Vintage Amp: Service or not?

[R.G.]

A lot depends on the heat the caps have been subjected to.

Yes.

If run with good ventilation and the tubes on the cool side,

If run - at frequent intervals to help stave off shelf decay and - run with good ventilation and the tubes on the cool side,

those caps will likely outlast any typical rock player or several owners.

OK.

If the ESR is good, and there is no indication of excess heat, I would leave them in.

The problem is (1) it's hard to tell what the history is and (2) simply not being turned on at all, even if stored in a cool, dry place, is also a limited life. The decision about leaving them in versus replacing them is not simple if there is any indication of long periods of storage with no polarizing voltage.

Caps, old quality models, fail a lot less than the internet "common knowledge" has convinced people.

Look up "survivors bias". Yes, conservatively rated high quality parts from any era last well. However, running to failure may or may not be an option. Replacing caps that have not yet failed is much like replacing or recharging fire extinguishers. The pressure meter may show it to be charged into the green area, OK. But do you want to bet your house and the lives of your wife and children that the meter is not stuck? Or that interior filling hasn't blocked the discharge hose just before the valve?

Where a part failure may cause collateral damage, the perfect situation is to replace the part just seconds before it fails. Unfortunately, unless one has struck some kind of deal with a deity, you can't tell when it's going to fail. So you do preventive maintenance. You replace perfectly serviceable parts precisely so they WON'T fail at an inopportune time or in a way that costs much more than replacing the part would have cost. It's the old "an ounce of prevention is worth a pound of cure" or "a milligram of prevention is worth a kilogram of cure" depending on what measurement system you use.

NOT replacing filter caps with a known wear-out mechanism is a bet, too.

If the caps are changed, new caps are a big question mark

... that is dealt with by burn in. Yes, infant mortality is a problem with all parts.

and an unknown quantity if boutique style. Those used in industrial, medical and communications, might not have the blessings of the golden ears types, but sure have the attention of those who really care about reliability and stability of the components; the design engineers.

Correct.

The two times in a component's life where the risk is highest is when brand new and when exceeding their design life or design operating circuit and environmental conditions. All that time in the middle is low risk.

This is correct. The problem with old amps is that there are two ways to exceed their design life - sheer power-on-hours, and shelf life. Both are exceeding the design life. What makes things difficult for old electrolytic caps and figuring out when to replace them is that non-destructive power-on-hours repairs shelf life deterioration a little, but not completely. It is always a guessing game as to when to replace them. But one thing is certain - one day they WILL fail.

[Mick Bailey]

The solder tab Mallorys can be rebuilt with new guts - just like new. They can also be stripped out and smaller, more modern cans fitted inside. In addition, there's a company selling new versions (think they're about $35 each).

F&Ts annoy me; the leads are way too thin and they come folded up so that the lead is often badly kinked right by the spot weld. To be sure of a longer life, I set them up vertically and do what Mallory used to do - reinforce the connection with epoxy. They always need to be well supported anyhow, but this is extra insurance.

[Pryde]

Thanks,
Looks like my supplier is out of stock on the 50/50 JJ cans so I agreed to them subbing in the F&T's instead. I am installing the can-clamps bolted to the chassis as well. I will keep in mind re-enforcing the solder tabs if need be.

[stokes]

Pryde,I believe Mick is talking about the axial lead F&T's,no need to worry about reinforcing the solder tabs.Just my prefference,but I think you are better off with the F&T's over the JJ's.

[Pryde]

OK makes sense. I have recapped a few vintage fenders with axial F&T filter caps but never have used their can caps. The F&T cans were only a dollar more per piece than the JJ's.

[Ted]

Before you replace anything with those JJ Electrolytics I suggest you take a look at their spec sheets. 1000 Hours at 70C for their TC and TE range does not fill me with confidence. I know this isn't avionics but that is a very unimpressive spec.
F&Ts are spec'ed for considerably more than that.
With proper grown-up modern components 10,000 Hours at 105 C is not unusual.

[stokes]

I've never used the JJ's myself,did take some out of an amp that failed in less than a year.I used to use nothing but sprague,I still do,but have been using the F&T's a lot,heard good things about them and after about 7 yrs using them have had no problems.For the price,much less the sprague,they are fantastic,every bit as good as the sprague.Those are the only 2 brands I use-ever.I had heard some negative things about JJ's,so I stick to what I have had success with.I think you'll be fine with the F&T's.

[Mick Bailey]

Pryde,I believe Mick is talking about the axial lead F&T's,no need to worry about reinforcing the solder tabs.Just my prefference,but I think you are better off with the F&T's over the JJ's.

Sorrry for the confusion - The F&Ts I was referring to are axial.

[Mick Bailey]

What other cap brands are people using? There's a choice of snap-in 500v rated caps that make good can caps. Some SS rectified Traynors (and others) use parallelled dual section caps 40uf+40uf and these can be replaced by a single value snap-in can. Specs appear to be better in a lot of cases than the caps intended for tube amps.

I've used Panasonic and Samwah with excellent results.

[nickb]

What other cap brands are people using? There's a choice of snap-in 500v rated caps that make good can caps. Some SS rectified Traynors (and others) use parallelled dual section caps 40uf+40uf and these can be replaced by a single value snap-in can. Specs appear to be better in a lot of cases than the caps intended for tube amps.

I've used Panasonic and Samwah with excellent results.

Here's an SVT I got in once


I replaced this unholy arrangement with snap-ins, I think they were Panasonics. My choice was primarily driven by ripple current ratings and case size:



Customer was very happy.

[Leo_Gnardo]

I replaced this unholy arrangement with snap-ins, I think they were Panasonics. My choice was primarily driven by ripple current ratings and case size

Some of our friends at Audio Asylum have been recommending the Panasonic filter caps for years. They use 'em to beef up power supplies in old McIntosh and Harman-Kardon (and other similar) power amps. Available at DigiKey.

[flyingdutchman]

What other cap brands are people using?

I have used axial Elna and Panasonic caps in classic Fenders, never any trouble.
Also, Philips and Panasonic snap-ins in place of chassis mounted cans on Marshalls, ditto.

Specs appear to be better in a lot of cases than the caps intended for tube amps.

You betcha. Some of those "boutique" caps fit the definition of snake oil rather well.

[km6xz]

Balancing experience with engineering principles seems to not square with the claims that filter caps fail so often.
The last 60,000+ repairs from my shop which did a lot of old amps, some owned by collectors but most by working touring musicians from all over the US and some from Asia and South America, doing a search of the database for failure codes indicated the failure of filter caps in tube amps was way down the list. It was much more common with early solid state amps from the 70s and early 80s.

When I had my large studio, there were 4 full time techs and me. I set up an aggressive pm schedule that resulted in replacing switches, pots and many coupling caps in 1-2 channel strips removed from the boards and enjoyed a very high rate availability for the controls rooms. After a dozen years of that, compared the scheduled replacement to the records of breakdown maintenance alone from a few other studios the same large frame consoles and there was little difference for my $100k a year investment in rolling rebuilds.

When I started the shop later, I kept track of all sorts of details of repairs and diagnostics, and studied them. Several manufacturers used my data in making warranty parts stock policies so when I made the claim that far fewer caps are failing than the internet rumors insist, it was from a wide range of repairs on many models, hundreds of most models. I doubt those insisting on the absolute need of replacing everything had the data to support the notion, and went by memory of a few standouts out of a limited sample.

Far too many perfectly good parts are replaced as a first resort, probably the majority of output transformers, and pre-amp tubes are replaced with the assumption they are the problem, instead of proven to be faulty or degraded. I would be more concerned with the problems introduced by all the parts swaps by well meaning techs of various skill levels. Most of my repair work now in my small side business, is refurb'ing poor tech work, which is much harder to correct than just repairing it in the first place.

[stokes]

Filter caps,like tubes have a limited life span,and should be changed periodically.Maybe good maintenance practice is the reason you see failure rates appear low.

[bob p]

Caps are wear items and they do need replacement. What amazes me though, is how some caps just continue to work forever, and maintain good capacitance and ESR in spite of their age.

I used to replace caps just because of their age, but now I use an ESR meter to test them before replacing them.

I've also embraced the use of snap-in caps when rebuilding amps. In most cases you can find a cap from CDE or Panasonic that has better specs. I'll often fabricate a little G10 board to hold them.