[Dr.J]

Hello everyone!

I purchased my ZD used and absolutely love it. The unit never came with literature and I assume it never did/does.

My question is: how much influence do the rectifier tubes have over the quality of the sound? Are a matched pair required and are they worth upgrading?

Also, are there any good sources of literature that explain how a tube pre/amp works, I mean for someone with limited understanding?

thanks,

John

 

[BobMajor]

Everyone has said that tube rolling the rectifier tubes has no effect.
Be advised that Craig changed the rectifier tubes at some point in his production. The latest ones have tube caps and are the 6D22S.
Craig had this to say about matching the tubes which must be done:
I match the rectifiers when the amp burns in. I look at the first filter after the rectifiers. This wave form should be 120Hz sort of triangle looking with even peaks. If the peaks are not even the tubes don't match. This is the best test because the tubes are loaded with the actual current the amp is running steady state.
You can test by ear. Power the amp up, and with the volume full counterclockwise listen for background noise. You will need sensitive headphones, like the RS-1's. Pull one rectifier and listen. You will hear a pronounced 60Hz hum in both ears. A tube mismatch will be between this level, and no hum. If you hear a hum with one rectifier, but not with both, they are matched close enough.

Before you guys ask, this procedure is all done with the amp on. I let the amp warm up for 30 minutes. Use a pot holder to remove the tube (don't remove any tube except the rectifier, either one will do). When Craig says that you'll need a sensitive pair of phones to hear the hum, he ain't kidding! This is one quiet power supply! The rectifiers are real cheap so the best thing to do is buy 4 and find the best two pairs among them.

 

[Dr.J]

Thanks, Bob.

Mine has a pair of rectifier tubes labeled 6DA4. The ZD sounds great, is without issue, but the tubes are showing signs of wear, the top plates corroding; otherwise, it's fine.