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Working on an amp for a friend. It's old, circa 1968. The problem is the tremolo, but the main power supply cap looks as thugh it might be leaking, so I'll replace that, too.

What I'm wondering about is the other electrolytic caps. Some, like the main power cap, are pretty expensive. Others, such as the coupling caps used in the signal path, are much smaller. I'm seeing a wide range of prices, from less than ten cents each to several dollars. The inexpensive caps say that they're for "digital power supplies", so I have to wonder if they'd be suitable for audio use. But if not, then why not? What makes a better cap  better in this context? I'm thinking ESR (equivalent series resistance) and inductance affecting the frequency response, but I'm not seeing any specs on those. Maybe the tolerance?

Here is an example of an inexpensive cap: https://www.alliedelec.com/product/nichicon/upw1h100mdd/70187276/

On the other hand, here are eleven(!) more types from the same manufacturer: https://www.hificollective.co.uk/components/nichicon.html

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On 2/1/2020 at 5:34 PM, daddymack said:

tolerance on most of those appear to be the same @ 20%

Seems so. Some are rated for higher temperatures. At least one says that it's mechanically damped, which might be an advantage in a guitar amp. But that one manufacturer has eight different lines (or at least eight different cases!) of caps specifically designed for audio (they say). Then there are all of the other manufacturers out there. How to choose? Too many choices can lead to the paradox of choice and analysis paralysis.

https://www.nytimes.com/2010/02/27/your-money/27shortcuts.html

Fortunately, we're not going to do a full recap right away, so we don't have to choose. Not now, at least.

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In caps size matters.  You need to pay careful attention to the voltage on the cap as well as the other numbers.  A cap designed to handle tubes running 500BV are obviously going to be huge in comparison to a SS amp running 12V. 

Current is the other factor.  Some SS amps will have a set of caps which are very large and the voltage rating much higher then what's going through the circuit..  This is because many SS designed amps will vary voltage instead of current when the load changes.  Many PA heads may only produce 100W at 16 ohms but 1100W at 4 ohms bridged.  The voltage across the power caps is likely to change drastically if they are supporting the output transistors. 

 

As far as your situation goes, Get the schematic, and post some pictures or what you have in that amp, And I'll do what I can to steer you to the right places for the right caps.  There are several on line stores that specialize in musical gear both SS and tube.  Low Prices, reliable products, and an honest vendor are important. I know several quite well having done business with them for many years too.  I need more details however.  There were tons or amps made in 1968.  a model type is essential for getting the right items. 

I should also note, Modern caps with exact spec matches have become more efficient over the years but you need to be real careful. The Chinese will try and sell you any piece or garbage whether it fits or not.  I'd be real leery about any cap that's more then 1/4 to 1/3 smaller then the original in size.  Caps are not that complex. They are essentially two pieces of copper foil separated by an insulator sheet wrapped up and stuffed in a tube.  Anything to make it smaller like thinner foil or thinner insulator also makes the component more venerable to damage, physically and electrically. 

 

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I purchased a cap with a higher capacitance rating (4700 v 4000μF) and the same voltage rating. It wasn't very expensive, so I'll give it a go and see what happens.

FWIW, the amp is a Heath TA-16. This should take you to the schematic: http://ctgelectronics.weebly.com/uploads/3/1/6/6/3166248/ta-16_schematic.pdf

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According to that diagram the power supply uses (1) 4000uf cap and (4) 100uf caps. 
 

I do not recommend using higher value caps on older amps like this.  If it was engineered for a 4000uf cap first in like it already has double the needed capacitance. Adding even more you risk having a power up surge which can have unforeseen consequences.  Old amps typically have components which values have drifted out of specs.  Bringing them back to factory specs is typically as far as I'd ask them to go at their age.  Adding high value caps in the power supply is like asking an old man with hardening of the arteries to do hard labor.  He's past his prime and much more likely to have a coronary.  If the caps are leaky, I'd replace them with the same values.  The only time you go with something higher is when the cap is so unique you cant find something at that particular value.   

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I have achieved tremolo!

I replaced the old LDR (light dependent resistor) with an optocoupler, and I have tremolo action, which is what was wrong with the amp in the first place.

Taking the advice of WRGKMC into account, I'm thinking of replacing the old 4000μF 50V filter cap with a 3300μF 100V cap. Higher voltage can't hurt, IMO, and the smaller capacitance rating should still be more than adequate to smooth the DC. It is, after all, about 100 times the capacitance used in my tube amps of the same vintage.

Why the higher voltage? Well, why not? First off, as I said, it can't hurt. Next, line voltage is higher now than it was in the 60s, usually 120vac rather than 110vac. So, I'm being cautious. Besides, it's bigger, closer to the size of the original cap, so it will just look better in the amp. Not that anyone other than me is going to see it.

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5 hours ago, Phil O'Keefe said:

Using a cap with a higher voltage rating should be okay. You definitely don't want to go the other way around though. 

No, definitely not!

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Replaced the filter cap. It's a lot smaller than the original. The original was clamped into place, and the new one is flopping around. I was wondering how I was going to hold the new one, as the old clamp is way too big. Yesterday, it hit me: tie wrap. Duh.

Searched through the giant pile o'crap that is my garage (I have strong hoarder tendencies) and found my strain relief tool, and removed the 2-wire power cord. Next step is to install a 3-wire power cord and test out the amp.

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I am annoyed.

I replaced the filter cap, got it tied down. Replaced the light dependent resistor (LDR) with a photocoupler and achieved tremolo. I cleaned up the reverb tank and remounted it using double sided tape, and checked that it worked. Then I put the chassis back in the case, and... no tremolo. Gotta take it apart again and figure out why it's there part of the time, and then not.

Grrr!

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Woohoo!

Thought it might be the tremolo pots, so I cleaned them. No help. Figured I had to have a loose connection someplace. Checked the wires on the pots, hoping to find a loose wire, but they were all solid. Checked the optocoupler I'd installed: solid. Bumped a transistor, and felt it move. Hmm, that's not supposed to happen. Wiggled it some more. Yup. Flipped the amp over to check it out, and found a wire moving in its solder. Cold solder joint, maybe. Maybe even my fault. Who knows? Anyway, soldered it up and tested the amp. Worked great. Cleaned the dust off of the speakers and flipped them over. Put the sjhole thing back together, and tested it again. It's good. Time to get it out of my back room!

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:thu:

funny, I've been dealing with intermittent issues on my old W7 computer I'm trying to resuscitate to give my daughter to use while she works from home, so  I can have my W10 laptop back! Every time I think I've got it working right, something goes weird...now it won't see the CD/DVD drive...:idk:

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On 5/2/2020 at 7:58 AM, daddymack said:

:thu:

funny, I've been dealing with intermittent issues on my old W7 computer I'm trying to resuscitate to give my daughter to use while she works from home, so  I can have my W10 laptop back! Every time I think I've got it working right, something goes weird...now it won't see the CD/DVD drive...:idk:

Try installing a version of Linux on it. Linux works quite well on older computers.

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Thanks, xS, for the suggestion, I would have, if it was for me, but I'm fixing it for MissyMack, and it would have to be compatible with her company's system....and I know it will handshake with Windows......plus, I'm almost done now, spent a lot of time dumping old files and defragging, now I just have to get wifi working [I've been running it hardwired]...probably tomorrow. Back when I got this machine, it was great, but the whole family started using it...and..well...they 'killed it'. At the time, it was faster and easier to salvage the important files and buy a new W10 machine...

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On 5/2/2020 at 6:58 AM, daddymack said:

:thu:

funny, I've been dealing with intermittent issues on my old W7 computer I'm trying to resuscitate to give my daughter to use while she works from home, so  I can have my W10 laptop back! Every time I think I've got it working right, something goes weird...now it won't see the CD/DVD drive...:idk:

Once (if) you get it up and running, have you thought about upgrading to Win 10? The free upgrade is still out there, you can find the details through a quick web search. We have a laptop at home that's about 10 years old but hasn't been used much. We got it out a few weeks ago to watch Sunday worship and Mrs. DeepEnd went on a tear about it having Win 7 so I installed the upgrade. All went smoothly.

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yephir, which is why I need to get the wifi functioning:thu:

The computer runs, like a champ...but now I have to find and download drivers for this generic wifi unit I'm plugging into it. I found it in my 'parts box', it was working when I tossed it in there many years ago...may be too slow, now, but I won't know until I can find the drivers for it. I may just order a new one from Amazon, they run like $20...

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Okay, so that amp went back to the owner without a major recap. I did replace the power supply filter cap but that was far as that went. Fixed the tremolo, and he was very happy.

Now I'm working on a Fender Deluxe Reverb. Same owner. He buys old shìt that doesn't work or breaks, then I fix it for him. This Fender falls into the latter category. He says it worked fine when he first got it a few weeks ago. Now, the reverb doesn't work, and neither does the tremolo.

I'm detecting a pattern here.

Troubleshot the reverb and found it was the tank itself, which surprised me. I've never known one to go bad. But I pulled this one out, and found both wires to the input transformer broken. I figured I could find a way to fix that, but I measired the resistance on the output transformer, and it's open. Too much trouble at that point, so he ordered a new reverb tank. Should get here tomorrow.

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On 7/1/2020 at 12:52 PM, isaac42 said:

Troubleshot the reverb and found it was the tank itself, which surprised me. I've never known one to go bad. . . .

Interesting. I bought a SS Fender several years ago that also needed a new tank. No clue how common it is but apparently it does happen.

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Recapping would seem to be wise I’m finding in late nineties to early 2000’s amps when it comes to power supply filters. So many terrible ones out there. A lot with cap disease and leakers galore. I have an Electar reissue on the bench with TREC caps and they’re all garbage. Granted it was a budget amp but COME ON. F&T are my go to.

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