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Thread: Fear of using old Rodgers amplifiers

  1. #1

    Fear of using old Rodgers amplifiers

    I recently bought a 70's era Rodgers 750E, a typical large two-manual electronic church organ for the day. It came with a whopping twelve speaker cabinets, a subwoofer, and five Rodgers S-101D amplifiers with big fat capacitors on them. The whole ensemble has been sitting dormant in a church attic for twelve years.

    I know little about electronics, but I've learned here on the forum that old amp capacitors that have been sitting for a long while are prone to fry upon being plugged in again. As one person said it, be careful or you'll have an oozing mess on your floor. From what little I understand there is something in a capacitor that in fact turns to ooze, leaks out, and makes a mess when an amp capacitor gives up the ghost.

    So questions:

    1) It's not practical for me to create an expensive extra long speaker cables to run the amps outside in order to test them this first time. I also don't want to move the organ. Can I just set each amp in a three inch deep foil baking/roasting dish next to the organ that first time to try it out in case it oozes? Or could these things actually splatter in some messy way? ie, Must this done outside regardless of how inconvenient? I'd really like to test them out indoors right next to the organ.

    2) If I had a best case scenario and all five amps work properly (unlikely after sitting for twelve years, but let's just say) ... am I still in danger of these things leaking all over the place in the future (assuming regular use) ...? I'm concerned that a number of these amps might work just fine, I'll put them to good use inside or near the speaker cabinets, and then at some point they'll surprise me by still oozing all over the place - although now possibly making a mess inside. Is that how it happens when these things give it up? They suddenly spill their guts wherever they happen to be sitting?

    I was obliged to work hard. Whoever is equally industrious will succeed just as well.

    -Johann Sebastian Bach (1685-1750)

  2. #2
    fff Fortississimo indianajo's Avatar
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    Dec 2009
    Jeffersonville, Indiana

    the slime in capacitors is installed at the factory. They are sealed in the aluminum can by rubber, except on special high cost epoxy sealed capacitors. While some high end medical and boutique hifi equipment had long life capacitors, nobody on organforum seems to have found any. If you like vintage rubber, try driving around on 30 year old tires. You measured the air pressure before going out, so that means the tires are good, right? The heat of operation causes vapor pressure in the water contained in an electrolytic capacitors, boils it out past the cracked seal, and eventually they short and pop open.
    Shorted capacitors burn rectifers, voltage regulators, or transformers. E core transformers over 20 watts start at about $75 now and go up in price fast.
    I don't test this stuff, I throw it away and buy new. I test them with a calander. >20 years = wrong. I bought some 3000 hour 4700 uf 100 V capacitors for $5.50 each recently, so they are not all that expensive. 10000 uf up is expensive, so I assembled 4700's into subassemblies for my 10000 uf caps, saving $15 each. Don't buy any 1000 hour or less caps unless you plan to sell this amplifier soon. I've had to replace the caps in my power amp 3 times in 40 years, although until the internet nobody stocked long life caps much.
    If you can afford to throw your amps away after you blow slime all over them, have fun with the old caps. Alternatively, you can disassemble them after the explosion, clean the slime out, and reassemble with new parts replacing any you burned up.
    city Hammond H-182 organ (2 ea),A100,10-82 TC, Wurlitzer 4500, Schober Recital Organ, Steinway 40" console , Sohmer 39" pianos, Ensoniq EPS, ; country Hammond H112

  3. #3

    Jo, it sounds like I might need to do some homework ... but I had a "all brands" organ repair guy here a few days ago looking at the organ itself (not the amps) and he ballparked the capacitors for my 70's era Rodgers S-101D amps at about a hundred bucks a pop.

    Has he been listening to too much E. Power Biggs? Or should I expect something closer to your $5.50 estimate?

    I was obliged to work hard. Whoever is equally industrious will succeed just as well.

    -Johann Sebastian Bach (1685-1750)

  4. #4
    fff Fortississimo indianajo's Avatar
    Join Date
    Dec 2009
    Jeffersonville, Indiana

    Read your cap sides to see how many uf (old style mf) they are. 10000 up ones are pricey. 10000 tall ones were $20 from newark and short 10000's that would fit in my amp were $25. Two 4700 shorts were $11. I'm not working so time is cheap. I took a two pieces of scrap lexan, drilled some holes for the leads, bussed the 4700 uf caps together to make 9400, and put a couple of #6 x 2 1/2" screws through the lexan to hold the whole sandwich together and bolt it to the PCB instead of the 3 legged excruciatingly correct caps. There was some glue to keep things from sliding around.
    You are not going to be filling a cathedral with sound, I would try to get by with two 4700 caps even if your amp has as many as 20 output transistors. My PV1.3k (watts @ 4 ohms) has 10 output transistors and 10000 uf per channel, 2 channels. That is enough watts to power the bass stack in an enormously noisy bar. In a home you can get by with 100 watts per channel, although 200 would be more fun. You don't have to delete the rest of the amp circuitry, just downsize the caps some. My 60 W/ch transistor amp has one central power supply 3300 uf caps and one more 3300 cap per channel. Modern split supply amps, they come in pairs, one for the plus and one for the minus supply. You may have to turn down the amp input gain potentiometer a little to keep the amp from making a loud thump at the beginning of a loud note then quieting down as the capacitors run out of current, or change a gain resistor if Rogers didn't provide a gain pot.
    With a pro having to charge $60 an hour to keep a parts/phone assistant and accountant, and an inventory room and run a car on $4 gas, there is no way he can make money cobbling stuff together the way I do. If he gets the part for $50, he will have to charge you $100. That is the way the repair business works. That is why reading an electronic tech manual, and buying $70 in tools is so remunerative on organs that are $500 junk and $30000 new.
    Last edited by indianajo; 03-04-2012 at 06:52 PM.
    city Hammond H-182 organ (2 ea),A100,10-82 TC, Wurlitzer 4500, Schober Recital Organ, Steinway 40" console , Sohmer 39" pianos, Ensoniq EPS, ; country Hammond H112

  5. #5
    mf Mezzo-Forte Guitarbro's Avatar
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    Mar 2011
    Muskegon, MI

    Nichicon capacitors are fairly high quality and inexpensive. I can usually recap an amp for about $20 with them.
    they also come in different shapes which is nice when you're working in a tight area.
    '60 RT-3
    '69 Leslie 147RV
    '77 Yamaha E-70
    '4x Conn Connsonata 2A2
    '6x L-133A

    '5x M2, '59 Leslie 25, '48 CV, '64 A-102, '6x M-143, '5x M3, '81 kimball stardust,
    '8x Hammond Aurora, A-102, M2, another M2, Wurlitzer spinet, Wersi DX350, Thomas chordian

  6. #6

    Do these photos give any indication of what I'm looking for?

    I was obliged to work hard. Whoever is equally industrious will succeed just as well.

    -Johann Sebastian Bach (1685-1750)

  7. #7
    p Piano Lucien Nunes's Avatar
    Join Date
    Dec 2008
    London UK

    The big one looks like 6200F at 100V, without shopping around I can get that for 8.50 here in the UK from one of the more expensive suppliers. There are different grades with different life expectancy and temperature rating etc, the best is priced in the same catalogue at 20.

    I especially like Indy's comment 'I test capacitors with a calendar' which is probably a very good idea. I would say though (being usually more optimistic about capacitors than he is) that they might be at least OK, and possibly fine. From where I am sitting I can see about 40 pieces of electronic kit as old as this organ, only three needed recapping in order to work. Some needed recapping to work their best, but at least they could be fired up and checked over before forking out lots of cash. I haven't had an electrolytic explosion for many years, despite working every day on vintage electronics.

    Sure, old capacitors can burst when they overheat which can be extremely messy, as they chuck out foil and tissue confetti soaked with corrosive electrolyte. They can short and kill other parts of your amp, either when you first power up or some time later when you least expect. I totally agree that where possible it makes good sense to replace large, power reservoir caps before anything goes wrong. However I find this the exception rather than the rule, especially if they can be reformed by slowly ramping the voltage up the first time you power the amps (do a websearch for 'reforming electrolytic capacitors'). In that case, they are much less likely to explode or leak, and might either work or perhaps simply perform poorly but without fireworks.

    Where I have had to power something up for the first time without the necessary equipment to reform the caps, I apply power for one second and allow one minute rest, then two seconds, five, ten, thirty and thereafter leave the power on. This allows the aluminum oxide film a few moments to reform before serious heating occurs, although of course it does not protect rectifiers etc from caps that are already short-circuited. If the correct fuses are fitted and you supervise the startup, there should be little risk of transformer damage if the amp is functioning and not getting hot.

    So to sum up, if you can't justify recapping, don't fear too much. They might just work!


    E2A: I'd be more worried about those presets having got knocked if the amps have just been kicking around, with possible transistor failure soon after startup if the bias has got nudged up too high. Check for the heatsink suddenly getting warm on no-signal. Also, I'd put a 10Ω 10W resistor or at last a sacrifical speaker across the output instead of a proper speaker to start with, in case it pumps out a lot of DC. Once the output has been checked to be DC-free, then go ahead and hook up the real L/S.

  8. #8
    fff Fortississimo indianajo's Avatar
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    Dec 2009
    Jeffersonville, Indiana

    You've got 6 electrolytic caps in your pictures. the two big blue ones, and 4 on the PCB. The ones with minus's in balls on a stripe on the pcb are electrolytic. The blue ones are probably screw terminal, which are particularly expensive. I'm buying snap-in to replace screw terminal to save about $20 each. I mount them on a little insulator board to loop the wires through holes and keep them from popping loose if the solder gets too hot. You'll need some sort of spacer anyway, the new ones are much smaller than the punched holes. Lexan from the lumberyard is one kind of insulator board that won't catch fire. I drill the holes myself. You can alternately buy CE laminate in 1/16" thickness from Both saw and drill with a sabre saw and an electric drill. Use safety glasses. Newark also might have some insulator board, but predrilled vector board is hideously expensive, about $20 for a 6x6" sheet.
    Reforming is wonderful for keeping the cap from exploding at first turn on. It does nothing for the rubber seal. If they get warm through use, the water evaporates out past the seal. If I went to London I would hope to see both the organ techs driving around in their 1970 MG's with the original 1970 tires. Andy's tech doesn't believe in replacing e-caps either.My 1968 Hammond organ had a wire harness fire that burned all the insulation off the yellow wire because an E-cap shorted in 97 (date on the new cap). Me&myM3 bought a "cherry" H100 for 3x the price what a hard use one goes for, and in fact it sounded really good, just like original:for about 2 weeks. The the caps boiled out (we assume, he hasn't replaced them) and it sounded like a kazoo, just like all the others. I put a new cap in my ST70 power amp in 1982, then used it about 2 hours before putting it away because I couldn't get new power tubes. I bought the new tubes last fall, operated the amp one night with great results, then it blew the fuse the next night because the 1982 e-cap had leaked out.
    There are seven of these left at Newark today at $7. They are 3000 hours which is decent. The next line there are some chemicons for $5 that are only 2000 hours rated, and chemicon has a c****ier ripple rating at their end of life test than Panasonics to make their numbers look good. Panasonic and nichicon both make both short life and long life caps, you pay for the better seal but get the benefit of less work in the future. If you are going to flip the organ like a house, buy the cheap short life caps. I've had to recap my dynakit equipment 3 times since I bought in 1970, for poor performance twice and the last time because of the leakout and short I said above.
    If I replaced the little leaded caps, I would not take the board out, but I would cut the leads, bend them over to make hooks, and bend the leads of the new caps over the hooks so they were held up without solder. Then I would solder them. To look up caps on click passive components, click capacitors, click aluminum electrolytic, then put a minimum and maximum voltage (I used 100-125) and a minimum-maximum capacitance in (I used 3900 to 6200). That way you can see what is on sale. Newark is in NC. Mouser is also good, in TX, but you have to look up the capacitor life yourself on the datasheet, they don'[t have it in the selector table. The higher temp rating you get the better, but your amp won't go over 85 deg C. I've been happy with the ratings on Panasonic, Nichicon, and Rubicon. The initial quality has been good on united chemicon but they are c******, the quality may be all on paper. Cornell Dublier now have come in all c******, I don't buy those unless I have to either. Spragues have no life rating, but have been made in USA. The spragues atomlytics I have bought in the past lasted about 10 years. If buying from newark, buy stock only, if you buy a farnell stock part there is a $25 charge to ship them in from the UK to NC. Click hold and ship all at once shipping option or they will sometimes send 3 boxes on 3 different days as stuff comes in. USPS shipping is cheaper to residences than UPS. UPS charges for distance, so over 700 miles I always go USPS priority.
    Remember if you decide to run with old caps, you can not only blow up the amp parts, you can also blow up the speaker if you get DC out on them. My Peavey CS800s amp has a DC detector that pulls a speaker relay if something goes wrong like DC going out on the speaker line. I don't see any relays in this picture. If this amp is an obsolete design that puts the e-cap between the transistors and the speaker, then that can't happen, but those designs are very rare after 1970. I don't see any heat sink or power (TO3) transistors on this, it may be just a power supply.
    Last edited by indianajo; 03-04-2012 at 10:37 PM.
    city Hammond H-182 organ (2 ea),A100,10-82 TC, Wurlitzer 4500, Schober Recital Organ, Steinway 40" console , Sohmer 39" pianos, Ensoniq EPS, ; country Hammond H112

  9. #9
    fff Fortississimo geoelectro's Avatar
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    Aug 2008
    Houston Texas

    10 dollars says the amps will work when you power them up.


  10. #10
    fff Fortississimo jdoc's Avatar
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    Oct 2010
    Belleville ON CA

    my money

    my money is with GEO .....they will probably work......caps...smaps.yes caps can be an issue,and at times a big issue but there are 1000's of working Hammonds and old amps out there with original caps, offense to the cap guys, it will increase safety and brighten tone etc.,definately redo old crossovers but............................try them(your amps)
    i would worry about the modern crappy caps in computers, video cards and consumer electronics of modern vintage and have seen total junk in industrial control gear lately too....old stuff built real good......imo
    Last edited by jdoc; 03-05-2012 at 02:39 AM.
    1956 M3, (2)51 Leslie under upgrade, 860 (130 powered)Leslie with Preamp, S08 Yamaha and two K2000S, Young Chang spinet, Korg Trinity
    and Korg KRONOS X73
    Looking for that mythical cheap or free A, BV, CV, C2, C3 or A100 but wouldn't say no to a free B3

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