Randall RG50TC DC Heater issue.

Discussion in 'Other Amps' started by RandallDude, Aug 1, 2020.

  1. RandallDude

    RandallDude New Member

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    I have Randall RG50TC Combo Tube amp with me. It has been working fine for a while and it suddenly went off, no sound only buzz as i opened the back, I could see that the 2 preamps v1 and v2 were not glowing but other preamp v3, v4 and powertubes v5 and v6 were glowing. I tried changing the v1 and v2 but they still didnt glow. The amp works throught the effects return but not from the input.

    I checked the schematics and voltage across the DC Rectifier for the heater pins, without the preamp tubes in,
    1) I get around 8 volts between pin 9 and 4,5 for both V1 and V2 sockets but as the preamp tubes are inserted in (load is introduced) the voltage drops to 0. So, basically, the tubes are not getting heated up and not working as they should be, so the preamp section is completely off.

    I am thinking about changing the bridge rectifier and the capacitors for the heater circuit, will that be enough to solve my problem?
    The V3, V4 preamp tubes and V5 V6 Powertubes seem to be working fine and glowing good.
     
    Last edited: Aug 1, 2020
  2. South Park

    South Park Well-Known Member

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    Most DC problems are in the grounding reroute the ground to the center tap. The circuit is working if the ether tubes are working . You can jump from ether working tubes sockets .
     
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  3. RandallDude

    RandallDude New Member

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    The Preamps V3 V4 and Powertubes V5 V6 are getting the 6.3 Vac on the respective pins. But the preamps V1 and V2 are not getting their heater voltage on their pins when the tubes are inserted. Without the tubes, i can read -4 vdc on pin 9 of V1, V2 and +4 vdc on pin 4, 5 of V1, V2. Then I insert the tubes, and only V3, V4, V5, V6 glow but not V1 and V2, as I measure the voltage on the pins, its 0 volts.

    What do you mean by rerouting the ground to the center tap, which ground do you mean?
     
    Last edited: Aug 1, 2020

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