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AUDIO FORUMS >> General Discussion and Support >> Vcap for a DIY dummy
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Message started by jonjin on 03/02/08 at 11:23:05

Title: Vcap for a DIY dummy
Post by jonjin on 03/02/08 at 11:23:05

Hi,

Don't mean to be thick but was going to ask some simple advice about how to change to the Vcaps. I'm quite happy soldering but which cap do I replace? I couldn't find any .1 uF caps in the circuit diagram?

Title: Re: Vcap for a DIY dummy
Post by Eli Duttman on 03/02/08 at 15:00:51

jonjin wrote on 03/02/08 at 11:23:05:

JJ,

The box shaped green and yellow parts are the coupling capacitors. IIRC, those are WIMAs. The box caps. get replaced by the PTFE parts. Yes, its tight in there. So, plan what you do carefully. It may be necessary to put insulating sleeves on the leads of the new parts.

Title: Re: Vcap for a DIY dummy
Post by jonjin on 03/02/08 at 15:59:23

Thanks!

I was advised by one of the local experts to replace the 1k Dale resistor (the gold rectangular one on the top left) with a choke as well. Don't know if there's room. Opinions on this?

JJ

Title: Re: Vcap for a DIY dummy
Post by Crazy Bill the Eel Killer on 03/02/08 at 20:18:00

Hello JJ,

A direct choke replacement will not work for two reasons.

One, a choke rated for 150ma will be too large to fit in there.

Two, the 1K resistor drops a certain voltage across itself so that your B+ is approx 300 vdc ( going by memory here, correct if it's wrong ). The dcr of the choke is considerably less ( probably 50-100 ohms ) and your B+ will be WAY too high. If you had to have a choke, and are willing to do chassis mods to make it fit, you have two options.

1). Replace the 1K Dale with another Dale whose value an d the dcr of your choke will add to the original 1K. Or, better yet, replace the 1K Dale with the choke, then make another filter section with the new Dale ( value figured as above ) and another filter cap.

Have fun, and be safe.

Cheers, Crazy Bill :)

Title: Re: Vcap for a DIY dummy
Post by veryoldcat on 03/02/08 at 20:20:47

First I can tell you the v-cap upgrade is quite dramatic. They're great at first, but then soften up with use. They seem a bit edgy with digital sources until they've been going for a while.

A nice thing to know is that the Wima's are attached with superglue. When you go to wiggle them out, they will seem very solidly attached, but then will come loose with a snap all of a sudden when you apply some muscle.

They're not terribly hard to remove, but the snapping loose of the brittle superglue bond can be a little unnerving, if you don't know it's coming.

When bending the leads on the v-caps, be careful, as they're quite stiff. You'll need to bend the leads up close to where they enter the body of the cap to make them fit. Whilst you bend, a good pair of electronics needle nose pliers is needed to hold the lead where it enters the cap to avoid stress on the lead/plate connection inside.

Some feel it is helpful to orient the outside plate of the cap towards ground, and the inside plate towards the plus side, thus using the outer plate like a shield to ground (some people think it matters and others think it a silly consideration). IIRC, the right hand side of the cap is the outer plate, when reading the data on the cap.

Karl

Title: Re: Vcap for a DIY dummy
Post by jonjin on 03/02/08 at 21:27:24

Crazy Bill the Eel Killer wrote on 03/02/08 at 20:18:00:

Thanks... there's no way I'm clever enough to figure all that our. Will stick to just replacing caps.

JJ

Title: Re: Vcap for a DIY dummy
Post by jonjin on 03/02/08 at 21:57:30

Any value in changing the other caps/resistors? Black Gates, Hovlands etc...

JJ

Title: Re: Vcap for a DIY dummy
Post by Hotsauce on 03/03/08 at 01:43:04

Wait till you do this one, then see if you still feel the need to tweak it more.

Don't change 2 things at once.

John C.

Title: Re: Vcap for a DIY dummy
Post by Crazy Bill the Eel Killer on 03/03/08 at 13:58:53

Hello JJ,

John C's advice is good advice when doing mods. Do one thing and then listen to get a feel for the changes.

As to your other questions, there are lots of component changes you can make that will improve/change the sound of your amp. I've probable done them all except for the coupling caps. There are lots of threads on this and the Hawthorne forums that will guide you. I probably won't have time for several days, but I'll try to find some of them for you.

Cheers, Crazy Bill :)