old style green axial ceramic capasitor

[Otto Olsen]

Hi!! im a newbe here on this forum, my current project is a redraw of the schematics and pcb of this little guitar amp, this series amp was made back in the 80's, and some of the components are not in production at this time, and some are hard to find. i need to find a good replacement for some of them. this green ceramic capacitors are one of them, do anybody knows a realy good replacement type capacitor for theese,  there is the possibility for both thruhole and SMD to be used, the current design is based on the old style pcb, but it will be a 2 sided board, not single sided as the stock was, in the future there may be an all SMD board design. but this require alot work, and i want to save the sound of the amp as mutch as possible.

Best Regards Otto

[Wimberleytech]

Do you have the schematic?

[DaJMasta]

If they are ceramic capacitors, replacing them with ceramic radials (not as many axials around) would work fine, though it may look goofy.  You can go up to polyester or other film caps in axial form factors if you want, but I suspect all the important caps in the signal path are probably the electrolytics, so the ceramic ones on the board are probably decoupling or are used in places where the potential for microphonics or other issues are very low.


Just make sure they aren't inductors!  I wouldn't expect it in an amp like this, but it can be tiring looking at a board with all this sort of package, because they exist as resistors, capacitors, and inductors...

[Otto Olsen]

Hi Yes i have the old schematics for this amp, it is not so good,made in the 80's but there is a light description of theese caps, and ofcorse there is the possibillity fo follow the tracks. i wil try to add it , i am pretty mutch a beginner in electronics, i do have some skills and most of the tools , and i have an expert friend, but he is often quite busy.
in this amp there are theese caps i need to replace, those and 4 Dual N CH JFET 8pin DIP  ( J406 )   that is out of production, and i cant find new old stock eighter + i realy want parts that is in production today.

Best Regards Otto

[Otto Olsen]

 Hi !! any caps that is propper for the amp will fit, because i have not made the pcb yet, it can be changed to fit any caps in a propper way, yes im aware of the inductors, but theese are ceramic caps. but i think there is a few inductors aswell they are darker green

Best Regards Otto

[Prehistoricman]

That's quite a nice schematic actually. You get a board view too which is lovely.

You can use singular JFETs to replace the J406. The J202 looks like a close match to that JFET in terms of pinch-off voltage and gain. J201 would probably work too.

[Otto Olsen]

Ok! nice i can work those in to the drawing, no problem,  thanks!! im hoping to save the sound of this little amp, it was pretty high end fore a solid state amp, for the size maybe the best ever made, david gilmour, garry moore ,iron maden ++ all used theese at some point in time, and the garry moore amp has a new ovner, he has a few problems with it, and it's about to get it fixed in UK, i have had some contact with him. and i have one aswell and this i why i desided to redraw it it is a good solid state amp it is all tubes (valves )now and this stands out . and i have some health issue due to diabetes, so i have the time, and for now it is just fun exept drawing symbols in easy pc  because i have to make most of them . do you have an idea for the caps, there is the disc caps, but i dont like them, if the amp has rugh use they will be flat on the pcb all of them.
garry more amp is on youtube + a few other, this amp in a bigger box with a pair of 10"speakers will sounds great.

Best regards Otto

[DaJMasta]

There are also some old stock obsolete parts on ebay and whatnot, there are commercial stores that have a large catalog of obsolete parts as well, but I don't know the specifics about them in the UK.  Just searching around could find you a good old stock replacement part, but it could also find you a way overpriced one or a whole lot of nothing, depending.

If you don't find any of the parts for sale online, even just finding the datasheet can be really useful, since you can compare to current parts or replacement options (like discrete JFETs) to find a close match.

[tooki]

I mean, if you’re spinning a new board anyway, then go with SMD, but if you wanted to clone it or repair existing boards, axial ceramic caps are still made, not sure why people are saying they’re hard to get. For sure they’re not as common as radial and SMD ones, but for example, Digi-Key has 330 different models/values in stock right now (and another 120 can be special-ordered in large quantities).

[Bud]

Ceramic caps are considered to have microphonic effect. I would not use them as the schematic shows they are part of the signal path. Go to Digikey.com, type Film Capacitor in Search and have fun.

[Otto Olsen]

Hmm,, all of you guys are right in what you say, theese are old style,expensive, data on them are hard to find, maybe near impossible to get, yes they are in the signal chain, and ceramic caps are microphonic, Still this blody amplifier is some of the best solid state amp made, and they all had theese caps and they did a perfect job, and there must be a replacement for them, and i maybe know 1 guy that possebly know, or can find out about theese caps. because if i change them to a diffrent style, i may destroy the sound of it, dave on eevblog had a video on youtube covered this caps. but he has asked not to be contacted due to to many requests for help, and i respect that, and i cant find the video. BUT theese caps are in my commodore 64 aswell, and maybe Bill Herd knows a thing or to about them, this is the guy that design the commodore 128 in the 80's :-) lets see if he can be contacted, anyway thanks for the support  Best Regards Otto

[graybeard]

The green capacitors are probably plastic film capacitors.  Any equal value with an equal or higher voltage rating will work.

You should be able to find one here https://www.mouser.com/Passive-Components/Capacitors/Film-Capacitors/_/N-9x371

I was looking at this before on a tiny screen and what I thought were capacitors is just RTV.  Now I see you are circling parts that look like resistors that are marked on the schematic and BOM as ceramic capacitors.

Since many are being used in filters it would be good to get ones with a low temperature coefficient like these: https://www.mouser.com/Passive-Components/Capacitors/MLCCs/_/N-bw5rvZ1yzvvqxZscv7Zgjdhub?P=1z0z819Z1yx4avvZ1yx6r6aZ1y9hzxqZ1yx6r6b

film capacitors tend to be more stable and work well in audio circuits, so you can try these: https://www.mouser.com/Passive-Components/Capacitors/Film-Capacitors/_/N-9x371Z1yzvvqxZscv7Zgjdhub?P=1z0z819Z1z0z7l5Z1yx4avvZ1yx4avuZ1yo18i8Z1yx4attZ1yx4atu

Or these if you want to stick to axial models: https://www.mouser.com/Passive-Components/Capacitors/Film-Capacitors/_/N-9x371Z1yzvvqxZscv7Zgjdhub?P=1z0z819Z1yx4avvZ1yx4avuZ1yx4attZ1yx4atuZ1yx4hjoZ1yx4ariZ1yx4as7

[Otto Olsen]

Hi !! yes this is correct, they look like a 1/4w film resistor, but are ceramic caps, and they are damn impossible to find online! no pictures, no one for sale,no data on them, or who made them.  i have found 1 cut out picture with to types,and the look is the same on the outside, but the ceramic core is diffrent, ofcorse GK who made the amp knows, but asking them, well i think i know the outcom of that. i have been looking at the mouser caps before, and they have many types that may be a replacement part, some of them quite expensive . thank you very much for the information, all ideas are most welcome
Best Regards Otto

[tooki]

Hi !! yes this is correct, they look like a 1/4w film resistor, but are ceramic caps, and they are damn impossible to find online! no pictures, no one for sale,no data on them, or who made them.

What are you talking about? Did you not see my post where I checked Digi-Key and found they have 330 values of axial ceramic caps in stock right now?!? 

[floobydust]

About the old caps, they are Japanese made part, Murata or Matsushita popular in the 1980's.  Don't use X7R for low distortion audio, the dielectric's properties are not great.
I would measure the old caps lead spacing and replace with boxed film caps. Polyester or polypropylene but they are larger.
More discussion was here: https://www.eevblog.com/forum/beginners/capacitor-looks-like-a-resistor/msg1429403/#msg1429403

[Otto Olsen]

Hi!! and thank you for a sensible answer, i have talked to a friend who is really good at electronics, and he thinks the same as you, there are some  x7r capacitors used on the board , but not in these circuits and is pretty sure it is a reason for that, so I've been trying to find more information on the old ones, so I can replace them with some that are suitable. and as I draw a new shematics and pcb ,the spacing can be adjusted to fit, i will look into those old brands se if i can find any information if not i will go for boxed film caps.   i will have a look at the link you gave me aswell.  Best Regards Otto