Purpose of 30k 20w resistor on late SF amps

[TonewolfAmps]

Hi longtime lurker first time poster here. I was wondering if anyone could explain the purpose of the 30k 20w wire wound resistor on the end of the b+ rail to ground on the later Silverface amps particularly the Twin, 135w ultra linear amps. Is it there to lower voltage or maybe bleed the caps on the other side of the standby? Gets plenty hot just at quiescence.

[xtian]

Welcome to TAG!

The schematic shows that 30K resistor is dropping 410vDC to ground, so 14mV and 5.6 watts. Yeah, that's some heat! And it must drag the HT voltage down some, but I wonder if that's the design goal? It will also bleed the caps, but as you point out, it will only bleed the reservoir caps when the standby switch is closed.

[pdf64]

Downstream of the reservoir, the HT caps are 500V. Without that shunt resistor, if standby wasn’t used, the voltage across those caps would be likely to exceed that a fair bit for 30 seconds or so, until the tubes warmed up. Especially if the mains was at its upper limit.

[TonewolfAmps]

I guess not the sexiest way to do that but understandable I suppose I'm sure electrolytic caps rated for that surge were huge and expensive. Id imagine they probably wouldnt fit under the cap doghouses they probably had a warehouse full of lol. Thanks for replying to my question.