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[email protected] tabbypurr@gmail.com is offline
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Default replacement cpacitors

On Wednesday, 10 October 2018 20:55:39 UTC+1, tabby wrote:
On Wednesday, 10 October 2018 20:02:23 UTC+1, Ralph Mowery wrote:

When restoring the old tube equipment (tube receivers ) does it make any
difference if the old paper capacitors are replaced iwth the ceramic
disk or should another type be used ?

I know for RF one needs to use capacitors that are rated for rf but in
the audio stages does it really matter what kind of capacitor is used as
long as it is the correct value ?


Reason for asking is that I bought an old receiver that someone has
replaced many of the capacitors. The book says pape capacitors for some
but they have been replaced by the ceramic disk type.


a lot of ceramic caps suffer severe loss of capacity once a few volts are applied. If it works fine, great. If the limited amount of original bass has vanished, that might be why. If rf drifts all over the place as mains voltage varies...

It depends on the type of ceramic, some don't suffer this but most do.


NT


it also can cause nonlinear distortion if C is changing as signal voltage changes.

The other cap type to be a bit cautious of in valve kit is polystyrene, the dielectric has low melting point.

The issues with electrolytics & paper are relatively well known.

Oh, also beware of reduced voltage rails that go very high during warm-up. Caps there might need 400v+ rating despite running at 20v.


NT