Progress of my 813 SE

[Fuling]

wd40: Looks great! What output transformers are you using?

 

[Jax]

Nice work there, wd40.

We all seem to agree over an approximate operating point

 

[wd40]

Hi Fuling

Thank you! The output transformers is my friend make for me.Like this.

 

[wd40]

Hi Jax

Thank you! I think so.

 

[Fuling]

Thos output transformers looks nice and big!

BTW: I think I´ve finally decided to use Lundahl LL1688 gapped for 85mA. Not cheap, but nor are the alternatives.

 

[AKSA]

Hi WD40,

Lovely job, very nice design, clean.

How many watts? Do you like the sound?

Cheers,

Hugh

 

[Peleus]

Hi, wd40

What a lovely amp!

What I am interested is the chock.

How to choose a chock for hihg voltage operation as 1050V ?

My friend told me that could be very dangerous when chock operate as 1000V or higher.

 

[Jax]

One way to operate chokes at high voltages is to let the choke float by insulating it from the chassis. Make sure nobody can touch the choke when in operation though

 

[wd40]

Thos output transformers looks nice and big!

Hi Fuling
Yes it's 7.5K 75W.I intend use it on next pentode connection 813 SE amp.

Hi Hugh
Thank you.It possess 12W's output power ,20Hz-20KHz -1dB@1W.I like the sound very much.

Hi Peleus
Thank you.I use Doubly 'C'chock.Like this.

 

[Fuling]

Wow! 7,5k 75W sounds just right for this tube!

Another way to avoid insulation problems in the choke is to put it in the ground line instead of in the high voltage rail.
That´s what I´m planning to do, since Hammond chokes can´t stand these voltages.

 

[wd40]

Hi Fuling

It just for this tube.I intend in the way of one step of drive 813 of 6SN7 SRPP.You possess the better proposal ?

 

[Fuling]

A 6SN7 SRPP has too low gain to drive 813 by itself, I think.

I´m going to use something like this:
PC86 DC-coupled to 6S19, IT coupled to 813.

 

[wd40]

Hi Fuling

PC86 DC-coupled to 6S19, IT coupled to 813.

I can't find PC86 and 6S19 in china.But the 813 pentode connection not need such tall drive tension .

 

[Peleus]

Thanks! Wd40!

I may not say quite clearly about the dangeous of using chock in 1000V sisuation. What I mean is using chock in such high voltage might short inner the chock in some time, thats my friend told me! Especially using LCLC structure. That is why I am interested the chock Wd40 used.

In Taiwan, I nearly could not find double C chocks, but EI form chocks is quite easily got!

Cheers!

 

[wd40]

Hi Peleus

You are welcome.
If you feel anxious 1000V,May adopt Jax's ideas.

 

[Peleus]

Hi! Wd40,

This morning, I contact with the freind I mentioned in early reply.
He told me one guy in Taipei made a 845 with B+ 1000V, then, a couple of days, the chock he used got buring and short!

I don't understand the words Jax suggested that "to let the choke float by insulating it from the chassis". What that mean?

 

[Jax]

If you mount a choke the normal way then the core of the choke will be connected to the chassis and that is normally grounded. Thus there will be a potential of 1000V between the winding and the core. This might be too much for the insulation.

If you let the core float it will adopt a potential near 1000V through the leakage capacitance between the winding and the core. This will reduce the risk of an arc between the winding and core. But the choke must be installed in such a way that you cannot touch it when in operation.

 

[wd40]

Hi Peleus

Maybe try this way.

 

[Peleus]

Thanks Wd40 and Jax!

Jan, I got you!
I'm very appreciated with your suggestions and detailed explaination!

I'll keep them in mind ! Thanks!