Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Colas LeGrippa on September 29, 2011, 10:07:06 pm

Title: paralleled SE output tubes
Post by: Colas LeGrippa on September 29, 2011, 10:07:06 pm

Hi,

I'd like to add an output tube to my new SE build. Can I just run wires straight from the first tube to the other ?

Colas

Title: Re: paralleled SE output tubes
Post by: RicharD on September 29, 2011, 11:16:20 pm

You can parallel SE output tubes but your Zout goes down by 1/2.  Assuming cathode bias, you either need separate cathode resistors or 1/2 that too.

Title: Re: paralleled SE output tubes
Post by: Colas LeGrippa on September 30, 2011, 08:23:13 am

I gotta check the filament supply current to see if it can feed another power tube though.
What about the grid stopper and coupling caps? Is it better to use 2 coup^ling caps or just one ?

Thanx

Colas

Title: Re: paralleled SE output tubes
Post by: RicharD on September 30, 2011, 08:13:22 pm

Individual grid stoppers so you form a summing network is how I've done it in the past. 

Title: Re: paralleled SE output tubes
Post by: Colas LeGrippa on September 30, 2011, 09:52:22 pm

thanx

regards

Title: Re: paralleled SE output tubes
Post by: HotBluePlates on October 01, 2011, 10:17:42 am

Depending on what you're already using, the grid reference resistor ( from grid to ground) may need to be lowered. This is more an issue in fixed-bias amps than cathode bias. In such a case, you might halve the resistor and double the coupling cap value.

Title: Re: paralleled SE output tubes
Post by: tubeswell on October 01, 2011, 03:57:26 pm

FWIW here is the schematic of a parallel SE I did at the beginning of the year. I used a switchable 470R in parallel to change the bias. The amp can also run 1 x 6L6 etc