Capacitor Codes!

Learn something new every day, they say. I have been stumped by a largish Murata ceramic capacitor that does not seem to be working. It's from a Stax SRD 7 electrostatic headphone energizer, c. 1975. Its mate is a charred mess so I have not been able to test either.

Here is the legend on the cap: PTH BD 4R7M

It's apparent that this is a standard value 47 (something) but where is the decimal point and what is the voltage?

Transtronics' wiki comes to the rescue on capacitor codes.

The 'BD 4R7M' is evidently a military style code. The R substitutes for the decimal point. There is not a number following the R so there is no multiplier. So, it seems that this cap has a value of 4.7 pico farads, about as small as is measurable. The B indicates that a capacitance drift is not specified. The D is the voltage rating, 500 volts. The M indicates the cap has a temperature range of -55 to 70 °C .

UPDATE: a good question has been raised in the comments. The number 7 is evidently never used as a multiplier as indicated in Table 1. The multiplier format would be something like 474 which would indicate a value of 47 times a multiplier of 10,000, or 470,000 picofarads which is the equivalent of .47 microfarads. It seems to me that one would either have a R for a decimal point or a multiplier but not both at the same time. I guess neither would be necessary for a 10 picofarad cap which could be represented with just a 10, but that actually is a 10_ with the (blank) implying a multiplyer of 1. Whew.

Despite its rather significant size this is a pretty low spec cap.

Now, what about the 'PTH'? A bit of googling reveals that 'PTH' is a registered trademark of Murata and indicates the cap is actually a PTC Thermistor... What???

A thermistor is not a cap, it is a sort of current limiter whose resistance varies with temperature. PTC stands for 'positive temperature coefficient' which means the resistance goes up as the temperature goes up. But the codes on the item conformed to a capacitor!

So, it appears that today I have learned that I am confused. I wonder if in 1975 the PTH was used as a different indicator for Murata and it is indeed a 4.7 pico farad capacitor, or perhaps those codes do double duty and are used as indicators for the various qualities of a thermistor. The charred condition of the second 'cap' might indicate it is actually a thermistor that gave its life to protect the SRD 7. Hmmm.

Back to the Transtronics wiki page on resistor codes...

If a thermistor is coded like a resistor it would seem that this device has been coded via the BS 1852(British Standard 1852) and has a resistance of 4.7 ohms with a tolerance of 20% (M). The 'B' and the 'D' are not addressed. Therefore I would guess that it is not a coincidence that the device in question does, in fact, measure a resistance of 5 ohms.

Obviously, more research is needed.

The World's Finest 8 Track Collection

Ahh, 8 Track tapes: anachronistic, clunky, low-fi and heat damaged from all those hours in cars sitting outside in the screaming Texas sun. One of the technological miracles of the '70s was an 8 track tape that would play long after the label had the color sun-blasted from it. They were serious yard sale fodder of a generation ago, but they are getting a bit rare these days.

A disproportionate number of surviving 8 tracks are by artists like Ray Conniff or the Carpenters. Not that I am sneering at Ray, Karen and that guy playing the piano. But, really. Were all those Camaro and Cutless drivers that focused on staying in the middle of the road? Didn't anyone have a really killer 8 track collection back then? This question has not exactly haunted my every waking hour for the last 20 odd years, but I have wondered. A bit.

If you think about it (and although it is pathetic and sad, I do), the 8 track question really is one of survival. It would seem to me that your average rocker with a beater of a car kept his 8 tracks on the floor or the seat. His mom kept hers in the carrying case. So Ray and Karen survived and Pink Floyd went into the trash when the label was no longer legible. So that killer 8 track collection needed to have been owned by an anal retentive rocker (has one ever existed??) for me to find it all these years later.

Eventually all things come to he who waits. Just the other day I discovered that there was at least one person who had a great collection of 8 tracks and, in fact, stored it in an industrial strength suitcase. Maybe his mom made him do it, maybe it was his own unnatural instincts, but whatever. I am thankful. Here is a smattering for your viewing pleasure:

Mott the Hoople??? Savoy Brown??? There was even a Redbone tape in the pile. Several were quad tapes, and all were in great shape. Now I need to finish the 8 track receiver project and give them all a listen.

My compliments to the collector, whoever you were.

The Sony CDP 520ES CD Player

This is just too rich.

Here is a photo of the innards of this $600 list, vintage 1985 cd player:


Hmm, does this look familiar???

It is a dead ringer for the innards of the non-Esprit CDP 302 cd player documented a few days ago. The exterior is also identical, save the name. Whatever could justify the Esprit badge? Could it be... why yes it is. Here tucked in the corner are a few differences:


Yup, 4 boutique caps, the round red 'uns at the lower left and at the middle and lower right (one is just peeking through the wires. These are Elna Cerafines in the analog stage, right where I put a pair of Elna Silmic II's and a pair of Panasonic FM's in the 302.

Oh, yeah, there is one other difference. The 4 power supply caps of the 302 included 3 3300 mfd caps and 1 4700 mfd cap. Two were black Nippon Chemicon SM's and two were blue NXD's. The 520ES has 3 at 4700 and only 1 at 3300, so the power supply was slightly beefier. These are the 4 large blue caps (all Nippon Chemicon NXD's) at the top of the photo above.

Now there could be a bit more to this than meets the eye. Sony could have done some hand matching/selection of components and maybe there is something different about the chip set that I cannot see. But still.

So, in 1985 the price of 4 small boutique caps, a very slightly beefier power supply and a some Sony ES bragging rights was 50 bucks.

UPDATE: I just hate it when I miss something. There is a slight difference in the transports at the left rail. The rail is visible in the 302 but not in the 520ES, plus there is a slight difference in the back with a small board mounted differently. Now I am going to have to pop the tops again...

The Sumo Gold Power Amplifier

Every once in a while Mike feels a need to remind me that should I ever stumble across any Sumo amp, he wants it. Sumo was the creation of audio legend James Bongiorno of SAE and GAS (Great American Sound) fame and Bongiorno is one of Mike's heroes. Since I evidently don't get out much, my exposure to Sumo had been limited to the delightfully named Charlie (the tuner) until last Saturday when a Sumo Gold walked through Mike's door.

That is a bit of an exaggeration since Sumo amps are huge and need significant help moving around. Here it is:
The Gold was in very respectable shape with just a dent on the lower right corner, the bane of many a very heavy amp. It was in for a very brief check up and put on an impressive demonstration with the Infinity Quantum 2 speakers just visible in the photo above. Mike's Quantums are not exactly favorites of mine, but they sounded good driven by the Sumo. The bass extension and control was absolutely stellar on Mike's organ demo disk.

Here is a photo of Jay, the proud owner of the Gold:


Jay, you are now officially famous, an intrinsic part of the Great Internet. For those of you not from Austin, this is how all of us look. Gimme caps, tee shirts and stubble are what make Austin great. Well, that and a local beer in hand like a Shiner or a Real Ale from Blanco, Texas.

Yesterday, Jay and his friend Tom informed me that they had each just purchased Sumo 9 amps (sort of) via eBay although eBay had messed with them quite seriously. With luck the 9s will be documented in the not so distant future. (And many of us are debating how long before eBay just crumbles under its own jerkiness. Maybe more on that sometime in the future.)

In the interest of completeness, here is a photo of the Gold, just a bit naked:



Jay was driving the Sumo with the interesting Northern tube preamp, pictured below. It drove the amp quite nicely and the build quality seemed good. I think this is Chinese made, proof yet again China can be more than just crappy DVD players sold at Walmart. See the earlier article Bill did on the Yaqin amp.

And one last photo of Mike, bopping to Copland's Fanfare for the Common Man:

All Austinites are required to wear tie dye at least one day a year. Mike takes his tie dye seriously and tries to observe at least one day a week. Mike is also wearing the mandatory magnifyer (techs only) but he is in serious violation of Austin's smoking phobia. We are still working on that aspect of Mike.

Lastly, thanks to Kevin for the photos. (And let me be the first to congratulate him on the web for his future arrival. No, not an amp: Kevin is going to be a father! The Stereo Club is thrilled at having a new junior member and vows to outbid People Magazine for the first photos.)

The Sony CDP 302 CD Player

Not that one can tell from this blog, but I really do wield a soldering iron once in a while.

Lately I have had this hankering to revisit the quality CD players of yore. Back when the Ipod listeners among us were in diapers, CD players cost serious money and were actually made of metal and stuff. Inside of these vintage units were parts galore, not just air and a couple of chips. These were serious components built to last a lifetime, i.e. built to actually be repaired instead of chucked in the landfill. These were often very spartan players by modern standards because features (like a headphone jack!) cost you dearly. Over the last few months I have acquired several vintage players in working condition, something I absolutely guarantee will not be possible with the vast majority of current CD/DVD players, and I hope to restore and document a few of them.

The first up is the Sony CDP 302 which was manufactured in 1985 and listed for a non-trivial $550. It powered up and did its best to find the index, but the belts were crispy, of course, so it would not play. I begged belts from Mike, swabbed a few nasty bits, applied a few drops of oil and it worked. Interestingly, it easily played modern burned disks.

The CDP 302 has a nice bottom plate so access is easy. Therefore, I figured it was time to try a total re-cap to see how it would sound. I replaced a total of 44 caps with mostly Panasonic FCs, with a smattering of FMs. The final output coupling caps were replaced with Elna Silmic IIs. The 4 3.3k mfd power supply caps were boosted a smidgen to 4.7k at a slightly higher voltage.

Here is a topless shot:Build quality is very good. The transport is a hoot, stainless steel rails and all. Mike had never seen this mechanism before. The lubrication on the rails had turned to goo so the door barely opened at first. And it has a real transformer, not the chimpy sort of thing found in a modern player. The board at the left is lovely, with the very detailed legend actually printed on both sides. Eg. cap C 351 is identified on the trace side, a very nice touch. The output stage has a significant number of film caps, and there are a total of 6 of those cool clear copper foil caps between the DAC and the output. They obviously cared about the A in the D to A.

Here is the flip side:

The traces were fairly stout although I had several lift when doing hot pulls. Wicking was easier on the traces. Look at all the metal in that transport! Sony is currently a maddening manufacturer. They obviously have lots of very capable engineers, but many of their recent products have very serious QC issues. However, they obviously cared back in 1985 when they built this CD player.

I have been mulling over the CD source at the dawn of the medium, and why it took so long for CD sound to be competitive with that of vinyl. First, CD players were incredibly expensive, so the best of the players were very rare. The vast majority of us heard CD via down market, early generation players because that was all that was affordable. Second, the art of actually producing a CD was primitive, so much of what was available was crap compared to vinyl. Garbage in, garbage out as they say. On the other hand, designing a quality analog stage was easily attainable. Digital processing was a new art at the time, but the analog side of the equation was not. It has seemed to me that a spruced up, high quality vintage CD analog section could blow away your typical modern CD/DVD analog section. So, the sum of these theories has been that the top of the line vintage CD players are worth pursuing despite some digital conversion inadequacies, especially since they are so very cheap to acquire. With new belts and caps the game is afoot!

So, how does the re-capped and re-belted CDP 302 sound?

Very, very good it seems. In fact, it sounds so much better than my workshop Marantz CDR 630 (Professional!) that I am afraid I need to take a soldering iron to it. I hadn't realized how veiled the Marantz sounds. The first few minutes of the Sony were a bit inconclusive, but within 5 minutes the new caps settled in and the sound just opened up. This is a very smooth and detailed player. It gets a bit confused on complex passages, but it sounds great with female vocals. I need to let it burn in a bit more, but the reclamation project has already met my expectations.

UPDATE: it seems that Mike has a Sony CDP 520ES that at least superficially is a dead ringer for the CDP 302. Next week I will pop the top to see what's makes the 520ES worthy of the Esprit line.

Here is one last shot from the front, and I really need to take better photos: