"Rambo" wrote in message
...
On Tue, 27 Jan 2015 14:49:49 +0000 (UTC), Custos Custodum
wrote:

"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.
Whats wrong with a 450volt rated cap?

Are they readily available?

On 1/27/2015 12:41 PM, gareth wrote:
"Rambo" wrote in message
...
On Tue, 27 Jan 2015 14:49:49 +0000 (UTC), Custos Custodum
wrote:

"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.
Whats wrong with a 450volt rated cap?

Are they readily available?

Yes. Did you even look for them?

--

Rick

On Tue, 27 Jan 2015 17:41:21 -0000, "gareth"
wrote:


Don't forget to include a suitable voltage divider chain.
Whats wrong with a 450volt rated cap?

Are they readily available?

How about:

http://uk.rs-online.com/web/p/alumin...itors/7441896/



http://uk.rs-online.com/web/generalD...ile=conditions
" All prices exclude VAT, which RS will add at the rate applicable at
the date of order despatch. RS reserves the right to change prices
without prior notice at any time."

On 27/01/2015 17:41, gareth wrote:
"Rambo" wrote in message

Whats wrong with a 450volt rated cap?

Are they readily available?

Yes they are commonly used in 3 phase applications for ripple control or
power factor correction.
They can range from diddy PCB types right up to tin buckets weighing
several kilograms.
You can get them from RS, Farnell etc

Andy

On 27/01/2015 17:41, gareth wrote:
"Rambo" wrote in message
...
On Tue, 27 Jan 2015 14:49:49 +0000 (UTC), Custos Custodum
wrote:

"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.
Whats wrong with a 450volt rated cap?

Are they readily available?


All credit to you for posing the question Gareth, but real enthusiasts
know the answer as they take apart failed or obsolete equipment just out
of interest to see what is inside - and if anything is worth recovering.
Switch-mode PSUs - either as PSUs or as part of TVs, VDUs, printers
etc. etc. are a ready source of such capacitors. There's usually about
400v-worth of a couple of hundred microfarads of electrolytics in there.

Computer power supplies become dated so quickly - change of specs /
change of connector styles - that these caps are likely to have a fair
bit of life left in them - although they may over-smooth in a design
meant for the old combined 8+32uF - red spot for the 8 - that used to be
the bedrock of valve receiver PSUs.

PA

"Peter Able" stuck@home wrote in message
o.uk...
On 27/01/2015 17:41, gareth wrote:
..

Computer power supplies become dated so quickly - change of specs / change
of connector styles - that these caps are likely to have a fair bit of
life left in them - although they may over-smooth in a design meant for
the old combined 8+32uF - red spot for the 8 - that used to be the bedrock
of valve receiver PSUs.


When not using the origional value of capacitor in the power supply it is
important not to go too large. If the supply has a tube rectifier, the tube
will have a maximum capacitor rating. Too large of a value is bad for the
tube. If way too large and simiconductors are used for rectifiers, they can
become a problem also. Mainlly blown fuses when the supply is turned on
unless a soft start is included. That is usually a resistor in the primary
line that is shorted out after a second or so.

On 28/01/2015 19:54, Ralph Mowery wrote:
"Peter Able" stuck@home wrote in message
o.uk...
On 27/01/2015 17:41, gareth wrote:
.

Computer power supplies become dated so quickly - change of specs / change
of connector styles - that these caps are likely to have a fair bit of
life left in them - although they may over-smooth in a design meant for
the old combined 8+32uF - red spot for the 8 - that used to be the bedrock
of valve receiver PSUs.


When not using the origional value of capacitor in the power supply it is
important not to go too large. If the supply has a tube rectifier, the tube
will have a maximum capacitor rating. Too large of a value is bad for the
tube. If way too large and simiconductors are used for rectifiers, they can
become a problem also. Mainlly blown fuses when the supply is turned on
unless a soft start is included. That is usually a resistor in the primary
line that is shorted out after a second or so.


Hence my warning about a design specifying 8uF, Ralph. What will narrow
the gap will be that several ex-SMPSU capacitors will be used in series
- so the effective will be less than the individual capacitance.

As for limiting inrush, the transformer secondary and rectifier
impedances will, hopefully, take care of that - but as you write, these
things should be considered.

I wonder how much carnage was caused by those rectifier replacements for
valves which were a set of semiconductor rectifiers potted in an
International Octal body plug? Plug-in replacements - like hell !!

As for fusing - I guess that one can still get slow-blow fuses?

PA