Looking for high-voltage tubes

[cvanc]

Posting capacitors to help with this is just gonna enable Jan to actually do this crazy project. Are we really sure we want to do that?

Yes! Yes we are! To wit

https://www.surplussales.com/item/_CFP/c44f8ez6100za0j.html

 

[smoking-amp]

The idea is direct drive, no output xformer.

My current solution is a cascode structure.
What I want to do is replace the top tube by an inductance to double (almost) the voltage swing at the output.

An inductor still has 90 degree out of phase core magnetizing current like an OT.

How about a HF Ferrite inductor driven by a LV winding to produce constant current at the HV end. (two phase flybacks) Then either a HV tube to pull down or another, -modulated-, HF Ferrite current sink at the low side. No HV tubes needed at all then. Magnetizing currents and switching would be inaudible. I suppose this would be called class D. You'll have to hide this in a black box with some tubes mounted on the top..

 

[Demonkleaner]

https://frank.pocnet.net/sheets/088/8/8163.pdf

Heathkit used 2 3-500Z's without the complications of a chimney.
A simple fan mounted with the air split between the top and
underside of the chassis cooling the envelope and socket/pins.
3-400Z's filaments could easily be lit with a SMPS. Just a thought.

 

[jan.didden]

There's a fella selling hundreds of these on FB markets:

Got a link Jack?

Jan

 

[jan.didden]

An inductor still has 90 degree out of phase core magnetizing current like an OT.

How about a HF Ferrite inductor driven by a LV winding to produce constant current at the HV end. (two phase flybacks) Then either a HV tube to pull down or another, -modulated-, HF Ferrite current sink at the low side. No HV tubes needed at all then. Magnetizing currents and switching would be inaudible. I suppose this would be called class D. You'll have to hide this in a black box with some tubes mounted on the top..

Well, my solid state amp doesn't need HV tubes either.
Read my lips (again): 'no output transformer'.

Jan

 

[gorgon53]

EIMAC has a 60W Pa pulse modulator that can take something around 20kVp. The much bigger 6C21 can take 30kVp.
I cant remember the type number of the 60W tube, but if you search through eimacs catalalog you should be able to find it

 

[banat]

Maybe I`m wrong but maybe this can be some sort of the basic solution ? , two GMI-83(V) 60W(65W) pulse modulator tubes operating in push-pull class AB1 , with both grids grounded (g1&g2) and semi indirect heated cathodes driven , direct driving ESL stators via two high voltage block capacitors ...
edit , maybe is better solution that both very high loaded anode resistors (Ra & Ra`) to be replaced with some suitable center taped inductor ?

 

[jan.didden]

That looks like a suitable tube at first glance, but at 50W heater power? I'm frugal at heart.
Also, I understand Vgk should be around -300V, so current-driving the cathode (which I favor) you lose 300V output headroom.
At this point I am looking at two parallel tubes of the 6JS6 variety, inductively loaded.

Edit - it's a very nice tube. Tempting.
What the difference with the -V version?

Jan

 

[banat]

Well 50W of heater power is must for those GMI and simmilar HV pulse tubes to get very very high anode peak current , that GMI-83 actually have four in line cathodes , and that model GMI-83V have semi-indirect heated single round cathode in diameter which is something like EL34 tube bulb ,
any way 6SJ6 and simmilar tubes can be also very good solution , inductively loaded ,
btw , my idea for around +250V on GMI cathodes is to automatically get anode B+ source for let`say EL84 tube triode strapped which in the same time drives GMI-83 cathode .

 

[jan.didden]

Yes that would work but I want to drive the cathode by a transistor current source controlled through an opamnp.
It's what I have in my current amp and that gives THD better than -100dB.

Do you know more of such tubes?

Jan

 

[banat]

You can find many and more powerfull GMI pulse modulator tetrodes on -GS.tubes.com-site https://www.gstube.com/catalog/2/

 

[jan.didden]

When I look at the GMI-6 I see 'limiting value Va 4kV'.
Is that DC, could it swing double that with an inductive load?

Jan

 

[hidnplayr]

That's an interesting tube.

I am wondering, those HV reg tubes with Va up to 25kV with Ia(max) 1.5mA.
Would they break if Ia was 25mA peak?
Is that 1.5mA a max because of the brittle fine wire/construction or is it 1.5mA to limit the Pa with those 25kV anode voltages?

Jan

I can hook you up with some new PD510's if you are willing to try. (For price of shipping, or local pickup)

 

[banat]

Jan
I`m pretty sure that limit is for 4KV-DC or B+ supply , but I noticed that there`s also anode disipation limit to only Pd-max=15W for both anodes connected in parallel , think that GMI-6 is one relative small tube from that GMI familly of pulse tetrodes tubes which is not very good choice for your ESL-OTL amp.

 

[jan.didden]

Yes I looked at the PD510 and family. What bothers me is the 1.5mA max Ia.
Why is that so low, is it a mechanical limit?
Could I draw 10mA at 3.5kV?

Jan

 

[gorgon53]

g2 at anode offcourse sets limits the the anode applicable voltage, so would not be a good idea. But maybe this datasheet is useful otherwise

 

[banat]

gorgon53
, that`s maybe how Serbian NAT tube amps manufacture pseudo-triode connected and used those GMI-83(V) tubes in their SET amplifiers ...

 

[hidnplayr]

Yes I looked at the PD510 and family. What bothers me is the 1.5mA max Ia.
Why is that so low, is it a mechanical limit?
Could I draw 10mA at 3.5kV?

Jan

Well, I just did a simple test on the bench and the answer is no.
It's not that the tube broke after 1.5 mA but more like you wont be able to pass that amount of current without making the grid voltage very positive.
With 600V at the anode and 0V on G1 and screen, it passed a measly 0.1 mA..

Maybe something can be done by playing with the screen, but it doesnt look too promising so far

 

[jan.didden]

Ahh. Thanks!

Jan

 

[gorgon53]

The GMI83 migth work in tetrode mode