Glad to see you mentioned pin 4. The tone corrector and IF bypass caps can be safely reduced to give a much brighter sound on what's left of the AM stations.
Video's are very interesting & nice to watch Tony, nice to see you just a lamp tester & multimeter the way I was taught back in the 70's, not racks of equipment, we did have an Farnell two channel oscilloscope, which the shop owner gave to me last man standing , when the doors closed for the last time, love your work. p/s I still have & use the scope & the fluke multimeter, plus a more modern multi meter.
This is another good reason to know your tubes (valves). I almost always print out the data sheets and put them in a folder with the schematic when I get a new set to work on. I really like your informative videos. Keep up the good work. -Dave
Dr Tony, I just discovered your TH-cam videos. I went through all 4 parts of your restoration videos today. You did a great job of explaining in simple easy to understand terms how you approached the analysis and what you did to fix the radios. I hope, sincerely, that you keep posting videos like these. I don't think I have seen a clearer explanation of what someone has done to find problems and fix them. Thanks so much. I'm working on radios here in the US so some stuff is a little different but the principles are the same. Thanks again.
So glad you found it useful. I do plan to make some more video's, but just at the moment I have too many things going on. Hopefully at some point next year
Thank you Dr. Tony for the instruction on how to rewind an output transformer and for your correct pronunciation of the letter l in "solder!" There is hope for the English language yet! Greetings from Melbourne, Australia in the second Chinese plague year.
Hello Garry. Good to hear from you. Do you have a transformer that you are going to tackle. If so, like me there is nothing to loose if it doesn't work
Great teaching point there on the "internal connection" pin. Thanks for a very logical telling of an arcane problem. Well done! Congrats on not having to rewind another output transformer.
The voltages in the circuit diagram are mesured with an analog multimeter with the specs. given in the diagram. There are a few tricks when you repair valve radios commercially and you have to work under time limits. You can hear the local oscillator in another radio tuned to the same band. When you touch the middle contact of the volume potetiometer with a screwdriver and hear a hum from the speaker the faulty stage is most likely in the rf or if stages of the radio. You can touch the grids of the tubes with a screwdriver beginning from the loudspeaker valve and work towards the antenna. If the stage works you hear a clicking sound in the speaker. A simple signal injector is a long wire and touch one end to the grid. This is a trick I have seen people doing it but I have not done it myself. Switch the radio on and off and if you short the filter capacitors in the pie DC filter you can see a spark if the high voltage is working. Back in the day they used this methods to find the faulty stage fast and started with meters for advanced trouble shooting.
Thanks Tony for that little gem with the connection on the final valve. I have a DAC90A and, yes the junction of those two resistors is to the 'unconnected' pin. That now will be removed. I have come across these 'hidden' connections on a Bush amplifier chassis on a radiogram which got me confused for hours! Keep up the good work.
Hello Dr. Tony, great to see someone new on the TH-cam scene, it's only through seeing different approaches that we further ourselves. You don't shy away from a challenge (as in tackling output xformers) that's for sure. I look forward to new videos in due course!
The leakage is caused by sputtering from the cathode depositing between the valve pins and you will find the leakage is much more significant when the vale is red hot , than when its cold , as a test connect your meter to a spare valve base and then run the radio for a few mins to bring the valve up to working temperature then with a cloth pull out the hot valve and plug it into your test socket, you will observe a much greater leakage , then as the valve starts to cool down you will see the leakage decrease , I use a TV valve 10P13 , as a sensible equivalent to the UL41 and its pin compatible with only very slight difference in heater voltage . Sometimes the UL41 leakage can cause a hum on the audio.
Thank you Michael. That's very interesting to know. I still think that it wouldn't have been a problem if bush hadn't connected to pin 4 which I am convinced they shouldn't have. And actually there was really no reason to do it in the first place with the way the wiring was set out
Thanks for sharing this videos and your knowledge with us. I have restored 3 radios I had sitting here and got them repaired completely. These are a National HRO Senior from 1938, an Allied Knight from 1938 and also a National HRO 60 from 1955. Still have not come across a radio needing the output transformer re-winded but I definitively will go for it after watching your videos. I know, it won't be easy task but I now know what to expect. I might fail again and again but will eventually get that type of re-winding done. RF coils could be a different story as their wire gauge might be too thin for me to find it locally on the first place but I believe you need special equipment to do RF coils. What do you think? I live in a small country, were people restoring this kind of radios is no longer available. Very few radio enthusiast still alive. Ham radio operators come down to less than 10 still locally active. We are slowly disappearing and this is becoming a lost art on itself! Thank you again with all my heart, for sharing with us. 73 Rob., YS1RS
Good to hear from you Rob. Glad you like the videos. I have to say that I haven't ever attempted to rewind an I F transformer so you may no more about it than I do it may be that they are wave wound but this may not be vital. The Q factor comes into this because of bandwidth but essentially it is just wire on a former. If you have a dead one I would certainly attempt to have a go. What have you got to loose ?
Excellent pointing out a very underrated but common problem with using free pins of all-glass power valves as anchor points. As the valves age the metallic deposit from the cathode which condenses between the pins becomes more and more conductive, causing unwanted leakage. Had the exact same problem with a German PE Amp with 4 EL500 output valves, 2 of which were red plating despite the grids being disconnected. Nearly drove me nuts till I discovered the unused pin next to the grid being used for the full plate voltage....
Thank you Tony. I have exactly the same problem on my DAC90A. I'm off to check the valve base tonight and I'll see if that's the problem. I thought I had a leaky valve after I'd eliminated the grid capacitor. Another great video.
@@tonydurrant I will but not able to work on it until weekend now. Due to other commitments. I will scope the output waveform before and after modification as well as checking plate and cathode. Cheers.
Didn't really have time this weekend. However I did move the parts off of pin 4 to the nearby tag. I didn't hear any discernable difference in sound quality but I have yet to check the voltages for comparison. This I hope to do next weekend. I'll scope it too.
look forward to more videos. the problem with the ul41 is quite well known and the problem of useing pin 4 as an anker. just to catch out mear mortals well done bush.
I enjoyed your video's very much reminded me of my apprenticeship day's where we used a AVO, which I still use today, sheet of paper to do the maths, no calculators, apprentice's were not allowed to use the only oscilloscope in the workshop until you were in your 4th year, by which time you had built your own signal generator I hope you bring out more video's.
Good detective work on the engineering design "cheat". Fix took a little thought but you are a doctor! BTW they do this on a few American radios where you would never expect them to do this either and just to save a few pennies.
Great job! No need for re-alignment at all? Just crossed my mind given that, all aging caps in there may change value slightly. Thanks for an entertaining video Tony. Greetings from Australia!
Well. In general the small caps associated with I F transformers don't tend to change as much as some other caps. But having said that it has been known for some to be unreliable. The other thing to note is that if only takes a very small change in value to be significantly away from the specified I F frequency. Unfortunately I think there is no hard and fast rule here but if you do realign the adjustment can be a but tricky
@@tonydurrant I couldn't agree more! A can of worms a realignment. I have spent quite a bit of time to get it right myself on occasion.. If it works and seems sensitive enough, best leave it alone! Thanks for the response. Looking forward to more of your videos Tony. Best regards, Arthur
Really liking this channel, especially as it's UK based, one thing though, after turning off should you be checking for residual capacitor charge before measuring ?
Hello, thank you for sharing your knowledge! I am an amateur at this and have in the past changed all wax capacitors and electrolytics under the pretence that they are failure prone. I notice that you don't do this yourself, may I ask why? Is it simply for authenticity and saving those original components?
Well what I like to do is to get the radio going first to make sure that I can actually get it to go. Once I have done that then a full restoration would certainly include changing wax capacitors for sure and probably the majority of electrolytics too. Authenticity is always on my mind but for a long lasting repair you really do have to replace them
British ac/dc radios are so confusing to me because of the 220v mains. Here in the US, ac/dc radios have a heater chain that adds up to 110v or so, and B+ is rarely over 125v. I don't even recognize the tube types used in these British radios
Hello Tony, liked your videos, but can you help? I am restoring an Ekco U319 and have a circuit diagram but cannot find any voltage values on diagram, the ones you used have values on them. Am I looking in the wrong place? I can identify the components and the resistors have values the capacitors have values but no voltages, any help greatly appreciated Pete G
Yes i like to about winding rf oscillator coils is there a right hand rule of thumb.I measured the the length of wire and also want to know do you have to use litz wire.
I'm not quite sure I fully understand your question, but if you have a coil that was made using Litz wire then it is certainly necessary to get a high Q factor. No one would use litz wire if it wasn't needed
I have a question. I noticed on the schematic a valve, V2, that is drawn with a diagonal arrow through it. I'm in the United States and I have never seen this particular symbol. Would you please explain this symbol? FYI, I am retired Navy and I have been working in electronics since 1966.
Yes. Good question. It means it a variable mu valve. Ok so what does that mean ?. It means you can vary the gain of the valve (gain being mutual conductance, that's anode current/grid volts) by changing the bias on the grid. This is how the AGC works
Wouldn't it have been an idea to use a fuse before OR after the transformer in video 2 ??? as a kind of safety for the transformer I mean! Healthy and Friendly Greetings from the Netherlands! Rob
Greeting back to the Netherlands Rob. Any extra safety feature is a good idea but low value fuses are not something I have in my shed !!. Having said that I know you can get 50mA fuses. This was really the point of trying it with a 100 ohm resistor first. If there was a high current flowing it would just burn out the resistor, a bit like a fuse, but I accept a fuse would fail quicker so you could argue that it would provide greater protection
@@tonydurrant It might have been a good idea back then, but yes you have already closed the case of course I understand! maybe for next time. thought it was brave, that rewinding of that transformer! Just about the video: Well done, what will become the next topic? ;-) ..... the 3D printer? ( also nice! ) greetings again from the Rotterdam area! Rob
I've watched all four now and enjoyed them very much.
Excellent. Glad you liked them
Glad to see you mentioned pin 4. The tone corrector and IF bypass caps can be safely reduced to give a much brighter sound on what's left of the AM stations.
Indeed. Good point
Video's are very interesting & nice to watch Tony, nice to see you just a lamp tester & multimeter the way I was taught back in the 70's, not racks of equipment, we did have an Farnell two channel oscilloscope, which the shop owner gave to me last man standing , when the doors closed for the last time, love your work. p/s I still have & use the scope & the fluke multimeter, plus a more modern multi meter.
Thank you for your kind words Paul. Really glad you enjoyed watching them
I've watched all 4 parts of this series, very well explained, well done!
Thank you Harry. Glad you liked them
Great detective work on the ic pin used as an anchor. As a newbie a very valuable lesson. Thankyou
Glad you found it useful
This is another good reason to know your tubes (valves). I almost always print out the data sheets and put them in a folder with the schematic when I get a new set to work on. I really like your informative videos. Keep up the good work.
-Dave
Thanks Dave - that's a good suggestion
Dr Tony, I just discovered your TH-cam videos. I went through all 4 parts of your restoration videos today. You did a great job of explaining in simple easy to understand terms how you approached the analysis and what you did to fix the radios. I hope, sincerely, that you keep posting videos like these. I don't think I have seen a clearer explanation of what someone has done to find problems and fix them. Thanks so much. I'm working on radios here in the US so some stuff is a little different but the principles are the same. Thanks again.
So glad you found it useful. I do plan to make some more video's, but just at the moment I have too many things going on. Hopefully at some point next year
Nice fix, interesting on the valve pin. Thanks regards Chris
yes same here sorted it on my two DAC90a
Truly outstanding Tony, fun and informative.
Thank you. Glad you liked it
Great Watched all your Videos, Hoped there was going to be more
Glad you liked them. More to come at some point for sure
Thank you Dr. Tony for the instruction on how to rewind an output transformer and for your correct pronunciation of the letter l in "solder!" There is hope for the English language yet! Greetings from Melbourne, Australia in the second Chinese plague year.
Hello Garry. Good to hear from you. Do you have a transformer that you are going to tackle. If so, like me there is nothing to loose if it doesn't work
Great teaching point there on the "internal connection" pin. Thanks for a very logical telling of an arcane problem. Well done! Congrats on not having to rewind another output transformer.
Yes - I was quite relived about that !!
The voltages in the circuit diagram are mesured with an analog multimeter with the specs. given in the diagram.
There are a few tricks when you repair valve radios commercially and you have to work under time limits.
You can hear the local oscillator in another radio tuned to the same band.
When you touch the middle contact of the volume potetiometer with a screwdriver and hear a hum from the speaker the faulty stage is most likely in the rf or if stages of the radio.
You can touch the grids of the tubes with a screwdriver beginning from the loudspeaker valve and work towards the antenna. If the stage works you hear a clicking sound in the speaker.
A simple signal injector is a long wire and touch one end to the grid.
This is a trick I have seen people doing it but I have not done it myself.
Switch the radio on and off and if you short the filter capacitors in the pie DC filter you can see a spark if the high voltage is working.
Back in the day they used this methods to find the faulty stage fast and started with meters for advanced trouble shooting.
Yes indeed. All very good tips
Thank you for sharing. Looking forward to seeing more of your videos.
Thank you Tony now makes sense values are on valve pins and this information is on notes in diagram. Simple when you know how. Pete
Thanks Tony for that little gem with the connection on the final valve. I have a DAC90A and, yes the junction of those two resistors is to the 'unconnected' pin. That now will be removed. I have come across these 'hidden' connections on a Bush amplifier chassis on a radiogram which got me confused for hours! Keep up the good work.
Thanks Martin. Glad you found it useful
Hello Dr. Tony, great to see someone new on the TH-cam scene, it's only through seeing different approaches that we further ourselves. You don't shy away from a challenge (as in tackling output xformers) that's for sure. I look forward to new videos in due course!
Well thank you Roundy. That's very kind of you to say so. I am very glad you got something out of the video's
The leakage is caused by sputtering from the cathode depositing between the valve pins and you will find the leakage is much more significant when the vale is red hot , than when its cold , as a test connect your meter to a spare valve base and then run the radio for a few mins to bring the valve up to working temperature then with a cloth pull out the hot valve and plug it into your test socket, you will observe a much greater leakage , then as the valve starts to cool down you will see the leakage decrease , I use a TV valve 10P13 , as a sensible equivalent to the UL41 and its pin compatible with only very slight difference in heater voltage . Sometimes the UL41 leakage can cause a hum on the audio.
Thank you Michael. That's very interesting to know. I still think that it wouldn't have been a problem if bush hadn't connected to pin 4 which I am convinced they shouldn't have. And actually there was really no reason to do it in the first place with the way the wiring was set out
Thanks for sharing this videos and your knowledge with us. I have restored 3 radios I had sitting here and got them repaired completely. These are a National HRO Senior from 1938, an Allied Knight from 1938 and also a National HRO 60 from 1955. Still have not come across a radio needing the output transformer re-winded but I definitively will go for it after watching your videos. I know, it won't be easy task but I now know what to expect. I might fail again and again but will eventually get that type of re-winding done. RF coils could be a different story as their wire gauge might be too thin for me to find it locally on the first place but I believe you need special equipment to do RF coils. What do you think?
I live in a small country, were people restoring this kind of radios is no longer available. Very few radio enthusiast still alive. Ham radio operators come down to less than 10 still locally active.
We are slowly disappearing and this is becoming a lost art on itself!
Thank you again with all my heart, for sharing with us.
73 Rob.,
YS1RS
Good to hear from you Rob. Glad you like the videos. I have to say that I haven't ever attempted to rewind an I F transformer so you may no more about it than I do it may be that they are wave wound but this may not be vital. The Q factor comes into this because of bandwidth but essentially it is just wire on a former. If you have a dead one I would certainly attempt to have a go. What have you got to loose ?
Excellent pointing out a very underrated but common problem with using free pins of all-glass power valves as anchor points. As the valves age the metallic deposit from the cathode which condenses between the pins becomes more and more conductive, causing unwanted leakage. Had the exact same problem with a German PE Amp with 4 EL500 output valves, 2 of which were red plating despite the grids being disconnected. Nearly drove me nuts till I discovered the unused pin next to the grid being used for the full plate voltage....
Yes, it's a real pain. Something to remeber and watch out for in the future I think
Thank you Tony. I have exactly the same problem on my DAC90A. I'm off to check the valve base tonight and I'll see if that's the problem. I thought I had a leaky valve after I'd eliminated the grid capacitor. Another great video.
Ah ha. Let me know what you find
@@tonydurrant I will but not able to work on it until weekend now. Due to other commitments. I will scope the output waveform before and after modification as well as checking plate and cathode. Cheers.
Didn't really have time this weekend. However I did move the parts off of pin 4 to the nearby tag. I didn't hear any discernable difference in sound quality but I have yet to check the voltages for comparison. This I hope to do next weekend. I'll scope it too.
It may or may not make a difference. It just depends how leaky the valve is
Muy buena página para restauradores
Hi Tony. Love watching repair videos of any kind, Keep up the good work, UK based and in the shed Always a good thing.
JHB Somerset UK :):)
Sheds are very important !!!
look forward to more videos. the problem with the ul41 is quite well known and the problem of useing pin 4 as an anker. just to catch out mear mortals well done bush.
Ah ha - well it caught me out - but it won't catch me out again !!
I'm glad to hear you're making some new videos. I have learned something from each of these four.
lo pp
00
Great series of videos! Just about to start on a RAP 646 - hopefully there is less work to do on the chassis as there is on the (once beautiful) case.
Good luck Kevin
@@tonydurrant May I ask where you get those very good service sheets from? Having the indicated voltages at the DC level is a godsend. Regards, Kevin
@Kevin Murrell
Nowhere specific. I normally just put into Google "service sheet for xxxxxx" and it normally comes up with something
I enjoyed your video's very much reminded me of my apprenticeship day's where we used a AVO, which I still use today, sheet of paper to do the maths, no calculators, apprentice's were not allowed to use the only oscilloscope in the workshop until you were in your 4th year, by which time you had built your own signal generator I hope you bring out more video's.
Excellent Paul. Glad it meant something to you
Looking forward to see more of your videos.
I have a BUSH DAC 90 A / 70 and now 10 (which is currently disassembled and awaiting an electronic clean.
Ah excellent. You'll have fun getting it running
Oh no, just been given a classic BUSH VTR 103C to clean up now!
Good detective work on the engineering design "cheat". Fix took a little thought but you are a doctor! BTW they do this on a few American radios where you
would never expect them to do this either and just to save a few pennies.
Ah well, I'll certainly watch out for this on other models now
Yes please, more videos :)
I'll do my best
Saludos desde Cuba.
Un Cordial Saludo.
Excellent to hear from you. Greetings from the uk too
Thankyou. I learned a lot
Excellent. I'm so glad it was useful
More,more,more.......thanks very much 👍
I'll do my best !!!
Great job!
No need for re-alignment at all?
Just crossed my mind given that, all aging caps in there may change value slightly.
Thanks for an entertaining video Tony.
Greetings from Australia!
Well. In general the small caps associated with I F transformers don't tend to change as much as some other caps. But having said that it has been known for some to be unreliable. The other thing to note is that if only takes a very small change in value to be significantly away from the specified I F frequency. Unfortunately I think there is no hard and fast rule here but if you do realign the adjustment can be a but tricky
@@tonydurrant
I couldn't agree more!
A can of worms a realignment. I have spent quite a bit of time to get it right myself on occasion..
If it works and seems sensitive enough, best leave it alone! Thanks for the response.
Looking forward to more of your videos Tony.
Best regards, Arthur
Cheers Arthur
Really liking this channel, especially as it's UK based, one thing though, after turning off should you be checking for residual capacitor charge before measuring ?
That's certainly good practice but I generally just wait a bit to allow things to discharge
Maybe a good idea for future video's, explaining schematics, rf section, mixer section, and so till the of section.
Thanks for that. I'll certainly bear that in mind
Hello, thank you for sharing your knowledge! I am an amateur at this and have in the past changed all wax capacitors and electrolytics under the pretence that they are failure prone. I notice that you don't do this yourself, may I ask why? Is it simply for authenticity and saving those original components?
Well what I like to do is to get the radio going first to make sure that I can actually get it to go. Once I have done that then a full restoration would certainly include changing wax capacitors for sure and probably the majority of electrolytics too. Authenticity is always on my mind but for a long lasting repair you really do have to replace them
shouldnt you replace the rest of those wax capacitors? even though they are good at the moment arent they prone to fail in the near future?
Yes. They will need replacing
British ac/dc radios are so confusing to me because of the 220v mains. Here in the US, ac/dc radios have a heater chain that adds up to 110v or so, and B+ is rarely over 125v. I don't even recognize the tube types used in these British radios
Hello Tony, liked your videos, but can you help? I am restoring an Ekco U319 and have a circuit diagram but cannot find any voltage values on diagram, the ones you used have values on them. Am I looking in the wrong place? I can identify the components and the resistors have values the capacitors have values but no voltages, any help greatly appreciated Pete G
Just looked in J P Hawker Radio & TV servicing and it tells me the following:
V1. No info.
V2 Anode 237V, Screen 124V, Cathode 2.6V 16.6mA
V2 (osc) Anode 86,
V3 Anode 208V, Screen 124V, Cathode 2.5V, 13mA
V4 Anode 57V, Cathode 0.25mA
V5 Anode 248V, Screen 124V, Cathode 8.2V, 41mA
V6 Anode 233V ac, Cathode 259V
Hope that helps
Yes i like to about winding rf oscillator coils is there a right hand rule of thumb.I measured the the length of wire and also want to know do you have to use litz wire.
I'm not quite sure I fully understand your question, but if you have a coil that was made using Litz wire then it is certainly necessary to get a high Q factor. No one would use litz wire if it wasn't needed
I have a question. I noticed on the schematic a valve, V2, that is drawn with a diagonal arrow through it. I'm in the United States and I have never seen this particular symbol. Would you please explain this symbol? FYI, I am retired Navy and I have been working in electronics since 1966.
Yes. Good question. It means it a variable mu valve. Ok so what does that mean ?. It means you can vary the gain of the valve (gain being mutual conductance, that's anode current/grid volts) by changing the bias on the grid. This is how the AGC works
@@tonydurrant Thanks for the answer. Makes sense.
Wouldn't it have been an idea to use a fuse before OR after the transformer in video 2 ???
as a kind of safety for the transformer I mean!
Healthy and Friendly Greetings from the Netherlands!
Rob
Greeting back to the Netherlands Rob. Any extra safety feature is a good idea but low value fuses are not something I have in my shed !!. Having said that I know you can get 50mA fuses. This was really the point of trying it with a 100 ohm resistor first. If there was a high current flowing it would just burn out the resistor, a bit like a fuse, but I accept a fuse would fail quicker so you could argue that it would provide greater protection
@@tonydurrant
It might have been a good idea back then,
but yes you have already closed the case of course I understand!
maybe for next time.
thought it was brave, that rewinding of that transformer!
Just about the video:
Well done, what will become the next topic? ;-) ..... the 3D printer? ( also nice! )
greetings again from the Rotterdam area!
Rob