audio-talk

On some Hammond data sheets they give a max working voltage and a hi-pot test voltage which is significantly higher.

On my choke (193Q) they only list the max working voltage of 1000V. I dare say it is safe to use above that voltage but I don't know the margin.

Finding a 10H choke safe for 1400V is proving difficult and could be expensive.

Perhaps I should stay at 1000v, and get the red spot by driving the grid harder ?

I dare say it is safe to use above that voltage

Well, by definition it isn't. Nobody makes something safe to 1500v and thinks, lets just sell it as safe for 1000v.

Finding a 10H choke safe for 1400V is proving difficult and could be expensive.

There is a reason for that.

Perhaps I should stay at 1000v, and get the red spot by driving the grid harder ?

A copy of photoshop would be simpler. Remember less voltage means more current to get the same power.

I’d go anyway on 1000v these days. I think me and Nick wound the GM70 past it’s max on Collin’s electrostatics which sounded flat. As GM70’s were plentiful and chepa those days, didn’t matter I had double figures GM70’s .... still do at the lockup.

No, these days, we don’t need to go past 1000 volts, especially now were more clued up on providing double figure grid currents; since to my ears such valves open out better when you incorporate the positive characteristic curves.

Nick wrote: ↑Wed Apr 29, 2020 9:23 pm

I dare say it is safe to use above that voltage

Well, by definition it isn't. Nobody makes something safe to 1500v and thinks, lets just sell it as safe for 1000v.

Yes, but it does not stop being safe at 1001v, or 1010v, so there would normally be some leeway.

Anyway, the question does not arise now.

Well in th gas world when you gas rate an appliance you allow a tolerance of 5% over 10% under, which would in our world be a very safe standard.

Yes, but it does not stop being safe at 1001v, or 1010v, so there would normally be some leeway.

But you don't know, that’s the point.

Also, I bet your meter is not calibrated against a known standard, so you may be running 5% higher than you think you are. Add the fact your mains may increase by 5% without you noticing, that's you at 1100v.

But its your call. You do ask for advice, its up to you if you chose to pay attention to it.

Nick wrote: ↑Wed Apr 29, 2020 10:55 pm

Yes, but it does not stop being safe at 1001v, or 1010v, so there would normally be some leeway.

But you don't know, that’s the point.

Also, I bet your meter is not calibrated against a known standard, so you may be running 5% higher than you think you are. Add the fact your mains may increase by 5% without you noticing, that's you at 1100v.

But its your call. You do ask for advice, its up to you if you chose to pay attention to it.

I am accepting unequivocally the advice I have been given. Thanks again for giving it.

I've got a 10h 500ma choke suitable for choke input off 2.1kv ct tx. I don't know it's insulation rating but can find out. If you need one? It's Majestic. But unless you need choke input, it's huge and of course very heavy.

I am really rusty but can you run the choke in the return line. Does that help at all?

izzy wizzy wrote: ↑Thu Apr 30, 2020 8:07 am I've got a 10h 500ma choke suitable for choke input off 2.1kv ct tx. I don't know it's insulation rating but can find out. If you need one? It's Majestic. But unless you need choke input, it's huge and of course very heavy.

One of us had a batch of 10H chokes custom made up north (further north than Yorkshire) quite a few years ago, might have been Will.

They are substantial, but I've no idea of the voltage or current rating. Can anyone else who got one (or two) remember ?

Max N wrote: ↑Thu Apr 30, 2020 9:31 am I am really rusty but can you run the choke in the return line. Does that help at all?

Yes, it helps the windings to core requirement at least.

pre65 wrote: ↑Thu Apr 30, 2020 10:07 am

izzy wizzy wrote: ↑Thu Apr 30, 2020 8:07 am I've got a 10h 500ma choke suitable for choke input off 2.1kv ct tx. I don't know it's insulation rating but can find out. If you need one? It's Majestic. But unless you need choke input, it's huge and of course very heavy.

One of us had a batch of 10H chokes custom made up north (further north than Yorkshire) quite a few years ago, might have been Will.

They are substantial, but I've no idea of the voltage or current rating. Can anyone else who got one (or two) remember ?

Yes it was Will, I found the thread. 10H @ 250ma and 95R DCR. My two were the ones Colin ordered.

http://www.audio-talk.co.uk/phpBB3/view ... oke#p27015

More playing with PSU designer.

Using the 800V transformer and a first cap of 10uf (2 X 5uf) I'm getting a nice 1000v HT

The first caps are MKP low inductance 5uf. Un = 1200v, Umax = 1680v ESR = 1.1Mw (?) Irms = 64A

It seems a good compromise.