Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: mresistor on February 21, 2018, 11:18:54 am

Title: Fender Super Champ X2 add a standby switch?
Post by: mresistor on February 21, 2018, 11:18:54 am

Guy wants to add a standy switch to his SuperChamp X2 pcb board amp.  Has anyone here ever done this or similar? I'm thinking this isn't really a good candidate for one. I guess I could interrupt B+ but I'm futher looking at the screen and inverter. Also don't know if I have enough room on the panel.  What do you guys think?


Heres the service manual link


http://music-electronics-forum.com/attachments/30019d1407933697-fender-super-champ-x2-service-manual.pdf (http://music-electronics-forum.com/attachments/30019d1407933697-fender-super-champ-x2-service-manual.pdf)

Title: Re: Fender Super Champ X2 add a standby switch?
Post by: mresistor on February 21, 2018, 11:25:38 am

What about breaking the ground connection to the power tubes?

Title: Re: Fender Super Champ X2 add a standby switch?
Post by: Colas LeGrippa on February 21, 2018, 11:25:59 am

just put a switch on the pt center tap to gnd


Colas

Title: Re: Fender Super Champ X2 add a standby switch?
Post by: mresistor on February 21, 2018, 11:30:09 am

Thank you Colas - wouldn't that be just like another ON/OFF switch? in that it would shut off all the power in the amp, bias, and all the nodes.


This amp doesn't have a center tap on the HV ..  it's got a solid state rectifier, but the rectifier has two ground points that could be interrupted.  The HV , screens and the PI are fed off this winding.


So I'm thinking interrupting either the grounds on the HV rectifier or the ground to the power tube cathodes.  Which would be better? The ground to the power tube cathodes would entail a pretty simple switch.
I'm wondering if that is OK to suddenly turn on the tubes like that..  Would it be a shock to them and detrimental or would it be safe?

Anyone?

Title: Re: Fender Super Champ X2 add a standby switch?
Post by: SILVERGUN on February 21, 2018, 12:11:08 pm

Since there is no center tap on the HV winding I'd interrupt P9 or P10 like the snip from Merlin's site

Title: Re: Fender Super Champ X2 add a standby switch?
Post by: mresistor on February 21, 2018, 12:13:16 pm

Thanks SG  looks like a good idea.. 

Title: Re: Fender Super Champ X2 add a standby switch?
Post by: mresistor on February 21, 2018, 12:23:39 pm

I suppose I could use a standard Fender Standby switch  ( carling ) ..  and tie on the 47K 2 watt resistor.. 

Title: Re: Fender Super Champ X2 add a standby switch?
Post by: mresistor on February 21, 2018, 12:48:04 pm

Well as luck would have it I don't have a 47K 2 watt resistor.. closest I have is 18K .

Title: Re: Fender Super Champ X2 add a standby switch?
Post by: sluckey on February 21, 2018, 01:15:58 pm

It will work just fine with no resistor.

Title: Re: Fender Super Champ X2 add a standby switch?
Post by: mresistor on February 21, 2018, 01:59:12 pm

Thanks Sluckey - that's good news. Also  think I'll use a mini switch which requires a smaller hole and is smaller in size but has the same rating as the Carling.

Title: Re: Fender Super Champ X2 add a standby switch?
Post by: mresistor on February 21, 2018, 04:50:46 pm

It worked perfectly.   Thanks for the help.

Title: Re: Fender Super Champ X2 add a standby switch?
Post by: PRR on February 21, 2018, 06:55:50 pm

> has the same rating as the Carling.

The Carling is not rated for 385V DC.

We "know it will handle it" from 50+ years of experience with Carling's over-built clunkers.

Are you still confident about that mini-switch?

(Do you care? Is this "guy" a good customer or friend?)

A "Mute" (but call it stand-by) can be done with about no load on the switch. HV stays up, but that should not hurt tubes, unless the standby goes on for many weeks.

Title: Re: Fender Super Champ X2 add a standby switch?
Post by: mresistor on February 22, 2018, 09:06:11 am

Thanks PRR -  I looked at other ways to do this and invariably they involve modifying or messing with the main PCB. I think the switch will be OK. Interrupting the ground of the power tube cathodes would have been a good way too, right? only 40ma at that point.