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Excelsior modification

Discussion in 'classic' started by djp150, Dec 24, 2021.

  1. djp150

    djp150 Member

    Hi , I have a Concordant Excelsior with the Explicit Power Supply . On the Exlplicit I have there only appears to be one half of the valve in use and Doug added a voltage regulator and capacitor to supply the voltage to the output socket directly from the regulator . So on the HT supply there are 2 220uf 400 v capacitors and one 100uf 400v capacitor . So my first question is has anyone else got an Explicit like this . Due to illness I have lost the valve that was in this and I’m trying to determine what it should be . If no one can help me with this I’m fortunate to have Dougs official circuit diagram so I can change the layout to correspond with that . If I go down that route I need to know the wattage of the2 22k resistors that Doug used . Can anybody help with this please . Many thanks Dave
     
  2. Dan K

    Dan K pfm Member

    Hi Dave, Sounds like you might be best sending it off to either Valvebloke (ampregen) or Jez.

    Isn't this thread a duplicate of your previous one? I think people are hesitant to offer help because they are worried that you might electrocute yourself, that and ruin a classic pre amp.

    The physical difference between a 0.5W and 2W or even 5W resistor is pretty obvious
     
    Last edited: Dec 26, 2021
  3. djp150

    djp150 Member

     
  4. djp150

    djp150 Member

    Hi Dan , thanks for replying. I have done quite a bit of work on valve amps so I do know how to be safe - but most of the work I have done is by substituting higher quality components into an existing circuit following the guidelines of a friend . What I’m trying to do is find someone who has the same circuit in their excelsior as mine to advise which valve Doug used . I’m beginning to think this is highly unlikely and mine was probably a one off . So the other route to go is to do a slight mod to change my circuit to be the same as his official circuit diagram . All I need to do is add a 2nd 22k resistor which already has the holes pre-drilled on my circuit board and solder the HT output to the resistor leg . (I will need to remove the existing voltage reg and capacitor). I will then be able to use the valve specified on the circuit diagram . I must admit I’m no expert on carbon/ metal film resistor sizes so I was hoping someone on here might have the knowledge of what is used . If not maybe the best thing to do is load Doug’s circuit diagram. I have no idea how many people on PFM own this preamp . Regarding the 2 people you recommend are they familiar with Doug’s Excelsior circuitry. Regards Dave
     
  5. Dan K

    Dan K pfm Member

    Big resistors are 2W

    Good luck
     
  6. chiily

    chiily PFM Special Builder

  7. djp150

    djp150 Member

    Hi thanks for the info . I didn’t realise that not knowing the valve used in my preamp was going to cause me such a headache but the fact Doug used to change the design often is why I have a problem . I have ordered a resistor so I can revert to Doug’s official circuit and hopefully get it up and running again , but if not I will try that site . I just need to be able to talk to someone who currently owns an excelsior with the explicit supply who would be kind enough to look inside for me . Not many excelsiors around I guess.
     
  8. chris@panteg

    chris@panteg pfm Member

    I used to have an Excelsior,the valve in the PSU was a 5965 computer valve as I remember.
     
  9. djp150

    djp150 Member

    Yes I think Doug used this at times and also the 6FQ7 which is the one shown on his circuit diagram . When I started off on this my preamp wasn’t working on phono and I believed I hadn’t put the valve back after testing in prior to illness . Well now I know it has NEVER had a valve in it since I’ve owned it and the fault was in the solid state device. The reason was starring me in the face and I couldn’t see it . The solid state device was doing the work of the valve . The 2nd heater output on the transformer has no wires attached to it and when I took the board out there doesn’t seem to be anyplace where the wire would be attached to unless Doug normally attached them directly onto pins 4 and 5 . There are holes in the front of the board where I’m guessing the 2 100 ohm resistors that are shown on the circuit diagram and coming from the transformer 6.3 v output should be attached . So good people I want to change this preamp power supply to be the same as the circuit diagram can anybody confirm from their own excelsior that on their power supply that the 2nd 6.3v taps should both be connected to a 100ohm resistor before then being soldered to pins 4 and 5 . This is for the explicit power supply . Am I missing anything out ? So I will probably never know if somebody in the past has changed Doug’s original circuit or if this was a one off trial by Doug
     
  10. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    There can't be 100R resistors in line with the heaters as they would drop virtually all the LT away! Possibly a pair in series across the LT winding with the centre point to ground to help minimise hum.
     
  11. djp150

    djp150 Member

    Ok, thanks for that - now you’ve said that I understand what the diagram is saying . So the transformer 6.3 outputs can be wired directly to the valve heaters ?
     
  12. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    If the output is 6.3V then yes. In valve gear that has a phono stage especially it is not uncommon (normal these days!) after maybe the mid '70's that a smoothed DC supply would be used at least for the early/first stages to avoid hum from AC heater supplies. It's not de rigueur but getting zero mains hum without it could be challenging...
     
  13. Dan K

    Dan K pfm Member

    Are they not bleed resistors to earth from the PSU caps?
     
  14. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    NO!! Assume around 250V HT and they would be pulling 625W each!
     
  15. Dan K

    Dan K pfm Member

    All this blind guessing is getting silly.

    OP, Just send the amp to Jez before something properly goes wrong
     
  16. djp150

    djp150 Member

  17. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    Hmmm.... The 100R resistors go to the HT output and float the heater supply for V1.... which, unless I'm missing something here.. appears to have no real purpose other than maybe to act as a soft and delayed HT turn on... the triodes seem to be in effect wired as diodes!

    The LT is a half wave voltage doubler followed by a 12v regulator so yes it does use DC heater supply. It's a bit crude but probably the transformer only had 6.3V heater windings and it was probably designed before LDO regulators ...
    Heaters use 12V here which many dual triodes can be wired to do. Any other heaters (in any single triodes or pentodes used as well if they indeed are) likely used in series connected pairs.
     
  18. djp150

    djp150 Member

     
  19. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    I couldn't have put it differently myself:D
     
  20. djp150

    djp150 Member

    Sorry I was going to reply -looked at the time and realised I should have been on the road . So first thank you so much for your time -you don’t know how much I’m grateful . I understand the 2nd part of your answer and when I measured the voltage at the preamp valves there was roughly 6.2 volts . I’m not following the 1st part however due to my lack of expertise . So after the 6.3 passes through the resistors it goes to pin 8 of the 6FQ7 ? So the 6FQ7 heaters are not connected to 6.3 or am I misunderstanding . Are you an excelsior owner ?
     

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