I can confirm that these RCA 1B01 are a very correct replacement for the stock HK/RCA 4216. I've got the RCA 1B01 mounted, the amp has been biased to 40mA using new pots, and its now "burning in". I've got cheap Polk speakers hooked up to them, I'm using a digital source playing through a spare Carver preamp. This really sounds good, compared to where it started. Its no Adcom, but the detail is there and getting better with time.
The "replacement" Sony TO-3 on the bad channel were TX-183S. I think they were as wrong a choice as anyone could make. If I had to guess, someone lost a channel on their amp, found these transistors in a bargain bin and tried to make them work. When it didn't, the thing got donated.
The problem is finally solved, and these new transistors have a slight bump in power from 60w to 70w, so they satisfy the "upgrade" itch as well. If I can calm down the slight bit of PS buzz this will be a real keeper.
The "replacement" Sony TO-3 on the bad channel were TX-183S. I think they were as wrong a choice as anyone could make. If I had to guess, someone lost a channel on their amp, found these transistors in a bargain bin and tried to make them work. When it didn't, the thing got donated.
The problem is finally solved, and these new transistors have a slight bump in power from 60w to 70w, so they satisfy the "upgrade" itch as well. If I can calm down the slight bit of PS buzz this will be a real keeper.
Congratulations.
My first adventure with solid state amps was a replacement of shorted transistors & drivers on a $50 hulk from 1970; Without any schematic or internet, which was definitely probing in the dark. When the unit then caught fire after a 3 hour rehearsal, the second base was hot-rodding the heat sink, which was totally inadequate for 10 w/ch 3 hours. Nominal 60 w/ch, HA! 3rd base involved circuit mods to eliminate crossover distortion by pushing output transistor idle bias up to 20 ma even cold and soft. Sounds as if citation got the 3rd round right from the beginning.
Electrical buzz can sometimes be helped by a snubber at the output of the bridge rectifier. First cut, a ceramic .01 uf. 2nd version, 5 ohms series .1 uf ceramic. 3rd cut, a steel cage between the transformer and the input stage.
If the transformer buzzes mechanically, I've tried drilling the rivets & installing screws & elastic stop nuts. But really, a new transformer is easier.
My first adventure with solid state amps was a replacement of shorted transistors & drivers on a $50 hulk from 1970; Without any schematic or internet, which was definitely probing in the dark. When the unit then caught fire after a 3 hour rehearsal, the second base was hot-rodding the heat sink, which was totally inadequate for 10 w/ch 3 hours. Nominal 60 w/ch, HA! 3rd base involved circuit mods to eliminate crossover distortion by pushing output transistor idle bias up to 20 ma even cold and soft. Sounds as if citation got the 3rd round right from the beginning.
Electrical buzz can sometimes be helped by a snubber at the output of the bridge rectifier. First cut, a ceramic .01 uf. 2nd version, 5 ohms series .1 uf ceramic. 3rd cut, a steel cage between the transformer and the input stage.
If the transformer buzzes mechanically, I've tried drilling the rivets & installing screws & elastic stop nuts. But really, a new transformer is easier.
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I tried doing a .01 1kV ceramic disc across the hot leads to the rectifiers but that just made things worse. The buzz was still there but I ended up with a "wompwompwomp" pulse going through the speakers. I cut the snubbers out and it went back to just buzzing.
Of course that was before I discovered the ridiculously bad output transistors. Maybe the snubbers would work better now?
The last thing I have to deal with on this would be the turn-off thump. It was horrendous on the old outputs and basically non-existent now, with the exception of some hilarious flatulence noises about two minutes after I unplug the amp. They're not loud but its enough to make every guy in the room yell, "It wasn't me! It was the stereo!" following a family Christmas music listening session.
I have no idea what size/rating/construction I should use for bleeder resistors to help eliminate that but I'll get around to learning that eventually. I plan on making power supply design for audio a priority in the following year.
Oscillating output stages can do weird things - the “whomp whomp whomp” is breaking in and out of oscillation. Often the presence of oscillation is a symptom of RF coming in from somewhere external - radio/TV, switchmode supply noise - even from your fluorescent light, rectifier ringing. That kind of junk can force an output stage into oscillations of its own, suppress one that exists without it, or even create additional mixing products.
I cut the AM radio coming in one amp from the RCA cable by increasing the parallel cap across the input jack from 56 to 82 pf. Another amp has 150 pf there.
Another organ amp lacked an output inductor and was picking up sports talk radio. I wound 12 turns 16 ga wire around a 10 ohm resistor and mounted it on the front wall of the chassis series the output hot screw terminal. Solved that problem. It had an output inductor in a disconnect timer relay series the output, but at age 30 years the contacts kept oxidizing and making it go silent. So I removed it. A better output disconnect relay 2020 is a couple of nfets source to source series the output. When gate is 5 v to the drain the nfets conduct music. When it is zero they don't. Like the weird bleep that organ produces 10 seconds after shutoff.
Another organ amp lacked an output inductor and was picking up sports talk radio. I wound 12 turns 16 ga wire around a 10 ohm resistor and mounted it on the front wall of the chassis series the output hot screw terminal. Solved that problem. It had an output inductor in a disconnect timer relay series the output, but at age 30 years the contacts kept oxidizing and making it go silent. So I removed it. A better output disconnect relay 2020 is a couple of nfets source to source series the output. When gate is 5 v to the drain the nfets conduct music. When it is zero they don't. Like the weird bleep that organ produces 10 seconds after shutoff.
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I tried the amp out on a friend's Zu Omen speakers today. It sounded quite good, and six minutes after unplugging the amp the flatulence hadn't occurred, so perhaps its just something to do with the damping ability of whatever speaker is attached to the amp.
The turn-on thump is very minor - no worse than any GFA-555 I own - but its accompanied by a tiny bit of scratchy static in the left channel. I noticed there was a little bias drift on that side, so I think there may be a cold joint or two over there. I'm done messing with it for now, too many other projects have been held up by this creature.
In the future I'll probably throw some of Hoppes' cap hats on there and see if that helps. Otherwise there isn't much left to change besides the transformers themselves. There used to be a couple of companies that would rebuild transformers inside and out but I've long since lost that info.
The turn-on thump is very minor - no worse than any GFA-555 I own - but its accompanied by a tiny bit of scratchy static in the left channel. I noticed there was a little bias drift on that side, so I think there may be a cold joint or two over there. I'm done messing with it for now, too many other projects have been held up by this creature.
In the future I'll probably throw some of Hoppes' cap hats on there and see if that helps. Otherwise there isn't much left to change besides the transformers themselves. There used to be a couple of companies that would rebuild transformers inside and out but I've long since lost that info.
Spoken too soon. My friend contacted me to say the pops and buzzes got very noticeable tonight, so I'll be getting back into this amp once again. The only thing I didn't touch were the transformers, the BJTs, and the diodes. I can't do anything about the transformers but I'll replace all the rest. There's a double diode at CR5 and CR6 on each side, which will take some figuring out, but the rest are 2A 100v, should be easy to find.
I forgot to consider the sandcast resistors and the bridge rectifiers. Should I bother with those?
I forgot to consider the sandcast resistors and the bridge rectifiers. Should I bother with those?
Per wgski post # 25 early designs were not protected well against RF intrusion on front or back end. Not everybody carried even a CB or business band radio in 1978, and certainly not a cell phone. I would put ceramic cap across front end and inductorparallelresistor series back end before serious oscillation patrol.
Parts swapping won't stop oscillation. Need to look with a scope, or an analog vom with quick response. Analog VOM is cheaper, $18 for some that have a 20 vac scale and ~$60 used for some that have a 2 vac scale. No electrolytic caps to limit life of an analog meter either. my Simpson 266XLPM is a 1984 model. Put .047 uf 200 v cap series negative probe on analog voltmeter to limit AC reading on DC voltages. Then patrolling for RF, use a 390 pf cap, which music will not pass through.
Also possible an individual part is not soldered down correctly, or has a intermittant weld inside. Have to find those by finding where the problem originates.
No, sandcast resistors (wirewound) and bridge rectifiers are not usual sources of RF noise. Except bridge rectifier needs sharp edge filtering of cutoff noted above.
Parts swapping won't stop oscillation. Need to look with a scope, or an analog vom with quick response. Analog VOM is cheaper, $18 for some that have a 20 vac scale and ~$60 used for some that have a 2 vac scale. No electrolytic caps to limit life of an analog meter either. my Simpson 266XLPM is a 1984 model. Put .047 uf 200 v cap series negative probe on analog voltmeter to limit AC reading on DC voltages. Then patrolling for RF, use a 390 pf cap, which music will not pass through.
Also possible an individual part is not soldered down correctly, or has a intermittant weld inside. Have to find those by finding where the problem originates.
No, sandcast resistors (wirewound) and bridge rectifiers are not usual sources of RF noise. Except bridge rectifier needs sharp edge filtering of cutoff noted above.
I think it would be good if we started from the beginning, namely:
what is original and what is no longer.
brand, reference and value of each capacitor.
etc etc etc
in short, that we start again on a good basis.
what is original and what is no longer.
brand, reference and value of each capacitor.
etc etc etc
in short, that we start again on a good basis.
Downloaded the service manual of "harmon kardon citation 12 power amp". It already has the 68 pf input filter cap and the 3 uh output inductor parallel the 10 ohm resistor.
Pops can be dirt shorting across, causing carbon tracks. Thorough cleaning on 50 year old products is in order. I use 409/fantastik/spic&span spray, and a paper towel. A screwdriver pushes the towel into crevices like under resistors/capacitors. Followed by DI rinse. Dry 48 hours in low humidity (winter) or 4 hours @ 120 deg F oven or environmental chamber.
The double diode out on the heatsink is an RF magnet. Also the wires leading to it are little antennas. I would put 5 turn inductors salvaged from a PCAT power supply (ATX) in both leads 23 & 25 out to the heatsink, inside the amp chassis. Other consumer products with switcher supplies have the little inductors also. I did this to my ST120.
Post 31 has a typo, plus original 2n3055 may leak too much at 41 Vce. 40636 were selected from 2n3055 stream for less leakage at higher voltage. Modern 2n3055 & 2n3773 by epitaxial process will have too high Ft and may oscillate. I replaced base leads flying out to the heatsinks on the ST120 with 10 ohm 1 watt resistors, which Mooly says is just the thing to keep a Maplin amp from oscillating with modern fast transistors. I did it to provide a sacrificial part to limit the damage on the PCB the next time the output transistors shorted. Duh! Stumbled into the right thing.
Pops can be dirt shorting across, causing carbon tracks. Thorough cleaning on 50 year old products is in order. I use 409/fantastik/spic&span spray, and a paper towel. A screwdriver pushes the towel into crevices like under resistors/capacitors. Followed by DI rinse. Dry 48 hours in low humidity (winter) or 4 hours @ 120 deg F oven or environmental chamber.
The double diode out on the heatsink is an RF magnet. Also the wires leading to it are little antennas. I would put 5 turn inductors salvaged from a PCAT power supply (ATX) in both leads 23 & 25 out to the heatsink, inside the amp chassis. Other consumer products with switcher supplies have the little inductors also. I did this to my ST120.
Post 31 has a typo, plus original 2n3055 may leak too much at 41 Vce. 40636 were selected from 2n3055 stream for less leakage at higher voltage. Modern 2n3055 & 2n3773 by epitaxial process will have too high Ft and may oscillate. I replaced base leads flying out to the heatsinks on the ST120 with 10 ohm 1 watt resistors, which Mooly says is just the thing to keep a Maplin amp from oscillating with modern fast transistors. I did it to provide a sacrificial part to limit the damage on the PCB the next time the output transistors shorted. Duh! Stumbled into the right thing.
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HighER fT outputs don’t cause things to oscillate unless there is really something else wrong with a design. Like flying base leads.
Good to know, thanks. Right now the 1B01 are working perfectly. Do you have any info on replacements for the 40595 and 40594 drivers or 40408 pre-drivers? I was able to find original 2N5087 for the differential pair extremely cheap, and the 2N5232 for the bias transistors with no trouble.
Good idea. Forgive my poor formatting, I tried to make it easier to compare with the OEM parts list:
electrolytics stock -> replacement
C1/C2 250uF/15V -> Nichicon UKW 220uF/63V (I should probably parallel this with at least a 33uF to get it up to design value)
C3/C4 6000uF/50V -> KEMET ALS81 7500uF/63V (ALS81 has a stud mount which helped fill the excavated original cap)
C5/C6 6000uF/50V -> KEMET ALS81 7500uF/63V
C703/C704 50uF/50V -> Nichicon UFG 47uF/63V
C705/C706 50uF/50V -> Nichicon UFG 47uF/63V
C707/C708 250uF/6V -> Nichicon UKW 220uF/63V (see note for C1/C2 above)
C712/C712 50uF/50V -> Nichicon UFG 47uF/63V
disc/mylar
C701/C702 68pF disc -> Wima FKP 68pF
C709/C710 150pF disc -> Wima FKP 150pF
C713/C714 0.1uF mylar -> Wima MKP 0.1uF
All the resistors were changed out for Dale/Vishay 1% metal film, with the exception of the 1W and 2W parts, which are 5%, and I've left the wirewound resistors alone.
Output transistors were switched from RCA 4216 to RCA 1B01, as mentioned above, with new mica insulators and thermal compound.
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40594 npn 40595 pnp TO-39 silicon transistors. Vcersus 95 Vebo 4 Ic 2 Ib 1 Pt 10 w case or ambient 25 C. Rbe 100 ohm EBC pinout
40408 npn Vceo 90 Vebo 4 Ic 0.7 Ib 0.2 P 1w Ta 25 Iceo 1 ua Icbo .25 ua Vbemax 1 v Hfe 40-200 Fttyp 100 mhz
thetaJC 35 degC/W EBC pinout case not stated but some on this page are TO5, others TO39.
I've tried TO220 equivalents for TO5 and a leg eventually broke off causing meltdown. surplussales.com of NE had some old TO5 To39 stock this summer but the voltages are not as high as these.
I found another thread here with information about the transistors so I think I've got this covered. The one remaining thing are the diodes. They're listed as "2A 100v", and nothing more. Would I be correct in assuming these are just common 1N4148 in a DO-3 glass body? What about that "double" diode at CR5/CR6? Theres no information at all, and the part number is meaningless 45 years after the fact.
1n4148 is a 1 amp rectifier at best, probably a little below RMS. Diode part numbers change from day to day. Get on digikey or newark, select semiconductors diodes axial leaded minimum current 2 A maximum current 6 A voltage minimum 100. I had some 6 amp A6 from diodesinc but not a current number. I had some mr751 but not a current number anymore. Motorola used to make 3 amp diodes but I think On quit.
The double diode, called a stabistor for some years, is no longer made IMHO. Peavey can still sell you some; they intalled hundreds of thousands of them. Part # SZ-13886. A red LED has the same voltage drop, but the pointy package won't fit in the milled slot in the heatsink of a Peavey amp. Those are made for DO41 package. You may be lucky and be able to fit a red LED. If not, heat sink epoxy compound at about $20 a tube is a suitable way to thermally couple the LED to the heatsink. Or you can probably buy $250 worth from Rochester, who has a $250 minimum for obsolete parts.
The double diode, called a stabistor for some years, is no longer made IMHO. Peavey can still sell you some; they intalled hundreds of thousands of them. Part # SZ-13886. A red LED has the same voltage drop, but the pointy package won't fit in the milled slot in the heatsink of a Peavey amp. Those are made for DO41 package. You may be lucky and be able to fit a red LED. If not, heat sink epoxy compound at about $20 a tube is a suitable way to thermally couple the LED to the heatsink. Or you can probably buy $250 worth from Rochester, who has a $250 minimum for obsolete parts.
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1N4148 is more like a 100 mA diode. 2 amp arent so common anymore - typical 1 amp 1N4003 may work depending on where it is and what it’s doing. 1N5403 3 amp may or may not fit the PCB - they have really thick leads (for heat sinking).
Thats pretty much how I found the "2A 100V" 1N4148 in the first place, and it shows a little of what I dislike about the vendor search engines.
I don't know enough about electronics to know what this thing is doing or how to properly apply the rig you're talking about. Thanks anyway.