Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: punkykatt on October 31, 2017, 07:44:47 pm

Title: DC power supply for Hammond organ preamp
Post by: punkykatt on October 31, 2017, 07:44:47 pm

Hey Guys, I need some direction in building a 200vdc power supply for the B+ operating voltages in a Hammond organ preamp. The owner (a good friend of mine) would like to run the keyboard and preamp without the leslie (which has the power amp that supplies the 200vdc B+) into a stompbox leslie pedal  and into a combo amp. He wants to sell the leslie, it takes up too much room.  I`m not sure how to calculate the mA  needed in the new power transformer and what would be the best and least costly way to build this power supply.  Here is  the schematic of the preamp.
                                                              http://captain-foldback.com/Hammond_sub/schematics/vibrato_preamp.gif 
Thank you in advance for any input.

Title: Re: DC power supply for Hammond organ preamp
Post by: shooter on October 31, 2017, 08:52:13 pm

fwiw
my calc's come up with;
1.8A filament, 2 - 2.5A with safety margin
~60mA plate current, call it 100mA for safety
and your 200 VDC can be had with ~ 160VAC into a SS bridge rectifier n some minor tweaks with dropping R

Title: Re: DC power supply for Hammond organ preamp
Post by: PRR on October 31, 2017, 09:32:17 pm

11mA plate current. Three very small tubes. Two 6SN7 with 8V on a common 820r cathode resistor.

None of the voltages are critical. I'd consider 120V/240V AC rectified to 330V DC and about 10K of resistance dropper. Probably like 40uFd, 5K 5W, 40uFd, 5K 5W, 40uFd. Shim another K or two to get near 200V.

Title: Re: DC power supply for Hammond organ preamp
Post by: punkykatt on October 31, 2017, 10:08:54 pm

Thank you Shooter for that info.  PRR,  You are saying I don`t need a PT, I can use the 120vac  line voltage from the wall outlet into a bridge rectifier, dropping R, filter cap, dropping R, filter cap, dropping R, filter cap, dropping R?   If I understand correctly would it be possible to show me a sketch how to wire this circuit ? Thank you for your time and help.

Title: Re: DC power supply for Hammond organ preamp
Post by: sluckey on October 31, 2017, 10:20:54 pm

Quote

PRR,  You are saying I don`t need a PT, I can use the 120vac  line voltage from the wall outlet into a bridge rectifier...

No! I think he is suggesting use a 120v to 240v transformer.

Title: Re: DC power supply for Hammond organ preamp
Post by: PRR on October 31, 2017, 10:34:31 pm

> I can use the 120vac  line voltage from the wall outlet

NO!!  Never-never-ever!!

Always use a transformer!!

I'm saying that 120V/240V is readily available, as isolation transformers or as a 120V:6V 6V:120V lash-up.

Title: Re: DC power supply for Hammond organ preamp
Post by: punkykatt on October 31, 2017, 10:59:09 pm

I didnt think so, its  been a long hard day my brain is tired. I saw the 120/240 AC and wall voltage came to mind. Thank you for your input.