Rebuilt the amp, set the bias and heated my coffee on the Siera 5521 / Philips 22RH521 - Part 3
ฝัง
- เผยแพร่เมื่อ 15 ก.พ. 2024
- Next step in the restoration was the rebuild of the main amplifier section and that took a bit more effort than expected. I also go over setting the idle current in this video and that's something special. This amp is biased really hot...
WARNING: Do not attempt to repair electronic equipment if you don't know what you're doing.
If you want go get access to more behind the scenes content, consider joining Club RTR:
www.youtube.com/@retro_tech/join
If you enjoy my content, consider buying me a coffee:
www.buymeacoffee.com/retrotech
Music by Karl Casey @ White Bat Audio
Noise video footage by Milan Matos
Electrocution logo by Nesdon Booth, The Noun Project - วิทยาศาสตร์และเทคโนโลยี
The output PCB have a service position that is very handy for changing components and even calibrate the BIAS. Between the upper part of the heat sinks and the upper part of the chassis there is a slot where the PCB stay fixed vertically and you have stable and perfect access to the output circuity...
Seriously! Why didn't I know this earlier?! Thanks for mentioning.
very interesting today 😊
Thanks, Andy!
Hi Kristof. I guess it must be pretty common for dual gang potentiometers to not track exactly together. I doubt that you would hear it in practice. I guess it would slightly affect stereo imaging but you'd never know. And this one will keep your tropical plants alive. Ort just keep it running in your workshop and you won't have to pay for heating!
Yes I guess... but it's quite difficult to estimate if the unbalance is normal or not. I would have to have seen the amp when it was new. 🙂
And yes, I can use the heating in my workshop. It was 9 degrees in there today. 😄
Video nog niet bekeken, maar al een duim omhoog omdat ik al jou video's heb gezien ;-)
🙂
Goed bezig en duidelijke uitleg..heb zelf de Philips 720 met radio maar de rest is het zelfde..bedankt.
Bedankt!
Just subscribed (thought I was already); enjoyed the work AND the theory talk on amp class/quiescent current setting, and that clever/strange stereo difference signal to the rear speakers.
Thanks a lot!
As long as the two signals are in phase they will not cancel each other out. You only put a resistor in series to ground for the two "rear" speakers making them lower in volum.
Remember, your not joining the signals together, it's the two grounds you join.
I'm not convinced that's correct. Since the 2 negative sides of the speakers are tied together and the resistor adds an increased impedance to ground, there would still be at least some interference. Looks like a variant of the Hafler circuit to me. Well, I guess we'll find out if I ever manage to set it up.
Thanks for the video. Definitely try out the 4 speaker system. Some manufacturers called it 'abiophonic' or something, and it was in vogue during the seventies. The rear speakers do not have to be HiFi ones. Just about any speaker capable of reproducing midrange will do. The more sensitive ones, the better. Play some classical music and enjoy the wide soundstage this poor man's quadrophonic system provides!
Well, I might need to try it then. Not really sure yet where I could set it up here. I have to think about it.
I've never watched an output transistor fail! It all makes sense when you saw low gain and such low bias current at what was probably the factory bias setting.
I shared this video with my brothers. One has a receiver that uses quasi-complementary outputs and we were discussing this topic last week. I think your exlplanation was excellent. Thanks for that.
Regarding the volume control, it would be interesting to measure the resistance for each channel at different volume settings and compare. Could it be a dirty pot that might clean up with some Deoxit F5?
I hadn't either. At least not while monitoring the outputs on the scope.
I've checked the volume control and there doesn't seem to be much wrong with it. I already cleaned it. So it must be in the circuit.
I have the same problem with a bit of channel difference and i think its the pots and i can't change them, because these pots are some special type with integrated motor (volume and balance is motorized). Wouldnt be a huge problem, but the "LED driven Watt-Meter" (which is IC-controlled and has no pots for calibration) is also 1 LED off :D Bummer.
Hi, I really love watching your videos. Just a question, I've got a Sony ICf 320 which needs restoration, possible will you like to restore for me and from the UK?
Thanks! Sorry, but I don't do assignments. I've not even got enough time for my own projects. 🙂
All of the lokfit transistors are suspect mainly from noise and low gain.
Thanks for the heads up!
Die lampjes zijn zo te zien ouderwetse fietsachterlichtjes. Elke fietsenmaker zou die moeten hebben.
Zou kunnen maar ik denk dat die over het algemeen 100mA zijn, niet 50mA.
Leuke video, maar nog steeds heb je de print die je steeds losmaakt, niet écht in de servicestand gezet, zoals getoond in de service manual.
Dat heb ik ondertussen ook door. Spijtig genoeg had ik dat nog niet door tijdens het maken van deze video. 🙂