Need Help Finding These Replacement Caps!

[Paul Marossy]

Not technically a stompbox thing, but I need the amp to use my stompboxes!  

I have a Seymour Duncan Convertible amp which has a pair of Mallory "Type CGS" 200uF 350V filter caps that are in need of replacement. These are big can type caps which are about 1-1/2" in diameter and about 3-1/2" long, with screw terminal connectors. It looks just like what is shown here: http://www.ebay.com/itm/MALLORY-CAPACITOR-TYPE-CGS-1200MFD-100VDC-/260303549551?pt=LH_DefaultDomain_0&hash=item3c9b4cf46f - these are the "main filter caps", and are the first ones right off of the tube rectifier so I assume they are the ones that "work the hardest".

I thought I had it fixed the other day, I took the whole amp apart and saw that the mechanical connections to these particular caps were corroded and apparently not making a good contact. I cleaned those up and it was working and sounding great. Used it for about four hours on Sunday, no problems. Fired it up yesterday it it was making an ugly static noise whenever I played anything under an open A in terms of frequency. Then it was "motorboating" as soon as I turned it on. I ruled out the modules as being the problem.

Do you know of a source for replacements or have any recommendations on what I could use in their place?

Any help would be much appreciated!

[R.G.]

Find the physical dimensions of the capacitors. Particularly the diameter, the length, and the distance between the screw holes. Also note how big the diameter and length could be and still fit in the amp.

The dimensions of "computer grade" caps (that's the nominal name for these typed) are highly standardized. Once you know the terminal hole spacing from center to center, you can look in any cap supplier and find on that will screw in to the same holes. The body length and diameter tell you what physical size you can stand. Then get on the net and look for caps that meet the dimensions and the cap size and rating. The rating is like any other cap replacement for power filters: get the same or more capacitance, and the same or more voltage.

[Paul Marossy]

I looked online before I posted here and didn't come up with anything. The ones I did find were like ten times what I need!

I'll keep searching though....

[iccaros]

if the CAP is good, but  the terminal are corroding, you could also do one of two things, you could apply solder to the plate to protect it from corroding, after cleaning first, or you could just clean them well and solder the terminal to the cap. Use a clip as heat sink while applying solder.

This could buy you lots of time to find a suitable replacement.

[Paul Marossy]

I already cleaned up the corroded terminals and all that, plus I put lock washers on them so they couldn't come loose again. The caps are definitely failing now. 

[SteveG]

"The rating is like any other cap replacement for power filters: get the same or more capacitance, and the same or more voltage.

With the caveat that you don't want to exceed the maximum capacitance value recommended for the valve rectifier.

Steve

[Paul Marossy]

"The rating is like any other cap replacement for power filters: get the same or more capacitance, and the same or more voltage.

With the caveat that you don't want to exceed the maximum capacitance value recommended for the valve rectifier.

Steve

Good point. It's a 5U4G rectifier, powering (4) EL-34 power tubes and up to (8 ) preamp tubes depending on what modules you use.

[SteveG]

I'm not familiar with that amp, but 200uF seems high for a valve-rectified design? They could be in series, I suppose, to give a rating of 700V, but even so, still high @ 100uF.

[Paul Marossy]

I'm not familiar with that amp, but 200uF seems high for a valve-rectified design? They could be in series, I suppose, to give a rating of 700V, but even so, still high @ 100uF.

They are in series actually, I never noticed that! The module tube filmaments are operating on DC power, plus each "channel" has more filter caps, too. Schematic is here: http://www.diyguitarist.com/PDF_Files/SDC-Powers.pdf - they are the ones connected to "V4", center left side of page.

[LucifersTrip]

Do you know of a source for replacements or have any recommendations on what I could use in their place?

I don't know what  price you're shooting for, but these guys just helped us out with replacing a can cap in a 1964 record player:
http://hayseedhamfest.com/capacitors/Capacitors.html

the other option was to actually re-stuff the large can with new cap(s). amptramp sent a cool link:
http://www.antiqueradio.org/recap.htm#replacing


good luck

[amptramp]

"The rating is like any other cap replacement for power filters: get the same or more capacitance, and the same or more voltage.

With the caveat that you don't want to exceed the maximum capacitance value recommended for the valve rectifier.

Steve

Heed this caveat.  The rectifier conducts only when the voltage is above the capacitor voltage which means that the higher the capacitance gets, the shorter the available time for the rectifier to conduct.  Of the 5U4 variants, the following ratings apply:

5U4GA average current: 225 mA, peak current: 800 mA
5U4GB average current: 250 mA, peak current: 900 mA
5U4GC average current: 275 mA, peak current: 1000 mA

[iccaros]

I'm not familiar with that amp, but 200uF seems high for a valve-rectified design? They could be in series, I suppose, to give a rating of 700V, but even so, still high @ 100uF.

They are in series actually, I never noticed that! The module tube filmaments are operating on DC power, plus each "channel" has more filter caps, too. Schematic is here: http://www.diyguitarist.com/PDF_Files/SDC-Powers.pdf - they are the ones connected to "V4", center left side of page.

Na the filaments are still AC.. they rectify to get 10.5 bias voltage H.
I do not see where A is going, which is your tube rectifier and the 100U (200 in series) caps..  its using silicon for the other voltages. ..Sorry it goes to your Power output center tap on the transformer for the EL34.
That is all this is feeding, so this is not a normal supply, looks like its engineered to provide SAG on the power tubes only.... interesting..

[Paul Marossy]

Na the filaments are still AC.. they rectify to get 10.5 bias voltage H.
I do not see where A is going, which is your tube rectifier and the 100U (200 in series) caps..  its using silicon for the other voltages. ..Sorry it goes to your Power output center tap on the transformer for the EL34.
That is all this is feeding, so this is not a normal supply, looks like its engineered to provide SAG on the power tubes only.... interesting..

No, the module tube filaments are operating on DC. The three preamp tubes that are doing the variable wattage circuit and the phase inverter are on an AC filament scheme. There are non-tube (solid state) modules that can't be powered via an AC tube filament connection where the modules plug in (that's what the LM317 is for). The preamp schematic is here: http://www.diyguitarist.com/PDF_Files/SDC-Preamps.pdf

Anyway, yes, this is not your typical amp. It's a quite different animal.

[Paul Marossy]

I found one that is 250uF at Mouser. Apparently a 200uF cap isn't made anymore.
http://www.mouser.com/ProductDetail/Cornell-Dubilier/CGS251T350R3C/?qs=u7ZFOgOpR2urm9VcXXMd%252bg%3d%3d

Do you think that would be OK to use as a substitute? That would make it about 25uF higher than it is currently...

[DavenPaget]

http://www.mouser.com/ProductDetail/Cornell-Dubilier/381LX221M350H452/?qs=sGAEpiMZZMukHu%252bjC5l7YV8H6sZiiPP7M0UOb%2fWj3Eo%3d

[Paul Marossy]

http://www.mouser.com/ProductDetail/Cornell-Dubilier/381LX221M350H452/?qs=sGAEpiMZZMukHu%252bjC5l7YV8H6sZiiPP7M0UOb%2fWj3Eo%3d

It's physically the wrong size, won't work. (needs "can clamps", 1.375" diameter)

EDIT: I suppose the clamp could be changed. But I would rather have the Mallory CGS type.

[davent]

http://thetubestore.com/ca-jj-250uf-500v.html

And more JJ options.

http://www.partsconnexion.com/capacitor_ele_jjcap.html

[iccaros]

Paul
I do not understand, unless part of the schamatic is missing
all of your tube EL34 and 12AU7 are AC filaments.
then is rectified to 10v through the LM317 dc which goes to first channel preamp and your effect loop buffer and recovery.


you can see that the tube rectifier tube is directly heated cathode coming off the 5v tap on the transformer -->
where once rectofied you get according to the drawing 575vdc riding on top of the 5v ac which is standard. They then do full wave rectification by having diodes pull from the plates and other taps to get other DC voltage


variably wattage is handled through changing the way the power tubes are wired to the output  transformer  where it lifts the output tube screen tap on the transformer and reduces the ratio to the plates, in effect reducing the primary impedance reflected to the output tubes.


in any case this is about capacitors, you can use this chart to find your max capacitance for 5U4 you can use this sheet to find your max capasitor value after the 5u4


we need to know the PT resistance to find a good new value, the data sheet shows 40uf as max first capacitor another shows 33uf. You could replace it with one capacitor if you could get 650 - 700v cap.

[Paul Marossy]

From the LM317, after the diode bridge rectifier D6-D9, there is an "H" supply which doubles as the filament supply FOR THE MODULES. This has to be DC POWERED because there are NON-TUBE modules which need a DC SUPPLY to operate. You can't operate a solid state FET or solid state IC module on an AC power supply.

Each module terminal on the main PCB has an IN, OUT, B+, GROUND, HTR GROUND and HEATER 10.5 VDC connection on it.

I'm the guy who reverse engineered the amp - http://www.diyguitarist.com/GuitarAmps/Convert.htm
Look at the modules section, at one of the layouts and maybe it will be more clear what I am talking about.

[iccaros]

now I understand, thanks, I assumed the MODULES were non tube based on the the schematic, but I see you can get tube based modules which is kind of cool, thanks for the patients.

but to your caps, I would not use larger caps,  depending on the impedance of the power transformer, is already exceeding the datasheet, which is 33u or 40u depending on make. They put 100u so I assume the Independence matches that, but to go over by 25u is a lot for rectifier tubes