Back in the day a schematic was seldom needed. Most problems were tube based and with block diagram knowledge and a simple tube tester a tech could fix 95% of radios. The same was true with TV servicing, I learned radio electronics on that very RCA radio you have on your bench,, however before I got to that stage I studied basic electronics. My years of experience and advanced knowledge grew from each set I worked on, learning about test equipment was another part of the courses I took at RCA Institutes in NYC. These days the problems that occur are mostly component based due to aging of the radio receivers. Yes today a schematic is much needed.with experience and practice expertise is finely developed.
As someone just getting into the world of radio restoration late in life, this made me very comfortable looking at schematics. After watching this video, which I will watch again, I find looking at schematics less intimidating. Thanks!
I found this very informative, especially the parts about changes on the schematic and also other differences in what something was called then vs now.
I have read through radio schematics in the past with some difficulty, this was a very helpful tutorial. I was able to pick up some new knowledge thanks to your step by step description.
So far this was the best video of this kind out there. This was very good and really helped. I would like to see you expand on this topic especially things like voltage in and out of tubes, current flow, and using a multimeter, etc.
You can download a RCA Receiving Tube Manual as a pdf. There is a lot of good information in this clip. About the AVC (- 13V max) is related to the amplitude of the carrier wave. The carrier is rectified and smooth to a dc voltage. Strong signal high AVC voltage, less amplification. Weak signal low AVC votage, higher amplification. Please correct me if I am wrong. The voltages given in the diagrams are messured with an analog multimeter specified in the diagram very often around 20kOhm/V. Today we use digital multimeters. No problem but the voltages can differ a bit. I think with the comments we make it a nearly complete good guide to read valve (tube USA) diagrams.
Found this video looking for how the loop antenna should be attached on an abused 1X, stayed through the whole thing! Wish I could send it back in time to when I started doing radio restorations, possibly the best explanation of schematics and how to map them to the circuits they represent, neither too technical or too simplistic; would have saved me a lot of frustration. Thanks!
Iain, just wanted to stop in and say thank you. This video was great. Luckily it was one of the first ones on this subject that I watched and it out down a great foundation of knowledge to build on. Thank you.
Good explaining. With my very limited electronic knowledge I was able to follow along knowing a lot of it while seeing a few things in a new light. I have a 1934 Philco that I have had since a small child over 60 years ago. It should be pretty much untouched and I am getting slowly geared up to go over and change capacitors before trying to play it anymore.
Just found your site…just (at age 66) getting into this hobby since grade school Heathkit builds. This is a great video! Thank you for making this, I know the time and effort involved. I know there is no reward in this save the immense appreciation from your “students”. Please keep creating.
Great video. Good quick high level summary of how to read tube schematics and what the sections do. I've read hundreds of schematics over my career and Iain is clearly very knowledgable. I have zero corrections for this well done video. I watched it at 1.7X - that was the perfect speed for me. At 1X it's too slow.
A few things that are now clear to me that I find are eye opening. This is a very good lesson I couldn't be thankful for, thank you. #1 I didn't know that the tube layout isn't the same on some of these schematics, I should always reference the actual tube layout, not the drawing to locate the pin-outs of the tubes. I always assumed the pin-outs always went from left to right in order. Now I know this is not true. Not being trained in schematics, I am self taught and I assumed many things, but the biggest assumption was the tube layout in the schematic. #2 the addition of the supplemental circuit on the schematic. I now know this is where I find the different version of a certain part of a circuit, where before I always thought it was on the drawing as an option. (Yes that may sound silly, but to an untrained person, this is the only thought process I had to account for that addition in the schematic.) A great lesson for me to keep in mind from now on. Also, I can now go back to some of these old radios I have set aside, because I've been having issues with, and correct my mistakes. Thank you.
I know I'm late to the party (as usual), but this is BY FAR the most helpful, useful explanation of a radio schematic I've ever watched. Extremely well done, sir! I've got an old Zenith console 8-S-463 (5808) that I hope to try some restoration on. As always, thanks so much for sharing. Steve
lain you are an excellent teacher! This layman now has hope to work on my 1937 Western Radio Patrol model 76. I noticed you never say "uh, um, hmmm" or the like as space filler. You wait for the right word. Again, excellent! Thank you for this top video.
Ian you have the best by far of any videos on here teaching how to read these old schematics. Please keep it up. I subscribed and got all notifications bro. Please please keep it up. You just helped me fix my Johnson. Messenger Two Cb radio. 🤘🏻
Very well done and helpful. can you suggest were to purchase parts. i just retired and have a collection of old tube radios that i would love to get working again. Looking forward to future video's. Thanks again..
I've just started too, but mouser and digikey are great websites for things like capacitors and other electronic components. No minimum order and a wide selection
I really appreciate this video. It answered so many questions for me as a beginner. THANK YOU...especially how to know when to use which capacitor. Thanks again
very good informative video. thank you. I like to use the term kilocycles when working on old stuff because that's how they said it back in the day. I use the term kilohertz when working on new things because thats how it is said now (when the item was made). I do this just because it drives people nuts but I am also being period specific at the same time so you cant really get mad.
This was super helpful as I'm starting repairs on an old Montgomery Ward's Airline radio! I looked back and forth between the schematic and the radio for quite a while and still couldn't make sense of everything, but this really helped clear it up, so thank you. I'm still not entirely sure how to make sense of all of the lines and dots and where they come together vs. where they meet at a tube's terminal (that doesn't seem consistent on my radio), but it may be worth a try!
F1FanWoodsie28 one thing to remember is that many times the manufacturer attaches the components to what ever the handiest place is under the chassis. Lets say a schematic shows a 1 ohm resistor and the B+ voltage connected to the plate of tube number 2 on the schematic. Now the B+ also connects to the plate of tube number 4. In the radio the manufacturer could have connected the 1 ohm resistor to the plate of tube 4 because the resistor couldn’t reach tube number 2. The schematic is still correct because since the pate of tubes 2 and 4 are connected together so even though the schematic shows the resistor connected to 2 and in real life it’s connected to 4 electrically it is the same thing. They drew the schematic in a way the keeps any one section from getting too crowded looking while in real life they assembled the circuit however they could to use as few wires and tie points as possible. It is confusing but after a while you get used to things being electrically like the schematic yet the physical construction is not laid out like it shows in the schematic. Sometimes it’s just a big game of connect the dots. I hope this explanation helps.
I agree with the others. This is easily one of the best vids on getting to know schematics, and definitely something every beginner should watch. Great work, Iain!
Awesome video! You are a master at teaching this stuff. I really learned a lot. I was wondering if you were going to do a video in the near future explaining the basic concept of the superheterodyne receiver? I’m still trying to wrap my mind around the concept of mixing signals to get an intermediate frequency. I would really like your explanation being that you teach these things so well. Thanks
Pin output for the converter, you can easily swap 2 and 7 since they're the heater and the pins will be exactly 1-8 clockwise. Yes, many times they do not put the pin outs exactly but when they use the image as in this schematic, it most likely will be exactly correct pin outs starting with the notch on top, counting 1 to the immediate right clockwise to 8. ;-)
gabevee3 I see you caught that. I swapped those pin numbers to make a point because this schematic really did have the pins in the correct order but I was trying to get people to not assume they always were in order.
Good video, I'M working on a Hallicrafter S20R,and I find so many things that don't match the diagram; But this radio looks 100% original every component is from that era. but I chase components on the diagram but too many are not on the radio...is Crazy.
I’ve found that sometimes the manufacturers make changes to the circuit throughout the production run and the updated schematics got lost over the years. I’ve got a couple Yaesu FT 101 radios and they are famous for having parts appear and disappear throughout their run. I have three different schematics for the FT 101e and they are all slightly different. The thing to remember is the manufacturer only truly cares about manufacturing the radio. They make a design change and may or may not update their records to reflect it.
I went to Tennessee Institute Of Electronics in 1979. All of the schematics back then were "Sams Photofact". I haven't watched your Video to the end yet but it looks great! I was lucky to get employment while still in that school from an AM/FM Radio Station and my supervisor/chief Engineer was an electronics instructor. I assume Sams books are still available?
A very good introduction into reading vintage schematics. Just one thing to note: Some very early schematics used M for 1,000 when referring to resistors. We are more used to seeing the letter K used for this, so a 3k resistor is 3,000 Ohms. But some old schematics might show resistors as being, say, 220M. That is NOT 220 Meg Ohms! That would be a ridiculously high value, in fact it would almost certainly mean 220k, or 220,000 Ohms in modern parlance. Just another one to look out for.
Thank you for posting excellent explanation.I just bought my first radio a Zenith 5d320 1937, I'm going through replacing capacitors and verifying resistors. But I noticed the schematic shows two R1 resistors and 2 C4 capacitors. Have you seen this,?
What a very good explanation Ian. Very well done, if you are not already, you would make an excellent teacher. So in my experience most of the schematics I've read vary dramatically as far as information provided. Unfortunately most have no voltages shown and occassionally no ohms for coils. Also, on really old ones the resistance for resistors can be represented by the letter M vs. the letter K for thousand, and meg for megaohm. The rake being chassis ground and the inverted lines being circuit ground, if a schematic has no brakes and all inverted lines, are those now chassis grounds or are they all still circuit grounds and no grounds to chassis? Excellent video!
Very good video. I learned a lot from this. One question...what is the difference between chassis ground and regular ground, and how does that present when you are looking at the radio?
This is fine if you have a decent schematic. My schematic is straight from the riders manual and Is quite terrible, and has Typo's. I can read most schematics relatively well but this one is bizarre. Riders volume 12 sears and roebuck chassis 110.400.
ditto, to the praise everyone else gives. very nice job. So I see, the two in each can, and on other vidios where the take a can apart & put two capacitors in there. now i know the reason. and some people put 2 seperate, & then leave them under neath is that right? thks again
