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  1. Now that you are back to 'usual' location, go...

    Now that you are back to 'usual' location, go down to the bottom left of this page and where it says 'vB4 default style' try the other 'mobile' setting and see if that was what you had at the other...
  2. I thought it improbable too, especially with the...

    I thought it improbable too, especially with the spring type retainers. BUT it is the only thing I can think of that explains the B+ dropping so much with the 6550's compared to the EL34's, even...
  3. Yes. Leave pins 8 connected and disconnect the...

    Yes. Leave pins 8 connected and disconnect the pin 1's. Retry your measurements. It's possible the 6550's they were using originally did not have the shell connection. Do the springs or their...
  4. Here's a wild guess. The 6550's are conducting...

    Here's a wild guess. The 6550's are conducting hard. This is shown by the low plate voltage compared to the EL34's.
    Something is messing up the measurement at the cathode. Measuring by the OT...
  5. Something is very strange about those 6550's....

    Something is very strange about those 6550's.
    They were measuring less current than the EL34's, yet they were pulling down the B+ greatly.
    If they were really conducting less, the plate voltage...
  6. Apparently Form D is 'make before break' aka...

    Apparently Form D is 'make before break' aka 'continuity transfer'. Form C is 'break before make', Form D is the same assignment as Form C but is 'make before break'.
    So during the switchover,...
  7. Were these parts all there when it was running...

    Were these parts all there when it was running EL34's? If not, which did you change?
  8. Replies
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    You don't have a spare LCD for that baby do you? ...

    You don't have a spare LCD for that baby do you? I have a 310 (same as HD series) but the display got broken. Great meter. I have a spare multi-processor and the service manual if you need...
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    But on top he's got a guitar he painted to match,...

    But on top he's got a guitar he painted to match, and now he's just going to let the amp go!
  10. Replies
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    Well, I couldn't think of a more deserving guy to...

    Well, I couldn't think of a more deserving guy to have a part named after him. ;)
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    How hot is the idle current? Measure the DC...

    How hot is the idle current? Measure the DC across the 6.8 ohm resistors. Typically these MM amps are biased very cold, around 6mA, so you should set for about 40mV across each of those 6.8 ohms....
  12. This gets a little interesting as to whether we...

    This gets a little interesting as to whether we are talking ground, chassis, or common. As far as I know for this model, the speaker jack is not insulated from chassis. So Helmholtz method is...
  13. Good job, but a tip for future reference: since...

    Good job, but a tip for future reference:
    since you are only concerned with removing the short from the supply rails, you only need to desolder the power pins on those IC's, so 8 connections in...
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    6,502

    Curious as to whether this was a NOS part, or one...

    Curious as to whether this was a NOS part, or one of the modern repro's like xvive?
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    Faulty filter caps where you have high AC ripple...

    Faulty filter caps where you have high AC ripple can give odd readings depending on the meter. As you have reported low DC on the filter caps, it could be that there is high AC ripple. In that case...
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    Sorry to jump in the middle here about tubes you...

    Sorry to jump in the middle here about tubes you don't want to talk about ( ;) ), but since the issue was brought up...
    Did this circuit work correctly for you (or others) with the 6C10 instead of...
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    Agree but the problem is going the other way, as...

    Agree but the problem is going the other way, as Justin outlined above. For example the era when Marshall dropped EL34's due to reliability issues and had stickers on their amps that said 'equipped...
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    The JJ and re-issue 'tung-sol' 5881's are 23W...

    The JJ and re-issue 'tung-sol' 5881's are 23W tubes and should be biased accordingly. (26W rating is for triode configuration as per JJ datasheet)
    It's unfortunate that when the 5881 moniker was...
  19. No elastomers or 'zebra strips' between the...

    No elastomers or 'zebra strips' between the display and board, like is often used for DMM displays?
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    What is the AC voltage at the actual primary...

    What is the AC voltage at the actual primary leads of the power transformer?
    What is the heater voltage?
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    342

    Is heater voltage also low?

    Is heater voltage also low?
  22. What does your meter say on diode check across...

    What does your meter say on diode check across those zeners?
    There's not a lot running off those low voltage rails. 3 IC's and a couple other items. Easy enough to de-solder the IC supply pins (4...
  23. Did you check if it is working? Just wondering...

    Did you check if it is working? Just wondering if there could have been a mix-up and you got shipped something that was actually a defective return or something like that? (although I'd be surprised...
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    You set bias for total current through standby...

    You set bias for total current through standby switch?
    That is what they specify.
    If you set for 75mA idle current at power tube, it would certainly pull down all the voltages.
  25. Sounds like this unit matches the Hot Rod, not...

    Sounds like this unit matches the Hot Rod, not the Blues.
    Here is Rev.B which shows the items you mentioned:
  26. Don't rewire it to match a different schematic....

    Don't rewire it to match a different schematic.
    Can you post some pictures of the board, including the bias circuit area and any board number markings?
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    If yours has a coupling cap into the tank, like...

    If yours has a coupling cap into the tank, like C43, check that signal is getting through it.
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    Do either of these schematics match up? 55253

    Do either of these schematics match up?

    55253
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