5e8a filter cap ground question

[Kindablue]

I'm trying to work out a ground scheme for a 5e8a and was wondering about the possibility of grounding filtercaps 2and 3 together separately from cap 4. Basically cap 1 i will be grounding directly to HV CT. But the schematic/wiring diagram shows caps 2,3,and 4 are all wired at negative together. Seems like 2 and 3 supply power tubes and I'd like to ground them separately from the preamp section. So I'm wondering what the effect of not wiring the negatives of 3 and 4 together would be in order to achieve this. I would make cap 4 the start of the preamp ground bus on the board, and caps 2 and 3 would be sent off to their own ground off by the PT. Any thoughts?

[blackeye]

That sounds like it would work. There are several time tested ways to quietly ground an amp. I would ground the power amp caps on the HT CT along with the first reservoir cap. Remember—all the HT current (power amp and preamp) eventually has to make its way to that HT CT one way or another. Keeping this in mind, avoid large currents (e.g. power amp return current) passing anywhere near the preamp grounds.

[Kindablue]

I was going to run the HV CT (red yellow) directly to neg of first filter cap then run a ground wire back from the first cap to a ground terminal strip over by the PT. To this terminal strip I would probably also ground 2)the 6.3v heater CT (green yellow) and 3)a grounding wire from the .047 cap off the standby switch. If I read your response correctly I could also send a ground wire from filter caps 2-3 back to this terminal strip. All told there would be 4 things grounded to that terminal strip although the HV CT would at least be going directly into the 1st filtering cap before getting grounded there.

I guess my original question concerned why in the schematic wiring layout caps 2-4 are wired at negative together...was it just so they could be grounded together (in which case it would seem ok to only wire the negatives of 2 and 3 if im grounding them separately from 4) or does it serve some other purpose that I would be causing problems with by separating the connection between 3 and 4. Cap 4 clearly seems to serve the preamp section and id like to make that the beginning of the preamp ground bus im running from the board. I wish I could post the schematic/diagram for all to see what im talking about.

[blackeye]

Sorry not the best resolution.

62EFDD9A-5981-4D59-A61F-502DD6CAAD9A.gif

9FB35F38-2ED0-4162-8C01-1DBB7A902EB6.jpeg

[blackeye]

If I read your response correctly I could also send a ground wire from filter caps 2-3 back to this terminal strip.

I think maybe this is overcomplicating it. Caps 2-3 grounds daisy chained to cap 1. Run a single wire from cap 1 gnd to your gnd terminal strip. Also connect HT CT to cap 1 gnd as you have stated.

1F2E80A5-254B-47E3-8B8F-27754BC20881.jpeg

I have also seen layouts that ground the bias supply cap positive end to the preamp ground bus. Seems reasonable to do it that way, but I don’t know how much of a difference that would make.

Combining the grounds of cap 1-3, severing the gnd daisy chain between cap 3 and 4 and having a separate preamp ground bus is quite a common mod. A lot of people do it that way with great success.

Why didn’t Leo do it that way? I don’t know!

[pdf64]

Looking at the voltages on that schematic, it doesn’t seem that the output valves can be overdriven. ie bias voltage is -42V, but the voltage across the cathodyne’s anode and cathode resistors is only 50 VDC apiece. The output waveforms will probably get very non linear before the extremes of cut off and Vg-k=0 are reached.

I suppose that newer, beefier 6L6 types will get biased hotter, so less bias voltage for the signal to overcome, so allowing the anode current to reach its Vg1=0 AB1 limit.

[Kindablue]

How would that effect the grounding situation?

[blackeye]

How would that effect the grounding situation?

It doesn’t.

[Kindablue]

Gotcha. Appreciate all the thoughts. I like the idea of running 1-3 together.

[martin manning]

I'm trying to work out a ground scheme for a 5e8a...Any thoughts?

Here's how I'd do it. Edit: After some more thought, better to run separate ground leads from the reservoir and bias supply caps.

[didit]

Hello Martin -

Applaud your thorough redesign. Bit unclear what's intended with the "ground" switch, which doubtless simply should be deleted. Adjustable bias would be a fine addition, and perhaps a set of isolated input jacks. If building I would swap in a 32uF cap for the parallel pair of 16uF to make space for a comfortable bias layout and migrating misc off-board caps. Inspires me to go check my work on a modified 5E3 again to see if there were things missed and/or messed up.

Best .. Ian

[pdf64]

I think that the ground switch is just being used for its handy, isolated terminals, as tie points for incoming live and neutral.

[sluckey]

Bit unclear what's intended with the "ground" switch, which doubtless simply should be deleted.

He's simply using the ground switch as a convenient tie point for the power cord. If unsure, just connect the line directly to the fuse and connect the neutral directly to the PT.

If you do decide to use the ground switch as a tie point, be sure you get the wires on the proper lugs. One slip here will likely explode the switch at the same time your house circuit breaker trips.

[didit]

Bit unclear what's intended with the "ground" switch, which doubtless simply should be deleted.

He's simply using the ground switch as a convenient tie point for the power cord. If unsure, just connect the line directly to the fuse and connect the neutral directly to the PT.

If you do decide to use the ground switch as a tie point, be sure you get the wires on the proper lugs. One slip here will likely explode the switch at the same time your house circuit breaker trips.

Like I said (albeit with excess brevity), it should doubtless be removed from any connections or simply deleted in any new builds. A small tie-point terminal strip is too easy an addition.

..

[martin manning]

Applaud your thorough redesign. Bit unclear what's intended with the "ground" switch, which doubtless simply should be deleted. Adjustable bias would be a fine addition, and perhaps a set of isolated input jacks. If building I would swap in a 32uF cap for the parallel pair of 16uF to make space for a comfortable bias layout and migrating misc off-board caps. Inspires me to go check my work on a modified 5E3 again to see if there were things missed and/or messed up.

Adjustable bias would be nice, as would using a single screen cap to make room. I was mostly focused on the grounds. I don't think isolated input jacks are really necessary as long as good chassis contact is made using toothed washers. I'm not a fan of ground bus bars or soldering to the backs of pots.

Steve has captured my thinking on the "dummy" ground switch. It can be made functional (as a line filter) by adding a type x-y cap to ground or as a cross-line.