KEL84 Feedback mod - cap value crucial?

[buddam]

Hi All

the notes on lowering f/b refer to a change to the 2 caps (16 &17) from 3.9nF to 3.3nF. I wondered if this is an exact requirement since I can get 3.6nF from Rapid, but from RS would need to parallel 1.5 + 1.8 (and would have to order 5 of each). This would also be awkward to squeeze in alongside the AN PIOs I have.

Thanks

Adrian

[jimangus]

Hi buddam,
don't worry about useing silver mica here it won't matter too much. Get a pair of nice polysterene +-2% from farnell if you want something that sounds very good.

Jim

[buddam]

Thanks Jim - any idea of the voltage rating required?

[jimangus]

I think they are two voltages, i went for the higher one of the two, i think it was 630v. Plenty spare then.

Just one thing to remember, these do not like too much heat when soldering them in, just be careful.

The feedback mod in my opinion was one of the best mods i did for the least output. It will be interesting to hear your opinion.

Jim

[buddam]

Hi Jim

according to the online catalogue, they come in 63V and 160V (is that enough?)

[jimangus]

Originally Posted by buddam

Hi Jim

according to the online catalogue, they come in 63V and 160V (is that enough?)

Just looked at my order history and yes they are 160v that i am using. part number 9520538.

However you need to buy £20 worth plus vat at farnell.

At rs you can get them. i am sure 63v will be sufficiant. That will be the one to go for as it is +-1%. However you have to buy five.

At rapid you can get polysterenes at 160v 2.5% one at a time. but they will charge you postage.

You pays your money you takes your choice !!

jim

[NickG]

The lower voltage parts will be fine in the feedback loop, the only voltage is that generated by the current through the feedback resistor, so "not a lot". Its there to apply additional feedback at higher freq.