My Kaiju kit shipped on 28th of November 2018. I finished it in the first days of the new year.
I encountered an issue with the PT-9 transformer. During first tests described in the manual everything was fine (including voltages) but as soon as the 300Bs were inserted and the high voltage line was drawing significant current the (mechanical) buzz started. This buzz is too loud to enjoy music on the long run. The mains voltage here is 230V and the PT-9 was wired for that value.
I tried a few things to mitigate the situation:
- Tighten the transformer screws using a hefty handgrip
- Put pressure from the sides on the lamination using a screw terminal
- Leave the driver tubes out, this eliminates heater current and ~22mA current from the high voltage supply
- Use an 1:1 isolating transformer to eliminate possible DC on the mains supply
- Soldered the transformer’s primary to 240V. BTW the description in the manual on page 33 is wrong and shows just an alternative way of wiring for 230V!
All these measures did not result in any change or improvement of the situation!
I eventually tried one more thing:
- Decrease the anode current of the 300B from 70mA to 60mA per channel by increasing the cathode resistor. For that purpose I soldered in an additional 220Ohm/5W resistor in series with the 1k/25W provided.
This resulted in a small decease of the buzz!
OK, now we are getting somewhere: I think the transformer’s laminations are fine but I suspect that the high voltage winding is somewhat loose and makes that noise.
I prepared two FLAC files I recorded with my KORG MR-2 recorder but unfortunately I cannot upload FLAC files in this forum. I can attach them to an email on request. In both cases the noise of the mains switch is included as a reference.
The sound from the Kaiju is the best of all my Bottlehead builds I have done so far and I did do quite few: Stereomour, SEX, Paramount, Seductor and Smash.
I definitely need help from the Bottlehead crew to resolve this issue!
Best regards, Norbert
