Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: dunner84 on October 01, 2018, 06:04:56 pm

Title: Help with rectifier/filtercap switch
Post by: dunner84 on October 01, 2018, 06:04:56 pm

Hello,

I am hoping for some help with adding a tube/ss rectifier switch with increasing amounts of filtering. The amp is a single channel ab763 with no trem/vibrato and a soldano SLO overdrive channel. The power section is identical to the ab763. I would like to add a 3 position switch for the following options:
1- stock (gz34, 40uf)
2 - GZ34, 40uf + 20uf
3 - SS , 40uf + 20uf + 20uf

I would like to do this with only adding 2 new 20uf caps to the board. Any ideas? I am not too sure how to draw it up.

Thanks

Title: Re: Help with rectifier/filtercap switch
Post by: PRR on October 01, 2018, 07:16:58 pm

Walll, sumthing like this. But I think it is too many too minor variations, and there are few "3 way" switches which can handle cap-surge at 420V.

Title: Re: Help with rectifier/filtercap switch
Post by: sluckey on October 01, 2018, 08:16:15 pm

Here's one way...

Title: Re: Help with rectifier/filtercap switch
Post by: dunner84 on October 01, 2018, 09:40:49 pm

Thanks for the quick replies. PRR, your solution is how I initially envisioned it, but the problem is I only have room for two switches, and one of them needs to be for a standby which I currently don't have on this amp. I need to add one for the SS rectifier if it's ever left in that mode on startup. Sluckey, that is exactly what I need to do! Thank you.

On a side note, why when switching from tube to diodes do we not need to break the HV connection on pins 6 and 4?

Title: Re: Help with rectifier/filtercap switch
Post by: sluckey on October 01, 2018, 10:57:14 pm

The diodes will be in parallel with the tube diodes, basically shorting them out.

Title: Re: Help with rectifier/filtercap switch
Post by: Diverted on October 02, 2018, 12:40:37 pm

Off topic, but I would love to see your schematic showing the no tremolo and overdrive channel. Thanks, good luck with the filtering/rectifier mods!

Title: Re: Help with rectifier/filtercap switch
Post by: dude on October 04, 2018, 10:19:46 am

Why the two 470K across the filters?
I assume these R's are bleeding R

Title: Re: Help with rectifier/filtercap switch
Post by: dunner84 on October 04, 2018, 07:19:47 pm

@ Diverted

I can't seem to find my schematic file; however, Sluckey has a very clean schematic for the stripped down ab763 circuit. My version cut the lo input, and added NFB switch, Raw control, non switched bright cap, and a larmar MV. My bias circuit is also slightly different to allow for a bigger voltage sweep, so I could use 6v6 or 6L6. Currently has 5881s.. The overdrive side of the SLO preamp is inserted at the mixing resistors just before the PI. I use a radial ABY for channel switching (and sometimes mixing)

I have a pen/paper schem for the whole amp somewhere. I will take a look for it this weekend, and scan it if you are still interested.