Where to use low leakage caps? Recapping preamp.

[Sam08861]

Hi All,

I posted on the solid state forum for some specific help, but no responses so far. (Here... has photos of the unit and link to service manual.... http://audiokarma.org/forums/index....-capacitor-list-for-the-technics-9070.841921/ )

I'm recapping a preamp (Technics Su-9070) and have the service manual, which lists all the electrolytics and also has notation for those that are non polar. For the electrolytics, I'm planning on using Elna Simlic IIs and Low ESRs for the power supply caps. For the non polars, I'll use nichicon muse.

Where there's a call for low leakage caps, I'll use nichicon ukl, but not sure which ones need this.

What I can't figure out is which ones should be low leakage? Any suggestions for which sections might need the UKLs or notations I should look for?

The amp, power, mc prepre, phono, etc. sections are all clearly separated and labeled on the board and the signal path from the inputs to the outputs is followable, so ever general guidance would be helpful. (i.e. the power supply caps should be all ESR as an example, but looking to understand which ones are low leakage specifically before ordering the caps)

There's also paper caps at the power switch and switched outlet on the back. Do I need to replace these? If so, what would you reccomend? PIO?

Below is a snap of the cap list. Ones in shaded grey are non polars.

• List is broken up by section. For instance the first grouping (C101,102 through C115,116) is the 100s or MC pre-pre amp,
• 200s is EQ amp and EQ subsonic
• 300s is DC flat amp
• 400s is power supply and muting section
• 600s is 2 caps next to the inputs
• 700s are the 2 pios I mentioned earlier.

The boards are physically sectioned off by these areas as well.


There's one more line on the next column, but it's just a repeat of the last line for the paper capacitor.

Here's how the layout is from some marketing materials. Same diagram is in the service manual



Any help greatly appreciated!

Thanks,

Sam

 

[c.coyle]

If the schematic doesn't indicate low leakage somehow, look for small electrolytics, maybe 10uf and smaller, that are a different color from other electrolytics. Often old low leakage caps are pink or orange. I just use films to replace old electrolytics 3.3uf or smaller, whether or not the original electrolytic is low leakage. Films usually have lower leakage than any equivalent electrolytic. WIMA MKS2 or Kemet R82 are easy to find at Mouser and Digikey, respectively.

 

[roger2]

Usually the LL caps have a different color sleeve. Orange is a common color but there are others. A good close pic of the caps in your amp should be helpful. The number of LL caps used varies. In amps that I have worked on there was some type of designation in the parts lists for the LL electrolytics. I am not familiar with Technics though.

 

[Sam08861]

Thanks all!

The unit in question is actually a Technics, so I'm guessing that all of the capacitors are Panasonic, if that helps. The triangular Matsushita logo and part numbers seem to correspond also.

I did find some orange ones and will take and post photos of each section now. Will also look at the schematic again.

Theres 2 orange ones in the MC section...

One below is c-109, which happens to be one of the bold ones. The purple one in the corner is a non polar, having no stripe and it (c208) is identified as such in the cap list.

Also, there are a few that seem to have outgrown their clothing such as the ones southwest of the orange cap. They have the same dark blue and gold as the ones on the bottom right.

 

[c.coyle]

Looks like 10uf. I would say low leakage.

 

[Sam08861]

Here are the various sections

EQ subsonic




MC pre-pre amp





Power supply

EQ preamp

DC Flat Amp

Input section

Power Switch paper cap

Muting section

 

[Sam08861]

Another close up of mc pre pre

 

[Sam08861]

Never mind on the input section caps, those are polyester.

 

[Lavane]

If the schematic doesn't indicate low leakage somehow, look for small electrolytics, maybe 10uf and smaller, that are a different color from other electrolytics. Often old low leakage caps are pink or orange. I just use films to replace old electrolytics 3.3uf or smaller, whether or not the original electrolytic is low leakage. Films usually have lower leakage than any equivalent electrolytic. WIMA MKS2 or Kemet R82 are easy to find at Mouser and Digikey, respectively.

I tend to do this as well. Replacing the small value electrolytics with stack films. Heck, I would use all film if not for the humungous size of large value caps along with the huge extra cost.

 

[Sam08861]

I see on the schematic, that the cap symbol for the orange ones (c110) has lines drawn between the 'plates.' Some of the others do too, but on the board they are the regular purple or blue/gold caps.

Might this be the symbol for low leakage?

 

[c.coyle]

I see on the schematic, that the cap symbol for the orange ones (c110) has lines drawn between the 'plates.' Some of the others do too, but on the board they are the regular purple or blue/gold caps.

Might this be the symbol for low leakage?

View attachment 1310632

No, those lines indicate electrolytic capacitor, as opposed to non-electro.

 

[Sam08861]

No, those lines indicate electrolytic capacitor, as opposed to non-electro.

Thanks c.coyle. Always good to learn something new!

Might it be that the two orange ones are only low leakage spec'd items?

 

[c.coyle]

Thanks c.coyle. Always good to learn something new!

Might it be that the two orange ones are only low leakage spec'd items?

I wouldn't stress too much. Replace the orange ones with low leakage electros, use regular electros or films for the rest. Modern "regular" electrolytics have lower leakage specs than equivalent caps from the '70s.

 

[Sam08861]

That's what I was thinking. Placing order now and thanks everyone for their quick responses. Sam

 

[roger2]

The shrunken sleeves are likely due to heat. I would replace those caps with low ESR, 105° rated caps.

Before pulling parts or placing the parts order, it is a good idea to check for local sources of heat that may be near any caps. Some diodes, big resistors, TO-220 transistors, etc. can run pretty hot. Any electrolytic that happens to be physically close to a significant heat source it is a good candidate for a 105° rated replacement.

 

[Sam08861]

Thanks again roger2,

I do see also the brown spots on the board wherever there are transistors and diodes. Was wondering why several of the smaller blue/gold items looked too big for their britches, lol.

 

[Sam08861]

Comparing the parts list in the service manual to what's in the actual unit, there are 2 differences (4 caps total)

The spec calls for 3300uf 6.3V caps in the MC pre-preamp positions c101, c102 but the actual unit has 2200uf 16V caps. (schematic and board diagrams also have 3300uf 6v)

Similarly, the eq amp as 4.7uf 16V in place of the service manuals 4.7uf 25V.

The 4.7uf is an easy decision, however for the MC caps, what do you think, go with service manual or with what's actually in the unit?

Or perhaps just order both to see what works better?

 

[roger2]

Usually you go with what is in the unit as design changes during a production run do not always make it into the manual. This assumes that the parts appear to be original.

You have the ability to check actual DC operating voltages assuming you know where not to touch probes or fingers inside a live amp.

EDIT: Simply going with the higher voltage ratings for the caps mentioned above would be the easiest route, and would not cause an issue.

 

[c.coyle]

Check your parts list and see if there are any VD1212 diodes in your unit. The power supply board looks like it could have a few. They can be troublesome, and one VD1212 can be replaced with a pair of 1N4148's soldered in series. There are several threads here on VD1212s.

 

[Sam08861]

the parts lists the following diodes..

MA 150 (4 of these)
SVDMA26-2 (10 of these)
SVDMA26-1 (4 of these)

might any of these be suspects?