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Now that my 91A amp is operational I am turning my old 300B into a test mule for future bread board experiments. It will consist of three chassis as follows:A psu chassis that has transformers for B+, 5 vac and 6.3 vac.
A tube chassis that carries a bunch of 8 pin relay sockets. I will make adapters for what ever tubes I work with. I already have them for 4 and 5 pin tubes.
A opt chassis that has opt's for pp and se amps.
I have the psu chassis mostly complete, but am unsure about how to handle the grounding. The 5 and 6.3 vac transformers each have their own switch and fuse so that I may use either or both. I also want them on their own mains power so that I can use a variac to adjust the B+ without affecting the filament voltages.
My plan for doing this is to have a multiple outlet plugged into my isolation transformer and then have the variac plugged into the multiple outlet and a mains chord going from it to the psu chassis and another mains chord from the multiple outlet to the psu chassis separate from the variac.
The psu chassis is set up with a ground bus bar right now, and I am wondering how to handle the ground of the other mains socket that I need to install for the filament transformers. Should I put a separate bus bar in for that outlet too? It would be connected back through the multiple outlet to the mains supply, but I am worried about a ground loop.
Anyone have any experience with this type of thing?
Edits: 04/28/15 04/28/15Follow Ups:
What started out as a simple little project to convert my old 300B amp into a test mule has blossomed into a major undertaking. I really do want to have the B+ adjustable for trying different designs, but even if I was willing to pluck down the $100 plus they want for one skookum enough to do the trick, there is no room on the old psu chassis for it. I suppose I could build a variac module and use that, but I already have a good variac.
Soooooooo it looks like I will have to go with 4 chassis instead of just two; one for the B+, one for the filaments and two others for the right and left channel tube and opt modules. Fortunately I have the last two already made from a previous breadboard project, so that will help.
Thought I would make one last plea for any other ideas anyone might have that would allow me to use just the two chassis from the old amp instead.
Edits: 04/29/15
What you are up against is that you have not sorted out what direction you really want to go and so are trying to be all things to all tubes.
What you want is something like an old tube Kepco power supply like the one at the link. That way you can mule out to anything.
Yep, that is it in a nut shell. I guess I will just have to go with the 4 chassis. I think I will skip the bias voltage and just pull that with a voltage divider when I need it.
Can I put one between the mains and the B+ trany?
Build a Variable Regulated HV Power $upply :) that way you can adjust B+ at your leisure. Pricey!
The bitterness of poor quality remains long after the sweetness of low price is forgotten”
With my budget i think I better go with the 4 chassis instead.
Gotcha.
I have always wanted to build a Tube Power Amp with Regulated H.V. (B+).
When I can get around to making the PC board for the circuit, I will use MOSFET regulation and have a listen.
A Tube Regulated Supply results kinda too big and bulky.
There is an audible difference between tubes when they are operated with regulated H.V. (B+) as I have a 6SN7 Preamplifier
where I can flip a toggle switch and listen to both conditions on the fly.
The bitterness of poor quality remains long after the sweetness of low price is forgotten”
Only two ground connections on the power supply - AC cord safety ground and a connection to your signal chassis. Everything else floats - though I'd connect B- to chassis through a 100 Ohm resistor. Same on the OPT chassis - secondary to (-) speaker terminal, then to chassis, no others except for connection to signal chassis. If you will use negative feedback, run a pair back to the signal chassis from speaker terminals rather than grounding it there.
I would NOT recommend two mains cords on one chassis - it is not allowed by product safety standards. If you really need separate inputs for B+ and heater, put them on separate chassis. Or build in a small variac.
The signal chassis should be quiet if you don't run power supply current through it. Heaters must be at AC ground (single point!). A ground bus should be fine, but it will be long to allow close connections to each socket. Keep ALL current loops out of it! All supply filtering should be in the PS chassis, though you'll want a bypass on the signal chassis,
I do not have the room for a variac on the psu chassis or that is what I would have done. It's beginning to look like I may have to mount one outboard style because I don't want to build any more chassis.
As long as you join all of the house grounds to one point you should be fine.
You should make a power supply chassis with all power transformers centralized in one spot. Then you can distribute the power to the amp(s) from there. Putting power supplies in different chassis can open you up to un-expected loops, however, you can really make any arrangement work with care.
I must not have explained the set up clearly. All power transformers are in one spot, on the psu chassis. What I am wondering is if both mains chords going back to a common multi-outlet is the equivalent of all the grounds going back to one spot.
Edits: 04/28/15
You should not have a ground loop issue if you tie the earth grounds together at the same point in the power supply chassis. Alternatively, you could just use one power cord to bring AC to your chassis
Can't do that and use the variac to adjust the B+. Might have to tag on a small variac outboard style.
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