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too high voltage with gz37 rectifier in kit 1

203.4.129.19

Hi,

Need advice with regard to using the gz37 in the kit1 instead of 5u4g. Even when I rewire the main trans to 240v (my main is 220v) I still have 450V on B+.
I feel this is a bit too high (dont want to shorten the life of the 300Bs). Im thinking 3 options:

1) place a 100ohm Mill wirewound resistor after gz37 should reduce the B+ by approximately 20v, but I've read that more series resistance will negatively effect the sound.

2) reduce the input cap to maybe 10uf or lower, but Im afraid that this will cause quite a bit of hum with my 98db speakers.

3) order a new transformer from Brian, I read him somewhere in this forum that he has a new patch of transformers with more correct voltages...

what would you do?

Thanks and regards,
Vi

Follow Ups:

RE: too high voltage with gz37 rectifier in kit 1 - GTCharlie 17:11:07 06/10/08 (2)
Hallo Vincin. WE's tabulation points to 460v, at the plate, into 5k5 load, as the point where the 300B will have the least odd order harmonics, so 450v at B+ is well within limits. A resistor will always have a little inductance, almost immeasurable, but they're are nothing compared to the 10 Hy choke you have in series with the B+. What will hamper dynamics is the DCR of a choke (and of the mains transformer and of the rectifier itself)
- RE: too high voltage with gz37 rectifier in kit 1 - Vincin 23:32:56 06/10/08 (1)
  Hi, are you saying I should keep things as is? and the 100ohm resistor should be fine also?
  Regardsh
  Vi
  - RE: too high voltage with gz37 rectifier in kit 1 - GTCharlie 18:18:36 06/11/08 (0)
    Hallo Vincin. The 300B can take that voltage. But a resistor (or a choke) maybe be used as filter component or voltage dropping device. But it will depend on your "operating point" --- plate voltage, plate current of final stage and driving voltage and current of your driver.
RE: too high voltage with gz37 rectifier in kit 1 - Aubs 12:27:39 06/09/08 (2)
Hi,

I would replace the input cap with 4uf - this will reduce the voltage as you require - the idea that reducing the input cap will worsen the hum figure is not true- in point of fact, a lower first cap value will in itself result in lower, yes, lower hum! If the input capacitor is too large, this will result in heavy AC charge current through this capacitor. The AC capacitor current peaks may cause hum radiation into the amplifier.

Rewgards

Aubs
- RE: too high voltage with gz37 rectifier in kit 1 - Vincin 23:43:26 06/10/08 (1)
  thanks for your quick response.
  
  first cap 4uf is a nice idea. have you tried this yourselve in the kit1 amp or run some sort of simulation - that you got such result?
  
  In my amp I currently have a 20uf Mundorft - choke - 100ufx2 BG WKZ then 2 x 100ufx2 BG WKZ for the 5687 and 6sn7 stages. Are you sure this should work and there wont be any hum because last time I tried a 10uf first cap it hum quite a bit.
  
  again, thank you very much for the inputs.
  
  Regards
  Vi
  - RE: too high voltage with gz37 rectifier in kit 1 - Aubs 00:35:55 06/12/08 (0)
    This is from personal experience with different 300b amps, not a stimulation.
    
    sorry for the late reply!
    
    Aubs

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