Tube DIY Asylum

RE: Using a CL inrush current limiter to lower B+

76.90.39.24

Tre'

In Reply to: RE: Using a CL inrush current limiter to lower B+ posted by DAK on August 29, 2017 at 09:42:12

You have 118 vac at the primary with 500vdc at the end of the filter.

You would need 104 vac at the primary to get 440 vdc at the end of the filter.

A 14 volt bucking transformer will give you that.

Tre'
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What he said... - Triode_Kingdom 21:03:55 08/29/17 (0)
I'll just add that a standard 12.6V filament transformer should be close enough to do the job.

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My AC must be more than 118 - DAK 20:47:46 08/29/17 (3)
Although i check it periodically, it could be higher nowadays. I soldered two CL90 right after the AC input from the IEC socket to each leg of the PT primaries and that actually made a big difference. The B+ after the filters, is now 460vdc. This is only 20 vdc more than i want but i might just leave it at that. Plate voltage is now 440 and G2 voltage is 420.
For single ended pentode, is this too much for KT88, KT90 , and KT120?
- RE: My AC must be more than 118 - Triode_Kingdom 21:09:17 08/29/17 (2)
  Using resistors to drop B+ to the output stage will ruin the regulation of the supply. This is OK for temporary test purposes, but it will turn a good amp into junk.
  
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  Buy Chinese. Bury freedom.
  - i am not using any dropping resistors in the B+ - DAK 23:04:42 08/29/17 (1)
    My Power Supply is LCLC. Then there is a 3.3K dropping resistor for the G2 voltage and then another 33K for the B+2.
    So as it stands now, i have 460vdc with 6550A power tubes. I am trying to get to 440vdc. I have a suspicion that with the kt120 power tubes the B+ will be around 440 volts. Do you think 410 volts on G2 is too high?
    - RE: i am not using any dropping resistors in the B+ - Triode_Kingdom 06:34:01 08/30/17 (0)
      Adding resistance on either side of the transformer degrades regulation. This is the wrong way to accomplish the drop.
      About G2, I haven't used the KT120. Someone like Jim McShane might be able to advise you regarding the practical aspects of this tube.
      
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      Buy Chinese. Bury freedom.
      
      Edits: 08/30/17

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