grey wire or black wire

[fopoman]

Just bought a hammond 270EX. If I'm in the US should I use the 115V or 125V? 115 right?

[iknowjohnny]

Thats cool. When i bought mine they didn't have 2 options for USA power, at least not that i recall. I think they did this because people were finding heater voltages too high due to the difference between mains voltages now and back in the day. So i think 125 would be the right choice otherwise assuming this PT has a heater winding, it might run high. Mine ran at i think 7.2v.

[fopoman]

so 125V it is

[David Root]

Conversely if you need the extra plate voltage you can use the 115V tap and put a couple of small value 5W sandbox resistors in the heater circuit to take it down.

[dynaman]

Conversely if you need the extra plate voltage you can use the 115V tap and put a couple of small value 5W sandbox resistors in the heater circuit to take it down.

Yeah, just use whichever one gives you the voltages you want. I also just bought a 270EX specifically for that 125V tap...and still wound up using the 115V! B+ is right where I want it, my filament voltage is still reasonable and the tranny doesn't run excessively hot.

[Phil_S]

I'd say filament voltage trumps plate voltage. Whichever tap gets you closest to 6.3 is the one to use. This will vary with line voltage. If you check it at different times on different days, you might be surprised how much it moves around. Hardly anyone sees 115 any more though. It's likely 120+.

Then consider the PT winding might not be precisely matched to it's rating. One turn on the filament winding is a lot of wire. I had a bad PT a while back, so, out of curiosity, I unwound part of it. The 5V and 6.3V windings were on the outside. Respectively, they are 17 and 21 turns. I was surprised to learn how few turns there were. This computes to about 3.4 turns per volt. Even a half or one-third of a turn could tip the scale with respect to filament voltage.

[dynaman]

I'd say filament voltage trumps plate voltage. Whichever tap gets you closest to 6.3 is the one to use. This will vary with line voltage. If you check it at different times on different days, you might be surprised how much it moves around. Hardly anyone sees 115 any more though. It's likely 120+.

Then consider the PT winding might not be precisely matched to it's rating. One turn on the filament winding is a lot of wire. I had a bad PT a while back, so, out of curiosity, I unwound part of it. The 5V and 6.3V windings were on the outside. Respectively, they are 17 and 21 turns. I was surprised to learn how few turns there were. This computes to about 3.4 turns per volt. Even a half or one-third of a turn could tip the scale with respect to filament voltage.

Yes, Phil is right and I prolly should have been more clear in my post. Using the 115V tap on my tranny netted me around 6.6V on my filaments when loaded (current draw was about 2A on a 4A winding). I found this acceptable and my final HV was just a bonus. However, I have used Hammonds in the past and wound up with over 7V on the filaments. I'd consider that excessive. You'll have to check and make adjustments if necessary.