A question about Sceptre

[phillip.lynn]

I noticed that the rectifier in this amp I bought is not the one listed in the schematic.  It has a 5U4GB (I think that's right) installed instead of GZ34.  I am about to buy a GZ and am wondering if I can just plug it straight in or if I need to take it to a tech to have some components changed as well. 

[EdBass]

I think you can drop the GZ34 in, and probably get a little more "juice" as well. If it were my amp I would put the GZ34 in and rebias the amp.

[johnk]

i just had and sold a '67 Sceptre. it had a Mullard GZ34 in it and it sounded great. a 5U4 is not the correct tube, but i have a feeling that someone put that one in it to lower the plate voltages.

[phillip.lynn]

Ed, John, thanks for your replies!  I did just drop it in and it did just fine.  I made sure to check for cherry spots, didn't see any.  I'm thinking someone thought that the 5U4 would lower the headroom.  I have heard something about a mod to make the level of NFB variable.  I think that will be next on my list...