ST-70 Filament voltage?

My St70 Filament is 6.7 on both sides instead of 6.3v. Should I be concerned and put a dropping resistor in series or just leave it?

tubey1 wrote:My St70 Filament is 6.7 on both sides instead of 6.3v. Should I be concerned and put a dropping resistor in series or just leave it?

Is this with all tubes connected ?

yes... with all tubes running,

tubey1 wrote:yes... with all tubes running,

I assume your mains voltage is a bit high. Any plans for reducing this ( with a buck transformer or similar) ?
If you can find 0.15 ohm ( 1w) resistor that would reduce filament voltage 0.4Volt
( one resistor on each side )

Yes... mains are 122V here. I'd have to order up a couple resistors. Do you think it's ok now with 6.7v or is it necessary to bring it to 6.3V ? There must be alot of folks in the US ... these old transformers were designed for less than 122v.. the voltages in the US have risen a couple times over the years.

tubey1 wrote:Yes... mains are 122V here. I'd have to order up a couple resistors. Do you think it's ok now with 6.7v or is it necessary to bring it to 6.3V ? There must be alot of folks in the US ... these old transformers were designed for less than 122v.. the voltages in the US have risen a couple times over the years.

It's not necessary but it will make life better for the tubes. ( too high filament voltage shortens
their life, BUT most likely your tubes will be replaced before that by normal aging)

bucking or step down or variac recommended to reduce your voltage to the amp from 122 to 117v

Purchased a varic last year per Bob's recommendation. Good $65 investment for my ST-70. Where I live, I had ranges from 116 to 126. Adjust it to 119 now. Also nice to have for bench work. It's a 5 amp model.