Ceramic Cap Voltage

[Kazooman]

I am working on restoring a 1960's Dynacord Echocord Super 65 that I got off Ebay. It came to me with a lot of issues from the last person who had his hands inside.

I have installed a three prong plug, replaced the old selenium rectifier with a silicon rectifier, replaced every electrolytic cap and replaced all of the larger caps in the signal path. While I am at it, I thought I would replace some ceramic caps that look a bit suspicious. They are the ones in the volume/tone stack section and those in the switching area on the attached schematic. All have low picofarad values but there is no mention of voltages on the schematic and the caps are not marked.

Any thoughts on the voltage requirement for these caps? All I have on hand are low voltage caps that I use in effects pedals.

[tedmich]

the schematic was too small for my old eyes to see, but tone stack caps are usually 50v tops, with higher voltage ratings having little if any downside. I usually go with NP0/C0G dielectric material as its more temp stable and distorts less or nice old polystyrene caps instead.

[Kazooman]

the schematic was too small for my old eyes to see, but tone stack caps are usually 50v tops, with higher voltage ratings having little if any downside. I usually go with NP0/C0G dielectric material as its more temp stable and distorts less or nice old polystyrene caps instead.

Thanks for the response. Sorry about the small schematic I was blown away by all of the options in the Mouser catalog and thought I should get some advice before placing an order. I haven't ever found the need to replace ceramic caps like these, but a few of them appear to be damaged by being twisted out of the way to get at other parts. The guy who worked on this before cut wires and left the ends hanging in space. He put a two pronged lamp cord on the unit. The wires were simply laid beside the connecting wire inside and held together with solder and tape. No twists at all.

[oc disorder]

Hi Kazooman , you must have quite a collection of this wonderful old German technology !

For observers here is a link to a larger schematic

The Free Information Society - Dynacord Echocord Electronic Circuit Schematic

I like the way they print the valve bases with the typical voltages displayed.

I guess the draftsman was also a service tech !

Regarding those small ceramic caps.. I can't help remembering the Marshall DSL C46 (22pF 500v) saga.

http://music-electronics-forum.com/t25541/

Completly different application and much higher voltages I know...

I would print out the schematic , make myself a nice coffee , sit down and draw a red line using a highlighter
or a fine tip red felt pen and highlight most of the HT supply.
Any ceramic hangin' off that I would make a 500v type.. well it's not going to break the bank !

[Kazooman]

Yep, I have four Klempt Echolettes, A Dynacord Eminent I amp that I completely restored, including making a new printed circuit board, and a mint Dynacord Eminent II. This is my first Dynacord tape echo.

Thanks for posting the link to the larger schematic. The caps I was referring to are C7 - C14 in the tone stack. As well as many in the complex switching area at the right hand side of the schematic. They are "hangin' off" the 215 volt plate supply for the input tubes. They should be OK, unless some other component opens up. I will take your advice and order some beefier caps rather than use the low voltage ones I have.

I agree that the diagram with all of the expected tube voltages is great. It helped me track down why the unit was not passing any signal. It seems the last guy broke the wire bringing that 215 volt supply to the input tubes. It was just dangling in space waiting for a chance to short to ground.