Howdy do all,
I’ve acquired a BC-224-D along with its original operators guide and notes made by the previous owner. I purchased it as a personal goal to learn more about analogue and tube circuits this year (I’m well aware of the hazards this radio presents while servicing). I’m coming to this community for advice, to also help me learn some more, and with any luck I’ll be able to get this thing working again with some knowledge gaps filled.
Electrically, it looks very complete. No missing tubes, and very clean on the inside (besides some zinc whiskers here and there). None of the components look burned, and all the resistors tested well within tolerance. It doesn’t appear to be serviced more than the previous owner’s work, who was a HAM (queue dramatic music). As everyone knows, this means it comes with modifications. Fortunately, he seemed to document in the manual most to everything he has done. Other than the resistors being checked out, I’ve been able to identify the ground, 300v and 14-16v lines.
Before applying power, I clamped my continuity tester onto ground and set the radio to both ON positions only to find that both seem to indicate a short somewhere in the system. I’ve been trying to find the source of the short, but it’s been hard to pinpoint. My assumption is that it is the capacitors, which leads me to the next observation to share. Best I can tell, there are two main types of caps: sealed oil and sealed mica. The sealed oil caps have their values and ratings on them whereas the mica ones are enclosed in red ceramic housings with three dots and such on the outside. I haven’t seen this before, and am learning a new thing. There also seems to be some cap’s that have 3 or 4 pins.
Never the less, should I assume/presume all the caps in this are bad and need replacing regardless of them being mica/oil? I haven’t detected a short across their pins, but then again, I’m not the expert in this domain.
Thank you for any insight, suggestions and thoughts you may have as I start this project. If asked, I can upload pictures of the manual and radio elsewhere and link it here.
Hi, first of all welcome to the forum. I am not familiar with the device and I see that you did not mention what a BC-224-D actually is but anyway a quick search online reveals that is an old radio and a really neat looking one I might add. So, to help with your puzzling decisions in regards to capacitors and providing that you are an active member of Mr. Carlson on Patreon site then on his list of videos there are 2 videos in particular I highly recommend that you watch and they should clear the fog in regards to the capacitor choice and designation of each. So, if you go to video 184 he presents a huge variety of caps (you name it) and each one explained what it is for, how it behaves in time, longevity etc. and after that video 24 presents and extremely useful list of what he calls a verified parts and strongly recommended especially when it comes to old vacuum tube equipment such as the one you just acquired. Now, just as a side note, being a radio you have to keep in mind that not all capacitors are to be touched or attempted to be changed. Certain ones might be hand picked at the factory (the so called graded capacitors) especially in the tuned IF cans or oscillators and if you are to change those then you will need a proper equipment to try realigning the IF chain of that radio er… but MCL has some videos explaining this matter on Patreon as well as on YouTube it just takes a bit of time to find the right ones etc. PS: the capacitors with 3 or 4 pins, if they have an aluminum (usually cylindrical type body) they are almost certainly electrolitycs serving as power rail filtering/smoothing. Good luck.