Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: RoadShow on August 24, 2023, 10:37:40 am

Title: 2203 RI schematic question
Post by: RoadShow on August 24, 2023, 10:37:40 am

Good morning,

So, looking at schematics, I don't understand something on the Marshall 2203 RI schematic.  The grid resistor on EL34 V4 looks connected like I would expect.

On V5-7 there's a dot that effectively connect it to ground with 1 & 8.  Any other 2203 I look at seems correct, all EL34s look like V4

Error? Or what don't I understand...

Title: Re: 2203 RI schematic question
Post by: sluckey on August 24, 2023, 11:02:29 am

schematic error

Title: Re: 2203 RI schematic question
Post by: shooter on August 24, 2023, 11:05:13 am

was just typing ^^^ that.   should G3 be at ground or at G1?  my tube brain is vacationing  :laugh:

Title: Re: 2203 RI schematic question
Post by: PRR on August 24, 2023, 02:32:17 pm

Quote from: shooter on August 24, 2023, 11:05:13 am

should G3 be at ground or at G1?

99% of designs put G3 at cathode or ground.

A couple TV sweep tube sheets suggest a small positive(?) bias to prevent snivets.

One transmitter pentode puts G3 significantly positive for more current.

Pete Traynor strapped some G3 from the V1 bias supply, not explained, but may reduce excess current in heavy abuse?