Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: pullshocks on February 22, 2020, 04:37:36 pm

Title: Solow Watt 12a_7 power supply question
Post by: pullshocks on February 22, 2020, 04:37:36 pm

Time to do something with the 6F4P's I got.  Looks like the Solo Watt 12a_7 is it.  I will be using a Hammond 125E for the output transformer, and the Hammond 269EX power transformer as shown in the schematic.


Studying the schematic and layout, I notice V1 gets B+ from the same node as the screens.  I am guessing this was done for reasons of wanting to keep B+ on V1 as high as possible in a power supply that is only 255 V to begin with.


But that way the V1 B+ has only been through 2 stages of filtration.  Is this a noise issue?  I have plenty of room to do a more elaborate power supply if that would be any benefit.


Thanks in advance


Pullshocks / Mark







Title: Re: Solow Watt 12a_7 power supply question
Post by: pullshocks on February 22, 2020, 05:02:47 pm

Should have included the link to the schematic and layout.


http://el34world.com/Forum/index.php?topic=13438.msg126186#msg126186
Title: Re: Solow Watt 12a_7 power supply question
Post by: sluckey on February 22, 2020, 05:16:36 pm
Quote
I notice V1 gets B+ from the same node as the screens... But that way the V1 B+ has only been through 2 stages of filtration.  Is this a noise issue?
Would be for me. I'd rather tap off from node B, Go through a 10K (or more more appropriate) dropping resistor to a 22µF or even 47µF cap. Feed that to V1 only. Experiment with the dropper to get the desired voltage.
Title: Re: Solow Watt 12a_7 power supply question
Post by: pullshocks on February 22, 2020, 10:35:03 pm

Thanks Sluckey.


Tubenit has a post on Ampgarage indicating VI is connected to Node D, after all.



https://ampgarage.com/forum/download/file.php?id=26323&mode=view (https://ampgarage.com/forum/download/file.php?id=26323&mode=view)


https://ampgarage.com/forum/viewtopic.php?f=6&t=20234&p=236316&hilit=solow+watt#p236316




Title: Re: Solow Watt 12a_7 power supply question
Post by: tubenit on February 23, 2020, 07:00:05 am
I do like Sluckey's idea to have another resistor and filter cap coming off node B for the V1 tube to have the voltage higher.

I sold this amp to a guy that opened for Derek Trucks and also Dave Matthews so I no longer have it. Years later, he said it was still his main practice amp.

Another forum builder built one called the BumbleWatt using the 5879 pentode.  He used node D also.  His workmanship was excellent (&much better than mine) so you might one to take a look at it. He also commented on what good bass response it had for small tubes.

http://el34world.com/Forum/index.php?topic=13151.msg122821#msg122821

With respect, Tubenit
Title: Re: Solow Watt 12a_7 power supply question
Post by: pullshocks on February 24, 2020, 02:15:03 pm

Thank you.


I transposed your layout from left to right, and re-drew in DIYLC with all power supply components showing.  I need to recheck a few more times, but I should be just about ready to drill the chassis and make the boards.