Evaluating Vintage Black Beauty and Bumble Bee Capacitors from a McIntosh Amplifier

A reasonably thorough study of vintage capacitors particularly, how they may leak DC thru the capacitor after the age of several decades.

[benadams]

Very nice, thanks.

Another concern with old capacitors is whether they are leaking DC at high voltages, as in e.g. when used for coupling to prevent messing with a grid bias. Some capacitors tend to degrade into a capacitor with a paralleled resistor.

[davidahiwaaynet]

That capacitor analyser instrument is really a beautiful piece of machinery. Would love to understand how it actually is working. Thanks for the demonstration!

[l_shaun_bunds_l]

For years there has only been a handful of maybe five YouTube videos concerning the massive breadth of genrad components and benchtop, the numerous applications their equipment has spanned. I love their 1920s-30s period as far as the aesthetic and general philosophy their components had: this is when they still had dealings with CRTs and they made their own tube sockets and you could order any number of awesome transformers or rheostats or even a power amplifier kit. I began collecting general radio and Weston as well as a few other contemporary manufacturers but general radio is my favorite. i love to the subtle evolution of their designs: how many bridges can you have? Let alone impedance bridges or comparators orhybrid instruments? My interest was accidental due time not being able to afford Manley or Shadow Hills pro audio or even the older analog audio which is has become outrageously priced: a Davenport attenuatir with famed viz skirted pointer Bakelite knob? 100? A langevin: 300? A simple Raytheon or Collins front panel with no internal Amps or power supply? 700-1000? WHY FOR? anyway I need to start doing some tear downs and demos of my equipment. My bench and area is a cluttered mess however. I need to get these Weston 686 9c and 10as modded for 1kv for power triodes and fix the other problems. If only I could befriend an experienced tech in the Southern California area or come join another stocked warehouse situation but with a boss who didn't promise me a job sorting out then, off sticks for moving millions of tubes to a central location and then guilt trip me about his ever failing and changing health or situation: come to find he had been accused of fraud by searching Koterba and audio asylum. Art lane. Blah blah.
Anyway sorry for the digressions and lack of focus. I really have been grateful for the integrity and humility displayed in your videos. . . And relative diligenc... And Comraderye with uncle Doug.

[aircooledcamper]

Leakage has always been my main concern too. That and the bumblees and black beauties exploding. I would think if they were leaking at the (AC) voltage that GR bridge applies, that would have to show up as an increased power dissapation on the null. Of course, they could still leak at high DC voltages, I suppose. Just thinking out loud....

[carlburgess]

Nice old equipment you have there. I use an old Knight kit capacitor tester to check for leakage. I have found that the new ESR testers call capacitors good that I tested as leaky on the Knight Kit tester. I think that the ESR cant provide the high voltage that will overcome the dielectric of the capacitor at test. On low voltage application I will use the ESR's findings in none critical circuits. Thanks for the fine videos, I enjoy them.

[mixolydian]

Hi thanks for the interesting video, yes what a beautiful instrument. Any chance you could test the capacitors you replaced them with? All the best.

[khurai]

And the tester you used. May I ask the name of it? Is it a good piece of equipment?

[bucyruserie]

Hi David, I had watched this video previously, and enjoyed just watching you use the old equipment....but I did not have any of those type capacitors, and wasn't looking to determine if any were good. Recently however I came across 2 1960's console type units at our town's local recycle. I scavenged all the tubes, transformers, speakers, resistors, and quite a few of those Sprague caps. Out of 18, only 2 read different then labeled for capacitance using my dmm. And only 1 read any resistance using my triplet multi meter. Its the only way I can test them. I doubt if i will use any of them, but they are all pre 1964 and I think they would still work fine (aside from the one that leaked). All the tubes I checked 12ax, at, au7's and el84's tested near new. I have purchased new tubes that didn't test as strong, or as well matched per triode (for the 12ax7's) I'm not saying they made things better back then, but time will tell. As you have stated in one of your video's, are the new capacitors were using now going to be working 50yrs from now?

[MichaelLloyd]

I have a General Radio 1650A. It's not as nice as yours. It doesn't have a power cord. Just a hole in the top right side that looks like it might take a tube full of batteries. There's plate on the outside that says it used to belong to the US Navy. I've never really looked into using it. I'd rather not part something this gorgeous out. How is yours powered?

[tjasont]

Leakage under high voltage is the only test that matters u don't need a bridge take your 5 dollar meter from harbor freight if it reads correct Capitence and u test leakage under high voltage and passes your good. I've had caps read great on esr meter and leak like crazy u can't use a esr meter or any low voltage test to check caps in vaccum tube gear I respectfully disagree with this conclusion. Also u have to take into account the composition of the cap some old black beauties were film caps judging from the size of those caps they were probably film caps. which may never go bad not that they can't but are much much more reliable. I just got in two Magnavox amp 142 twos with paper bumble bee caps and every one of them leaked under DC infact I can't remember when I have found a paper cap in the last 5 years that didn't leak at it's specified voltage I have plenty of caps that test great on an esr meter that leak like crazy don't waste your time with esr test on small signal caps it's useless. Unless they are shorted it will tell u nothing how can it the series resistance is much lower than the parallel leakage resistance so it just won't see it.

[khurai]

I'm pretty impressed. I really heard horrible things about Bumblebees, BBs.. oil caps. Those things in guitars devalue like hell. But those look still good. Is it because they weren't used for all those years? Or is it because they are just good?

[mrGoesto]

Although I certainly appreciated the verification with science tools rather than anecdotes, I wouldnt want to be the customer with the Mac that just lost some nice old in spec vintage caps.

[patim]

The DF is not 0 to 1, it can be much higher, my HP measures up to 50. It is the ratio between the real resistance R, and the reactance Xc. Not the resistance and capacitance.

It is very easy to calculate the ESR from DF.

By the way, most ESR meters do not measure ESR but impedance at 100kHz. Most cap manufacturers give the DF and ESR (or tan-d) at 120 or 1000Hz. Not at 100 kHz.

By the way, like your videos, I have a lot of GR too (and also your VTVM and Tek 130)