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xlr8or

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Everything posted by xlr8or

  1. Very hard to say. If the right channel was working you could swap the OT with the left OT and check it out.
  2. I suspect what is happening is that fried resistor has such high resistance that excessive current is being drawn in regardless. I don't want you to void the warranty. I would have suggested a further measure to fault find but that measure would have easily breached the warranty as it required removal of that resistor. On a separate note, can you share further details of Ken's amp that you have/had?
  3. Okay. Sounds like there is excessive current draw on power up and the fuse is blowing. I'd recommend returning the unit to Amazon.
  4. Yes, did you try removing the tubes or is the house fuse tripping?
  5. Bummer. If you're wanting to check if the other channel is working firstly remove the tubes from the non-working channel and secondly replace the fuse and see how you go with the other channel.
  6. If it's the same tube socket position that caused the Tesla EL34 tube to fail and the bias socket adapter to take out the resistor with another EL34/KT88 tube inserted into the same socket then there may perhaps be something wrong with the circuitry going to that socket. Just keep an eye on that particular socket position.
  7. Watch out as well for those specific tube sockets and their soldered pin connections underneath as the problem may lie there.
  8. Yes, and apologies I should have clarified the 6SN7 tube should also be removed with the middle one left intact. However, based on what you've shared that isn't going to help. I believe your problem is more centralised. Tube wise the middle 6SN7 tube being a voltage regulator may be responsible. I'd be inclined to check for cold joints and cap irregularities closer to the single voltage sources stemming from the PT secondaries and any associated parts of connected circuitry. Now, what I would also suggest though if servicing is not an option and you're keen to give it a go is to clone parts of the circuit to fault find. If you're handy with a soldering iron you can disconnect parts of the circuit and replicate those parts of the circuit on a breadboard instead and reconnect, and evaluate if the noise returns back to what it used to be prior.
  9. Is the noise coming from both channels? Perhaps try isolating each channel by removal of the 6SL7 tubes and power tubes in that channel to see if the noise persists. Make sure to have both ICs connected. It sounds like there is a cold joint of some sort within the grounding schema. Static/crackling noise can also be associated with a bad cap. Once the cap is warmed up it behaves differently. Is the noise apparent all the time and on cold boot up as well?
  10. You can't go wrong with any metal base vintage 6H9C's or 6H8C's. As many have indicated regardless of which ones you purchase some reflow of the solder in the pins may be necessary. Also, be sure to pick up pairs with matched internal construction features and hopefully matched/similar date codes. Feel free to share any photos here for confirming vintage.
  11. Very confusing .... Don't see 807 or KT90 mentioned anywhere.
  12. The VS55 does 50 watts. It appears the VTL amps are generically biased for 27-30mA according to the following article. I suspect as you have alluded the 6550/KT88 plate voltage is set higher. https://www.vtl.com/support/tube-biasing/ The thing to be mindful of though is that the R8 is configured to use triode and UL modes. In lieu of new production tubes, the restricting plate voltage that applies to both EL34 and KT88 tubes is a function of the triode mode of the tube. Please note that many manufacturers are reporting that their new production tubes are not reilable for > 450v plate voltage for triode mode. If triode mode was not an option and say pentode over UL mode was only available then 600v plate voltage would be possible using the existing bias current pot range of the R8. Higher plate voltages > 600v are even possible with vintage tubes. On a side note, I really like tetrode mode over both triode, UL and pentode modes. The R8 can be configured for tetrode mode minimally using the PT secondary voltage rails and their existing plate, grid and screen voltage circuitry configurations.
  13. It really depends on what the objectives are of the amp. Conventional AB PP configuration is best suited to manual biasing. SET configuration best prospers from auto biasing configuration. However, if you're into experimenting with different power tubes in the same amp circuit design and different bias points are required, manual biasing works best.
  14. Yes, fully agreed and just adding that cathode biased works best for the 90% of the maximum power dissipation setting of the power tube.
  15. Plate voltage = 420v and plate current = 65mA. Latest manual revision from ARC suggests 55mA to preserve the life of the 6550 or KT88 tubes.
  16. The real Tung-Sol 6550 grey solid plates from 1961 in my ARC VS55. More Tung-Sol magic in my Mentmore TVA-1. These ones are the 3-holed perforated grey plates from 1966.
  17. Good deal and highly recommended. Please send to me.
  18. This is the most sensible approach for running KT120 tubes and for that matter KT88 and EL34 tubes if the plate voltage is non-adjustable and one desires to run all 3 tube types at the same plate voltage on a modified R8. Always obey the tube datasheets for the operating parameters shown within the range of interpolation. Avoid interpreting operating conditions where extrapolation is required beyond the maximum x-y axes values shown. We are unsure of how the behaviour of the various curves change in their relationship accordingly. Furthermore, always obey the maximum operating conditions and parameters specified for each tube type as per the tube datasheets. I am also a strong advocate of biasing fixed/manual biased PP AB amps at 60% of their maximum power dissipation value utilising the following online bias calculator. https://robrobinette.com/Tube_Bias_Calculator.htm
  19. Weston Acoustics and Earle Weston is your best bet. The Willsenton R8 Mk2 still requires a crap load of mods to be applied to rectify poor circuitry design problems and bring it up to speed. No such issues are apparent with Earle's fully tested builds. You may also want to consider 2nd hand units listed in the classifieds here from more reputable brand names.
  20. Hi John. Can I suggest you please reach out to Stephe and ask for her help in redesigning a circuit for you using the Edcor PT that you have just purchased? I believe that would be the most productive outcome for you here. Happy to contribute funds for Stephe's involvement.
  21. When you switch from KT88 use to EL34 use the grid voltage changes accordingly. I believe the resistance values for achieving the different grid voltages have been quoted much earlier in this thread. If you could find those values or if someone here can share them we can explore what needs to be done to the KT88 resistance value to up its value by 10kohm to offer the 100mA option for KT120 use.
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