X100B 'Honey Do' List?

Discussion in 'Fisher' started by jertub, Jul 28, 2017.

  1. gadget73

    gadget73 junk junkie Subscriber

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    Its a relatively easy answer honestly. The side connected to the plate of the 12ax7 has a much higher difference in voltage than the side connected to the cathode. A lot of other manufacturers of gear with similar designs did the same thing with the cap voltages. If I were replacing them now though, it would be a 630v cap in both spots.
     
  2. jertub

    jertub Member

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    Question about diodes/rectifier, I can order 1N4007.... are those the right replacement and do I have to change anything else if I decide to replace with those?

    ps I also found these in my junk drawer : radio shack 06P15 (276-1114) which is 1.5A, 50A peak, 1000V. These will work too? It would save me an order but wanted to confirm they are ok.
     
    Last edited: Aug 6, 2017
  3. larryderouin

    larryderouin You can be sure if it's Westinghouse??????? Subscriber

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    Yes you can use the 400v parts in both places. It won't hurt anything.
    1n4007 are the diodes for the 2 diodes at the doubler cap. The rectifier is a different call, entirely. No need to change anything else with these.

    Put the Ratshack part back in the Junk Drawer. .
     
  4. gadget73

    gadget73 junk junkie Subscriber

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    A 1N4007 is good for 1 amp at 1000v. A diode good for 1.5 amp at 1000v will handle that just fine. I'd lay money on the originals being a fair bit lower for both current and voltage rating.
     
  5. jertub

    jertub Member

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    Larry, Notdigital, Gadget etc all....

    I got all the filter caps replaced and nothing blew up. Prior to replacement the bias was dead on 40vdc as long as I had the amp. After replacing it increased to 45vdc which I dialed back. Is that because of the increase in capitance on the new C3?

    So KNOCK ON WOOD, its playing right now on the bench and sounds great. Probably still run as hot as f'ing toaster though.

    At this point, Im only going to replace the burnt resistor and maybe the diodes and nubber cap. I will get at the coupling caps down the road and will try out the ero caps in the meantime.

    Thank you for all the help.
     
    Last edited: Aug 19, 2017
  6. jertub

    jertub Member

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  7. larryderouin

    larryderouin You can be sure if it's Westinghouse??????? Subscriber

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    Jerry; It's more than likely the change from the selenium rectifier to a Silicon rectifier. The schematic shows 42V and the instructions say 40V. This is the total of the 4 heaters on V1 thru V4 used for the bias voltage. This would make the heaters approx 10V each. 42v would make it 10.5v. 44v is 11.v each. 45v is 11.25v each on the heaters of V1 thru V4. This is the reason it takes forever and a day, plus 1/2 of tomorrow, to warm up to run. At 40V it's running fairly cool, but to your hand will feel hot. This is normal for these. My X-101-B (same except for 7591's) @ 40V runs hotter than my Sansui 1000A. And that's HOT! But hotter than the hubs of hell to your hand is about 130*F holding hand on it uncomfortably for about 5 seconds. Thumper and I took FLIR readings on a 400 yday after about an hour and the Main Power transformer felt hot, but surprisingly it was 117*F. I actually thought it was hotter like about 130-140. Hands are LOUSY thermometers.

    Add a 10ohm cathode resistor off pin 3. Unsolder the pin 3 wire. Then install a 10 ohm resistor in place of the wire at pin 3. Attach and solder the wire removed earlier, to the free end of the resistor. Do this for each of the output tubes. You can then read each of the output tubes for cathode draw. This will be in mV. Convert to mA by dividing by 10. I need these numbers taken with the bias at 40V and again at 42V, and finally 45V. This will help determine optimal voltage on the BIAS Adjustment.

    List each of the reading groups under headings of 40V BIAS, 42V BIAS and 45V BIAS. list the 10 ohm resistor readings at each of the voltages.

    CUT & PASTE The Following. Then add your readings to the right of each tube number at each voltage.

    40V BIAS
    Plate voltage on Pin 9
    Screen Voltage on pin 1-7

    PIN 3
    V7
    V8
    V9
    V10

    42V BIAS
    PIN 3
    V7
    V8
    V9
    V10

    45V BIAS
    PIN 3
    V7
    V8
    V9
    V10

    Larry
     
  8. jertub

    jertub Member

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    Larry-
    I didnt change the rectifier yet... my rookie assumption was the higher bias was because of the new filter caps or maybe line voltage was higher than usual. Or maybe i simply bumped the bias pot while working.
     
  9. larryderouin

    larryderouin You can be sure if it's Westinghouse??????? Subscriber

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    All true. Just keep an eye on it then.
     
  10. gadget73

    gadget73 junk junkie Subscriber

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    Better filter caps can bump the voltage some. So can larger values.
     
  11. jertub

    jertub Member

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    Today's "problem" is am trying to decide what to do about tubes. Money is tight.

    I currently have 4x slyvania 7868 and 6x ge long plate dimple foil horseshoe getters for the 12ax7. One of the 12ax7's are bad, I had intermittent static in the right channel a few weeks ago that went away when I swapped the inverter tubes with the phono tubes. Everything sounds nice now but I don't have access to a tube tester.

    1. How important are matched pairs for the signal tubes?

    2. What would you replace the 12ax7's with? What did they come with from the factory?

    I know my options for the power tubes.
     
  12. gadget73

    gadget73 junk junkie Subscriber

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    Usually I only try to make the tubes matched per function, meaning the two phono tubes will be the same, the tone amps will be the same, and the phase inverters will be the same. I don't tend to bother much about matching beyond making sure the tubes are in good working order.

    If you've got one bad one, I might spring for two to swap into that position and keep the good one as a spare.
     
  13. larryderouin

    larryderouin You can be sure if it's Westinghouse??????? Subscriber

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    More than likely it came from the Factory with Telefunken's. In the Phase inverter position(V6&V5), the sections (2 halves) don't need to be matched, although the sections 1 & 2 should be close between tubes, as the sections are doing different jobs. in the phono(V1&V2) they should match sections and tubes. The Same for the tone amp(V3&V4) tubes, The 1/2s should be very close and tubes close.
     
  14. jertub

    jertub Member

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    Hi again, I think I made a mistake and got the wrong resistors for the ones referenced above.

    I purchased 2.2K ohm 1/2w Vishay Metal Film Resistor - Through Hole
    http://www.mouser.com/search/ProductDetail.aspx?r=594-SFR16S0002201JA5

    These things are TINY! The old dep. carbon are huge in comparison.

    edit: Since the values are the same, I came to the conclusion that modern metal film resistors are just smaller than their carbon friends of yesterday. So I installed it, hopefully my assumption was correct.
     
    Last edited: Aug 15, 2017
  15. larryderouin

    larryderouin You can be sure if it's Westinghouse??????? Subscriber

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    That's fine. And yes today's parts for a particular value and voltage can be smaller by as much as 2/3's. You should see the difference in Electrolyic caps. For Example a 100uf 50V caps back then was as big or bigger than a "D" cell battery. Now they are 1/2 the size of a "AAA" battery for the same voltage/value.
     
  16. fred soop

    fred soop Super Member

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    When restoring 600-T s/n 43453K, the replacement 2 watt resistors are smaller than the half watt units of years ago. The 10,000 µF, 100 V capacitors are the same diameter (to fit the clamps) and shorter than the old 4,000 µF, 40 V caps.
     
  17. jertub

    jertub Member

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    I was thinking about leaving the ERO FOL coupling caps in place. I read reference in other threads that they rarely go bad and that they are responsible for "the fisher sound". The amp sounds very nice now and I fear altering it.

    Is my fear justified or is it a poor idea to leave them in place?
     
  18. larryderouin

    larryderouin You can be sure if it's Westinghouse??????? Subscriber

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    If you like how it sounds, leave it. The sound of the unit is dependent more on the design of the circuits than individual parts. I agree the Erofol's rarely go bad. if the voltages on the output's are within spec, go ahead and leave them in. And stop worrying. The main thing is that it works and you like the sound. If one of them does go bad, then and only then should we talk about coupling caps, and which one to get.

    There are as many if not more caps than there are owners, although there are good inexpensive caps that are very close to the original sound. The Erofol's are what are called Mylar which is Dupont's name for polyester sheet. See this link https://en.wikipedia.org/wiki/BoPET Actually any polyester cap will sound pretty much the same. I tend to use Polyester axial's from Antique Electronics Supply (www.tubesandmore.com). Two brands Mallory and the house brand. I suspect the house brand is a Mallory. These are the Yellow axials. The other used is the Orange drop. These are also good. There is an Internet rumor going around that using all one type in an amp will change the sound. I'm on the fence on this one. I use the Yellow axials, Cornell Dublier DME's or Orange drops depending on what fit's best for that value an voltage. And it will sound fine. Some guys are in to exotic caps that cost upwards of $100 each or more. Not needed and it won't change the sound appreciably. But it will empty your screaming and kicking wallet faster.
     
  19. gadget73

    gadget73 junk junkie Subscriber

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    For whatever it may or may not be worth to you, I have a little German console amp from about the same era as your X100b. It came with the same ERO caps Fisher used. All of the ones I pulled are fine, tested for value and leakage on the appropriate tester. Just keep the soldering iron away from them. I've bumped them before in German radios and they short out. I think they may be polystyrene. PS caps change value with heat too, so double reasons for not poking at them needlessly.

    I did some redesign work on the amp so most of the original values could no longer be used, but I did re-locate two of the originals to a different spot in the circuit.
     
  20. jertub

    jertub Member

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    Thank you both.

    Like I said it sounds great right now. I think I will leave the coupling caps for the time being. Im comfortable doing this with the idea that if they went south, it would not be catastrophic to the amp and could be addressed at that time.

    I have changed all electrolytic caps and have replaced the rectifier. I am under the assumption that the power supply is the most critical and if that went bad it could smoke the amp. When I tested the old cans with my meter, they had drifted 30 percent for some of them.

    So the bottom line is I have a new matched quad as well as preamp tubes ready to go ....

    Is it a poor idea to put new tubes into this amp without updating the coupling capacitors or upgrading the bias circuit in any way?
     
    Last edited: Aug 18, 2017

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