I find it hard to believe that polyester capacitors, which are spiral-wound film types, would be better for RF bypassing than ceramic capacitors, which have two small plates and a solid dielectric. The inductance on ceramic capacitors has to be way lower (which has to be way better, right?), and that's why they're used in RF applications. Think about all the TV tuners you took apart. Did they have polyester capacitors? No, they all had ceramic capacitors.

This seems to be an error in the errata, at least to me! Maybe they used polyesters because they ran out of ceramics, and forgot to replace them when they came in. They found that it still worked, and so thought it best to get users to do the same. But it seems better to use the proper capacitors, regardless of what was in the prototype.

An interesting comment Vandos.

Some time back I purchased 50V assorted cheap ceramics and found 7 out of 10 microphonic. Tap them and they sing, grunt, scratch and probably recite poetry. Bloody useless for my high gain low noise preamp.

So perhaps there is no errata----rather poor performance from modern ceramics, and the author decided to stay on the safe side? Just a thought.

Oh, by the way. I had several boxes of "old ceramics" left to me recently from a departed friend. I promised his widow they will go to whovever needs them for restoring vintage gear.

I will never use them all in my life time, so if anyone is looking for a particular value let me know. They are free, but NOT for commercial purposes please, genuine restorers/hobbyists only.

Heaps of mica caps as well, but I read somewhere on this forum that they "turn into water"???? What the hell does that mean?

Is there a chemical process involved here? Any thoughts anyone?

Cheers.

I would be cautious not so much with ceramic, but with disc type ceramics especially of a large diameter, I have had to remove them, not so much for microphonics at audio frequency but more so for them acting like butterfly antenna, being inductive and dragging in rubbish.

Some time back I purchased 50V assorted cheap ceramics and found 7 out of 10 microphonic.

Yes, ceramics are known to be affected by piezo pressure both ways. They can also "sing":

https://product.tdk.com/en/contact/faq/31_singing_capacitors_piezoelectric_effect.pdf

Yes I got caught out with singing capacitors in one of my contemporary SMD designs.

DC - DC converter, taking +9 volts to -9 volts for a row of RS232 drivers. The two 2.2μF charge pump caps are ceramic in 1210 package.

I can't hear it but all the younger people (they are all younger than me!) can. Drives them nuts!

Spec for chip said it should be 25kHz, it actually runs around 19kHz. I can't hear 19kHz any more.

Fix - run the converter at nominal 50kHz and put a cut in the PCB around the caps so the PCB doesn't act like a sounding board.
Solved!

You should research the characteristics of different ceramic caps, you might get some surprises. They do strange things.

I found that some polyester capacitors can be acoustically active, making faint clicking sounds. This was in a battery charger switching nearly 400 V, listening for arcing over the printed circuit board. These were pretty large, 2μF 275 VAC, perhaps 40 x 30 x 10 mm.

I'm also aware that some surface mount ceramic capacitors have awful reaction to their DC voltage, and can barely be called a capacitor at all. Still good for power supply bypassing. But I would have thought that a typical low value (<= 0.01 uF) RF ceramic capacitor would be fine. But thanks for the warning.

I didn't think I could proceed with this project until I had the metalwork specially made, but now Evatco have a Hammond aluminium chassis (type 1444-16, 10 x 6 x 2 inches) that's exactly the right size. The front panel's easy, I can do that myself. More action when I get over the next comic art deadline.

I'm interested in this receiver, as I commenced a build many years ago -it remains today, an uncompleted project which I may resurrect.
Any further comments regarding the construction and performance?