Identify some Wima caps?

[brucew268]

My preamp has a number of Wima film caps. The larger ones are MKP, but the smaller 5mm ones say 'DO', as in 0.1, 63-A, Wima, DO.

Any idea what these 'DO' are? They are in a 1993 Classe preamp, original spec.

 

[Bill_P]

DO is the date code. The capacitors are MKS2 metalized polyester.

 

[brucew268]

Thanks. How can you tell? Since these are used as decoupling caps around the op amps and as bypass in the PSU, I wonder if they would benefit from changing to MKP2?

 

[Bill_P]

I used information from a 1995 WIMA catalog I have. The case size and color are two clues. MKP2 parts will be a bit larger and therefore have higher inductance which translates into worse decoupling at high frequencies. With the parts being pin-in-hole, there is some distance between the capacitors and op amps so that printed circuit board trace inductance may dominate. In the end it probably isn't worth changing the MKS2 parts for MKP2 in this application.

 

[ticktock]

Probably Bill is right with MKS2. There are some MKP2 or MKP3 I have im my spare box
with similar lead spacing, but more height. If capacitance isn't critical, it's even more
likely to find an MKP or even FKP3 (film-foil) to fit. Is this 7.5 mm lead spacing (RM7.5)?
The green Wimas are certainly already FKP2s, 1000 pF = 1 nF. Current ones are red
similar to MKP and MKS etc..

Search for the Wima parts catalogue or see wima.com . In many applications there are
sonic advantages for film-foil poly caps, even when they're lower capacitance.

 

[brucew268]

They are 5mm spacing, not 7.5

 

[ticktock]

There's an 15 nF ( = 0.015 µF ) FKP3 with 7.5 mm spacing ( # FKP3C021502C00),
which are fine for bypassing. Don't know if the specific value is critical. If the your
current 100 nF caps are indeed MKS2, then MKP4s would be a worthwhile upgrade.

0,10 µF - 63 V - MKP4D031002D00
0,10 µF - 160 V - MKP4F031002D00
0,15 µF - 63 V - MKP4D031502E00
0,15 µF - 160 V - MKP4F031502E00

all with 7.5 mm spacing.

FKP3 with 10 mm:

0.033 µF - 63 V - FKP3C023303D00
0.033 µF - 100 V - FKP3D023303G00
0.033 µF - 160 V - FKP3F023304D00 (15 mm)

MKP4 with 15 mm:

0,47 µF - 63 V - MKP4D034704D00
0,47 µF - 160 V - MKP4F034704D00

If there are caps with 15 mm lead spacing I'd prefer these:

0.10 µF - FKP3C031004C00
0.15 µF - FKP3C031504F00
0.22 µF - FKP3C032204J00
0.22 µF - FKP1G022204D00
0.33 µF - FKP1G023304F00

For the Wima MKP4, FKP4 0.47 µF come with at least 27.5 mm (FKP4J024704J00).
Suspectively the current ones are smaller in physical size. I'd leave them and just
bypass them with a small value FKP on the underside.

As the green Wimas are already FKP2s - I forgot to say, leave them. MKPs are
better than MKS caps, FKPs are better than MKPs.

BTW, "VR101" and "VR201 on the PCB are empty. Is there a bigger model with the
same PCB? If so I'd get the service manual and consider to retrofit the regulators.

 

[lcsaszar]

BTW, "VR101" and "VR201 on the PCB are empty. Is there a bigger model with the
same PCB? If so I'd get the service manual and consider to retrofit the regulators.

VR is variable resistor for Offset Adjustment, as marked.

 

[ticktock]

Pardon me, I didn't see the "offset adj." printing. Nevertheless it's empty,
implying there may have been another model where these are mounted.

 

[oncle_tom]

Holger,

where can I buy Wima FKP3/4?

Peter

 

[ticktock]

Tach Peter,

from what I remember Mouser stock all FKP1, FKP2, FKP3 and FKP4,
Farnell stock at least FKP3 and Bürklin stock FKP1 and FKP2 only.

You'll also find some FKP3/4 on Ebay.