Spin from Bipolar caps

Archived from groups: rec.audio.pro (More info?)

This may be a little OT, but it still has to do with caps.

I've got a Fender '65 Twin thats got old GE paper electrolytics in the B+
circuit.
Most are 20uf @ 450 volts. I'm a relunctant to replace those with NOS for the
obvious reasons the NOS probably are not gonna be an improvement over whats in
there now.

First. Is it advisable to replace with something else, since technology
changes and this is 40 year old design.?

Second, I'm having problems finding new replacements because of the 450v
requirement.

Third, should I also replace all those .1mfd and .047mfd while I'm at it and
with what?

BTW, I'm really not interested in changing the "sound" of the Twin. It's a
great amp as is!!! Just wanting to clean up some of the hum, etc.

I can solder and do the light stuff, but I'm not an schooled in electronics.

Thanks,

--Wayne

-"sounded good to me"-

Archived from groups: rec.audio.pro (More info?)

Wayne wrote:


> I've got a Fender '65 Twin thats got old GE paper electrolytics in
> the B+ circuit. Most are 20uf @ 450 volts. I'm a relunctant to
> replace those with NOS for the obvious reasons the NOS probably are
> not gonna be an improvement over whats in there now.


Brand new ones will be fine. www.tubesandmore.com

Yours should have had 525-volt, since there's more than 450 volts on them.


> First. Is it advisable to replace with something else, since
> technology changes and this is 40 year old design.?


Sure.


> Second, I'm having problems finding new replacements because of the
> 450v requirement.


450's are stocked about everywhere, like www.mouser.com. But you should
use a higher rating.


> Third, should I also replace all those .1mfd and .047mfd while I'm at
> it and with what?


Not if they're not causing a problem.


> BTW, I'm really not interested in changing the "sound" of the Twin.
> It's a great amp as is!!! Just wanting to clean up some of the hum,
> etc.


Therefore you *should* replace the power supply filters; do the 50
that's in the bias supply too.



> I can solder and do the light stuff, but I'm not an schooled in
> electronics.


Since lethal voltages are present, don't even start this yourself. Take
it in to someone who won't get killed.

Archived from groups: rec.audio.pro (More info?)

>Brand new ones will be fine. www.tubesandmore.com
>
>Yours should have had 525-volt, since there's more than 450 volts on them.
>
>

You're right. It's the AB763 schematic which specifies 525. Most of the
working voltages are around 450.

There's also some 25/25 in there. I'll probably just change the 20/525's, the
50/50 in the bias circuit and the 25/25's.

Thanks for the hi-voltage warning, but I'm already familiar with that. I
usually just unplug from the wall and do the screwdriver to chassis welding
function. I used to work on microwave ovens and those trash cans can flat ruin
your day alright.

Thanks for the help


--Wayne

-"sounded good to me"-

Archived from groups: rec.audio.pro (More info?)

"Paul Stamler" <pstamlerhell@pobox.com> wrote in message news:Eu1sd.86067>
The problem is, you *are* going to change the sound. Why? Because as the
> capacitors have aged, you've gotten used to the sound of an amp with bad,
> saggy, worn out supply caps. When you replace them with caps that actually
> do what they're supposed to, you'll hear a different sound, probably
> pretty
> close to what the amp sounded like when it was new (discounting the
> changes
> in the speakers, of course).

A bit like changing your guitar strings really !

geoff

Archived from groups: rec.audio.pro (More info?)

If the caps are old they my no longer be 20 uf @ 450 volts should not be
that hard to find. Be wary of tantalum caps since the failure mode is to
chatch on fire. Go for the aluminum electrolytics, they just explode or go
open.

Bob

"Wayne" <ybstudios@aol.com> wrote in message
news:20041203112003.07275.00001307@mb-m10.aol.com...
> This may be a little OT, but it still has to do with caps.
>
> I've got a Fender '65 Twin thats got old GE paper electrolytics in the B+
> circuit.
> Most are 20uf @ 450 volts. I'm a relunctant to replace those with NOS for
the
> obvious reasons the NOS probably are not gonna be an improvement over
whats in
> there now.
>
> First. Is it advisable to replace with something else, since technology
> changes and this is 40 year old design.?
>
> Second, I'm having problems finding new replacements because of the 450v
> requirement.
>
> Third, should I also replace all those .1mfd and .047mfd while I'm at it
and
> with what?
>
> BTW, I'm really not interested in changing the "sound" of the Twin. It's
a
> great amp as is!!! Just wanting to clean up some of the hum, etc.
>
> I can solder and do the light stuff, but I'm not an schooled in
electronics.
>
> Thanks,
>
> --Wayne
>
> -"sounded good to me"-

Archived from groups: rec.audio.pro (More info?)

Scott Dorsey wrote:

> Wayne <ybstudios@aol.com> wrote:
> >This may be a little OT, but it still has to do with caps.
> >
> >I've got a Fender '65 Twin thats got old GE paper electrolytics in the B+
> >circuit.
> >Most are 20uf @ 450 volts. I'm a relunctant to replace those with NOS for the
> >obvious reasons the NOS probably are not gonna be an improvement over whats in
> >there now.
>
> NOS caps will probably be worse, since they will have been sitting on the
> shelf for a long time.
>
> >First. Is it advisable to replace with something else, since technology
> >changes and this is 40 year old design.?
>
> If you change them with a modern technology cap, the amp will sound different.
> This could be good or bad. If you replace them with a new cap of old
> design (Antique Electronics Supply has a nice selection), it will sound
> much the same.
>
> >Second, I'm having problems finding new replacements because of the 450v
> >requirement.
>
> Panasonic makes some modern ones. Mallory I think makes some old ones.
> Are these metal can types? Personally I would go to a 600V one for
> somewhat longer life.
>
> >Third, should I also replace all those .1mfd and .047mfd while I'm at it and
> >with what?
>
> If they are paper caps, putting anything else in there will change the
> sound but improve reliability.
> >
> >BTW, I'm really not interested in changing the "sound" of the Twin. It's a
> >great amp as is!!! Just wanting to clean up some of the hum, etc.
>
> Anything you do will change the sound, which is the problem.

OTOH you may be well pleased with the changed sound !

I had a few original Vox AC30s in for repairs many years ( decades ) back.

Most of the problems were 'burnt out' 100k anode / plate resistors and horrible
'Hunts' 0.01uF coupling caps that degrade with time to the extent that the plastic
case would literally 'crumble' like dry bread !

Relaced those parts with new stock of modern characteristics - e.g. metal oxide /
film Rs and plastic film caps.

Also found a poor output stage biasing problem ( used cathode bias alone ) that
meant that the 2 paralled EL84s on each side of the push-pull arrangement ( 4 x
EL84s total ) shared -ve bias and therefore there was no way of assuring any remote
chance of matching Ia. Changed this to a proper individual bias arrangement.

The owners were well pleased with the results. It was like giving the amps a new
lease of life and a breath of fresh air.


Graham