Zesto Andros PS-1 Tubes

@Roblanger

Reviving an old thread. Did you ever find out the tube layout for the Andros? I'm using NOS 1960's Brimar's with good performance, but the bass is a little loose and I wanted to try something else. It would be cool if I could try to swap out one pair, but which pair should I start with?

Answering my own question:

Front Left = V1 = Left Output
Rear Left = V2 = Left Input
Rear Right = V3 = Right Input
Front Right = V4 = Right Output

I started tube rolling last night. I have been listening to a set of NOS Brimar's for about a year. They sound great, just a little on the warm side of neutral.

I picked up a pair of 1966 Amperex Holland (labeled Electrohrome) and installed in V1/V4. Brimar's are still in V2/V3. The Amperex appear to have about 2db more gain. The soundstage really opened up, it's much more 3D than the quad of Brimar's. Vocals (both male and female) sounded breathy and fantastic. Everything sounds more lively and I really like this combination.

I have a pair of military Mullard's and a quad of Telefunken's being delivered soon, so I'll try a few more configurations and post my results.

Installed the NOS Military Mullards in V2/V3, Amperex still installed in V1/V4.

At first I couldn't hear a difference between the Mullards and the Brimars. I did notice a slight loss of that Amperex 3D magic. After about 3 hours of play, the Mullards really grabbed control of the bass. This is the first time I've gotten any real slam out of my analog front end!

For reference: VPI Classic 3 -> Sumiko Pearwood Celebration Mk II -> Zesto Andros.

The Telefunkens should arrive in the next couple of days. I'm not sure I'll be swapping the Amperex/Mullard combination out any time soon, but if I try the Tele's I'll post an update.

Rob, thanks for the update. I'm sticking with the Amperex/Mullard config for now.

One update to mention: The 2dB observed increase in gain might have been due to the Brimar's being weak. I installed them as NOS about a year ago but when I pulled them they only tested out at about 50%. Not sure what happened there. I did make the assumption the Andros was self biasing so maybe I damaged the Brimar's? Does anyone know if you need to re-bias the Andros when installing new tubes?