Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Mook on June 05, 2015, 08:47:27 am

Title: Pentode/Triode switching = need a 4PDT switch?
Post by: Mook on June 05, 2015, 08:47:27 am

For a duet of power tubes, yes, we need DPDT switch, but I cannot figure out how to switch Pentode/Triode with 4 power tubes.


Seems you need a 4PDT switch, right?

Title: Re: Pentode/Triode switching = need a 4PDT switch?
Post by: VMS on June 05, 2015, 08:58:00 am

No, here is an example how marshall did it with DPDT on jcm900:

(http://www.drtube.com/schematics/marshall/2100-60-34.gif)

Title: Re: Pentode/Triode switching = need a 4PDT switch?
Post by: PRR on June 06, 2015, 12:28:49 am

Connect 4 plates together, you have 2 wires.

Connect 4 screens together, you have 2 wires.

Screens go to the corresponding plates, or to B+.

DPDT.

Title: Re: Pentode/Triode switching = need a 4PDT switch?
Post by: vicentebd on June 08, 2015, 08:13:08 pm

Quote from: PRR on June 06, 2015, 12:28:49 am

Connect 4 plates together, you have 2 wires.

Connect 4 screens together, you have 2 wires.

Screens go to the corresponding plates, or to B+.

DPDT.

By the experience, could you  tell me if Pentode/Triode switching, is normal make a "pop" sound ?
thank you 

Title: Re: Pentode/Triode switching = need a 4PDT switch?
Post by: PRR on June 09, 2015, 12:20:41 am

> is normal make a "pop" sound ?

Probably.

With most switches, the screens will disconnect from B+ (and fall to zero) for an instant, before they connect to plates. Also it is unlikely both sides of a double-pole will break and make at the SAME instant. If the pop is real loud, turn the amp off (or standby) before flipping the T/P switch--- it isn't really something you should change mid-song.