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  1. 2

    Amp still makes sound even after turning master volume down to zero on VALVESTATE VS232

    If pre amp volume and guitar volume are turned up the pre amp still amplify signal and use power and obviously this effect stages after the MV thru operative voltage fluctuating? Or mechanism is EMI (electromagnetic interference)?
  2. 2

    Paired Tubes

    Idle Bias balance is only one feature. Transconductance has more role when push pull tubes amplify the signal. Good tube tester make tube testing easy. Using an oscilloscope, signal generator and output load resistor tubes operation is possible to veryfy quite reliably but it is time consuming...
  3. 2

    Channel switching with relay on 1974 TMB

    It should be safe enough when footswitch metal box is connect to the Safety Earth. Footswitch metal button is also connect to box / SE. If filament elevation is used the switch voltage inside the box come to about 60VDC. Compare this to amp Mains and HV switches? Choose a cable which has a SE...
  4. 2

    Channel switching with relay on 1974 TMB

    Relay coil operate without 0VDC reference so you can use filament coil voltage and rectify and filter and even regualate it. If its current is good for extra relay coil which it should be. Bridge rectifying and filtering increase AC load 1,41 times. Filament can also be elevated to lessen...
  5. 2

    Marshall jcm800 power up issue

    Voltage measures over Mains switch contacts tell you does the switch work or not. There is mains voltage when switch is Off and no voltage when switch is On. Also resistance measure between mains plug hot and neutral when switvh is Off show infinite or Megaohm reading and about 5 to 10 ohms...
  6. 2

    does Larry ground scheme require insulating pots from chassis?

    Making operative secondary current flow thru chassis will increase EMI (electromagnetic interference) to Mains Safety Earth because there is resistance in SE wire. SE wire is installed to same cable or installation tube with Mains Live and Neutral. Obviously there still are old buildings where...
  7. 2

    Cloning An SV20

    Interesting schematic but rated powers are odd! Edit: Obviously I did interpret PT wrong and secondary voltages are 141VAC and 101VAC which drop voltages to about 200VDC and 140VDC. Then powers are 9W and 3W. (20W setting calculated HV comes 397VDC and if OT is 5,3k there is potential to...
  8. 2

    Need 5E3 Build Troubleshooting Help

    I use mostly Toroidal Power Transformers because they are lighter and often cheaper. Best feature is they interact electromagnetically less with Output Transformers when mounted flat to chassis. You already bought EI-core PT but this is how I mounted toroid to 5E3 chassis using wax thread...
  9. Kaiutin


  10. 20230105_222440.jpg


    Clyserine Water mixture cone softening.
  11. Vahvistin


    Teknisiä kuvia.
  12. IMG-20230202-WA0001.jpg


    Wax thread mounted Toroidal PT
  13. 2

    JMP 2004 1978 power switch wiring.

    When I install a HV/Stby switch I always add a resistor over its contact or two resistors when there are two contacts. Then capacitors pre charge to perhaps 100V and some current flow thru tubes and no "cathode poisoning" happen. Now when you have DPDT switch you could add two 18k, 22k or 27k 2W...
  14. 2

    does Larry ground scheme require insulating pots from chassis?

    Larry grounding use chassis for secondary current and it is not good practice! Chassis is first a Safety Earth and second role is a Shield. Return current should flow in single Bus-wire or few Star wires. Potentiometer case is a Shield and it make good enough contact with metal chassis when it...
  15. 2

    Differences in plate-CT OT resistances - when to be concerned? (1202-84 repro)

    Yes, what is good for HiFi OT wide and even frequency range can make guitar amp sound sterile and less interesting! Voltage between primary halfs come exactly the same despite their possible resistance difference when wound count it the same. And there is no shorted wounds.
  16. 2

    Internal fuses for home built amps

    I recall that tubes filaments are designed so that there can't come a short which will increase current considerably without filament itself soon burn open circuit? There can come filament leaks to other electrodes but when PT filament output float against other voltages the PT should not get...
  17. 2

    Differences in plate-CT OT resistances - when to be concerned? (1202-84 repro)

    To me this voltage asymmetty is a sign that on a side which voltage comes 2,1V there is a short in coil. 5V : 0.318 would make 15,7 : 1 winding ratio and with 8 ohm speaker 1980 ohm primary load but not now because OT is faulty. It was someone else who mentioned "shunt voltage"
  18. 2

    Differences in plate-CT OT resistances - when to be concerned? (1202-84 repro)

    It is not unusual that the resistance between primary halfs is even 20% different. There comes shorter length of copper wire to the coil half which is wound earlier closer the core. "Better" OT coils are interleaved so that other half has two sections, bith side of the other half and wire length...
  19. 2

    Negative Feedback

    Testing NFB using an oscilloscope and signal generator is very easy. NFB detached driving for example 20% of clean power to a power resistor the output voltage is measured. Then NFB is connected and output is messured again. If output voltage drop to half NFB is 6fb. If to 0.7 then NFB is 3db...
  20. 2

    JTM50 Build

    Old electrolyte capacitors might get a short. Then B+2 dropper resistor should burn. This will quit you playing so test few practices before you take without a spare to a gig. I have read that old electrolyts voltage should be gradually increased. I have used about 15 at least 20 years stocked...