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Vintage Radio (domestic) Domestic vintage radio (wireless) receivers only. |
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23rd Jan 2019, 7:42 pm | #21 |
Dekatron
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Re: Restoration novice part 2
Something else to read, a book full of useful information, it’s a 25MB download, you can choose from several different formats, I have the PDF version.
https://archive.org/details/RadioServicingPocketBook
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23rd Jan 2019, 8:50 pm | #22 |
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Re: Restoration novice part 2
To be fair I have never had any dealings with valves, other than those in the final output of my Yaesu FT 101, and Harry Leeming took care of those! There used to be a Mullard factory in Haydock where I was born, long gone now. Yes there used to be valves in TVs I owned but I never messed with them especially after one of my uncles who was an ex RAF wireless operator/technician was hurled across the room after he touched the wrong thing inside a tv he was repairing.
A good friend of mine was a tv technician for many years so if I had any problems with any of my amateur gear it was dispatched to him for repair. Unfortunately he is not in the best of health these days. He does have quite a stock of old (and new unused) tv valves but he is unsure what to do with them. As for me I am at the bottom of a learning curve with valve sets, treading very slowly and carefully. The last time I used ohms law/ac theory was well over 45 years ago so please excuse the basic questions. Once again many thanks for all the help from all the people on the forum. It is much appreciated. Cheers Lynton |
23rd Jan 2019, 10:02 pm | #23 |
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Re: Restoration novice part 2
Hi Lynton,
There’s no entry level for this forum; I’m here, and so are many others, partly for community and everyone is welcome. So please don’t feel you need to justify any questions you may have. I hope there’s a way forward for your set; I’m sure there can be! And ‘slowly and carefully’ sounds wise. I hope you also enjoy the journey along the way!
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23rd Jan 2019, 10:18 pm | #24 | |
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Re: Restoration novice part 2
Quote:
Lynton
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23rd Jan 2019, 10:46 pm | #25 |
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Re: Restoration novice part 2
That’s my understanding Lynton, editor of many of the Newnes Radio &TV servicing books as well, G3VA I think his call sign.
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23rd Jan 2019, 10:51 pm | #26 |
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Re: Restoration novice part 2
I think his article was called ‘Technical topics’. Used to enjoy reading it even if I didn’t fully understand it!
Lynton
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26th Jan 2019, 5:59 pm | #27 |
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Re: Restoration novice part 2
Spent a little more time on the radio over the last day or two. Cleaned the topside of the circuit board and replaced the Hunts and Plessey capacitors.
I’m a bit confused with some of the components however. To my eye there are a number of old fashioned resistors (dog bone) but the circuit diagram shows that some are capacitors? My question is how do you tell the difference when they appear the same? The only difference I could see was the body colour of the components. Some are grey and some brownish? Second question is how closely do you have to match the value when replacing resistors? Several need changing due to heat damage and I can match the values by using two resistors in series but how accurate do you need to be? Lynton
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27th Jan 2019, 12:46 am | #28 |
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Re: Restoration novice part 2
Resistors.
If you know the tolerance, change them if they deviate too much. It is easier to put two resistors in parallel. The originals are often high in value and can be dropped to correct level without touching the circuit board. |
27th Jan 2019, 1:32 am | #29 |
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Re: Restoration novice part 2
To check if they are a resistor or a capacitor in an original radio trace what they are connected to in the set and check that with the circuit. You will get used to the different items by experience.
If the radio as been "got at" then this may not be true. The markings on the component should also give some clues.
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27th Jan 2019, 7:30 pm | #30 |
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Re: Restoration novice part 2
From what I can tell by looking at the photo on the other thread (see link), and on the assumption that your PCB is identical, I would say that the light (grey?) dogbone parts with the open ends are tubular capacitors, but the darker beige/brown parts with the capped closed ends are resistors. I can't be 100% sure from the photo, but the colour bands on the capacitors appear to be short stripes across the top of the component, whereas the ones on the resistors appear to run all the way around the body. Having said that, this may not be true or consistent across all of the parts in the set so I would also recommend what has already been said, namely to trace the circuit and compare with the circuit diagram.
https://www.vintage-radio.net/forum/...5&d=1295469652 If, after consulting the circuit diagram you are still in doubt, you could always post a pic here and I'm sure someone will be able to help identify the part for you. |
27th Jan 2019, 9:09 pm | #31 | |
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Re: Restoration novice part 2
Quote:
If the ends are hollow they are capacitors. If the ends are flat and solid they are resistors. If they have numbers and or letters for identification rather than colour bands it is usually possible to decipher the the component that way. WaveyDipole's description is correct for the picture posted. |
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28th Jan 2019, 10:52 pm | #32 |
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Re: Restoration novice part 2
When I replaced capacitors the other day two were electrolytic. I changed in the same positions with respect to polarity. On the manufacturers circuit diagram it shows C50 a 4uf capacitor with the positive side connected to ground? Is this a mistake on the diagram or does it really fit this way?
Lynton
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28th Jan 2019, 11:05 pm | #33 |
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Re: Restoration novice part 2
The schematic is correct, +ve to HT-ve (ground/chassis)
Lawrence. |
28th Jan 2019, 11:34 pm | #34 |
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Re: Restoration novice part 2
The capacitor Trader C52 + to ground
R&TV C50 + to ground. This is the capacitor in the Foster Seeley FM detector and is used to reduce the effects of AM in the signal. |
28th Jan 2019, 11:40 pm | #35 |
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Re: Restoration novice part 2
Extremely simplistic view but look at it as the diode it is with AC on its cathode pin 3 with the output on its anode pin 2 conducting on the negative half cycle to charge up C50 with a negative voltage.
No doubt someone can give a full explanation.
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29th Jan 2019, 3:00 am | #36 | |
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Re: Restoration novice part 2
Quote:
Lynton
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29th Jan 2019, 3:04 am | #37 |
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Re: Restoration novice part 2
Excellent answers. More knowledge gained. Many thanks gentlemen.
Lynton
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29th Jan 2019, 11:35 am | #38 |
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Re: Restoration novice part 2
No problem, by the way the FM detector in your receiver is a Ratio Detector as opposed to a Foster-Seeley Detector.
Also interesting to note the AF amplification arrangement on FM as opposed to AM.... Lawrence. |
31st Jan 2019, 6:07 pm | #39 |
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Re: Restoration novice part 2
Big Bang test today! Connected the set via the isolation transformer and the lamp limiter. Switched on and stood back. The result was an almost imperceptible buzz from the speaker and after connecting the G5RV via some croc clips the set burst into life! Works on all three bands. To say I was chuffed was an understatement.
Left the set running while I rigged up a connection to an external FM dipole (my shed is all metal) and I do need a decent long wire, but the set worked fine. It does produce a fair amount of heat, but nothing showed any signs of over temperature. I suppose the more experienced members would now start checking voltages to see if anything else is amiss, but I’m not experienced enough at this stage to do this. I’m just thrilled that I brought a dead set back to life. Finally a comment for Nuvistor- Yes the indicator lamps are 12 volt! Thanks to everyone who helped with their comments and suggestions. Cabinet needs painting but that will have to wait for the warmer weather. Lynton
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31st Jan 2019, 6:19 pm | #40 |
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Re: Restoration novice part 2
Well done Lynton, so what’s next?
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