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Photoflash Capacitors

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Posted on April 22, 2017 at 15:39:28
Lee of Omaha
Dealer

Posts: 1800
Location: Omaha NE
Joined: September 8, 2006
At one time these were considered a good thing to use in power supplies.

How about now? I've got an opportunity to buy some at what seems a good price.

I guess the question in whether it would be sonically better to use standard 'lytics bypassed by a nice film or paper in oil capacitor or to use photoflash caps (which could still be bypassed).

Experience-based opinions?

 

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RE: Photoflash Capacitors, posted on April 22, 2017 at 16:23:32
Chip647
Audiophile

Posts: 2633
Location: The South
Joined: December 24, 2012
There have been advances in electrolytic caps in the past 10 years that have increased reliability and decreased ESR. The one thing in your amp that literally explodes. Just look for low ESR caps, not "old cheap caps".

The reason people used them is because they were high voltage and cheap. People had the impression that since they are labeled "photoflash" they are designed to discharge super-fast that it would make music sound superfastdynamic.

From Jim McShane from 22 years ago:

Photoflash Caps

From MLJS45-(at)-rodigy.com Sun Oct 8 11:15:45 CDT 1995
From: MLJS45-(at)-rodigy.com (James Mcshane)
Newsgroups: rec.audio.tubes
Subject: Forming Surplus Photoflash Caps
Date: 8 Oct 1995 15:17:36 GMT
Distribution: world

I've been watching the posts on using photoflash caps, and wanted to
offer a safety and performance tip that has worked well for me. When
working with surplus photoflash caps, it is very important to SLOWLY re-
form them before even considering using them in regular service. I try to
keep current flow through the cap to <1ma. as I bring the applied voltage
up. I form them to rated voltage +5% as a safety factor.

Be advised I have had about 10% literally explode during forming! That's
why I use a small wooden box to contain the cap during forming. And I
always form the one at a time, not as a "bank". Caution is very important
here!

One last tip- if you happen to get hold of Rubycon branded caps the key
that you have a bomb, not a cap, is that the bottom of the cap begins to
expand out, sort of dome-like, before you get to rated voltage. Discard
these units. They will fail.

I too have used these caps in a variety of units for years with zero
failures- after proper re-form. I like 'em a lot. Poor man's Black Gates?

-
JAMES MCSHANE MLJS45-(at)-rodigy.com

 

RE: Photoflash Capacitors, posted on April 22, 2017 at 17:34:24
sser2
Audiophile

Posts: 2571
Location: Pittsburgh USA
Joined: July 30, 2003
In my experience, they are nice. They are very small compared to regular electrolytes. There is a precaution though: the AC component should not exceed a few volts. They should not be used as filter capacitors, but are pretty good for decoupling or ultrapath in a differential transformer-coupled stage with low signal level, where high voltage rating and large capacitance are needed.

 

RE: Photoflash Capacitors, posted on April 22, 2017 at 21:15:06
Michael Samra
Dealer

Posts: 36118
Location: saginaw michigan
Joined: January 30, 2005
Lee
Photoflash caps can sound very good but the problem is they have very high leakage.I use to take them out of disposable cameras and wire them in series and they sound very good in an Mk3s and old vintage.Lets face it tho.Film caps put all these things to rest.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken

 

RE:I use them in rebuilds of vintage amps, posted on April 23, 2017 at 10:16:31
DAK
Audiophile

Posts: 2712
Location: PACIFIC
Joined: August 8, 2010
Their compact size allows you to put them under the chassis especially in slim units. They can replace a bunch of can caps. Like others have mentioned they are not designed to filter AC in a power supply so just keep them out of C1 duty.

 

Agree with Lee of Omaha, posted on April 23, 2017 at 17:15:15
garymuffley
Dealer

Posts: 445
Location: Maryland
Joined: March 29, 2006
Photoflash caps have low inducatance and fast discharge, but are NOT good for filtering large amounts of ripple or current. Use a good computer grade for initial filtering and photoflash for decoupling (with a film bypass), where they work very well. I measured some 500mfd/500vdc photoflash caps that had less than 40 miliohms ESR--cn't get that in an electrolytic of that size. Film caps can have even lower ESR, but can't store nearly as much energy.

 

RE: Photoflash Capacitors, posted on April 24, 2017 at 00:21:15
horny
Audiophile

Posts: 745
Location: holland
Joined: October 17, 2003
are they use full as cathode decoupling cap i see them in 330 volt 100 or 160 uF
the value is perfect but would they work ?

 

Jim McShane is the one knows about Photoflash caps and he uses some , posted on April 24, 2017 at 02:56:36
Michael Samra
Dealer

Posts: 36118
Location: saginaw michigan
Joined: January 30, 2005
if you read bis systems bio page however,he uses special ones and he makes sure the leakage is under .5ma.I've used the ones out of cameras in series and they sounded good but Jim told me not to use those years ago so I took them out. I only put them in my Dyna MK3s in the Stokes power supply board and they sounded ok but they couldn't be trusted.I use good low ESR, high ripple current Panasonic and Nichicon 105 degree lytics and then use 50uf film caps for added decoupling or for the first stage off a tube rect.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken

 

RE: Photoflash Capacitors, posted on April 24, 2017 at 11:03:11
Jim McShane
Dealer

Posts: 5910
Location: Chicago
Joined: January 13, 2003
Chip,

Thank you for finding and posting that! It is still 100% relevant today after 22 years. And BTW - when they pop it's a darn good "ear-ringing" bang!!

I still use photoflashes (older stuff that goes through my torture test) but not in high ripple applications. Gary Muffley is spot on - they don't belong in those applications. As Gary said - use them AFTER the first cap which gets most of the beating from ripple.

I have a full case of "strobe" caps which are designed to be used in continuous pulsing duty as part of the circuit that powers falshing strobe lights. These are 2500uf at 360 volts, CDE model 7P caps. I have some plans for them - but the testing MUST come first and the caps MUST pass with flying colors.

Finally, just an update on my 22 year old post... the caps in my "McShane" amp are Marcon photoflashes and have been in service for 25 years. ZERO failures! But they are going to be retired soon as the amp gets a mid-life makeover - even though they stil make GREAT sound in the amp.

 

you probably don't need them and are likely better off without, posted on April 24, 2017 at 11:10:22
Ralph
Manufacturer

Posts: 4769
Location: Minnesota
Joined: April 24, 2002
In audio applications they aren't all that reliable. They don't take to heat well for one thing and for another, DO NOT use them right off the rectifier (C1) as at least one other has pointed out on this thread (they can't handle the ripple current). Trust me, oozing caps are no fun.

But here's the kicker:

The trick is to set up your power supply so that it has lower frequency poles than your amp does. It really is that simple- if you do that, the amp won't be able to significantly modulate the supply and so IMD will be minimized. So you can see that you have some math to perform, working out the low frequency poles of the amp and the various legs of the power supply.

Here's the formula, modified to allow you to use microfarads and results in Hz:

f=1,000,000/CxRx2Pi where

f is cps, C is in microfarads, R is in ohms.

As a usual rule of thumb, set your power supply poles at least 3-4 octaves below the cutoff of the stage that it feeds. So if the coupling caps at the input of the output section are cutting off at 5Hz, the power supply should have storage for about 2-4 seconds.

I think what you will find is that you don't need to add all that capacitance! Not saying that a good number of amps don't have enough, but once you have enough you don't get a benefit by adding more. So the photoflash caps might be irrelevant, and as far as reliability goes, that's a good thing.

 

RE: Photoflash Capacitors, posted on April 24, 2017 at 11:29:15
maxhifi
Audiophile

Posts: 584
Location: Alberta, Canada
Joined: August 4, 2004
I bought a bag of them years ago, the guy got them from a shop who pulled them out of disposable cameras. I used them to recap a bunch of old radios... really they're nothing special. In this day and age of tubes and transformers being so darn expensive, no sense to create a potential short to ground through a capacitor which isn't designed for use as an AC filter.

 

RE: Photoflash Capacitors, posted on April 24, 2017 at 12:34:11
sony6060
Audiophile

Posts: 1465
Location: USA
Joined: August 8, 2014
Not good for high current ripple, but suffice in amps using up to 250ma.

 

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