Those Photoflash Electros: OK After a PS Choke?

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7/2/1999 9:12 PM

Carl B

Those Photoflash Electros: OK After a PS Choke? I've a few of those "volumetrically efficient" (read: dinky!) 450Vdc/220uF Nichicon photoflash caps.         Any caveats on using those in a tube amp? If there might be problems with high ripple currents, how about using one on the output of the choke (either that first cap in a choke-input filter, or after the screen/preamp choke in a cap-input filter)?         I went ahead and wired one in parallel with one section of a 50u/50uF @ 450Vdc cap, the one right after the choke-input filter's choke. No problems so far (bench-top idle, also full-bore 30 watt sinusoid output for tens of seconds). Vpp ripple on a 320Vdc B+ is 300mV (Dang! Forgot to measure it *before* wiring in the photoflash, and everything's wired to the photoflash now!)         "Just Tain't Natural?" "Temptin' Fate?"         - CarlB

 

7/3/1999 1:06 PM

MKB

Hello, Carl. I have used a bunch of photoflash caps in some tube stereo projects I have built in the past, my tube phono preamp has a bunch of Nichicon 250uF220V photoflash caps, it has worked fine for about 10 years. A friend used some 750uF 220V photoflashes in seriesparallel in a Dynaco ST70 for about 15 years, no problem. I have seen the photoflashes recommended for some tube preamp projects.         Of course, hifi gear wants to sound neutral, while we want our guitar amps to have lots of character; some of that character comes from the power supply. I haven't used photoflashes in a guitar amp so I don't know how they sound. Perhaps others here can comment.

 

7/7/1999 6:02 PM

Don Symes

You could take your 300mV ripple and do (V**2/(cap ESR) +     V**2/(cap ESL at, say, 10kHz) to get your worst-case ripple power. It may take some digging in the datasheets to extract the data, and it probably isn't worth the trubl.         Come to think about it, photoflash is a pretty punishing application - charge to near-max over a second or so, then discharge to near-zero at near-max current in a few tens of microseconds. Extreme, but low duty cycle. It should be pretty happy as a PS cap if it doesn't get too hot.         How much more to these puppies cost?

 

7/7/1999 7:25 PM
R.G.	>How much more to these puppies cost?         They're free if you find a tech at a place that processes film from one-use cameras with flash in them. The camera body, including the whole flash mechanism is thrown away.

 

7/7/1999 10:27 PM

Craig

Man, this is a trip - a few months back, I asked this same exact question, and most folks recommended that I steer clear of those for guitar amp applications. Several folks warned me off adamantly. If I remember right, the issue was whether or not they would handle the long-term demands of a tube amp PS. I still have a lot to learn, no doubt, but I kind of figured it the way Don does - pretty tough puppies to withstand the application they are intended for - probably fine for guitar amps. Now I'm pissed that I threw 'em all out. Oh well, more where that came from...         FWIW: I found that every single retailer I asked was willing to save these for me, and for a few months I picked up regularly at 3 neighborhood drugstores on a weekly basis. I learned that it was better NOT to mention the caps - that sort of talk tended to make managers nervous - I just said I was an artist who wanted the whole unit for a peice I was working on. The beauty of these things is that they are virtually unused when you salvage them. What, like 24 charge/discharge cycles and thats it? No wonder the mfg's get the retailers to recycle them. Talk about stretching your investment...

 

7/8/1999 2:21 AM

R.G.

OK, here's the down side. The caps have only had under 50 cycles. Of course, they were only *designed* to last only a few cycles, bought with that in mind. Even if the first flush of cameras used off-the-shelf caps, I can guarantee you that the makers had bright, eager new buyers scouring the world to get caps a penny a cap cheaper.         I suspect that the economics of the situation are that the price of the caps and flash mechanism had to be driven through the floor to be able to afford to throw them away. Hence they're probably optimized for modest shelf life, maybe two years, and only a few dead-short cycles. I don't know this for certain, but I've had enough brushes with our corporate finance people to be able to predict some things, a little.         They may hold up longer under light filtering duty, but I still wouldn't trust my power transformer to their reliability. They're optimized to be zapped hard - a few times.         More conventional photoflash caps may be more reliable. I'd still be cautious. Economics is as much a natural law as Ohm's law and Maxwell's equations.

 

7/8/1999 5:34 PM

Craig

Economics is as much a natural law as Ohm's law and Maxwell's equations.         I see your point(s). One thing is certain - high quality caps are readily available at pretty reasonable pricing to begin with, so its not as if there is a huge incentive to risk damaging expensive/hard to replace parts. All things considered, the power supply is probably the last place one should scrimp.         Craig

 

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