How to safely test the output tube - Tube Radio Restoration Back to Basics part 5

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Finalising the output audio stage lets us test this part of the radio. I also look at an LTSpice simulation of the basic tone controls. Powering it up safely comes next.
I hope you enjoy the series, and invite you to comment.
🎥 Other videos in this series:
■ Back to Basics 1 - Tube Radio Anatomy: • The Parts That Make Up...
■ Back to Basics 2 - Tube Radio Anatomy: • Checking the Power Sup...
■ Back to Basics 3 - Follow the B+: • How to Check the B+ Sa...
■ Back to Basics 4 - Testing the power output: • How To Check the Power...
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26 апр 2024

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Комментарии : 54

@DavidSmith-zx7wz Месяц назад

I have very much enjoyed your series on Restoration Basics! Thanks again.

@electronicsoldandnew Месяц назад

👍

@timflynn3218 Месяц назад

Great series here Manuel. The devil is in the details, and you are showing the details everyone needs to know. It's easy to forget that not everyone knows the things you know and assumptions start to get made. Electricity is one of those things that is very unforgiving if a mistake is made. There is nothing wrong with taking protective measure to save your scope!

@electronicsoldandnew Месяц назад

👍

@darrenbird2526 Месяц назад

Thanks again for this series, very educational! Cheers, Darren

@electronicsoldandnew Месяц назад

👍

@ruijorgecocas 2 месяца назад

This is the best RU-vid channel in this area, congratulations.👍

@electronicsoldandnew 2 месяца назад

Muito obrigado Rui … and it’s also based in Madeira 😊

@ruijorgecocas 2 месяца назад

You don't have to be grateful, it's true for me he has been a teacher in the technical area, As for living here, yes he lives in Funchal, I also know that he is a fellow countryman of ours who lives in Caniço. Congratulations once again, I will continue to follow your videos because I really like vintage appliances Compliments.

@maartenschapendonk6345 2 месяца назад

getting smarter every week ;-) Thank you for taking this time to explain so much

@electronicsoldandnew 2 месяца назад

Pleasure

@tubeDude48 2 месяца назад

👍👍👍 EABC80 sure is one-of-a-kind...a real odd-ball.

@electronicsoldandnew 2 месяца назад

👍

@paulperano9236 2 месяца назад

Well done Manuel, thanks.

@electronicsoldandnew 2 месяца назад

👍

@fotoralf 2 месяца назад

Having a look at the frequency response curves around minute 14:00, it becomes clear why this circuit is known in German as a 'Kuhschwanzentzerrer', a cow tail equaliser. 🙂

@JonRig 2 месяца назад

OK, the bass button is the pickup. The actual bass button is on those top buttons along with the other tone shaping stuff speech etc. The order of those buttons on the lower section is Aus, TA, L, M, K UKW. You would need to plug in those tone shaping buttons to do that test!!🙂Now it makes sense!!!!

@electronicsoldandnew 2 месяца назад

👍

@EJP286CRSKW 2 месяца назад

The shunt capacitor between the two resistors in the triode plate circuit isn't just there for filtering. It provides an AC ground so that the plate AC load consists of only the lower resistor. Otherwise it consists of _both_ resistors. This is its main purpose. The extra filtering is a bonus.

@electronicsoldandnew 2 месяца назад

I guess you could look at it that way. True. However, every stabilised supply point is a good AC ground, which means that the same effect could be achieved by simply using one 220k resistor instead of two. The plate voltage would be higher, however, but the stage gain would be the same.

@EJP286CRSKW 2 месяца назад

@@electronicsoldandnew But then you have both plates powered off the same AC node, which is a recipe for instability. There isn't another way to look at it.

@electronicsoldandnew 2 месяца назад

I think the idea was to create an AC ground path (for high frequencies) one step (resistor) away from the B2+ supply, hence avoiding the possibility of HF getting to that supply line. I believe we’re both saying the same thing. It’s a path for ripple of any frequency (including HF), which is why I call it a filter.

@EJP286CRSKW 2 месяца назад

@@electronicsoldandnew The idea is to create an AC ground node so that the plate resistor is the only AC load. Everything else is a beneficial side-effect.

@HyyskanPolttaja 2 месяца назад

"High voltage can kill you -- so let's hit it!" 😁

@electronicsoldandnew 2 месяца назад

😊 you can’t live in safety forever 😊

@waynethompson8416 2 месяца назад

Let me know if I misunderstood something but when you were showing the first graph with the waveforms for the steps of the bass boost, you mentioned that the graph was the opposite of what you would expect. It occurred to me that the waveform is what would be on the Control Grid of the OUTPUT tube (valve), and being a tube it is going to invert the signal on the grid to what you would want. Am I correct with that?

@electronicsoldandnew 2 месяца назад

No, the polarity isn’t in question. It’s the relative amplitude for the frequency that will remain the same even when inverted (because all frequencies get inverted).

@xsc1000 2 месяца назад

No. Tube is just inverting the phase of the signal, but not amplitude. So what is attenuated in g1 stays attenuated on anode too.

@jackclay-ud5km 2 месяца назад

Hy, i could use a hand with my old radio, i know very little about it, im too scared to plug it to 220v the original cable isnt present, i dont even know if it work as is. It an old Evernice i think. I would really like to restaure it to it former glory... any pointers would be great... thanks.

@electronicsoldandnew 2 месяца назад

I would suggest you do a lot of watching others at work, and perhaps get someone with some experience to repair yours. It’s dangerous to tackle a radio repair knowing very little .

@BobAndersson 2 месяца назад

Hmmm. If n1/n2 and c3/c2 (FM and BASS on your schematic) are both closed then any signal trying to pass through C182 is being "shorted" directly to the B2+ supply isn't it? So the tweeters are only active if n1/n2 or c3/c2 (or both) are open circuit. You'd expect the tweeters to be in circuit when FM is being received. It seems that they also enable the tweeters if Bass is selected when FM is inactive? I've had a long day so if I'm talking rubbish please excuse me. 🤣 P.S. Edited twice. Yes I'm confused as well!

@electronicsoldandnew 2 месяца назад

My brain went round and round looking at the logic of that selector, so I know what you mean.

@xsc1000 2 месяца назад

Yes, you are right. Tweeters are active only when FM or Phono/AUX (no Bass) is on. All other combinations put tweeters to B++ that is AC grounded. Then the 2000pF capacitor is effectivly connected from anode to ground, so it cuts off high frequencies on AM band and stabilize the output.

@electronicsoldandnew 2 месяца назад

👍

@danielsaturnino5715 2 месяца назад

Nice one. Update on my Philips, I got the FM back. Its just so low that I couldnt hear it 😅. Now I need to to figure out how to align it without a sinal generator...

@electronicsoldandnew 2 месяца назад

Use a strong local station

@danielsaturnino5715 2 месяца назад

I will give it a try :) One has to start somewhere...

@electronicsoldandnew 2 месяца назад

👍 a local station near the middle of the band can be used to do the IF alignment. If you have two known stations near each end of the band, and you know their exact frequency, you can do the RF alignment too.

@mackfisher4487 2 месяца назад

Question Has anyone run a frequency response curve test on electrostatic speakers? Listening to a known piece of music on a phonograph using one of the German radios with electrostatic speakers, how well does it compare to newer Tweeter designs, This being totally subjective.

@electronicsoldandnew 2 месяца назад

I haven’t seen one, but sure would be interesting. However, I think it needs to de an actual acoustic test with a measuring microphone etc, as simply testing the signal with a scope won’t really give a true representation.

@fotoralf 2 месяца назад

The trouble with those electrostatic tweeters is that 95% of them don't work anymore, because the insulation has failed.

@electronicsoldandnew 2 месяца назад

True, but quite easily repairable. We’ll see how these are.

@JonRig 2 месяца назад

I think that Bass button is the AUS and the AUS is the Bass. It has to be! Surely!! 🤔 (but it's getting power so what i just said does not make sense either!!!)

@electronicsoldandnew 2 месяца назад

AUS, TA, L, M, K, UKW 😊

@JonRig 2 месяца назад

That bass button makes no sense. If that bass button only operates on it's own then what is the input? It looks like it is popping all the input buttons up so there is no input (AM, FM or Pickup). It needs to be an on/off indepedent toggle, surely? Othewise all it is doing is muting all inputs! That aside, it makes sense that the electrostatics would kick in for FM and I can see the logic to kill those on AM (lower quality sound) but it's all a bit weird because why would you not want the electrostatics on the external input. And if that base is popping all inputs up then it's a mute button. Very strange!!

@robturner3065 2 месяца назад

I think it's in parallel with the FM button not series. It's just shunting the tone correction

@JonRig 2 месяца назад

C1/C2 on the schematic is on the pickup button (not the bass). N1/N2 is the FM button but, as you say, those have to be in parallel for them to enage separately (as they appear to be doing in the video). I think the schematic is misleading and the bass button in the video is actually the pickup button!! That would then explain it. 🙂

@electronicsoldandnew 2 месяца назад

Looking closely at the shattered dial glass I realise that I misread the button designations: it’s actually AUS, TA, LW, MW, SW and FM 😊 Now it makes sense 😊 The tweeter frequencies are shorted to the supply in all but the TA and FM selections. Now it makes sense 🤦

@electronicsoldandnew 2 месяца назад

No, my mistake. Looking closely at the shattered dial glass I realise that I misread the button designations: it’s actually AUS, TA, LW, MW, SW and FM 😊 Now it makes sense 😊 The tweeter frequencies are shorted to the supply in all but the TA and FM selections. Now it makes sense 🤦

@JonRig 2 месяца назад

@@electronicsoldandnew That was a fun misreading of the buttons. It got us all thinking!!! 😂