Tantalum decoupling caps

[CJ]

Marantz uses tants on the phono preamp and on the tone board.

The low leakage can possibly mean saving pots from sounding scratchy so Marantz uses them in places where they connect to pots.

Tantalum caps have kept me employed for many years, without their short circuits i would have nothing to do.

Finding them on a big circuit board can be a pain. what are you going to do if you find zero ohms on a power rail, pull every part on the board til you find the culprit?

So i developed a way to find the pesky bastards, i hook up an external power supply to the shorted board and energize it til the current meter almost rails out, don't want to fry any traces, then i run my hand along the board feeling for heat. Usually a shorted tant will generate a little heat but not always.

Just used this on a Mesa Pulse 600 bass amp.
Most people gonna buy a new board so i don't feel bad about stressing out a pc trace.

In some cases i just crank up the current til the trace melts, pull the cap and run a jumper.
But this has to be on a dumpster amp.
That's right,people around here pull amps out of the dumpster then bring them to me for cheap labor, then flip them on evilbay.

How do i know they came out of the dumpster? We won't get into that, this is a family forum.

 

[CJ]

looks like Carvin did not like tants either, yellow film caps on this X100 git board,

Marantz tant phono inputs changed to Wima

bonus pic: Elvis drag show, vintage Randy Hansen and Nirvana plays second bill to Melvins,

and on the front of the shop poster board there is a new band in town, Drunks With Guns,
when a band gets 86'ed around here they just reform under a different name and re-book.

 

[RoadrunnerOZ]

As I recall, Rubert Neve actually preferred the sound (euphonic distortion?) of tants in the signal path.

There was (is, still around) also a bucketload of Neve gear that has only can electrolytic caps in the signal path. One thing I’ve noticed with Neve gear and the like is they do have a characteristic sound - the good thing I find with recording on some Neve consoles for example is getting a great drum sound recorded and then virtually no EQ required in the mix. If it ain’t broken don’t fix it.

 

[Gold]

There are a bunch of tant caps in the signal path of the Telefunken M15 tape machine. When I had mine restored my instructions were only replace what needs replacing as I wanted to hear it as close to original as possible. The bad caps were about half Al and half tants.

The machine sounds fantastic. I don’t know if it would sound less or more fantastic replacing the tants. The low frequency response has dropped from a few years ago so some of those AL caps probably should go.

 

[abbey road d enfer]

The machine sounds fantastic. I don’t know if it would sound less or more fantastic replacing the tants. The low frequency response has dropped from a few years ago so some of those AL caps probably should go.

Assumng TFK engineers have done their due diligences, they should have managed their circuits to minimize voltage across coupling caps.
It would be interesting to see if they have restricted the use of Ta caps for decoupling, which was all the rage at the time.

 

[Gold]

It would be interesting to see if they have restricted the use of Ta caps for decoupling, which was all the rage at the time.

That was the only exception to my rule. I don't like tants on the rails. I had all those replaced with Al. I do that on the Neumann lathe electronics too. No tant coupling caps in the Neumann VG66.

 

[Gold]

I don't like to use ceramic for audio as they are microphonic. One can argue that as bypass caps it doesn't matter but even with bypass everything counts.

I've been using through hole C0G in some EQ circuits. I've been liking the sound. I've been using my Barry Porter EQ's everyday for over a year now and there is nothing about them I don't like. They sound crystal clear. I'm not making an argument, just a data point.

 

[RoadrunnerOZ]

There are a bunch of tant caps in the signal path of the Telefunken M15 tape machine. When I had mine restored my instructions were only replace what needs replacing as I wanted to hear it as close to original as possible. The bad caps were about half Al and half tants.

The machine sounds fantastic. I don’t know if it would sound less or more fantastic replacing the tants. The low frequency response has dropped from a few years ago so some of those AL caps probably should go.

Those machines use some pretty big caps in the power supply - worth checking those out as well - I think they’re all 10,000uF can electrolytic.

 

[Gold]

Those machines use some pretty big caps in the power supply - worth checking those out as well - I think they’re all 10,000uF can electrolytic.

They are fine. It's been my experience that those big PS caps rarely go bad. I've never changed any of the big PS caps in the Neumann VG66. I always test them thoroughly and have never found a bad one. From the 1960's. They rarely go bad in Studer A80's either.

 

[CalavoBob]

I'm refurbishing a Lexicon Primetime 93 and noticed alot of tantalum caps for decoupling the power rails, analog and digital side.

I'm also refurbishing a Lexicon Prime Time 93. After ultrasonically cleaning the slider pots (which really needed it) and repairing one resistive slider trace with conductive paint, I discovered four blown analog 4558 OP amps which is much rarer than bad cap problems. After replacing them I got suspicious of their ceramic disc local bypass caps and found that this group of caps had dropped significantly in value and had become leaky. Replaced them with COGs and the unit is much happier. I think I'm going to shotgun them all. The tantalums seem ok but from the comments above I'll be checking them closely.

 

[JohnRoberts]

I'm also refurbishing a Lexicon Prime Time 93. After ultrasonically cleaning the slider pots (which really needed it) and repairing one resistive slider trace with conductive paint, I discovered four blown analog 4558 OP amps which is much rarer than bad cap problems. After replacing them I got suspicious of their ceramic disc local bypass caps and found that this group of caps had dropped significantly in value and had become leaky. Replaced them with COGs and the unit is much happier. I think I'm going to shotgun them all. The tantalums seem ok but from the comments above I'll be checking them closely.

My advice when working with old gear is to replace all similar capacitors (same value, type) when you discover bad components because they are likely from the same production lot and could suffer similar failures.

JR

 

[abbey road d enfer]

I'm also refurbishing a Lexicon Prime Time 93. After ultrasonically cleaning the slider pots (which really needed it) and repairing one resistive slider trace with conductive paint, I discovered four blown analog 4558 OP amps which is much rarer than bad cap problems. After replacing them I got suspicious of their ceramic disc local bypass caps and found that this group of caps had dropped significantly in value and had become leaky. Replaced them with COGs and the unit is much happier. I think I'm going to shotgun them all. The tantalums seem ok but from the comments above I'll be checking them closely.

These 4558's are solid workhorses. It looks like there may have been a power surge. That may explain he defective ceramic caps. Then it is mysterious that the tants survived...

 

[RoadrunnerOZ]

My advice when working with old gear is to replace all similar capacitors (same value, type) when you discover bad components because they are likely from the same production lot and could suffer similar failures.

JR

No matter what brand of equipment and no matter how reputable the maker, no manufacturer of now vintage gear could have built and no manufacturer today can build anything with absolute knowledge of the reliability of the components used and forecast 40 years into the future that they will still be functional. Added to that the “batch failure” likelihood of some capacitors or known failure characteristic of certain types of caps from the past, sometimes the sensible move is to just recap all likely suspects. I have done this sometimes far more cost effectively than trying to trace through, component by component, audio and power rail faults.

 

[JohnRoberts]

These 4558's are solid workhorses. It looks like there may have been a power surge. That may explain he defective ceramic caps. Then it is mysterious that the tants survived...

Generally but depending on the circuits where used especially on inputs or outputs, excessive voltage from outside the unit can blow up any op amp. The path is from the op amp to the power supply rail, so nearby failed decoupling caps is more evidence of such a fault vector.

JR

 

[PermO]

Point of interest to any Hammond tone wheel organ owners or repairers - also totally unrelated to tantalum capacitors - I’ve seen many expensive quotes for replacing the motor that drives the tone wheels, when in fact it’s the run/start capacitor that is failing which costs less than ten bucks. To check all you need to do is twirl the motor shaft with the power on and if it runs then it’s the capacitor. Owners tend to not refill the oil bath and it makes the bearings dry out and it becomes hard to start. The old style paper capacitors dry out.

Not to derail this tread any further but you seem to know a thing about Hammond motors.

I have a tonewheel assembly in a box that I put solid state realais on the bass section to play via MIDI.
Works great.
I have lubed the tonewheel assembly with the original oil and it runs pretty smooth.
I have replaced the motorcap for a modern one.
And with the assembly connected it all runs pretty smooth betwee my two fingers.

But that motor gets really really hot while running, and I don't see why ?

 

[RoadrunnerOZ]

Not to derail this tread any further but you seem to know a thing about Hammond motors.

I have a tonewheel assembly in a box that I put solid state realais on the bass section to play via MIDI.
Works great.
I have lubed the tonewheel assembly with the original oil and it runs pretty smooth.
I have replaced the motorcap for a modern one.
And with the assembly connected it all runs pretty smooth betwee my two fingers.

But that motor gets really really hot while running, and I don't see why ?

In the operation manual for the source organ for the tone wheel assembly you should find a section outlining all the lube points, make sure all the lube felts are moist with oil - depending on model some have a start motor and a run motor and others use a single self start/run motor - single switch models. It will have two very small cups on each end of the motor. The cups will have little spring loaded caps covering them. Here you put drops of oil into the cups until they are filled. Stiff dry motor bearings can cause them to run hot.
Handy info here:
https://bentonelectronics.com/oiling-instructions-for-the-hammond-organ/

 

[PermO]

Yes, I found all these oil points and all runs smooth, when I cut the power the assembly + motor keeps spinning for 5 seconds or so.

But it gets really hot.

there's a whole of gunk on the inner wires on the motor, don't know if this is collected filth or some gunk to seal the windings.

 

[RoadrunnerOZ]

Yes, I found all these oil points and all runs smooth, when I cut the power the assembly + motor keeps spinning for 5 seconds or so.

But it gets really hot.

there's a whole of gunk on the inner wires on the motor, don't know if this is collected filth or some gunk to seal the windings.

You can remove the motor, give it a good wash and relube the bearings. If any of the gunk is conductive and is joining the winding termination points it can cause heat but this is unlikely. A buildup of oil-wet dust gunk can result in the motor not cooling itself properly - best bet is to disconnect the motor from the tone wheel shaft, switch on then off and see if the motor runs on free after power-off - it’s bearings may be failing. You can remove the motor, and brush it down with a petrol or kerosene dampened soft paintbrush to remove the gunk if it is gunk (and not just the varnish for sealing the windings).
I don’t know if yours is 240 or 110 Volt motor but you could always get a new motor - there is a complete tonewheel assembly for sale dismantled including 110V motor:
https://ssl.tonewheelgeneral.com/build_page.php?category=Hammond+Organ+Parts&subcat=Vintage

 

[Ike Zimbel]

I've been using through hole C0G in some EQ circuits. I've been liking the sound. I've been using my Barry Porter EQ's everyday for over a year now and there is nothing about them I don't like. They sound crystal clear. I'm not making an argument, just a data point.

+1! COG caps are a very different animal than ye olde ceramic disc cap. I have been using them for years in place of polystyrene and have no complaints.

 

[PermO]

I will check the gunk again when I have the time for it, take pictures and start a topic... about motorgunk.