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 Post subject: Anyone Rebuild A Sencore Sub Box?
PostPosted: Aug Mon 19, 2013 8:19 am 
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Location: Miami,Fl
I'm trying to figure the best combination of current EIA value caps to come close to the panel at the 450V series. Mine's the RC-167, but the earlier ones should be the same using the two weird valued multi-section 'lytics. They use a scheme of a switch wiper that makes contact with three contacts at a time after the first two values paralleling them to get the panel value. Actually I have two of these and the caps are shot. I've replaced the dual section 500 and 1000mf caps for the 500,1K, and 2k values, but the rest are going to have to be the best I can with available values. At 450V, not all EIA non preferred values are easy to find. Radials would probably be better here mounted on a perf board and using the original wires going to the multisection caps. If the EIA interstital values were readily available, you can calculate values within 5%. Fortunately with lytics, this isn't very critical in non timing situations anyways, so I'm probably going to go with the best combos i can easily find.

Anyone else recap one of these?
Probably the same caps they used in the older Handy 75/ RC-146 and the original Sustituter/ RC 121.


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 Post subject: Re: Anyone Rebuild A Sencore Sub Box?
PostPosted: Aug Mon 19, 2013 11:44 pm 
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I agree that if you are gonna have to buy new parts with different values than the ones originally in the box, than get the closest available values and perhaps relabel the switch positions. As if the original cap was 30 UF and you can only find like 27 or 33 or such, might as well use those as subs as if you find the sub box values satisfactory in the circuit, and those is the same values that are readily available on the market nowadays, then you are good to go. Or if it is critical, you will have to test the actual values of the caps you buy and maybe parallel an additional cap to get the exact value anyway. For most of those HV caps, they are presumably just power supply filters, and if you get either the next higher value or a lower value with a plus tolerance that brings it close to the original in fact, then you are fine for that purpose. Say, a 27 UF that actually reads 29 on a tester and you are replacing one marked 30 UF. Voltage rating is more of a critical factor most times when trying to find a sub for something old in a power supply.


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 Post subject: Re: Anyone Rebuild A Sencore Sub Box?
PostPosted: Aug Tue 20, 2013 6:42 pm 
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I just purchased 2 different B&K Master Resistor-capacitor substitution boxes and I just looked inside And also looked in my Paco and Micronta boxes, and they are all 10% tolerance parts inside. So any value within 10% should be acceptable.

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 Post subject: Re: Anyone Rebuild A Sencore Sub Box?
PostPosted: Aug Tue 20, 2013 9:07 pm 
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Joined: Jun Sat 30, 2012 9:26 pm
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Location: Miami,Fl
I guess for those of you that don't have any familliarity with the Sencores, they use an odd arrangement of 7 values in two multisection , custom caps to make up for the first 7 pre-EIA standard values of 10. To make it even odder, the RC-167 (the one with the tray) was made well in during the shift to EIA standard values I think into the late 70's or maybe even early 80's. Of all places, I don't need to explain this difference to folks working with and replacing vintage caps. It would seem that they either had an existing contract or a whole lot of excess inventory from the earlier RC-121 and Handy 75 units that used the same arrangement. My guess is that caps at 450V were still physically large and they didn't want the headache of stacking individual caps and opted for the old multisection method.

So for the unfamilliar, the 'lytic section uses a 2 section rotary wafer switch with a rotor contact that makes 3 contacts at a time with the first two only one contact and then the second, two contacts followed by a paralleling of 3 caps at a time. The second section of the switch on the revers side does the same with 2 500mf caps and one 1000mf. (I've already replaced those with two 470's and a 1000mf that dwarf the originals) so we're good on the last 3 positions. Let me make a table and hopefully the formatting will remain lined up in the message composition.

Cap section value---Position Value

2mfd--- 2mfd
3mfd--- 5mfd
5mfd--- 10mfd
12mfd--- 20mfd
33mfd--- 50mfd
55mfd--- 100mfd
112mfd--- 200mfd

Rear Wafer

500mfd--- 500mfd
500mfd--- 1000mfd
1000mfd--- 2000mfd

As you can see the left side is made up of some oddballs to make pre-EIA standard values because of the paralleling of 3 at a time except for the first two positions.

Large value caps are smaller now and this is a matter of just picking the right combinations. This should be a piece of cake to get within 5% using today's standard values. Unfortunately standard stock values of large value 'lytics don't play nice because nobody is going to order or stock the EIA interstitial values and then even the preferred values aren't always available. The better availability is usually radials. That shouldn't be a problem because the easiest and least messy route is to cut the wires molded into the multisection caps and run them to perfboard with radials on it sharing a common bus. Doing this with Axials would be a very messy situation requiring extentiions, etc.

Now, there's a second option that I'm not going to try, but the rotor can be dremmled down to one contact per position. That's nuts. Removing the plating and taking a chance on an old phenolic wafer is idiocy. Best leaving dogs lie.

In most cases, 'lytics are used for power supply sections and values aren't that critical. I also work on high power studio strobes and there are timing sections that do things like mediate current inrush during charging the bank, timing for afterglow of the tube and so forth. To make this more complicated, many of these supplies have long since the early 70's given up power transformers in favor of voltage multipliers to decrease weight. Also bear in mind,despite the complexity, these are considered vintage now. You got it, hot chassis problems. So you're dealing with something potentially deadly with the capacity of a high voltage arc welder in current. Some systems work on 450V, higher power units work at 900V. The cap banks are almost always 450V caps operating in series in the higher power units. The control boards are hung either at the top of 900 and bottom 450 or 450 to 0. My isolation transformer and variac will give you a hernia. It's been a while since I've done repairs and I'm setting up again now that I'm having to shift work gears. This RC box works well for the situation.

I'm sure some of you have purchased these and most likely the caps are dead, especially in the older units and need to be rebuilt, so this should be very much of use to quite a few folks if the brisk sales of these on Fleabay is any indication.


Last edited by Dawn on Aug Tue 20, 2013 9:16 pm, edited 1 time in total.

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 Post subject: Re: Anyone Rebuild A Sencore Sub Box?
PostPosted: Aug Tue 20, 2013 9:14 pm 
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Posts: 2987
Can't you get close to the values by parallelling caps?


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 Post subject: Re: Anyone Rebuild A Sencore Sub Box?
PostPosted: Aug Tue 20, 2013 9:22 pm 
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Joined: Jun Sat 30, 2012 9:26 pm
Posts: 1508
Location: Miami,Fl
Yeah you can. Actually, you're already doing that and it's making this even more complicated. Caps are smaller nowadays at 450V, but room is still a consideration. The guys with the older boxes have more room to work with because the original caps had much longer leads then these units and mounted on the case. I'm just trying to see how close I can get with preferred values and keep in mind each step is paralleling caps, not just contacting one cap at a time that can be easily paralleled. Paralleling here is aggregate with three positions at a time and that's getting complicated to keep the numbers right.


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 Post subject: Re: Anyone Rebuild A Sencore Sub Box?
PostPosted: Aug Wed 21, 2013 1:53 am 
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It is somewhat ironic that you have to parallel standard values to get the odd values that are then paralleled by the switch to get the standard values.


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 Post subject: Re: Anyone Rebuild A Sencore Sub Box?
PostPosted: Aug Wed 21, 2013 6:11 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 1186
The front panel labeling on the RC-167 seems to be using 10 positions of a standard 12 rotary switch. Why not replace the switch? You might have two open unused positions and have to use a two layer switch if you want to preserve the "surge protector" function, but you'd end up with the simpler one-to-one cap-to-label relationship.

I think I'll try chopping up the original switch and use the above as the fall back :idea:

Greg


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 Post subject: Re: Anyone Rebuild A Sencore Sub Box?
PostPosted: Aug Wed 21, 2013 10:54 pm 
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Joined: Jun Tue 12, 2012 1:47 am
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Anyone know where I can get a manul/schematic for SENCORE THE SUBSTITUTOR MODEL RC167?
Thanks


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 Post subject: Re: Anyone Rebuild A Sencore Sub Box?
PostPosted: Aug Thu 22, 2013 8:24 pm 
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Joined: Jun Sat 30, 2012 9:26 pm
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Location: Miami,Fl
For those of you following this thread with an interest to rebuild a 121,141, or 167 on the 'lytic side, I think I've come up with a reasonable series of caps from standard, preferred values within 10%. The original spec was 20% variance. Caps are smaller now and raidials mounted on perf board seems to be the best workable solution in the space where the original two caps were. Cutting the wires off the original cap's potting compound is probably better then new wiring. It's long enough and can make for a neat job. I haven't done this yet and need to see if I can source these values at the correct voltage rating of 450V and still not break the bank. There are some compromises as I'm trying to stick as close to standard stock values. See the original equivelents above. I've tried each series of 3 after the first two running the numbers for tolerance.
Caps all in Microfarads 450V:
3.3 : 2 ea.in series = 1.65uf
3.3
4.7
15* For a standard,preferred stock value, these appear hard to find especially at 450V. I haven't calculated out the effects using a paralleled pair of 6.8mf to see how it affects the progression or tolerance
33
47
68 : 2ea. in parallel = 136uf

This should approximate the two multisection caps. Note the original 2,3,and 112 were in the same tube and the 5-55 were in another. This shouldn't affect anything providing rebuilding on a perf board with a common bus.

The large 'lytics can be substituted with and a higher rating then the original 100V with current caps.

470
470
1000

Replacing the switch is not a viable option as it will make more of a mess. The front handles the first 7 and the rear handles the large 3 caps requiring 500,1000,and 2000, the last most likely would require paralleling. Room where the clamp is would make this a mess too. I mentioned modifiying the rotor on the front switch with a rotary tool. Possible, but risky and invites corrosion by damaging the plating.


If you're restoring one of these, both of mine had totally oxidized slide switches with no continuity as received. They are extremely cheap switches with pressed paper backing. The cleaned up well with a few drops of deoxit and some working of the switches. The banana plugs on the older one looked good when I got it, but immediately crumbled after some insertions of plugs. I tried to snug the compression collar on one as most were loose. That busted the jack in half, so they all have to be replaced.


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 Post subject: Re: Anyone Rebuild A Sencore Sub Box?
PostPosted: Aug Thu 22, 2013 10:47 pm 
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Quote:
That busted the jack in half, so they all have to be replaced.

My test equipment re-building is usually for function, not for restoration of appearance, so I have mostly used the solid plastic molded "Johnson nylon" 5-way binding posts for banana jack replacement. Gives more choices for hook-up leads, too.
And I just hate those spring washer push-on retaining rings on so many banana jacks.

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 Post subject: Re: Anyone Rebuild A Sencore Sub Box?
PostPosted: Aug Fri 23, 2013 1:31 am 
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Joined: Nov Thu 22, 2007 11:31 pm
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Location: Johnston, Iowa
I just realized I picked up one of these last fall at a hamfest and it came with a manual. If anyone's interested here's the schematic and parts list.
Keith


Attachments:
parts list 001.jpg
parts list 001.jpg [ 235.82 KiB | Viewed 6045 times ]
sencore 167 schematic 003.jpg
sencore 167 schematic 003.jpg [ 190.91 KiB | Viewed 6045 times ]
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 Post subject: Re: Anyone Rebuild A Sencore Sub Box?
PostPosted: Aug Wed 28, 2013 1:55 am 
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Location: Washington
Keith, thanks for the post.

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 Post subject: Re: Anyone Rebuild A Sencore Sub Box?
PostPosted: Jun Sun 22, 2014 6:09 am 
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Joined: Jun Sat 30, 2012 9:26 pm
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Location: Miami,Fl
Old topic, I know.

I finally accumulated the caps I needed and did some extensive testing on my proto board with the LC-53 to see if I could find a combination of EIA preferred values to either duplicate the pre-EIA values presented by the unit or attempt to come up with an alternate progression that approximates today's standard values. In short, it can't be done within the 20% spec tolerance targeting current EIA values, but can be done within a + 3%-16% spread of the original panel values.

I have two RC-167's. One earlier model used the spring press fit jacks that were brittle and a later '73 unit that used what appears to be a resin based jack with a threaded base and nut. The older unit also used crumbling, tapped, wirewounds that were similar to those used in the earlier RC-121 and RC-142 units that all the resistors were way out of spec and obvious arcing on the switches. The newer unit was rather prisitine. Despite that appearance, the switches were intermittent and very oxidized and the multisection caps were all bad and leaking with corrosion of the gavlenized chassis.

I did a heavy rebuild using perf board and fresh HV lytiics that fell within spec. The stock resistors are all within 5%. The only part left that needs some work is the first 6 steps of the low ceramic caps from .0001 to .01 which were part of a proprietary PEC. That's going to need a rebuild using ceramics and one value per contact. Values are in some positions worse then 40% and confirmed using DMM capacity measuremenst against the Sencore. That's going to be an easy fix.
Amazingly, the two tubular wax/paper caps showed no leakage and spot on. They were replaced anyways with fresh polyester/oil film caps as a prophylactic measure after 41 years. The ceramics are going to be a non issue and easy substituion unlike the paralleling scheme of the 'lytics.

I took pics of the rebuild process and would be willing to post them if ther is any interest and the cap sequneces used for the 'lytics. Let me know if any of you have any interest in what I did. Personaly, I wouldn't recommend buying one of these no matter what the seller claims. The rebuild even if you received one of these for almost nothing isn't worth it when you factor in the cost of 450V caps and any incidental repairs.


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 Post subject: Re: Anyone Rebuild A Sencore Sub Box?
PostPosted: Jun Sun 22, 2014 10:50 pm 
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No, I don't have one, but thanks for your summary evaluation.

Posting the 'cap sequences' could have lasting value for someone doing a repair on one of these.

There may even be other sub-boxes that used the same switch design so the data could have wider applicability.

I just had to go open up a 0 to 10 mfd cap decade. (Old red brick, Cornell-Dubilier Electronics/Federal Pacific Electric, CDE model CDC-3, 600VDC/220VAC Max)
To see how it is switched.
It uses only four caps to give the 0 to 10 by steps of 1mdf.
The four are in two dual-capacitor solder-sealed metal boxes; the hot terminal markings are 1, 2, 3, 4 which could have been just terminal numbers (each box also has a "C" Common terminal) but appear to be the number of mfd.
mfd-terminals:
0----None
1----1
2----2
3----1+2
4----4
5----2+3
6----2+4
7----3+4
8----1+3+4
9----2+3+4
10---All, 1+2+3+4

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 Post subject: Re: Anyone Rebuild A Sencore Sub Box?
PostPosted: Jun Mon 23, 2014 2:21 am 
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Location: Johnston, Iowa
Please post your pics. Maybe the photos will inspire me to restore mine. I just opened mine up and all the electrolytics are shot but everything else is in great shape. Justradios has 450v caps that are the same or close for most of the values.
Keith


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 Post subject: Re: Anyone Rebuild A Sencore Sub Box?
PostPosted: Jun Mon 23, 2014 12:55 pm 
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Joined: Jun Sat 30, 2012 9:26 pm
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Location: Miami,Fl
I tried posting last night and got a log-in error. I'll try again this evening when I get a chance. Short form answer to the caps that I used is the ones above. I couldn't do any better without throwing off the progression. The values above work. I tried posting the panel listed values and measured values last evening to show the % error was within the 20% original spec.


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 Post subject: Re: Anyone Rebuild A Sencore Sub Box?
PostPosted: Jun Mon 23, 2014 4:54 pm 
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Location: Miami,Fl
Here's some pics during the rebuild. You can see the corrosion from the cap leakage where the double sided foam tape is. I tried using GooBGone to remove the tape residue and it only got some off after serveral applications. I ended up using a glass razor scraper to remove the rest. I also used a brass wire wheel on my flex shaft tool to remove the corrosion to the base galvanized steel. The scraping and removal of the corrosion left bare steel that needed to be sealed to prevent rusting. I carefully masked off the switches with plastic baggies and newspaper to the left of the abraded area and used Rustoleum's Universal Metalic self priming, satin nickel in two light coats and baked the area overnight with a halogen lamp. You can see in the next photo that you can't tell the transition from the original galvanized finish to the painted area. The replacement board is mounted on two standoffs using the original holes from the clamps. I purposely left extra space on the board for any future additions. After scrubbing the case, I applied two coats of NuVinyl that really brightened up the finish and a little moly grease on the nylon parts drawer glides. Hope the table formats decently. Spread is 3%-16.5% which is better then the original spec of 20%. There was no attempt to cherry pic caps for closer values as I used what I could get. Had I had a selection and different manufactures, I probably could have matched it closer.

Panel Marking Measured Value

2mf 1.75mf
5mf 5.18mf
10mf 11.3mf
20mf 22.1mf
50mf 51.5mf
100mf 107mf
200mf 233mf
500mf 469mf
1000mf 960mf

All are 450V except the last 3 ranges which are 100V (2 ea. 470mf and 1 ea. 1000mf) Values used to emulate the original caps are the ones listed in the beginning.

Replaced 800V Paper Wax/oil with Poly/oil 1500V caps
.1mf .107mf
.5mf .511mf
2000mf 1940mf


Attachments:
File comment: Orininal caps with clamps in place and paper caps on adjacent lower values/non-lytic cap selector.
IMG_1167.JPG
IMG_1167.JPG [ 184.85 KiB | Viewed 5437 times ]
File comment: Mess underneath from leakage.
IMG_1170.JPG
IMG_1170.JPG [ 164.1 KiB | Viewed 5437 times ]
File comment: Surface after painting. Waxpaper/oil caps replaced with poly/oil on switch adjacent to 'lytic switch
IMG_1172.JPG
IMG_1172.JPG [ 176.34 KiB | Viewed 5437 times ]
File comment: Replacement board wired and mounted in place on standoffs.
IMG_1175.JPG
IMG_1175.JPG [ 181.29 KiB | Viewed 5437 times ]
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 Post subject: Re: Anyone Rebuild A Sencore Sub Box?
PostPosted: Jun Mon 23, 2014 5:37 pm 
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Joined: Jun Sat 30, 2012 9:26 pm
Posts: 1508
Location: Miami,Fl
Oh, one thing else. the 12mf value of the original cap section worked better with with two 6.8mf caps paralled together rather then a 15mf. The 112mf value was made up from two 68mf caps, the 2mf section made from 2 ea. 3.3 in series (measured 1.75mf) rather then use a (2.2mf which measured 3.1mf) cap which tilted the progression too high. values are as stated above, but let me add the original and replacements again so nobody has to slog through my reasoning in the earlier posts.

Multisection cap #1 is comprised of:

112mf (Red lead replaced with two 68mf in parallel)
2mf (Blue lead replaced with 2 ea. 3.3 mf in series)
3mf (Yellow lead replaced with 3.3mf)

Multisection cap #2

55mf (Red lead replaced with 47mf)
33mf (Blue lead replaced with 33mf)
12mf (Yellow lead replaced with two 6.8mf in parallel)
5mf (Green lead replaced with 4.7mf)

Multisection cap #3 is a dual section 500mf/100V
Replaced with two 470mf/100V

Single 1000mf/100V cap replaced with same value

.05mf/800V Paper/Oil replaced with poly/oil .047mf/1000V
.1/800V Paper/Oil replaced with poly/oil .1/1500V

Check the PEC wafer values in yours that are.0001mf-.01mf
Mine are way off. These should be easy to replace as there is no paralleling scheme and individual ceramics can be substituted with standard EIA values.

Use the original wires cut at the base of the potting compount of the multisections and the original wires soldered to the large lytics to keep things simpler and neat. Even under the vinyl jacket, mine were a bit oxidized and wouldn't tin. I used a drop of Kestler 951 on each and they took solder well.


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 Post subject: Re: Anyone Rebuild A Sencore Sub Box?
PostPosted: Jun Tue 24, 2014 1:07 am 
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Joined: Nov Thu 22, 2007 11:31 pm
Posts: 875
Location: Johnston, Iowa
Well done!!! Thanks for the excellent write up. I'll attempt to mimic your work when I start on mine.
Keith


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