Advice needed on use "general purpose" film capacitor as coupling cap in a tube amplifier.

[Mr Boochie]

probably not as many as you might think. The only part in a tuner thats legitimately audio path is downstream of the detector.

Man! What are all those other disc caps for, then? Must be in the pre-amp section. Have to be in the signal path. Right?

I checked the service manual, and many were silver mica types, too. UGH! Silver mica disease! I wonder if that unit is still working? The guy I sold it to moved back East. I lost track of him since he moved.

I just remember it had a LOT of tubes. And they were all Mc-labeled, Amperex (Dutch), TFK, or Siemens-Halske-made. Really, really nice tubes.

MX 110 Service Manual.

 

[Tom Bavis]

"Ceramic" covers a wide range. Porcelain ceramic capacitors are some of the best capacitors that exist, and are the only feasible choice in many high power RF applications. But they only go up to a few thousand picofarads and are relatively expensive. NP0/COG/S1 dielectrics are very good, but also somewhat limited in value - can be a better choice than mica in many cases. And there are temperature compensating types to make circuits thermally stable. The "high K" dielectrics (Y,Z prefix) have considerable variation with temperature and applied voltage - can cause distortion with high AC voltage. And Z5U will drop to less than 50% of the marked value at rated voltage!

Silver Mica are very stable and low loss. "Silver Mica Disease" happens when exposed silver has moisture and voltage to cause silver migration across exposed insulator, creating intermittent shorts. IF transformers (even McIntosh!) were often made with capacitors made of thin mica sheets with plated silver exposed. Input and output caps on the same sheet, so there was B+ voltage across an insulating gap They haven't aged well in many cases. Dipped or plastic cased mica caps are protected from moisture and seldom give problems. My previous employer had a design rule that silver mica should not be used with DC voltage across them - so with that rule, would be fine for most feedback compensation, but not for most shelf networks (or feedback from a plate or OPT tap).

 

[Mr Boochie]

Thanks for that explanation!

My MX110 couldn't pull in distant or weak FM stations well. And keep them locked in stereo. Even with a roof Winegard antenna and a rotator.

I took it to a tech (Mike Zuccaro) in San Diego (he was the Marantz 10B expert). He told me that once these old McIntosh units start to fade, it's hard, $$$, and annoying to keep them up to spec. And I didn't want to keep driving down to SD (though it's a great place to visit).

I sold it and bought a used NAD 1600. That thing is amazing. It can pick up stations like 75-90 miles away. With an indoor wire dipole! I mean, locked in solid. No overload, no funky MPX stuff, really nice.

The sad thing, I never listen to FM anymore. Not with streaming available. Oh well, I always have it available.

 

[wdecho]

All I really know, do not remember the specific ceramic cap or specific audio component under test but a youtube guy measured distortion with a ceramic capacitor in the signal path, could be acceptable amount for many, then replaced it with a film cap, nothing special, and the distortion dropped significantly. Both capacitors were good quality ones.

Not something I would use in the signal path these days being film capacitors are much cheaper now. Years ago the designers used transformers and autotransformers instead of capacitors because capacitors were more expensive to use. The opposite now. I am sure ceramic capacitor were used much more years ago then nowadays. If I were working on an old audio device and found a ceramic capacitor in the signal path I would replace it with a film one.

I watch a lot of instructive youtube videos for entertainment rather the filth and trash blasted at us from others forms.

 

[Mr Boochie]

All I really know, do not remember the specific ceramic cap or specific audio component under test but a youtube guy measured distortion with a ceramic capacitor in the signal path, could be acceptable amount for many, then replaced it with a film cap, nothing special, and the distortion dropped significantly. Both capacitors were good quality ones.

Not something I would use in the signal path these days being film capacitors are much cheaper now. Years ago the designers used transformers and autotransformers instead of capacitors because capacitors were more expensive to use. The opposite now. I am sure ceramic capacitor were used much more years ago then nowadays. If I were working on an old audio device and found a ceramic capacitor in the signal path I would replace it with a film one.

The odd thing, I never knew how many disc caps were under the Mac's hood. I mean, a big boatload! Had to be good stock at the time. Right?

The tech said the pre-amp section tested really well, and it was one of the best-sounding pre-amps that I have ever owned. Not any of the brightness or brittleness some people associate with ceramic or silver mica disc caps. I thought the darn thing was loaded with Black Beauties, or something similar.

The FM section was always a struggle, though. Just didn't hold an alignment well. And tubes were getting really $$$.

 

[wdecho]

The odd thing, I never knew how many disc caps were under the Mac's hood. I mean, a big boatload! Had to be good stock at the time. Right?

The tech said the pre-amp section tested really well, and it was one of the best-sounding pre-amps that I have ever owned. Not any of the brightness or brittleness some people associate with ceramic or silver mica disc caps. I thought the darn thing was loaded with Black Beauties, or something similar.

The FM section was always a struggle, though. Just didn't hold an alignment well. And tubes were getting really $$$.

If there are ceramic caps in the audio chain all one can say is Mac made it work. Proof is in the pudding as the old saying goes. McIntosh is McIntosh. Some of the best engineers in the business.

 

[Mr Boochie]

If there are ceramic caps in the audio chain all one can say is Mac made it work. Proof is in the pudding as the old saying goes. McIntosh is McIntosh. Some of the best engineers in the business.

The unit DEFINITELY had the Mac House sound. That was some pre-amp. But so many tubes...

 

[wdecho]

The unit DEFINITELY had the Mac House sound. That was some pre-amp. But so many tubes...

Makes one wonder how much better it would sound if the ceramics were replaced with modern film ones. That is if they are in the signal path. I bet the numbers game would improve. I would bet there are not many if any in the signal path. It would take a schematic to tell.

 

[Mr Boochie]

Makes one wonder how much better it would sound if the ceramics were replaced with modern film ones. That is if they are in the signal path. I bet the numbers game would improve. I would bet there are not many if any in the signal path. It would take a schematic to tell.

The list.

 

[wdecho]

View attachment 3844612
The list.

Judging by the values they are not in the signal path. More than likely that is the Multiplex section of the tuner. Amazing what one small chip can replace these days.

 

[Mr Boochie]

Judging by the values they are not in the signal path. That is the Multiplex section of the tuner. Amazing what one small chip can replace these days.

Those are all the capacitors according to the Service Manual.

 

[Mr Boochie]

Sorry it took a bit to cut-and-paste and clean up the image.

The audio section of this unit has few coupling caps. Click on the image to enlarge it.

 

[Mr Boochie]

The rest of the input/audio section.

 

[wdecho]

Sorry it took a bit to cut-and-paste and clean up the image.

The audio section of this unit has few coupling caps. Click on the image to enlarge it.

Judging by the values of the coupling caps they are film ones. The ceramics appear to be in the tone controls and IF stage. Image is fuzzy and hard for me to read values. Judging by the numbers and sound must not affect the audio signal. No arguing McIntosh knows their stuff. you cannot argue with success. Back when it was built they used what they had.

 

[Mr Boochie]

Judging by the values of the coupling caps they are film ones. The ceramics appear to be in the tone controls and IF stage. Image is fuzzy and hard for me to read values. Judging by the numbers and sound must not affect the audio signal. No arguing McIntosh knows their stuff. you cannot argue with success. Back when it was built they used what they had.

Yeah. I noticed that some high-end stuff from that era did not use many coupling caps. I think they called it direct coupling. Cleaner sound, but the specs and setup of each stage were much more critical. And it depended on using the best-quality tubes of the time.

I'm almost certain the ceramic and silver mica caps used were the best available. Maybe better than the usual non-polar ones.

Believe me. I would never have done any cap swapping on that unit. It sounded so good. And Mike Zuccaro, who I trusted, never mentioned doing anything like that.

 

[knotscott]

I'm no where near as tech savvy as some of these guys, but it's been my understanding that coupling caps are more of contributor to the sound of a tube amp than just about any other cap in the circuit, so it's a good place to put your best foot forward. Ken Stevens from Convergent has been rolling his own caps since he first introduced the SL-1 preamp in the mid 80s, and now puts his Black Path caps in all his preamps and amps. I was fortunate enough to score some Gen 1 convergent caps for my Dyna/VTA amp mods, and I think they sound spectacular....since then I've scored some Gen 2 CAT caps, and am looking forward to installing those.

I'm using silver mica caps as an inline high pass filter for those amps too, and those have been excellent in that role as well.

 

[Mr Boochie]

I'm no where near as tech savvy as some of these guys, but it's been my understanding that coupling caps are more of contributor to the sound of a tube amp than just about any other cap in the circuit, so it's a good place to put your best foot forward. Ken Stevens from Convergent has been rolling his own caps since he first introduced the SL-1 preamp in the mid 80s, and now puts his Black Path caps in all his preamps and amps. I was fortunate enough to score some Gen 1 convergent caps for my Dyna/VTA amp mods, and I think they sound spectacular....since then I've scored some Gen 2 CAT caps, and am looking forward to installing those.

I'm using silver mica caps as an inline high pass filter for those amps too, and those have been excellent in that role as well.

Enjoy your rolling!

 

[wdecho]

I am still going to say you do not want to use a ceramic as a coupling cap or in the audio path. There are better alternatives these days.

 

[GrisPato]

radial lead caps and may be less convenient to use when replacing axial lead caps

Jantzen Audio Cross Caps

So, because i just looked at the schematic to put some capacitors to an order for some other amplifiers I did check lead length.
Decided to open up the AU-70 to check if they would be long enough.
Not for all of them!
So checked out the mentioned Jantzen caps, I get them here in the Netherlands, and for a very reasonable price.
Just for some of the smaller values probably have to go for the 716P for they have longer leads.
Sansui also used some bipolar electrolytic 4 uF for coupling and they are big with long leads. I think I will use some Jantzen for them to.
These 100 nF caps were labeled mp in the service manual, 2 of them look like this the other 2 are Suzuki paper oil caps. The 2 in the picture look like Mylar to me.



I am happy I asked some advice and looked inside !
Many thanks!

 

[gadget73]

Years ago the designers used transformers and autotransformers instead of capacitors because capacitors were more expensive to use.

The reason transformers were such a thing in the 20s and early 30s is the very low gain the early triodes provided. The transformers were cheaper than tubes, and when things run on batteries, having a lot of tubes wasn't a selling point because it would kill the batteries faster. Once pentodes and wall sockets existed, gain and battery life became not a problem. Out goes the lump of iron and copper, in with a capacitor and a resistor. Honestly easier to make a not-awful capacitor than it is to make a not-awful transformer too. When the source is AM radio or a 78 RPM record none of it is terribly critical but if you want full frequency range low distortion audio its a lot more difficult.

about the only time interstage transformers were still a thing after about the mid 30s were designs that ran the output tubes into grid current. No way to do that with a capacitor, so its either a driver transformer or a cathode follower.