I pulled the old trimmers (R110, R134, R210, R234) and checked them.  They initially measured a higher ohm value across their contacts than what should be valid for 100 ohm variable resistors.  If I moved the pots back and forth the measured ohm values looked much better.  So I take that as meaning they are oxidized.  Since I have four new ones in Dillen's kit and intended on changing them, I went ahead and swapped out the trimmers with the new ones.  I just have to remember to do the no-load current and DC offset adjustments first thing when I finish putting the receiver back together.

The 08 Module is the FM tuner board.  It takes a little more care getting out than the others so far because it has a big wire bundle going across one side (you can see that in the earlier picture of this board when it was still in the chassis).  Once out here is the front and back.

Here is the 08 Module after the recap.  I noted the one bipolar cap.  I also noted the two orange 0.47uF electrolytic caps that were not recapped.  Those weren't in the kit.  I was wondering if those are a small enough capacitance where they could be replaced by a polypropylene film capacitor?

I would leave them tbh, it is very unlikely they will be causing any issues which is why Martin won't have sent you replacements. If you want to replace then anything that isn't physically too big will be fine, but why not electros?

You were right in replacing all those trimmers in the amp, they would have been ready to cause no end of trouble!

sonavor wrote:

The Beomaster 6000 opens up really easy for maintenance. It's like opening the hood of a vehicle.  This is quite a change from the Beomaster 4000 I just finished.

How freaking cool is that?

The reason I asked about replacing the two 0.47uF electrolytic caps with polypropylene was because I had read that the poly caps don't wear out. They also usually have high voltage limits so can take a lot of punishment. Aren't the poly caps generally used in small capacitance values because they are affordable at those values?  Is the reason there are polarized electrolytic caps in the circuit because they are most cost effective for those capacitance values?  I know people talk about using certain type of electrolytics in the signal path because it affects the sound but if it were possible (cost and size availability) wouldn't it be ideal to just have polypropylene caps instead of the polarized electrolytics?  I have often Googled and searched about the use of capacitors and I don't really have a good feel about why there are electrolytic caps (especially polorized e-caps) in these circuits except for the fact that they are the types of caps that have the capacitance values needed at a reasonable cost.  Is that the case? Or is it also because of electrical characteristics provided by the electrolytic caps that are favorable to audio signals?   

I am not seriously looking at changing the way I recap my audio equipment but I was just wondering why we replace the parts with the shortest life span with the same type.

sonavor wrote:

The reason I asked about replacing the two 0.47uF electrolytic caps with polypropylene was because I had read that the poly caps don't wear out. They also usually have high voltage limits so can take a lot of punishment. Aren't the poly caps generally used in small capacitance values because they are affordable at those values?  Is the reason there are polarized electrolytic caps in the circuit because they are most cost effective for those capacitance values?

Basically you're right there. However, neither of these two particular caps are on the audio signal path, and neither of them is in a position where they could easily die prematurely (8C2 stabilizes the tuning voltage, which is essentially DC, while 8C46 filters the AFC signal coming out of the FM detector - again, rather stable and it even has a small ceramic by its side to help).

You can of course replace them, but it's not going to affect anything unless the old caps are outright faulty, which they most probably are not. Increased ESR of aging caps doesn't really matter at these positions.

Generally B&O receivers, which used electronic switching and tone controls very early compared to most other manufactures, usually have a lot of capacitors on the signal path. Above 1 µF, plastic film capacitors were physically large and quite expensive back then, and both reasons probably contribute to why B&O used so many electrolytics on the signal path - and tantalums when the space was tight.

These can be replaced and it may alter the sound audibly (sometimes even to the better...), but it takes some experience and understanding of the circuits to judge when it might be useful and when it will be just wasted time & money. I've installed MKS2 caps instead of tantalums here and there in kit that I use myself, but mostly I just use the same kind of components that were there originally. Even bog standard aluminum electrolytics have improved a lot in quality during the last 30 years. Not to mention in physical size!

Thanks for the reply Mika.  The experience and understanding of the circuits part is what I would like to get to.  Until then I play it safe and try to match what was existing.

-sonavor

Hi sonavor, great project you're working on. I'm following this closely, last week I bought a BM6000 locally. The only issue I've found so far is a slipping volume control belt. It's time to place another order with Dillen.

Thanks

John

Great, thanks.

I will be changing my belt too with one I got from Dillen.  I am almost done with the base PCB recaps.  Then I will start on the PCBs under the lid.