Cap forming Dual Rec EL34 JTM45/100

[Homebelly]

Hi.

Metro is down again, so thought i might try my luck in here.
I have been reading as much as i can trying to figure out a way to form the rifa's in my 45/100 build.

i came up with the idea below.
Although i am thinking there might be a better way just by disconnecting one rectifier bridge and the connection to the centre rail..?

Any way, here is the diagram for my initial idea, can some one drop in and offer some guidance?

[img:500:354]https://farm4.staticflickr.com/3687/13097923574_1e66d7f123.jpg[/img]
cap forming by Homebelly, on Flickr

[martin manning]

You've got the right locations for the 100K resistors, but you don't want to disconnect any wires from the PT or you won't get any current flowing at all (looks like A-C and F-D are separate windings, but you can verify that). What I don't understand is why the positive end of the reservoirs are connected to ground.

[Homebelly]

Hi Martin..

Thanks for the reply.
When you say "reservoir" are you referring to the rectifier diamond?

The grounding plan is based off this idea built around Larry's grounding scheme adapted to this build..

[img:500:354]https://farm3.staticflickr.com/2853/11609783036_25ea93c7a4.jpg[/img]
Grounding fixed II by Homebelly, on Flickr

[martin manning]

The reservoir is the first filter cap, in your case the four 32uF feeding the plates. You have the positive end connected to ground in your drawing.

[Homebelly]

The reservoir is the first filter cap, in your case the four 32uF feeding the plates. You have the positive end connected to ground in your drawing.

I think it might just be that it looks that way because i keep flipping the orientation of the drawings..
This one shows how all the filters are hooked up..
[img:500:354]https://farm8.staticflickr.com/7097/6869095312_da1a7109ee.jpg[/img]
Final filter cap hookup by Homebelly, on Flickr

This has been an almost three year project, so keeping track of everything has been a bit of a task what with moving house twice, having two kids and changing city a couple of times chasing work..

[martin manning]

See below. Both the diodes and the caps indicate the first filter ground is on the wrong side of the board. It needs to be moved to the top of the bridge at the top of the picture.

BTW, what's up with the resistor going from pin 1 to pin 8?

[rp]

Are you trying to reform old caps? Why not use a Light Bulb Limiter. Start with like a 15W bulb for like half a day, then 25W -> 40W -> 60W etc, each for a few hrs.

[Homebelly]

See below. Both the diodes and the caps indicate the first filter ground is on the wrong side of the board. It needs to be moved to the top of the bridge at the top of the picture.

BTW, what's up with the resistor going from pin 1 to pin 8?

The resistor from pin 1 to pin 8 then goes to ground and is there to help bias the out put tubes.

The wiring of the mains filters as shown in the diagram is the same for all of these style amps that i have seen pictures of, including a couple of build threads on the metro forums of Black Flag style amps..

[martin manning]

The resistor from pin 1 to pin 8 then goes to ground and is there to help bias the out put tubes.

The wiring of the mains filters as shown in the diagram is the same for all of these style amps that i have seen pictures of, including a couple of build threads on the metro forums of Black Flag style amps..

The current sense resistor used for setting bias is usually connected between the cathode (pin 8) and ground, and for EL34 pin 1 (suppressor) is shorted directly to the cathode (pin 8). As drawn, you would connect pin 1 to ground so the resistor will sense cathode current. That means the suppressor will be 40mV or so below the cathode potential. I don't think that is a problem, but it isn't the usual connection.

Grounding the B+ as you've shown above, however, is a big problem. I see smoked diodes and exploding caps in that arrangement!

[Jana]

It is preferred to tie the suppressor grid to ground and not elevate it slightly when using the sensing resistors from the cathode to ground. Some even hook the suppressor grids to the negative bias.