Comments on: Audio Engineering Magazine Pt 4: Schematics

By: bafflegab

bafflegab — Wed, 29 Jan 2014 03:44:45 +0000

In reply to Kevin Strom. The 1625 also has a seven pin base. The 807 has a five pin base.

By: willie g

willie g — Fri, 01 Mar 2013 20:14:35 +0000

There is no way a 6AS7 is going to give thirty watts out.

In push pull with itself maybe ten, probably less. NEVER try to parallel the triode sections, they always differ a lot because of how the tube is made.

By: Bafflegab

Bafflegab — Sun, 09 Sep 2012 03:57:19 +0000

Figure 2 is the Curtis Schafer amp in the first Audio Anthology. It would be a good thing to reprint Mr. Schafer’s comments on these.

I met him in the late seventies: he was still active then, and that was in Chicago as I recall. I remembered his name from an article in one of the audio magazines at that time and we talked, but not about this stuff. If I had only known….

By: Kevin Strom

Kevin Strom — Fri, 07 Sep 2012 00:23:23 +0000

With the 807, it is the plate, not the grid, that is on the top cap.

The very cheap 1625 is identical to the 807, except that it has a 12.6 Volt filament.

All the best,

Kevin Strom.

By: Brad Rinkert

Brad Rinkert — Wed, 19 Oct 2011 06:36:48 +0000

The 6AS7 has a mu of 2 or thereabouts, which means it needs a LOT of drive.

Using a driver transformer is one way to do it.

Using a power supply with a straight output in the 200 volt range (it’s a low B+ design too) and a voltage doubler for the driver section, or a tapped PT secondary, would be another. The driver tube needs to swing as much as the B+ of the output tube itself, so must have nearly twice the B+ itself.