not good, not good 🙂 , test the Siemens capacitors before you replace it, they are really good.
I got the question from papaudioparts what is the form and dimensions of the pointer lamp. Mine is not original it was replaced with normal LED as whole 6V AC line was modified to DC by one of the previous owners. Could one of you please send me a picture and dimensions of this pointer lamp?
They also asked if I would like to replace 12V/3W lamp next to the fuse with LED. I am not sure that this lamp is there to actually enlighten something it looks to me that it has other purpose like an indicator of current or sort of curent limiter/fuse. In that case there would be no point in replacing it with LED. What do you think?
Hello, you should not replace the 12v3W lamp by LED. It protects the transistor ! The current is so low that it works forever ( almost ) . The pointer max dimension is 3x7mm. If it's smaller no problem, I use +/- 2x5mm . It should have the long 'legs' min 20mm
The pointer is a "grain of wheat" lamp. I would use just a normal bulb. Well, I don't like LEDs.
LEDs create RF noise. I heard somewhere someone remodifying something that had been LEDified back to incandescent bulbs because the LEDs created noise. Not sure about this though.
I guess the advantage would be less heat, less current draw on the transformer and maybe longer life.
The bulb in the pre amp supply, by the fuse, you can not replace it with a LED, just as Pawel said, it is a sort of current limiter. Don't replace it, they last like forever. I also have this prejudice that old times lamps are better quality that the lamps that are produced today.
I have the strong LED lamp at my desk and I can hear it in the loudspeakers when the radio is opened 🙂
Thanks guys, I ordered T10 LEDs and pointer incadecent. If LEDs turn out to be noisy I can always put back incadescent.
In the meantime I am still fighting with the amp. It turns out I still have huge intermittent output noise. I replaced diffential pair transistor but that didn't solve it. Transistor oxidation looks the same like on Pawel's picture.
Next I will isolate power amp from the preamp to eliminate possibility of preamp problems and look further. I'll probably replace all other capacitors(electrolitics already replaced) just in case.
It's been a while since my last update. The problem with crazy signal on one channel should be solved now. After trying different things what probably solved the problem was just cleaning the solder joints. Once I could actually see the sparking between two transistor pins on the back side of the board where solder joints are.
I will have to do some more testing though. Yesterday I quickly tried out the step response. I was expecting a faster response(stabilization) after the step. Did somebody try ot or could somebody try the step response? As I replaced differential pair and some other transistors with non-original parts maybe that is the reason for a slower response. On the picture is 1 kHz square wave.