"I would like to find out what problems are specific to the Hallicrafters
SX-99. Where is a good place to look? "

Inside the Hallicrafters SX-99 would be my first guess.

"
I'd be interested in which of the old caps were known to have "issues".
or to fail. Sure, they are all old (in any tube equipmnent), and they
are paper caps, which are no longer made, but I'm sure some brands were
better or worse than others. "

The bad caps in old tube radios have already lasted longer than any normal engineer would plan for. The people who made those caps, by default, made them to last forever. so much for that. Of course as you know some of them can be reformed. Not that I would trust that in a heart/lung machine, but maybe for a table radio.

"(snipped the BS about older caps) Paper caps
seem to have passed the test of time. We wont know if these newer
materials pass the test of time or not, until we get there. "

We do know, and they don't. Newer capacitors have failure modes that'll put hair on your chest, curl it and take it off in one fell swoop.

I worked on bigscreen TVs, which were a fad here in the US and I made alot of money off of it because nobody else could understand it.

Well there were YEARS of Mitsubishi product out there with defective caps. someone (Rubycon ?) stole a formula for the electrolyte which was not yet perfected. but they made the caps and they had higher density, which means capacitance and voltage ratings in a smaller size. Thatis what determines the value of an electrolytic capacitor on the market. You got ESR, ESL, intolerance to heat as minus, microfarads and voltage are the plus. And the smaller the better.

You have to think outside the box to really understand this, electrolytes are not necessarily insulators. In fact when they leaked out on the board of $3,500 Mitsubishi TVs they caused leakage paths on the PC board.

Forget air and vacuum as an electrolyte, they are actually not. The electrolyte is more like the acid in your car battery.

Anyway, I have done alot of service and streamlined many the process. If you look at the damn schematic you can tell which caps are stressed worse and you know to replace them. New caps have hours before MTF based on ripple current. Well some do. Elcheapo ones do not give specs because they are so dismal, like the THD rating of a loudspeaker, they could never sell amps with 0.03 % distortion if people knew that actually good speakers usually have 5 % or more at normal listening levels. Of course some are lower, go have a look at the Martin Logan website for that, and if that doesn't make your wallet hurt go find some Quad ESL-63s.

In other words some things matter, others do not. Like I am about to work on a Pioneer SX-737. I am NOT replacing all the caps, and BTW, those big ones in the power supply, when they are bulging they are not necessarily bad. I am replacoing a bunch of PNP transistors because they were prone to failure ad could damage other components. there are a few caps I am going to change and I will (upon request) supply the schematic and my professional judgement as to why these caps get changed and why the others do not. If you understand the circuit you realize that some of these caps are nowhere near the audio path and do not affect the sound. If they pose a reliability problem that is different.

Now, you brought up old caps, and upon that I would like to expound a bit. A couple few years ago my sister's PC monitor crapped out. I had already been working on flatscrteen TVs so I knew the deal. I found a bank of caps, which is usually what they are, all bad. See, in business toward the end I did not replace all kinds of caps, I just bridged one in and when it worked I knew the caps would fix it. this was my job.

But this was far from professional. Her power supply of course worked up in the hundreds of KHz. I had no caps at the house but a thirty years old one.. Originally in the circuit there was a bank of 1,000 uF @ I think 35 volts, I only had 25s.

I took and old 100 uF @ 160 volts and stuck it in there and it worked. Think about it, a good cap, 100 KHz ? /Of course it worked.

I told her I really did not have the right part right now so be ready for it to fail, and I will order the right part.

It has been running for over three years now.

These engineers are idiots, they use banks of caps of poor quality instead of just a few good ones. But then they need to design next year's product you are forced to buy because this one failed. Like the government, is it complicity or incompetence ? To me it does not matter, they need for some heads to roll. They are wrecking the ****ing planet.

Guy on here talking about Taiwan or whatever dog country saying it is a dumping ground for our junk electronics. GOOD ! That is where the garbage came from in the first place ! Take it back. In fact take it all back. I want to go back to where I have only six channels on the TV. I **** you not.

And I want a table radio in the kitchen.

Know what ? Off to eBay, or better yet Craigslist.