Old caps need to be replaced, as well as selenium rectifier? Loewe-Opta Truxa 1701W pt.2
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- Опубликовано: 2 окт 2024
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The first step in restoring this Loewe-Opta Truxa 1701W requires looking closely at the power supply and making any necessary repairs to this section, prior to moving on to other stages of the circuit. The usual problems of old filter caps was sorted out, but here I also decided to replace the selenium rectifier with silicon diodes.
Next comes the audio stage, but I decided to do a full re-cap, replacing all the old paper capacitors with good quality foils caps, just to avoid problems with leaky caps on the radio.
Does it work? Well, see the video for yourself and find out.
Enjoy.
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Happy to see that you have new frames so you don't have the big ones to this small radios. Thanks for great videos.
Pleasure
Manuel, I'm looking forward to your inner Dave Tipton cabinet refinishing. I hope I'm not causing a jinx, enjoyed this episode.
No jinx at all 😊 maybe the woodworking Gods will smile on me
This is a fascinating problem you have with the FM reception. It's had my brain whirring in terms of the various things it could be. I am looking forward to seeing your next update!! Great work as always!!
Thanks 👍
Carlson also shows the reason why paper CAPs should be in the correct orientation, especially in tube gear. But many scoff at that. They are wrong!
👍I test the orientation on all my caps just before fitting them, as a matter of course.
@@electronicsoldandnew - Same here! 👌
Whats method do you use to determine that caps orientation?
@@Kemi0692 - Either build the one Mr Carlson's Lab describes, or the simplest trick is to connect across an Oscilloscope leads, holding the CAP in front of the scope, and see which way the scope shows the lowest peak. A number of YT's shows how to do this.
👍
Quite a conundrum with the FM but who doesn't like a bit of troubleshooting. Is that a new stand Manuel? it looks pretty flash. Don't tell me I went to sleep during one of your excellent videos 🤔
😊 yes, it is a new stand. The last one was too wobbly 😊
Like your approach very much. A lot of skill and experience shows 😊
Thank you
I wonder why there aren't direct replacements with a 12V heater and a B+ of 12V so the PSU could be replaced with a socket and the radio run of a computer PSU giving 12V and a special transformer used to drive the speaker, it would mean no danger of electrocution.
Nice job !
Thanks
Parabéns Manoel muito top …
Obrigado
Your rectifier replacement board provides for resistors for the reduced voltage drop. Was it not necessary for this project or will you add external resistors if necessary?
I’ll add externals if necessary. Didn’t want to place resistors inside the tube as it would heat up.
Hi Manuel, in your first video about this lame (Teal) duck at about 24 minutes you pointed out some loose wire on a coil under the ECC85. If there is a disconnection could the resonance of the circuit be altered so as to both shift the top end frequency and damp the lower frequencies?
You can do that, and I often do just that to extend the top range a little bit, as my favourite station is at 101.6MHz.
Good progress. Curious as to whether you got more oomph after restuffing the bridge. Electrons leaking through a resistor, is my kind of circuit description. Looking forward to the cabinet episode, not even a glasslinger Ajax, scrubbing brush and wire wheel method, will shift that blue.
😊 probably a heat gun and scraper 😊
Actually 197 V is just a hair less than the 220 V +/-10% that the radio was designed for so I'd expect it to work more or less as intended even at that voltage.
👍
The green is awful 😖
Do you put in a dropping resistor when changing the selenium rectifier to the diodes? I know when I restore the old radios and put in solid state rectifiers I put in a B+ dropping resistor, and make it larger than the calculated value as to keep the B+ proper. That is because the original line voltages here were 110V and now are 120-125 V. In the AA5 radios, if they have a 35L6 output I use a 50L6 (Or up the 25Z5 to a 35Z5) to keep the filament voltages managed. As a note: If you put in rectifier diodes, did you know that the entire lead length is calculated as part of the "heat sinking" for the full current dissipation of the diode? That came from the ECG/ Sylvania engineering department back in the late 70's when diodes kept failing in an organ amp. Leaving full length leads solved the problem, as the rectifiers were running very close to the full rated current. of 1A, IIRC.
Typically I put a loop in my leads to shorten them and still allow full heat dissipation. (I had noticed the loop in many of the rectifier diodes leads used in the Japanese TV sets and some stereo equipment. had always wondered why).
I’ll fit the dropping resistor at the end when I can see exactly how much current is being drawn. The option of fitting the resistor inside the tube is not a good one to prevent heating. The diodes operate at about 10% of their rated current so should not be a problem here, but your point is a good one.
Was someone in a fit of rage when someone ripped out some of the wires of the radio.
😊
Resistors age alot due to how the radio has been stored. In a garage with much umidity is devestating to electronics.
True
Great video again. When you replace the paper capacitors, do you care about having the outer foil layer on the ground side?
Yes. I test them individually on the scope. The schematic actually gives the “polarity” which is unusual.
Always very good content
Thank you
No need to put a resistor in series with the silicon rectification since it should see a considerable additional amount of voltage? I am about to do this same repair on an old 62 turntable and trying to figure out what is truly needed.
I’ll see later if the resistor is needed.
"buggar all reception" very old english expression esp in Australia .. laughing out loud
And in South Africa too 😊 that’s where my use of the expression comes from.
Fascinating. A lot of useful points. I'm a late beginner I'm afraid, but hopefully a fast learner. Thanks. Jaime
👍
Very good 👍
Thanks
Sodering technique, I was taught that you do not rely upon the solder as a connection but rather a mechanical connection such as making a loop around the terminal and closing it and then soldering thus the equipment in my case commercial could withstand the vibration of a mobile vehicle. However It's more difficult to replace components. 14:51
That is the proper way to do it, and some of these radios have been done like that. The problem is removing the components without damaging the solder tag 😊 I normally fit it through the hole and bend it back 180 degrees, then solder. This is a compromise but makes life easier if I ever need to replace the same part again.
Life is a compromise, except in the Congress of the United States@@electronicsoldandnew
😊
Nice video. As my late father would say, it looks like someone may have 'twit fiddled' with the IF or RF section. 😀
Agreed. Lots of twits around 😊