Like this:
Darren 212 / 833 SE amp
#46
Its not working becuae there is no path to ground from the cathode. only connect one end of the interstage to one end of the cathode, the other end of the interstage to 0v, and the fill supply as before with no connection to anything else.
Like this:
Like this:
#47
Hi Nick, doh! shows me up doesn't it.
Still doesn't work I'm afraid, no music just high pitch hi freq clicking
Found out how it gets music with no power though. The signal was going through the Farnell heater supply (switched off) and somehow coming out through the speakers. How I dunno, but that was the path it was taking. Nothing to do with the 833 which of course makes sense at least.
Just took my graphite plate 833 out and tried a steel plate, if thats what it is?
Nothing much to report except it works, always a relief....
Still doesn't work I'm afraid, no music just high pitch hi freq clicking
Found out how it gets music with no power though. The signal was going through the Farnell heater supply (switched off) and somehow coming out through the speakers. How I dunno, but that was the path it was taking. Nothing to do with the 833 which of course makes sense at least.
Just took my graphite plate 833 out and tried a steel plate, if thats what it is?
Nothing much to report except it works, always a relief....
#48
I just thought of something, someone please correct me if I'm wrong..
As I'm using the PX4s original output transformers which give a 20:1 step down ratio. I'm having to turn the amp up to get volume. Don't get me wrong it goes pretty loud as it is.
But, whilst doing this I'm also amplifying the PS noise and to be honest there isn't much. It's certainly less than using the PX4 on its own.
Therefore, if I was to use 4:1 ratio step downs I would get a higher signal from the PX4 and need to turn the amp up less. Thus the result would be even less signal to noise ratio.
When you consider how simple this PS is, thats quite something.
PS = Noisy Variac, 1000v mains trans (buzzing under the strain), two salvaged diodes of unknown quality, 20uf cap, 20H choke, 50uf cap.
Not the way I would build the final setup as I just grabbed a few parts to rig something up.
As I'm using the PX4s original output transformers which give a 20:1 step down ratio. I'm having to turn the amp up to get volume. Don't get me wrong it goes pretty loud as it is.
But, whilst doing this I'm also amplifying the PS noise and to be honest there isn't much. It's certainly less than using the PX4 on its own.
Therefore, if I was to use 4:1 ratio step downs I would get a higher signal from the PX4 and need to turn the amp up less. Thus the result would be even less signal to noise ratio.
When you consider how simple this PS is, thats quite something.
PS = Noisy Variac, 1000v mains trans (buzzing under the strain), two salvaged diodes of unknown quality, 20uf cap, 20H choke, 50uf cap.
Not the way I would build the final setup as I just grabbed a few parts to rig something up.
#49
Hi Paul,
I measured one of your large interstages and it seems to be 1:0.8 ratio. (Or 4:3.2)
It it feasible to unwind one section to create a 4:1 ratio?
I realise it would be trial and error and a real pain, but they are here and when you tried them before you didn't really like the result.
From what I can work out we need stepdown transformers for the 833 and the 212 to drop the voltage and up the current to drive the grids.
As almost 1:1 I'm not sure they are much use for us with these high mu valves?
What do you think?
I don't want to ruin them unnecessarily...?
I measured one of your large interstages and it seems to be 1:0.8 ratio. (Or 4:3.2)
It it feasible to unwind one section to create a 4:1 ratio?
I realise it would be trial and error and a real pain, but they are here and when you tried them before you didn't really like the result.
From what I can work out we need stepdown transformers for the 833 and the 212 to drop the voltage and up the current to drive the grids.
As almost 1:1 I'm not sure they are much use for us with these high mu valves?
What do you think?
I don't want to ruin them unnecessarily...?
#50
Umm,Darren wrote:Hi Nick, doh! shows me up doesn't it.
Still doesn't work I'm afraid, no music just high pitch hi freq clicking
just occurred to me, my heater supply isn't floating (remember the powered off signal funny business) so it won't work.
I'm not about to make floating DC heater supplies for these, so for now I'll have to shelve your idea for the moment Nick.
#52
No worries Nick,
I've learnt quite a bit trying and that's whats it's all about after all. I've enjoyed it.
I just need different heater supplies and sometime I'll get around to it again.
When I move I hope to setup a proper workshop cos at the mo you just don't wanna see my front room
I've learnt quite a bit trying and that's whats it's all about after all. I've enjoyed it.
I just need different heater supplies and sometime I'll get around to it again.
When I move I hope to setup a proper workshop cos at the mo you just don't wanna see my front room
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Paul Barker
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#53
Hi Darren,
yes you could unwind the last section and see what you get.
I'm afraid my winding machine broke a few years ago. It's such a complicated doo hickey not possible to fix. There are a few thing wrong with it, the dc break motor doesn't always want to start (hardly at all, and the traverse doesn't want to traverse but when it does decide to it doesn't want to change direction. Otherwise I would rattle you off a pair of what you want.
As I don't see any money in winding transformers to an average standard I haven't bothered to do anything about it.
There are many ways to skin a cat. You could get a reasonable result using a 1:1 IT cathode drive from a 6em7 cathode follower.
Same as Nick's drawing but put the primary of the transformer on the cathode of the 6em7 and smoothed reduced (160v say) ht directly on the anode.
yes you could unwind the last section and see what you get.
I'm afraid my winding machine broke a few years ago. It's such a complicated doo hickey not possible to fix. There are a few thing wrong with it, the dc break motor doesn't always want to start (hardly at all, and the traverse doesn't want to traverse but when it does decide to it doesn't want to change direction. Otherwise I would rattle you off a pair of what you want.
As I don't see any money in winding transformers to an average standard I haven't bothered to do anything about it.
There are many ways to skin a cat. You could get a reasonable result using a 1:1 IT cathode drive from a 6em7 cathode follower.
Same as Nick's drawing but put the primary of the transformer on the cathode of the 6em7 and smoothed reduced (160v say) ht directly on the anode.
#54
On my Farnell Power supplies the + & - outputs has removable links to connections called "Feedback"
Anyone know what this Feedback is? A form of regulation perhaps?
I wonder if I remove them the supply will then float. I'll try it later.
Anyone know what this Feedback is? A form of regulation perhaps?
I wonder if I remove them the supply will then float. I'll try it later.
#55
The feedback link will be for the regulation. Its so you can apply the point the supply regulates at remote from the box. ie. you run the leads to the thing being powered, then run a lead from the feedback to the end of the leads. That way it will compensate for the losses in the leads.
I would guess, lifting the earth on the supplies would make them float, if that doesn't work, that and a isolation TX would do the trick.
I will just bask in the joy of not expecting someone to post and point out just how dangerous that is. Coz we don't know that do we chaps?
. Meanwhile back to the totally safe clipleads and Kv supplies.
I would guess, lifting the earth on the supplies would make them float, if that doesn't work, that and a isolation TX would do the trick.
I will just bask in the joy of not expecting someone to post and point out just how dangerous that is. Coz we don't know that do we chaps?
. Meanwhile back to the totally safe clipleads and Kv supplies.#56
Made me smile, ta...Nick wrote:
I will just bask in the joy of not expecting someone to post and point out just how dangerous that is. Coz we don't know that do we chaps?
#58
Just so you can sleep at night Nick there are now no clip leads in the HT. All soldered joints.
Have now got two channels up and running so some pics to update.
Here's a pic running at 1150 B+, 225ma with the plates glowing quite nicely,
Due to limitations of my current output trans I run at 730v 140ma which is around 40-50W output.
They work from 25-35V B+ with a little distortion, become quite clear at around 150 B+ & more power as you go up in voltage.
Have now got two channels up and running so some pics to update.
Here's a pic running at 1150 B+, 225ma with the plates glowing quite nicely,
Due to limitations of my current output trans I run at 730v 140ma which is around 40-50W output.
They work from 25-35V B+ with a little distortion, become quite clear at around 150 B+ & more power as you go up in voltage.
#59
That a relief, I was running out of fingernailsJust so you can sleep at night Nick there are now no clip leads in the HT. All soldered joints.
What I want' to know is why we always end up doing this stuff in the summer.
Winter should be 212, GM70 and now 833's, summer should be 45's and the like.