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RCA console amp RS-199C

Discussion in 'Tube Audio' started by HBrown, Mar 19, 2017.

  1. HBrown

    HBrown Active Member

    Messages:
    325
    Location:
    South Georgia
    RS199B_Schematic_Beitmans.png

    I recently pulled this RCA RS-199C amp out of an old console. I've hunted high and low for a 'C' schematic- its supposedly in Sams 683-13 but I cannot seem to find a file that will open on my android device. If someone has a pdf, I sure would appreciate it. I did find a schematic for the RS-199B. I saw where another poster said there were not large differences in the 'B' & 'C' variant, so I am referencing the 'B' schematic so far.

    I have repurposed several console amps in the past. Mostly amps that worked as-is with just power switches, and RCA inputs being added without too much effort being put into them. That being said, I am confident working with the voltages, I am just not really deep into the tube amp engineering side of things. I have a Dynaco ST-70, an Allied tube receiver, and multiple console amps I have been into over the years. I mainly repair and refurb SS units, but I like a nice tube amp as well. I know the electrical safety issues involved here, and will observe all caution.

    So, I looked at the amp, and schematic and determined that jumpering pins 2 & 3 on the 9 pin socket should power the amp up. I hooked a pair of bench speakers up to the outputs, and a cd player up to the signal inputs. No sound, no hum, no nothing. The tube heaters are lit up, but it seems there is no B+, or something is open somewhere. I did try it in the whole console before pulling the amp- The console lit up, and controls seem in good shape, but no sound at all then either. I figured I would try because the console is really in very decent condition. If I can get the amp going, I may return it to the console.

    I'm not very 'up' on the whole understanding of the voltage multiplier circuit used in this amp. The main transformer wiring colors are miserable- can't be certain which wires are which.

    Firstly, can someone help me determine if my main transformer is good? I'm not finding B+ anywhere. I need to isolate the transformer and see if it is doing anything. What voltage should I be getting from the transformer itself before the voltage multiplier circuit? If it is not good, then I just have more 'old tube amp parts' for my parts warehouse. If it is good, then I wouldn't be adverse to putting a few bucks into some caps & parts. I realize those tubes don't look so great. I do have some working, but not great 6BQ5's I can try in it, but I'm just trying to get B+ at this point.

    In my underside pic, what is that wire to the left of the red wire in the top right corner connected to the terminal strip lug? it goes to nowhere- there is nothing else connected to that lug. The 'B' schematic I'm referencing has an 'F401' in between the red lead of the HV transformer output and the rectifiers- is that a fuse? I see nothing like that anywhere?

    IMG_20170319_211715371.jpg IMG_20170319_210813251.jpg
     
    Last edited: Mar 19, 2017

     

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  2. kirkendoll

    kirkendoll Luke.kirk on instagram Subscriber

    Messages:
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    clinton, arkansas
    Both of those output tubes look toasted, do you have some to swap in and then try it.
     
  3. BinaryMike

    BinaryMike Pelagic EE Subscriber

    The high-voltage secondary should be in the neighborhood of 116VAC to yield 330VDC from the doubler. Is the fuse (F401) present and intact? If it's blown, check for shorted rectifier diodes. If that stuff is all okay, then I would suspect totally open (dried-out) 100uF caps. You can just clip new ones in parallel for troubleshooting purposes.

    'Fuses' in these chassis sometimes are just very thin wires, which might explain the wire that apparently goes nowhere. Look closer.
     
  4. larryderouin

    larryderouin Turn it UP, POP? PLLUUEEEZZZZZEE Subscriber

    Messages:
    21,791
    Location:
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    Get the 1964 BEITMAN's from this link. Files are pdf. Page 134 thru 136 handle the models that use the RS-199B with the RC1205 or the RS-177 with the RS-1205.
    http://www.americanradiohistory.com/Beitman-Manual.htm

    You'll also need to check the rest of the leads on the MOLEX, as the Tuner/preamp is powered off the AMP. So you have different voltages going out and back.
     
  5. HBrown

    HBrown Active Member

    Messages:
    325
    Location:
    South Georgia
    Ok, I have it running now, but it's redplating something fierce.

    I was able to get voltage from the transformer itself, so determined it was working.

    Thank you for the description of the 'fuse'. I was able to see a very short remain of a really thin little bare filament sticking off that terminal that nothing else goes to. (I saw it previously, but just thought it was a stray strand) I determined where it needed to go, and stripped a single strand out of a 16 GA wire and soldered it across the gap. I put my beat-up, but working spare 6QB5's in- and let her rip and it plays! I turned it back right side up, and saw the tube going nuclear and quickly snapped a pic & then shut it down!

    Ok, so what all should I definitely replace, and what should I be looking at to remedy the redplating? Have I most likely toasted that tube as well? It was like that for less than 1 minute.

    Thanks again for pointing that out about the tiny 'fuse' wire. I've never run across that before- it would have stumped me forever.

    Thanks for the link to beitman's- I appreciate it.

    IMG_20170320_003332262.jpg IMG_20170320_003201599.jpg
     
    Last edited: Mar 20, 2017
  6. cademan

    cademan Addicted Member

    Messages:
    8,984
    I would start by replacing all the capacitors. A bad coupling capacitor can cause red plating on the tubes.

    Switch the tube that red plated to the other socket. If it red plates also, the tube is most likely bad. If it doesn't, its probably a coupling capacitor associated with that socket.
     

     

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  7. HBrown

    HBrown Active Member

    Messages:
    325
    Location:
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    Ok, thank you cademan, I will try that.
     
  8. gadget73

    gadget73 junk junkie Subscriber

    Messages:
    36,547
    Location:
    Southern NJ
    Usually coupling caps cause the red plating, but the rest are probably not in ideal condition.
     
  9. HBrown

    HBrown Active Member

    Messages:
    325
    Location:
    South Georgia
    Did a bit more investigating. Both 470k resistors from pin 2 of the 6BQ5's to ground were bad. I threw in some I had on hand and it relieved the red plating- at least enough where I can run the amp and check things out. I'm putting together a list of parts to order.

    The tube heaters were still glowing madly- so I checked the voltage- they are running high at 7.4V. I checked the transformer output ahead of doubler/filters and it is 126V. The B+ from the doubler/filter is running 338VDC where the schematic calls for 330. My line voltage was running 119.8V. The schematic calls for 120V line voltage- so what is driving these voltages high?

    What sound I'm getting out of it has reasonable sound quality, but is not very loud. I'm not expecting it to raise the roof- but based on other smaller or comparable SE units I have it should have a little more balls than I'm getting. I'm driving straight from a CD player. I'm still not sure if it's gonna go back in the console, or become a standalone. Gonna get the parts on order in the next few days, then see where I'm at afterwards.
     
  10. CJVx

    CJVx AK Subscriber Subscriber

    Messages:
    217
    Location:
    NJ
    For high B+ and filliment voltage, could be high since it might be shared with the tubes from the tuner section, therefore loading it down to the proper voltage when all is connected together.
     
  11. BinaryMike

    BinaryMike Pelagic EE Subscriber

    That 6FQ7 input stage doesn't provide much voltage gain. You might consider revising the design to use a higher-mu tube, but it looks like re-optimization of the feedback network would be necessary. Are you up for that?
     

     

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  12. HBrown

    HBrown Active Member

    Messages:
    325
    Location:
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    BinaryMike, thanks for your help. Revising for more input gain may be what needs to happen if I decide to keep it out of the console as a standalone and I would be up for learning about it. Let me get the coupling caps and the other parts replaced, and see what I think of it in the console first- if the tuner functions. I'm not a guy who is a console purist, but it really is a pretty nice unmolested console. If that doesn't pan out exceptionally, then I wouldn't mind doing a little learning/experimenting on this amp. I may HAVE most of the needed parts already.

    Which input tube/circuit would you think would be the ticket?
     
  13. HBrown

    HBrown Active Member

    Messages:
    325
    Location:
    South Georgia
    CJVx, thanks for pointing that out, I didn't consider that this amp/power supply powers the whole console- tuner/record player as well. I can see where that would be a factor. What do guys usually do to correct for the excess voltage?
     
  14. BinaryMike

    BinaryMike Pelagic EE Subscriber

    The heater winding CT is grounded in this case, so I suggest adding 0.27 ohm 2W resistors in series at each end of the winding. You might have to make more than one attempt at this to get it right because heater resistance is nonlinear (changes with temperature). Try to get within +/-5% of 6.3VAC.

    The B+ voltage isn't high enough to be a significant concern.
     
  15. HBrown

    HBrown Active Member

    Messages:
    325
    Location:
    South Georgia
    Are you saying to knock down the heater voltage a bit to add the .27 Ohm 2 W resistors to the heater circuit like I sketched in my attachment?

    Also, what type caps should I order for the doubler caps (100uF, 200VDC) and the coupling caps (.27uF, 400VDC) I assume AES is a good place to shop for these?

    I will replace the multi cap as well. Is the general consensus to go with a new multi cap, or individual e-caps for it? IMG_20170321_131709.jpg
     
    Last edited: Mar 21, 2017
  16. maxhifi

    maxhifi AK Subscriber Subscriber

    Messages:
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    General consensus on an audio forum, really? :)

    It's a cost thing, new multi-caps are kind of expensive, advantages are preserving the original layout, and it's insurance that you don't accidentally make some ground loops or something. If this was a McIntosh or something valuable I would say a new can is the way to go, but for an old console amp it just isn't worth the money.. my vote is buy some axial capacitors and make sure to ground them all where the old can was grounded (even leave the can in place, and ground them on one of the tabs.

    What you don't want to do is ground the individual capacitors somewhere else, and then end up with a difficult to figure out hum problem.
     

     

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  17. BinaryMike

    BinaryMike Pelagic EE Subscriber

    Correct. And the multi-section can caps make sense only if appearance is a major factor.
     
  18. HBrown

    HBrown Active Member

    Messages:
    325
    Location:
    South Georgia
    Thanks, I was thinking Nichicon PZ from mouser for the replacement filters.

    What brand & type caps would you recommend for the doubler caps (100uF, 200VDC) and the interstage coupling caps (.27uF, 400VDC) Where is a good place to shop for these?
     
  19. larryderouin

    larryderouin Turn it UP, POP? PLLUUEEEZZZZZEE Subscriber

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    Nichicon UPW or UHE for the doublers. ,27uf are kinda hard to find. Try www.justradios.com for those. .33uf isn't too much of a leap (about 20% so should be ok). Mouser for the Nichicons.
     
  20. gadget73

    gadget73 junk junkie Subscriber

    Messages:
    36,547
    Location:
    Southern NJ
    If it has an extra heater winding, you can wire it up as a bucking winding to effectively drop the mains. Can't quite tell from the schematic, but it looks like the yellow/green winding could possibly be for tuner heaters that no longer gets any use.
     

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