UPDATE ** problem solved, read through to my post on pg 3 **
For the people following my Citation repair which has turned into a refurb and slight modification, this looks like the final chapter.
I've previously replaced all the passives - electrolytics are now Nichicon KZ/FG, the polys are now all Wima MKP, and the resistors are Dale metal film 1% tolerance. I've also put new mica insulators and Wakefield thermal paste in. Everything I've done has reduced noise so far, but there was one buzz that has remained consistent in the left channel. I've reached the final stage, where I tracked down the source of the buzz.
It was when I was redoing the thermal coupling that I discovered the left channel outputs were no longer the original Harman Kardon 43024216 (RCA 40636), they'd been replaced with Sony TO-3 devices, TX 183S, and they are noisy. I moved them to the right channel to make sure there wasn't anything failing in the left channel voltage gain section, and the noise followed them. I was able to get it to abate somewhat by splitting the devices across the channels, so each channel had one original and one Sony, and while that worked it also increased the distortion in both channels.
Now i have to either find NOS outputs, or some vintage pulls, or more preferably some modern equivalents. I can read parts sheets but there still will be effort spent on trial and error until I get parts that play well with the rest of the circuit and sound great.
If you know of any TO-3 devices that will replace the RCA 40636 NPN in the Citation 12 amp please let me know.
For the people following my Citation repair which has turned into a refurb and slight modification, this looks like the final chapter.
I've previously replaced all the passives - electrolytics are now Nichicon KZ/FG, the polys are now all Wima MKP, and the resistors are Dale metal film 1% tolerance. I've also put new mica insulators and Wakefield thermal paste in. Everything I've done has reduced noise so far, but there was one buzz that has remained consistent in the left channel. I've reached the final stage, where I tracked down the source of the buzz.
It was when I was redoing the thermal coupling that I discovered the left channel outputs were no longer the original Harman Kardon 43024216 (RCA 40636), they'd been replaced with Sony TO-3 devices, TX 183S, and they are noisy. I moved them to the right channel to make sure there wasn't anything failing in the left channel voltage gain section, and the noise followed them. I was able to get it to abate somewhat by splitting the devices across the channels, so each channel had one original and one Sony, and while that worked it also increased the distortion in both channels.
Now i have to either find NOS outputs, or some vintage pulls, or more preferably some modern equivalents. I can read parts sheets but there still will be effort spent on trial and error until I get parts that play well with the rest of the circuit and sound great.
If you know of any TO-3 devices that will replace the RCA 40636 NPN in the Citation 12 amp please let me know.
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I presume you mean just the MJ15003, because the MJ15004 is PNP - all 4 of the Citation 12 outputs are NPN, according to the schematic.
Did you use the MJ15003 on your amp?
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I forgot that citation 12 was full NPN,I answer from my workshop where I work on something else...
it's just that the rca40636 is very close to the 2n3055, so the mj15003 is naturally needed but wait for the opinion of other people
it's just that the rca40636 is very close to the 2n3055, so the mj15003 is naturally needed but wait for the opinion of other people
40636 was a homotaxial part with 400 khz? ft. Some amps oscillate when you replace them with 2 mhz epitaxial parts like mj15003 or even TIP3055. Or even 2n3055 made by the epitaxial process.
You can sometimes patch in a 10 ohm base resistor on the part to prevent the oscillation.
Electronicsurplus.com had some 2n3055h homotaxial in Ohio 2 weeks ago, $4, but I don't know if they are selected for use at 35 to 40 v the way the 40636 was. I don't know what the Ft is either; I can't test for it.
You can sometimes patch in a 10 ohm base resistor on the part to prevent the oscillation.
Electronicsurplus.com had some 2n3055h homotaxial in Ohio 2 weeks ago, $4, but I don't know if they are selected for use at 35 to 40 v the way the 40636 was. I don't know what the Ft is either; I can't test for it.
I know the 40636 is derived from the 2N3055 but I've also read that they were parts that were selected out of each run for having higher characteristics. I think they had better forward gain and higher breakdown voltage, among other things. The end results is that while a 40636 would work in a 2N3055 design, putting a 2N3055 into the 40636 circuit was asking for trouble.
Then again, I have no idea, I'm just repeating what I probably incorrectly remember.
Then again, I have no idea, I'm just repeating what I probably incorrectly remember.
Maybe this would work then?
RCA - RCA1B01 - Transistor, NPN. House No RCA1B01. 70Watt Audio Amplifier
according to my books, if you find some real 2n3773 you shouldn't be very far, just have to see the pinout and the specs with the model specialist.
the bdx50 can also be a good candidate
the bdx50 can also be a good candidate
This is getting more interesting as time passes. I looked at the text from the link I posted just above, and after the host name this is the subdirectory:
rca-2n3773-house-transistor-npn-house-no-rca1b01
I would think these two are very close. The numbers look correct, and as Indy mentioned, anything chosen should be homotaxial, which fits the RCA1B01. I don't know enough about the in-depth specifications or how these things are affected by the upstream components to make a decision.
rca-2n3773-house-transistor-npn-house-no-rca1b01
I would think these two are very close. The numbers look correct, and as Indy mentioned, anything chosen should be homotaxial, which fits the RCA1B01. I don't know enough about the in-depth specifications or how these things are affected by the upstream components to make a decision.
yes but it's hard to find ,you might as well look for original 40636 taken from a citation 12 on the net
2n3773 or bdx40/50 are easy to find
2n3773 or bdx40/50 are easy to find
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I just bought 10 of the RCA1B01 from the link I posted. If these work I'll keep the extras for other projects.
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Plenty of them, but thats for doing a complete modification of the circuit to switch from BJT to MOSFET. Maybe I'll try that next time.
Those outputs are at least as hard to find as the originals too.