• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

ARC SP3A-1 Repair Advice

Those filament caps could be bad also, causing more ripple in the filaments and the cathodes. I replace every capacitor in the power supply of every SP3 I get these days. They are time bombs. My friends and I love those preamps, I have 3, my friends have an addition 1/2 dozen or so. All of them have new power supplies.
 
stanko said:
Those filament caps could be bad also, causing more ripple in the filaments and the cathodes. I replace every capacitor in the power supply of every SP3 I get these days. They are time bombs. My friends and I love those preamps, I have 3, my friends have an addition 1/2 dozen or so. All of them have new power supplies.
Click to expand...

When I woke up this morning, I realized my diagnosis did not make sense because if there's no ripple on the main B+, there should be none on the derived B+5 even if those caps are bad. Also, the ripple is showing as too high on the main B+ and the filament voltages.

Your probably right, I should rebuild the whole PS (even though it appears to have been done in 1992.) I'll probably replace some of the resistors and the small caps but I think all the diodes and the transistor are OK to leave.

As per post 22 just above, I need to find the parts.
 
I can make you guys a list of the last set of parts I used about a month ago, I think. The preamp is in Portland Oregon now, so I don't have access to that one. I do have another I did recently that I will post pics of soon.
 
stanko said:
I can make you guys a list of the last set of parts I used about a month ago, I think. The preamp is in Portland Oregon now, so I don't have access to that one. I do have another I did recently that I will post pics of soon.
Click to expand...
Be great to see what you did. I did one for Tom in Seattle. Thinking maybe restuffing a set of cans for mine. But there are lots more things to change with the carbon comps in there.
 
stanko said:
I can make you guys a list of the last set of parts I used about a month ago, I think. The preamp is in Portland Oregon now, so I don't have access to that one. I do have another I did recently that I will post pics of soon.
Click to expand...

Blue Shadow said:
Be great to see what you did. I did one for Tom in Seattle. Thinking maybe restuffing a set of cans for mine. But there are lots more things to change with the carbon comps in there.
Click to expand...

Here's what I came up with for a PS rebuild. I don't plan to replace any diodes or the transistor and I think this list covers everything else on the board: the large cans, the small caps and the 4 2-Watt resistors.

Per the ARC parts list in the manual, C43 and C44 are supposed to be 300 MFD / 300 V. The pre-amp I have has 200 MFD caps there for some reason and this is the main B+ supply. I ordered 330 MFD / 400 V replacements.

I used this video for guidance. The large-can replacement caps on my list for C29, C30, C45 and C46 are the ones used in this video. The video used Panasonic replacements caps for C43 and C44. I could not find those 330 MFD / 400V Panasonic versions used in the video so I ordered some 330 MFD / 400V Nichicons that are similar to the Panasonic versions.

I ordered everything today (11/30) costing about $93 with tax and shipping.

This is a jpeg of a pdf printed from excel, hope it's readable. Else I can send the pdf or original spreadsheet. AES = Antique Electronic Supply.

SP-3A-1 Repair.jpg
 
Last edited:
I need about 5 of the tapping screws that hold the cage top and bottom to the chassis as a few are missing.

Any idea where I can find some of these?

The ARC parts list says these are: "Screw, Tapping, #6 x 1/4" Hex., Wshr. Hd". I count 5 threads in each 1/4" screw which means these are #6-20 x 1/4".

I found one place on the Internet that has these with a minimum of 250 screws for $11 plus tax and shipping. I hate to pay that when I only need five plus I don't want a stash of 245 of these leftover. I might call Audio Classics (mostly a McIntosh resource) on Monday.

Any ideas?

Thx.
 
Pictures. You have to be careful with diameters, it ain't easy fitting new stuff on these boards. ARC also made at least 2 different boards depending on supply issues so your board may be different. I ran various jumpers on the bottom of the board to wherever I needed one. I located the new caps as close to original position as possible to the old ones._DSC3215.JPG _DSC3216.JPG _DSC3218.JPG _DSC3217.JPG
 
Board closeups. This board did not match the schematic for SP3A-1, there was only one capacitor after the diodes, not two in series with dividing resistors. I had to find a place to put the dividing resistors on the bottom as I wanted to use 2 capacitors in series after the diodes as the schematic shows. Some units used a single capacitor rated at 525 volts.arc1.jpg arc2.jpg arc3.jpg
 
SP3B power supply rebuild pictures. These had SP6A power supplies installed at the factory. As one can see, diameter can be important in selecting caps._DSC3219.JPG _DSC3220.JPG
 
TSmith8605 said:
Any idea where I can find some of these?
Click to expand...

Local hardware store. #6 sheet metal screws should be available in the bins of assorted screws and such. Probably need more of a local store than a big box one, they tend to have a much bigger selection of such things by the piece.
 
verify that the threaded holes will hold the screw. I have 1 or 2 that are a bit loose with stock screw and have bumped that up a bit for a good fit.
 
You must log in or register to reply here.
Back
Top Bottom