caps all by themselves:
The signal meter, lamps, and the tuning capacitors were next:
The radio is starting to take on some form too. Lots of work has been done so far. Still, the band switch has yet to be wired. I'm on page 12 of the instructions where the IF and RF boards are pre-wired and installed:
This is the current state of the underside of the chassis. The panel light wiring and the transformer/rectifier circuit is complete and the audio board is installed. I'm on page 14 where the factory modifications are to be inserted. It appears that the modifications are adjustments to the grounding points:
So, with the band switch mounted, it's time to solder 50 wires to it!
One thing is for sure, if one had to use an old-fashioned soldering iron to assemble this, it could easily become a mess. Plus, they didn't have Teflon sheathed wire back then either!
The first two wafers are done:
The third wafer was easier. The small blue cap is C-33 (.047uf NP0):
The last wafer is almost finished. The small blue cap is C-32 (.0022uf NP0). Ten more wires to go:
And now the band switch is D-U-N!
Up next is the tuning shaft, the flywheel, and the mode switch...
*I pulled the trigger on an older HP spectrum analyzer on Ebay. It was being sold for parts but I feel some good "vibes" about it. Hopefully it works and can be used for radio repair projects
https://www.eevblog.com/forum/repair/hp-3588a-spectrum-analyzer-gamble/
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The mode switch was next and it was better wired while it was loose in the chassis than after it was mounted as the booklet required:
But what made things confusing was that there are more soldering tabs on the "real" switch than what was printed on the instructions, plus, look how they numbered the tabs
You literally had to go by the little circles that represented the rivets to be sure you were in the right spot!
Anywho, the switch is installed and now it's off to installing the speaker, the line cord, and the tuning string.
Four more pages of instructions to go
I followed a few of FloobyDust's links too and downloaded the catalog page from Allied's 1970 catalog:
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You have loads of patience, I couldn't do the band switches with dial cord nearby?
Looking at the old magazines, newfangled transistors appears to have fostered a kit radio boom. These are $500-600 in today's dollars and wages were tiny back in 1969. Heathkit you would need a bank loan to buy one. I guess radio was the killer app for electronics hobbyists.
It doesn't look like you did the grounding mod to prevent hum in the AF amp? I would say volume control VR-45 ground wht/red does not go to the chassis GND turret, but instead connects to AF Board point 68. If the AF Board 65 is grounded on the other side of the filter caps, closer to the bridge rectifier it would give 120Hz hum. The radio chassis should be grounded not at CR-7 but instead after the filter caps, at say C-37 or C-38. This is to avoid the C-37 ripple currents from making 65 have hum. -
FloobyDust, the angle of the picture makes it look like the mod wasn't done but the white/red wire that you see going to the grounding tab is actually coming from pin 1 of VR52, which is one pot over.
Here's a better shot of that area:
I haven't purchased a dial cord yet but the search is on The original dial cord was shipped in with the original wire pack and whatever was leaching-out ruined it 
Btw, the last pages of the assembly manual has the specs and alignment steps for the R-195:
...and if I have any issues, I'll just mail them a letter
With the line cord and the speaker connected, the manual reads, "this completes all the wiring and soldering of your kit."
Over the next few nights, I'm going to go back and check every step
And even though the dial cord is on order, it doesn't stop me from powering-up the radio
I tested the 14V rail with the oscilloscope probe in the location of R-41 and C-38:
...and the ripple:
Under 20mV and looking good!
No antenna is installed but the local AM radio station came in strong!
The dial cord came in so I started with tying loops on the ends using super-small Bowline knots. I put a drop of super glue on the knot to make it solid. One end hooks over a metal tab on the pulley and the other loops over the spring's eye which puts tension on the cord.
Now with VC-2 tied up, the dial cord work is done
The Bandspread Dial and the aluminum faceplate was next. I replaced the aluminum washers with plastic ones that go behind the switch nuts so not to scratch the faceplate. The back of the faceplate is bare aluminum so it makes good contact with the chassis. All of the faceplate parts were polished with Mother's carnauba wax too:
The pointer was next. It has a couple little flaws in the paint but it still looks great:
Next was to drop in the dial scale
I still have a few small things to do. I want to make sure it tunes to a station accurately before I slip it into the chassis. I'm currently searching for a good RF signal generator. I also need to make or buy an antenna. I'll keep updating the progress as it happens
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If anyone felt that this radio didn't belong in the "repair" category of EEVblog, let me easily put that thought to rest
I had the radio almost together and decided to turn it on to see how well the dial pointer aligned to the dial scale and to see how far off our local AM radio station was (680 WPTF).
So I turn on the radio and all I hear is faint static through the speaker! Pretty much nothing
Up to this point, I did nothing other than turn the band switch, the volume control, and the tuning knob
So I went back and checked all voltages throughout the radio and everything measured near perfect compared to what is printed on the schematic.
What did I do? short something? Jeez!
I went back and checked everything and began to look closely at the band switch and all of the wires and all of a sudden something caught my eye!
Do you notice something odd in this picture?
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When I turn the Band switch to A, notice how the notch in the brass disc is centered around pin 1 on wafer S-1B, but when you look at the brass disc on wafer S-1C, it isn't! It's actually making contact with both pins:
Wafer S-1C selects between coils L-6, L-7, L-8, L-9, or L-10:
On the other side of S-1C, you can see that a brass disc with a tab selects one of the five coils. The tab appears to perfectly align itself to the pin:
So when you turn the Band switch and select band A, B, C, D, or E, one side of wafer S-1C selects the correct pin (coil) and isolates it while the other side of the wafer is supposed to group the remaining pins bringing those coils to ground.
That's not happening.
For a quick test, I removed the wire from pin 2. This should totally isolate pin 2 from pin 1. It doesn't. I used my DMM and I get continuity to pin 1. The notch in that brass disc should be around pin 1 only and not touching it:
Lovely! The brass disc wasn't indexed correctly when it was made. What worries me is since the radio doesn't have the same "gain" as in the Youtube video, was damage done to the three FETs on the RF Board?
I'm going to pull them and do some basic tests on all three FETs on the bench to see if one isn't responding like the rest. They are MPF-102's.