274B a direct replacement for 5AR4/GZ34?

[oldtexasdog]

I've been told that I could replace my 5AR4/GZ34 Rectifier tube with a 274B as a direct replacement in my Pilot 505 amp?

 

[HollowState]

While the pin-out is compatable, comparing specifications indicate that the max current & voltage capacity of the 274B is slightly less then a 5AR4. Also, it is a directly heated cathode which will heat up a little faster even though all WE tubes are slower heating then most others. And it's a little taller then most 5AR4s. Using it in a Pilot 505 would be OK since it only uses 6BQ5s.

However, with the absurd prices that I've seen original WE 274Bs bring on eBay, you could buy 10 (or more) 5AR4s. If you're talking about a Chinese 274B copy, I have no experience with them because I dislike all of them. So be cautious.

edit: If your amp is like the one shown below, the rectifier is very close to the filter capacitor. Since a 274B is a curved or ST shaped envelope, it may touch the capacitor can which isn't good. Too much heat.

 

[jrenkin]

You need to watch out for inrush current. The specs for the allowable 1st capacitor are different. As long as it is small, you could sub in, but if you have a large cap there, like more than 4u you will damage things. You may also experience a fairly significant drop in voltage.

 

[oldtexasdog]

Thanks