You should be able to find suitable capacitors in car stereo set ups, there
are lots of options on eBay too

"Custos Custodum" wrote in message
...

"gareth" wrote in
:

The problems associated with replacing (or even obtaining) the HT
reservoir capacitors in valve projects might be replace with a series
/ parallel arrangement of those dinky 100uF 35V SMD ones?

There's still a significant market for valve-based guitar amplifiers, so
somebody must be making the HT capacitors for them.


Probably could be rolled up and placed inside the original aluminium
can, too!

Don't forget to include a suitable voltage divider chain.

On Tue, 27 Jan 2015, gareth wrote:

The problems associated with replacing (or even obtaining) the HT reservoir
capacitors in valve projects might be replace with a series / parallel
arrangement of those dinky 100uF 35V SMD ones?

Probably could be rolled up and placed inside the original aluminium can,
too!

You didn't specify what voltage you need.

For "average" high voltage, there are all those line side capacitors in
switching supplies. I thought they were about 450volts, but it's been a
while since I checked. So one can extract from a scrap computer supply,
or likely buy those as replacement parts. If they aren't high enough
voltage, then they are a better start for combining than 35v ones.

I was actually surprised 20 years ago when I discovered ripple in my
Tektronix scope. I found which of the many supplies was the problem by
using the scope itself, touching each of the high voltage lines until I
found one where the ripple increased. The needed capacitor wsa much larger
than "average" value in the days of electrolytics, I figured it would be
hard to find. Yet I checked the bins at the local surplus store, and
easily found a replacement, high enough voltage, and some large value like
100uF (which is large for tube power supplies).

If you're talking about high voltage for power amplifiers, I thought a lot
of those oil-filled capacitors from the old days were still viable. They
were sealed and hence don't dry out. The relatively small capacitance
ones but which have ceramic insulators for the leads to come through. They
were useful fifty years ago, they are apparently still good now. All you
have to do is dig deep enough to find them under more recent items.

If this is for a receiver, run it at a lower voltage. I gather the
Collins 75S line of receivers used "relatively low" voltage on the plates,
not real low but low relative to what other companies put on the plates.
I remember an article in CQ by Fred Brown where he updated his HRO for
subminiature tubes, and he followed this line about lower plate voltage,
though I can't remember the benefits he mentioned.

Michael

Michael Black wrote:

On Tue, 27 Jan 2015, gareth wrote:

The problems associated with replacing (or even obtaining) the HT reservoir
capacitors in valve projects might be replace with a series / parallel
arrangement of those dinky 100uF 35V SMD ones?

Probably could be rolled up and placed inside the original aluminium can,
too!

You didn't specify what voltage you need.

For "average" high voltage, there are all those line side capacitors in
switching supplies. I thought they were about 450volts, but it's been a
while since I checked. So one can extract from a scrap computer supply,
or likely buy those as replacement parts. If they aren't high enough
voltage, then they are a better start for combining than 35v ones.

I was actually surprised 20 years ago when I discovered ripple in my
Tektronix scope. I found which of the many supplies was the problem by
using the scope itself, touching each of the high voltage lines until I
found one where the ripple increased. The needed capacitor wsa much larger
than "average" value in the days of electrolytics, I figured it would be
hard to find. Yet I checked the bins at the local surplus store, and
easily found a replacement, high enough voltage, and some large value like
100uF (which is large for tube power supplies).

If you're talking about high voltage for power amplifiers, I thought a lot
of those oil-filled capacitors from the old days were still viable. They
were sealed and hence don't dry out. The relatively small capacitance
ones but which have ceramic insulators for the leads to come through. They
were useful fifty years ago, they are apparently still good now. All you
have to do is dig deep enough to find them under more recent items.

The oils in these old capacitors are often PCBs (polychlorinated
bi-phenyls) which are quite toxic. And they can leak slightly even if
not visibly. So I wouldn't have them in a house occupied by any non-old
non-amateurs. (A bit late for me to take up H & S on my own behalf.)





If this is for a receiver, run it at a lower voltage. I gather the
Collins 75S line of receivers used "relatively low" voltage on the plates,
not real low but low relative to what other companies put on the plates.
I remember an article in CQ by Fred Brown where he updated his HRO for
subminiature tubes, and he followed this line about lower plate voltage,
though I can't remember the benefits he mentioned.

Michael


--
Roger Hayter

"Roger Hayter" wrote in message
...
The oils in these old capacitors are often PCBs (polychlorinated
bi-phenyls) which are quite toxic. And they can leak slightly even if
not visibly. So I wouldn't have them in a house occupied by any non-old
non-amateurs. (A bit late for me to take up H & S on my own behalf.)


The PCB is not really that toxic. The problem is that it almost does not
break down and gets into the food chain. You can touch it and even get a
small ammount in your mouth without any harm to you. I don't mean drink it,
but say you get some on your hand and lick a drop or two off your finger.

On 1/27/2015 7:59 PM, Ralph Mowery wrote:
"Roger Hayter" wrote in message
...
The oils in these old capacitors are often PCBs (polychlorinated
bi-phenyls) which are quite toxic. And they can leak slightly even if
not visibly. So I wouldn't have them in a house occupied by any non-old
non-amateurs. (A bit late for me to take up H & S on my own behalf.)


The PCB is not really that toxic. The problem is that it almost does not
break down and gets into the food chain. You can touch it and even get a
small ammount in your mouth without any harm to you. I don't mean drink it,
but say you get some on your hand and lick a drop or two off your finger.

Wow! What is your basis for saying that? Are you trying to say if it
doesn't kill you outright there is no danger?

--

Rick

On 1/27/2015 9:47 PM, rickman wrote:
On 1/27/2015 7:59 PM, Ralph Mowery wrote:
"Roger Hayter" wrote in message
...
The oils in these old capacitors are often PCBs (polychlorinated
bi-phenyls) which are quite toxic. And they can leak slightly even if
not visibly. So I wouldn't have them in a house occupied by any non-old
non-amateurs. (A bit late for me to take up H & S on my own behalf.)


The PCB is not really that toxic. The problem is that it almost does not
break down and gets into the food chain. You can touch it and even get a
small ammount in your mouth without any harm to you. I don't mean
drink it,
but say you get some on your hand and lick a drop or two off your finger.

Wow! What is your basis for saying that? Are you trying to say if it
doesn't kill you outright there is no danger?


He's right - it isn't really that toxic. It takes multiple exposures
over a long time to do any harm; getting some on your hands won't hurt
you. And even when it does harm you, it's not fatal. But it does cause
nervous system disorders.

There are a lot of things much more toxic you can easily find, even at
the grocery store. Drain cleaner comes to mind...

--
==================
Remove the "x" from my email address
Jerry Stuckle

==================

"rickman" wrote in message
...

The PCB is not really that toxic. The problem is that it almost does not
break down and gets into the food chain. You can touch it and even get a
small ammount in your mouth without any harm to you. I don't mean drink
it,
but say you get some on your hand and lick a drop or two off your finger.

Wow! What is your basis for saying that? Are you trying to say if it
doesn't kill you outright there is no danger?

PCB is often talked about like a few drops will kill you. Many things
around the house are much more toxic. Look at all the dangers listed on the
drugs they advertise on the TV.
While we don't want the PCP oil to get into the food chain, some tree
huggers just jumped on that and tried to make it sound like it would kill
you or cause brain damage or some such junk as that. While it will do that,
it takes more than a few drops and not many people are going to just drink a
glass of it.

On Tue, 27 Jan 2015 13:01:55 +0000, gareth wrote:

a series /
parallel arrangement of those dinky 100uF 35V SMD ones?

Ripple current?



--
He who throws dirt loses ground.

Every switch PSU uses high voltage capacitors