Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: stevehoover on June 24, 2013, 02:08:14 pm

Title: Is a selectable B+ switch for different preamp voltages doable without popping?
Post by: stevehoover on June 24, 2013, 02:08:14 pm
Hi folks, I'm trying to figure out if it is possible to switch B+ voltage without getting a loud pop.

I've built a "Fender Time Machine" with separate BF and tweed preamps mixed down to a single ended 5881.

I would like to be able to safely switch preamp voltages in each of these channels for "period appropriate" voltages...(it sounds pretty cool when I do).   However I'm concerned about damaging some expensive NOS
Preamp tubes as well as other components and speakers.  It's a bummer to have to power down the amp to do this now.....not the end of the world, just inconvenient.     Any input would be appreciated..Thx!
Title: Re: Is a selectable B+ switch for different preamp voltages doable without popping?
Post by: PRR on June 24, 2013, 10:35:47 pm
Won't pop much:
Title: Re: Is a selectable B+ switch for different preamp voltages doable without popping?
Post by: jojokeo on June 25, 2013, 01:24:00 am
 It's a bummer to have to power down the amp to do this now.....not the end of the world, just inconvenient.
Can't you simply either turn off the standby or just turn down the volume before switching? Or better yet, build two separate sections with their own input jack and design the voltages separately for each. Then join the two as a typical Fender amp would then no switching is necessary on the amp itself. You then could use an AB-Y box to switch between both channels on the fly via foot pedal if that is what you're truly after?
Title: Re: Is a selectable B+ switch for different preamp voltages doable without popping?
Post by: kagliostro on June 25, 2013, 02:29:59 am
What PRR says

K
Title: Re: Is a selectable B+ switch for different preamp voltages doable without popping?
Post by: jjasilli on June 25, 2013, 06:14:41 am
Instead of a SW maybe you could use a variable voltage circuit.