A first SE design

simon · Post by **simon** » Mon Feb 11, 2008 1:32 pm

Hi Steve,

I like the idea of a separate PSU for each stage, but I might run out of iron, or have to make a compromise. It would be hernia-inducingly heavy too. Three mains txs, a minimum of three PSU chokes, a pair of opts, a pair of opts as anode chokes on the 45s, and possible another pair on the 76s.

And then interstages

.

And it's still a baby compared to Paul's power supply on a trolley.

My missus is not going to be happy

.

simon · Post by **simon** » Mon Feb 11, 2008 1:46 pm

Nick wrote:They may not have enough inductance for the 76, more like 200H is needed, the little Hammonds give 150H

Well, it looks like I'm going to have to build this after all

. It'll be a little while till my iron turns up from Holland, and I need another pair of 2.5V filament transformers as I only have one pair at the moment. So if I'm ordering from Philip is it worth me getting a couple of the 150H Hammonds as well?

Just a thought, I have a couple of 10H 40mA chokes in the 2A3 amp. I'm going to have rip the amp apart for bits so could I use these for anything?

Post by **Nick** » Mon Feb 11, 2008 2:05 pm

Yes, I think its worth having those TX's on hand anyway. usefull things.

You could use the 40ma chokes in the 76 supply maybe.

simon · Post by **simon** » Mon Feb 11, 2008 3:54 pm

Right, I'll draw the next version tonight complete with anode chokes etc. if I get chance.

The 10H 40mA should be ideal in the 76 supply I guess. I'll have to have a stocktake and see what my options are.

simon · Post by **simon** » Mon Feb 11, 2008 9:48 pm

Okay, something like this?

andrew Ivimey · Post by **andrew Ivimey** » Mon Feb 11, 2008 9:59 pm

Okay this is where I get laughed out of court but I'd use the plate tubes instead of the plate resistors.

Hold on!

Larff all you like. I care not.

It works.

I have got amazing voltage swing and welly out of valves by just using a choke and to hell with the HT. (300v is nothing anyway so ... rock & roll!)

al newall · Post by **al newall** » Mon Feb 11, 2008 10:45 pm

but I'd use the plate tubes instead of the plate resistors

Does this mean ....use the plate resistance of the tube rather than the anode resistor?

to hell with the HT.

Does this mean i'm wasting my time trying to get my head round all these calculations, load lines and stuff?

Post by **Nick** » Mon Feb 11, 2008 10:50 pm

Loose the resistors in the anode, you only need the chokes. Change the 76 B+ to 240v or so.

andrew Ivimey · Post by **andrew Ivimey** » Mon Feb 11, 2008 10:52 pm

No, but as I see it, the choke becomes the anode resistor so once you are in the ball park for DC (and you may need a resistor to cut the HT down to what the particular valve enjoys) then the choke allows the valve to give so much more of the AC i.e. the signal

How unscientific! - How subjective!

Yeah but ...

here's a chap with four -ology degrees and I still can't hold on to proper valve theory ( I see load lines a a great big block- a playground where all sorts of games can take place) ultimately I suppose this might be a weakness but right now it still works.

Darren · Post by **Darren** » Mon Feb 11, 2008 11:31 pm

andrew Ivimey wrote:No, but as I see it, the choke becomes the anode resistor so once you are in the ball park for DC (and you may need a resistor to cut the HT down to what the particular valve enjoys) then the choke allows the valve to give so much more of the AC i.e. the signal

How unscientific! - How subjective!

Yeah but ...

here's a chap with four -ology degrees and I still can't hold on to proper valve theory ( I see load lines a a great big block- a playground where all sorts of games can take place) ultimately I suppose this might be a weakness but right now it still works.

Amen !!

You've seen the light !!

Now begins the learning....!!

simon · Post by **simon** » Tue Feb 12, 2008 9:08 am

Okay, no anode resistors and smaller HT on the 76. Better get in touch with Philip and get some bits ordered.

Any thoughts on using a 6.3V secondary of the mains tx for the 45s? I guess I'd have to regulate to get down to 2.5V, which is a bit of a drop, and both valves would probably have to share the same winding. Or should I just get another pair of Hammond 2.5V filament txs and have done with it? I'm thinking I'll get the Hammonds as it's something less to go wrong at this stage, and 2.5V AC should be okay to get quiet.

Post by **Nick** » Tue Feb 12, 2008 9:33 am

Its always worth having spare TX's for fillaments anyway, but you could also use a current reg to drop the voltage from a 6v TX, thats what I did in the 45 driver stage of the 211

simon · Post by **simon** » Tue Feb 12, 2008 2:05 pm

Yeah, no substitute for having the bits. Current regs are easy enough though, even I managed to get one to work

. It's voltage regs with the sense resistor I had problems with. Should give it another go sometime.

Lee S · Post by **Lee S** » Mon Mar 17, 2008 12:45 am

Any further progress on this project Simon?

simon · Post by **simon** » Mon Mar 17, 2008 8:59 am

Of a sort. I've been collecting bits, and some of the bits have taken a while to arrive. Might get chance over Easter to drill the ally plate.

audio-talk

A first SE design

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