PT for JTM45 build - GZ34 on a 430-0-430 secondary?

[StingRay85]

Got two of those from a Hammond K-40 speaker cabinet. Besides using a 5U4, they were also supposed to drive field coil speakers, hence the low B+.

If I would use this PT for a JTM45 build with a GZ34, am I risking a too high B+?

The Philips datasheet is a bit confusing. Here it says it would a good 450V.



This curve however puts its well above 600V. That would obviously make a large difference concerning the filter capacitor ratings and expected B+ during operation.



So first question to be solved: which one of the two would it be? Am I somehow misreading the Philips datasheet? Or does it also assume you have two tubes idling and the current draw drops it to that idle level? Better not install a standby switch then, regardless of hot switching...

Would it make sense to go for the choke input filter rather than capacitor input? Or look for a rectifier with larger voltage drop? The goal would be to drive a pair of Sylvania 5881 tubes.

 

[Pete Farrington]

I think the 450-0-450V in the Philips info must be no load voltage.
With the 2 x 150R protecting resistances, it’d be a saggy HT supply, 600V DC @ 0mA, 480V DC @ 250mA.

With your 430-0-430V transformer, I guess the idle HT might be well over 500V DC, which seems kinda high.

I think the choke input supply may be worth investigating.