Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Bubbastain on January 18, 2018, 10:43:44 am

Title: Sound City PI tube
Post by: Bubbastain on January 18, 2018, 10:43:44 am

I’m a bit confused as to which tube in my SC 50 PA Plus is the phase inverter tube. The schematic we have been referring to in my bias issue thread only shows V1-V4 and V5 and V6 being the two power tubes. My amp however has 5 “preamp” tubes. I read somewhere else that a different SC amp has V4 and V5 out of order. The amp calls for a ecc81/12AT7 in the pi slot. So, can someone tell from a picture of the guts which one is the pi tube? Thanks in advance

https://i.imgur.com/N2hLHMh.jpg

Title: Re: Sound City PI tube
Post by: sluckey on January 18, 2018, 11:08:43 am

...

Title: Re: Sound City PI tube
Post by: Bubbastain on January 19, 2018, 03:46:07 pm

Thank you. There was a Sovtek LPS 12AX7 in there. I put a 12AT7 in and it sounds noticeably better.

Title: Re: Sound City PI tube
Post by: sluckey on January 19, 2018, 04:05:25 pm

Did you resolve your bias issue or you gonna let it ride?

Title: Re: Sound City PI tube
Post by: Bubbastain on January 19, 2018, 09:00:47 pm

Quote from: sluckey on January 19, 2018, 04:05:25 pm

Did you resolve your bias issue or you gonna let it ride?

Just posted about it in the other thread. Since Radio shack closed down there isn’t anyplace to get stuff quickly in a pinch.