Rectifier Voltage Question, Is This Typical?

[rp]

I just got a new 5F1 up and running. I was making a voltage chart as I've learned to keep records, and I noticed that on the loaded 5Y3 rectifier, all tubes in and quiescent, I get 5.4VAC on pin 2 and 4.2 VAC on pin 8. Unloaded with no rectifier I get 5.5VAC on both sides. I'm taking the B+ off pin 8.

I've tried two 5Y3s too.

I don't think I've noticed a discrepancy like this before on any amp I've made, and maybe I never checked the 5V taps loaded, but I really think I have. I usually check the secs, the heaters, and the 5V right after I check the B+ and Plates.

Is this OK? Is it normal? it's a 1.2VAC difference, seems like a lot, is it a PT defect? It's a Hammond 300 Series PT BTW.

[rdjones]

How are you reading this ? With respect to ground ?

The only measurement that's going to tell you what's going on with the rectifier heater supply is from pin 2 to pin 8.
So a 5.x V reading is correct.
If you're reading these points to ground, it's coupled through the high voltage DC filter cap to ground.
The difference (5.4VAC minus 4.2 VAC = 1.2 VAC) is the ripple on the DC.

rd

[rp]

How are you reading this ? With respect to ground ?

The only measurement that's going to tell you what's going on with the rectifier heater supply is from pin 2 to pin 8.
So a 5.x V reading is correct.
If you're reading these points to ground, it's coupled through the high voltage DC filter cap to ground.
The difference (5.4VAC minus 4.2 VAC = 1.2 VAC) is the ripple on the DC.

rd

Yup I was measuring to ground. Learned something, excellent. I guess I must have never measured the 5V to ground before.

[greekie]

Just goes to show that a voltage potential is just that - a potential. What we are interested in is the potential across the filament, not from the filament to ground.