Home Tube DIY Asylum

Do It Yourself (DIY) paradise for tube and SET project builders.

RE: blown gz34 st70

The ST70 is a worse case design for the rectifier and filter caps.

Most 5Y3's won't survive, I wouldn't chance it. A 5U4GB is just fine short term if you don't have a 5AR4.

Also running the ST70 with no output tubes is a recipe for disaster. The B+ will rise above the ratings of the marginal 525v filter cap with no load. Leave output tubes in at least one channel. If you don't have good EL34's you can substitute KT66's or 5881's in a pinch (just rebias).

The best trouble shooting is to lower the AC voltage by 20% with a variac.

If the fuse blows instantly suspect the rectifier. If it doesn't blow until it begins conducting (say 15-20 seconds) then you probably have a bad filter cap. Thats probably 95% of ST70 failures. The other 5% are a shorted output tube, bias failure or other wiring error.

- Gary
http://www.the-planet.org



This post is made possible by the generous support of people like you and our sponsors:
  Signature Sound   [ Signature Sound Lounge ]


Follow Ups Full Thread
Follow Ups

FAQ

Post a Message!

Forgot Password?
Moniker (Username):
Password (Optional):
  Remember my Moniker & Password  (What's this?)    Eat Me
E-Mail (Optional):
Subject:
Message:   (Posts are subject to Content Rules)
Optional Link URL:
Optional Link Title:
Optional Image URL:
Upload Image:
E-mail Replies:  Automagically notify you when someone responds.