B+ current?

[Tom-s]

What is the B+ current the S3X is working with for each tube?
Or, what is voltage drop expected across the 680Ohm powersupply resistors?
I'm asking because i'm looking for a choke to use in S3X and Triad C-7X are easily sourced.

In another topic i found that a Triad C-7X, 10H 270 Ohm drops 13V less compared to 680R resistor.
https://bottlehead.com/smf/index.php?topic=2210.msg17244#msg17244

So that gives me about (680-270)/13 -> 32mA of current.

Am i correct? This would make for a 680*32mA -> +-22V voltage drop nominally.

 

[Paul Birkeland]

It's going to be a rough experience to fit a pair of C-7X chokes into the SEX chassis.  I would look at maybe the Hammond 154G to minimize how difficult this will be for you and to more closely mimic the DCR of the 680R power supply dropping resistors.

Your calculations are correct regarding current draw, but it increases slightly with the addition of the C4S upgrade.

 

[Tom-s]

Why is the 680R resistor 3W?
If i use 0.35A with 680R resistance i come up with something like a 1w resistor?

 

[Paul Birkeland]

Why is the 680R resistor 3W?
If i use 0.35A with 680R resistance i come up with something like a 1w resistor?

Yes, that is correct.  If you run a 1W rated resistor at 1W dissipation, it will last a few years.  If you run a 1W resistor at 0.3W dissipation, it will last 30+ years.  Additionally, the 1W resistor running at 1W dissipation will produce enough heat that it can damage other nearby components.

If you're building throwaway electronics or you have forced air cooling, then you can push the limits a bit more.

 

[Tom-s]

Alternative to Choking the S3X, would the power transformer-10 HV current headroom handle a shunt regulated powersupply +50mA? Voltage headroom is limited and means lower power output?

 

[Paul Birkeland]

No, the PT-10 isn't going to appreciate the extra current needed to make that happen. 

 

[Paul Joppa]

The power supply is maxed out in the stock amp. Best way )IMHO) to do a shunt regulator would be to make it a monoblock, with one tube regulating and the other amplifying.