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RE: How do I tell if I have a 200C or 200CX

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In Reply to: RE: How do I tell if I have a 200C or 200CX posted by PaulMC on November 20, 2008 at 18:22:46

I found two schematics online. One, which is supposed to be for the 200cx, uses Motorola MJ21194 and MJ21193 outputs, the other, which is supposed to be for the 200c is hand drawn and shows NEC 2SD555 and 2SB600 outputs. The rest of the circuit layouts are similar in design, but completely different in the details of implementation and in the choice of devices. The 200c schematic shows a JFET input, while the 200cx one has a MOSFET input.

Do these sound likely?

I've also seen someone on eBay claiming that the 200cx had a copper cover for the transformer while the 200c did not. My unit has the copper transformer cover but NEC outputs, so I'm not sure if this is correct.

I have also seen posts from people that have Sanken outputs (2SC1586 and 2SA909); were these an alternative to the NEC's? If so, which are preferred?

Follow Ups:

RE: How do I tell if I have a 200C or 200CX - PaulMC 06:18:21 01/13/09 (15)
This all seems correct. The outputs were pretty similar sounding if I remember correctly, the NEC's being the better choice if there was any. The Motorolas were what we wound up with because of supply.

The JFET was definitely preferred to the MOSFET. The copper cover was always there as best I can remember.
- RE: How do I tell if I have a 200C or 200CX - SQLGuy 07:23:59 01/13/09 (14)
  Thank you for your quick and thoughtful response, Paul. I just bought a 200c (NEC outputs) that's in need of repair (previous owner shorted both channels at different times) and am trying to line up my plan of attack as far as parts I'll need. It's being shipped in, so I should have it late this week.
  
  I do have two other questions (at this time, at least :-) ): did you guys hand match these outputs, or were they close enough within the manufacturing specs already? Also, I see that there are bias test points for each output. Can you tell me what the average voltage should be across the emitter resistors at proper bias, or a bias adjustment procedure?
  
  Thanks again for the help,
  Paul (my name as well)
  - RE: How do I tell if I have a 200C or 200CX - PaulMC 11:34:25 01/13/09 (13)
    We did not match the outputs, instead we used emitter resistors on the outputs to keep everything even. I do not remember the setting across the resistor for the output current but I seem to remember setting this so there was no crossover notch and then upping it slightly from there.
    - RE: How do I tell if I have a 200C or 200CX - SQLGuy 07:10:40 01/15/09 (12)
      Thanks again, Paul.
      
      I do now have one more question that I would appreciate your help with:
      
      I am finding that the original NEC outputs do not seem to be readily available except from eBay. I am also hearing that these devices are some of the most commonly counterfeited transistors on the market. Looking at the datasheets, and reading various forums, it seems that the MJ21193/94's, which you used in the 200cx, are pretty good direct subs for the NEC's (better current and power handling, slightly higher hFE, comparable fT, etc).
      
      The one thing I can't tell from the datasheets I've found is how the On Semi's and NEC's compare in terms of thermal gain behavior. Can you tell me whether the 200c bias circuit would be stable with the MJ's? I.e. would a 200c bias and driver setup with MJ outputs be a viable solution?
      
      Thanks again for your help,
      Paul
      - RE: How do I tell if I have a 200C or 200CX - PaulMC 08:29:40 01/15/09 (11)
        
        In Reply to: RE: How do I tell if I have a 200C or 200CX posted by SQLGuy on January 15, 2009 at 07:10:40
        
        Shouldn't be a problem.
        
        RE: How do I tell if I have a 200C or 200CX - SQLGuy 20:14:07 01/18/09 (10)
        
        In Reply to: RE: How do I tell if I have a 200C or 200CX posted by PaulMC on January 15, 2009 at 08:29:40
        
        Hi Paul,
        
        Sorry to keep bugging you, but one more question came up.
        
        I finished pulling all the blown parts out of my amp - this included all but one of the outputs, half the drivers, and one pair of bias transistors. It also included a burned up resistor between the two drivers. In the schematic I have, this resistor is shown as 83.2 Ohms. In my amp, it is 39 Ohms. One other difference between the schematic and my amp is that the schematic shows 20 Ohm 1 Watt resistors between the drivers and the bases of the outputs. In my amp they're directly connected, and there is no place on the circuit board where such resistors could have been included.
        
        I realize this was about 20 years ago, but would you happen to remember the reasons for these changes? Do you think I should mod my amp to include these differences?
        
        Thanks,
        Paul
        
        RE: How do I tell if I have a 200C or 200CX - PaulMC 14:08:22 01/26/09 (9)
        
        In Reply to: RE: How do I tell if I have a 200C or 200CX posted by SQLGuy on January 18, 2009 at 20:14:07
        
        It's all pretty fuzzy. I would guess the resistors between the drivers and the outputs were there to increase the impedance of the output devices and to make it easier to drive the outputs. If I were building the amp today I would certainly remove them and I would lower the 83 Ohm resistor to something smaller and run a bit more current through the drivers.
        
        I would think the amp you have is better than the one on the schematic.
        
        RE: How do I tell if I have a 200C or 200CX - SQLGuy 14:14:22 01/26/09 (8)
        
        In Reply to: RE: How do I tell if I have a 200C or 200CX posted by PaulMC on January 26, 2009 at 14:08:22
        
        Sounds good. I'll let you know. All the new parts are in, and I'm just waiting on a Variac I ordered so I can fire her up, see how things look, and set bias.
        
        You want I should bring the beast by for a visit up in Boulder some day?
        
        Thanks for the help,
        Paul
        
        RE: How do I tell if I have a 200C or 200CX - PaulMC 17:56:56 01/26/09 (7)
        
        In Reply to: RE: How do I tell if I have a 200C or 200CX posted by SQLGuy on January 26, 2009 at 14:14:22
        
        Sure! Come on by.
        
        RE: How do I tell if I have a 200C or 200CX - SQLGuy 06:06:11 03/09/09 (0)
        
        In Reply to: RE: How do I tell if I have a 200C or 200CX posted by PaulMC on January 26, 2009 at 17:56:56
        
        Hi Paul,
        
        I've got my 200c running now, but I have one more question:
        
        How much mechanical tranformer noise (buzzing) is expected from one of these amps? On mine, the contactor hums a bit and the transformer hums more, especially once it's really warmed up. It doesn't drown out the music or anything, but it's certainly noticable from several feet away in a quiet room. Paraline has offered to revarnish the transformer if I send it out to them, but I'm wondering whether what I'm hearing is characteristic of these transformers.
        
        For reference, the amp that the 200c is trading places with is an Adcom 555 Mark II, and its so quiet that I actually have to press my ear to it to hear any mechanical noise.
        
        Thanks again,
        Paul
        
        RE: How do I tell if I have a 200C or 200CX - SQLGuy 20:24:54 03/08/09 (5)
        
        In Reply to: RE: How do I tell if I have a 200C or 200CX posted by PaulMC on January 26, 2009 at 17:56:56
        
        Hi Paul,
        
        I've got my 200c running now, but I have one more question:
        
        How much mechanical tranformer noise (buzzing) is expected from one of these amps? On mine, the contactor hums a bit and the transformer hums more, especially once it's really warmed up. It doesn't drown out the music or anything, but it's certainly noticable from several feet away in a quiet room. Paraline has offered to revarnish the transformer if I send it out to them, but I'm wondering whether what I'm hearing is characteristic of these transformers.
        
        For reference, the amp that the 200c is trading places with is an Adcom 555 Mark II, and its so quiet that I actually have to press my ear to it to hear any mechanical noise.
        
        Thanks again,
        Paul
        
        RE: How do I tell if I have a 200C or 200CX - PaulMC 18:02:57 03/09/09 (4)
        
        In Reply to: RE: How do I tell if I have a 200C or 200CX posted by SQLGuy on March 08, 2009 at 20:24:54
        
        What we noticed years ago is that sometimes the laminations came loose and all you had to do was tighten the bolts that hold the lams together. Try that. We never had much luck with varnish. Cyno acrylate in a vacuum chamber worked well to quiet the lams, but I think possibly tightening the four bolts might do it. Most had noticeable hum only if you put your ear up to the unit. It can also be that your AC has a bit of DC on it. Try measuring the DC voltage on the power line and see.
        
        RE: How do I tell if I have a 200C or 200CX - SQLGuy 21:08:05 03/09/09 (3)
        
        In Reply to: RE: How do I tell if I have a 200C or 200CX posted by PaulMC on March 09, 2009 at 18:02:57
        
        Hi Paul,
        Well, I've checked already for DC on my lines... none there. This transformer does run pretty hot, though. After a couple hours idling the laminations are too hot to touch for more than 1/2 a second or so.
        I tried tightening the through-bolts further, but that didn't make any noticeable difference in hum. I just did a test, and, with the amp pretty well warmed up, I can hear it pretty clearly from 15 feet away. It sounds, though, like the transformer is resonating at some harmonic of 60Hz... at least, there are definitely overtones to be heard.
        Can you recommend a place that can do the CA treatment you mentioned? I had contacted Paraline since they are the original manufacturer for this transformer.
        Thanks,
        Paul
        
        Edits: 03/09/09 03/10/09
        
        RE: How do I tell if I have a 200C or 200CX - PaulMC 05:34:38 03/10/09 (2)
        
        In Reply to: RE: How do I tell if I have a 200C or 200CX posted by SQLGuy on March 09, 2009 at 21:08:05
        
        The cyno treatment would have to be done at the time it is manufactured. I don't think it would work now. I think the heat is right, or at least it seems so. Maybe have Paraline make a new one for you?
        
        RE: How do I tell if I have a 200C or 200CX - SQLGuy 18:12:16 07/13/09 (1)
        
        In Reply to: RE: How do I tell if I have a 200C or 200CX posted by PaulMC on March 10, 2009 at 05:34:38
        
        Hi Paul,
        
        I finally got my re-dipped transformer back from Paraline. It still hums a bit, but it's manageable for now. I also replaced the contactor (which was humming quite a bit itself) with a Teledyne solid state relay. Dead quiet and a drop-in replacement for the contactor... I'm pretty happy with that.
        
        Anyway, the one last thing I'd like to do is add some balanced inputs. The amp suffers from a decent amount of ground loop noise in my system, even when everything's plugged into the same outlet; I'm hoping/expecting that running it balanced will cut this down quite a bit.
        
        Do you have any recommendations on what kind of an input circuit to use to add a balanced input to this amp? I had heard of some other owners that had had balanced inputs added to their 200c's or cx's, but I don't know whether that was a factory service you guys offered or something third party.
        
        Thanks,
        Paul
        
        RE: How do I tell if I have a 200C or 200CX - PaulMC 14:54:53 07/17/09 (0)
        
        In Reply to: RE: How do I tell if I have a 200C or 200CX posted by SQLGuy on July 13, 2009 at 18:12:16
        
        Adding balanced inputs probably wouldn't be that hard as the input has a diff pair if I remember correctly. You might want to contact Dr. Bob Odell out in Pasadena California who designed the amp. I am pretty sure I have Bob's email address somewhere so if you email me I can give it to you. The other option would be to send it to Rick Cullen www.cullencircuits.com and ask Rick what he'd charge to modify the amp for you.

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