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  1. Replies
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    I think either will work. Did you check all...

    I think either will work.

    Did you check all the other components listed? I should add C15 to the list but that would be a rare failure.

    For the first test, remove R11 (or R12) to disable the...
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    Check T3 and T4 for shorts. If either is bad...

    Check T3 and T4 for shorts. If either is bad check all associated driver components i.e T1, T2, T5, T6, R1, R2, R28, R5, D24, R29, R7, D25 and IC1. When one of these FETs blow it often takes a bunch...
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    I've done this in the past by using an...

    I've done this in the past by using an inexpensive dual 50uf + 50uf 500V radial can cap plus a single axial 47uF 500V.
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    The problem is it takes a long time to research...

    The problem is it takes a long time to research and compare parts. Per my comment above I suggest you find one with a lower forward voltage drop. I don't think the switching speed is crucial,...
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    The cap is in the feedback path. If it develops a...

    The cap is in the feedback path. If it develops a higher than designed-for internal resistance then you will have too much feedback at higher frequencies. If you also have an extra 180 degrees of...
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    Do you see oscillation on the speaker out? ...

    Do you see oscillation on the speaker out?
    What if you turn the master to zero?
    Does it still happen if you have so speaker connected?
    What are the characteristics of the probe you are using?
  7. Replies
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    It's close but the forward voltage drop is quite...

    It's close but the forward voltage drop is quite a bit higher. Therefore the power dissipation will be significantly higher too. That might not matter if the thermal margins are good.
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    But one input is 5Meg and the other is 5K! Why...

    But one input is 5Meg and the other is 5K! Why not just use a differential amplifier? You'll get about 20db of gain too.

    54916


    But anyway. One signal is dry and the other is wet from the...
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    Let's wait and see it in the final context. It...

    Let's wait and see it in the final context. It seems that this is just a part of the picture.

    BTW, I'm actually more envious of the drill press.
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    Ah! Okay doke. Done like that Zin is 220 ohms.

    Ah! Okay doke. Done like that Zin is 220 ohms.
  11. Replies
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    Please note my revision above. I made a boo...

    Please note my revision above. I made a boo boo...
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    About 820 ohms. Remember the model might be...

    About 820 ohms. Remember the model might be poor....

    PS: Ignore that. I should have AC bypassed the 10k resistor so the DC conditions were changed to be closer the the answer you needed. Zin by...
  13. Replies
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    @HH Some observations using the 6111 model...

    @HH

    Some observations using the 6111 model above, I see the input Z as
    2.5K for the circuit shown
    If you AC ground the grid of the second stage the Zin goes down to 600 ohms. Not a surprise...
  14. Replies
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    I think you find it here ...

    I think you find it here

    https://music-electronics-forum.com/attachment.php?attachmentid=29682&d=1405871043

    Good luck. These things are almost impossible to work on due to the internal layout.
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    I don't there is anything wrong with your...

    I don't there is anything wrong with your measured voltages. The "Ampeg" numbers are patently wrong. According to them the current through the 221k plate resistor is (275-124)/221 mA = 0.68mA. ...
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    Did I miss something? 1V in with 1K ohm source...

    Did I miss something? 1V in with 1K ohm source impedance and 850mV out? Doesn't that imply a input resistance of 0.85/(1.0-0.85) * 1k= 5.66K ohms?
  17. The relay is fed form the DC heater supply of the...

    The relay is fed form the DC heater supply of the preamp. Do the heaters of V1 in the preamp glow? These can sometimes be hard to see so adarkened room will help. If yes then check the connection to...
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    6.2V will be fine for that FET. I have a...

    6.2V will be fine for that FET.

    I have a saying -"If in doubt, throw it out". Just fit a new zener and rest easy.

    PS: I you haven't got 6.2V 12V will also work just fine. The Vgs max is +/-...
  19. Thread: What's My Name?

    by nickb
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    Lastly, here are the tone control responses....

    Lastly, here are the tone control responses. Certainly quite unique:

    BASS
    54850

    MID
    54851

    TREBLE
    54852
  20. Thread: What's My Name?

    by nickb
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    More pics: Getting the PCB in and out was very...

    More pics:

    Getting the PCB in and out was very fiddly, one step away from impossible:
    54841

    This is the front panel control PCB, temporary knobs for testing. I had to replace all the switches...
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    I know from personal experience that sometimes if...

    I know from personal experience that sometimes if you publicly endorse the product you are offered a discount. I haven't used this particular company so I don't know about them. I think on my case I...
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    I'm sure he is. They way these guys work I'm...

    I'm sure he is. They way these guys work I'm pretty sure Nigel gets a discount as a result of the endorsements.
  23. Thread: What's My Name?

    by nickb
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    I got quite a bit more info on this from the...

    I got quite a bit more info on this from the owner. Interesting but still no name. The following is edited from the owner, any opinions expressed are just that.

    "Tam Lynch was the guy that made...
  24. Thread: What's My Name?

    by nickb
    Replies
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    The polyfuse was one of the things I was going to...

    The polyfuse was one of the things I was going to mention. On reflection I don't think the concern is warrantied for a couple of reasons. First, it's a 7.5A trip current device i.e. 450W into 8 ohms...
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    You can have NPTH's wherever you want them with...

    You can have NPTH's wherever you want them with any number of layers. You just specify it in your gerbers / drill files.
  26. Thread: What's My Name?

    by nickb
    Replies
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    I guess I missed that branding. Never mind. The...

    I guess I missed that branding. Never mind. The one you linked is different but this is still a 50W combo. On checking I see simply upload the wrong photos.

    They clearly went to some trouble to...
  27. Thread: What's My Name?

    by nickb
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    Dang - I missed that I thought I had obscured all...

    Dang - I missed that I thought I had obscured all the names in the interest of fun.
  28. Thread: What's My Name?

    by nickb
    Replies
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    What's My Name?

    Something completely different came my way. I think this is something very few will have seen. I haven't got a full set of pics yet, but I'll add when I have it back together. I know the name of...
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