Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: HARodgers on March 10, 2018, 07:52:40 pm

Title: Switchable Rectifier Variants
Post by: HARodgers on March 10, 2018, 07:52:40 pm

Hi,
I was just wondering if there was any benefit to using the first switchable rectifier (taken from http://el34world.com/charts/Schematics/files/mesa_boogie/boogie_dualrectifier.pdf) over using the second? (taken from http://sluckeyamps.com/misc/Amp_Scrapbook.pdf) The only potential benefit I could see is that there would not be constant voltage going to the tube rectifier in the first, and could this be resolved by adding a 100k 2w resistor around the switch? (as in http://el34world.com/Forum/index.php?topic=17671.0) The second would be much more convenient as it does not require an additional standby switch.

Cheers
(apologies for the drawn diagram!)

Title: Re: Switchable Rectifier Variants
Post by: shooter on March 10, 2018, 08:33:40 pm

I don't use tube rectifiers of standby switches, but i'll vote for option2

Title: Re: Switchable Rectifier Variants
Post by: pdf64 on March 11, 2018, 04:10:49 am

'Hot switching', switching a capacitor on to an operational tube rectifier is the most stressful, worst case scenario for a tube rectifier, as it results (if only momentarily) in very high plate current, in charging the cap from 0V to full HT.
Circuits should be arranged to avoid that, eg consider trickle resistors.

Title: Re: Switchable Rectifier Variants
Post by: HARodgers on March 11, 2018, 07:45:32 am

Considering that, would that mean that the second option with a 2w/100K trickle resistor around the switch be safer? Or alternatively removing the standby switch from the first and using a centre off on the switch from the transformer? I presume both of these would resolve hotswitching a cap onto the tube rectifier?

Title: Re: Switchable Rectifier Variants
Post by: pdf64 on March 11, 2018, 02:33:37 pm

Quote from: HARodgers on March 11, 2018, 07:45:32 am

Considering that, would that mean that the second option with a 2w/100K trickle resistor around the switch be safer?...

Yes, that would be ok I think.

Quote from: HARodgers on March 11, 2018, 07:45:32 am

...alternatively removing the standby switch from the first and using a centre off on the switch from the transformer? I presume both of these would resolve hotswitching a cap onto the tube rectifier?

It's the same current, whether it's switched at the end of the winding or the CT, so that's no good.
Plus breaking the CT ground return might bugger up some bias supply arrangements.