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SE Amp with Thoriated Tungsten output tube

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#81
Inductance depends of the core's permeability as well, and larger cores have increasing permeability, so inductance catches up. AC flux density is not dependent of inductance, but DC flux density is. In SE OPTs, we kill a lot of the core's permeability anyway with the addition of an air gap.
 
#83
If the core magnetic path length is kept the same, permeability is proportional to core surface area. Inductance is proportional to permeability. So for example, when doubling the core area but cutting the windings amount in half, inductance will be still the same if the MPL is kept intact.
 
#84
50EA, examine the book-ends...the one on the big side being the important one for this discussion. There are *NO 500W high-fidelity output transformers made. Take one that is claimed to accomplish that, and try it at a half-Watt...let me know how it measures.
cheers,
Douglas
 
#85
The issues with big transformers arise when one has to get high power. For small power, say 15-20W or less, one can "cheat" with the bigger core and less turns. 15-20 real watts I mean, down to 25-30Hz for SE amps. Easier to do with C cores....
The bigger core will inevitably cause larger capacitance (this might put some limitations on the source impedance respect to an "optimal" solution but one has to evaluate case by case....) but leakage inductance can be kept under control and so the bandwidth.
 
#86
50AE said:
If the core magnetic path length is kept the same, permeability is proportional to core surface area. Inductance is proportional to permeability. So for example, when doubling the core area but cutting the windings amount in half, inductance will be still the same if the MPL is kept intact.
Click to expand...


What is the scaling relation of permeability to core surface area? It would have to be a square function to keep up with the square function of turns, since inductance is a linear function of permeability.



Thanks,
Chris
 
#87
sumotan said:
Silly question, why is there no interest in the likes of Svetlana Sv811 or 572 tubes. They still can be bought at reasonable price.
Click to expand...

Those tubes had a secret failure mode. If the anodes were not run hot enough, the zirconium getter would not reach minimum temperature to degas the tube..
That was kinda a shame - the SV811-3 in particular was a very nice tube - and there were a number of circuits out there from Italy and Eric Barbour that explored these tubes. Not enough volume for the plant to justify making them.

The SV572 series had graphite anodes... The 811 metal. I built an amp using the SV811-10 and listened to it for awhile. At that point, the SV811-10 become discontinued. I moved to the Chinese 845s.
 
#89
Bandersnatch said:
50EA, examine the book-ends...the one on the big side being the important one for this discussion. There are *NO 500W high-fidelity output transformers made. Take one that is claimed to accomplish that, and try it at a half-Watt...let me know how it measures.
cheers,
Douglas
Click to expand...

500W for PP task are still quite on the easy side. I can see ohmic resistances and power dissipation kick in. I see no problem reaching 1kW though.
 
#91
minhaj said:
Eric barbour's circuit for SV811-10
SV811/SV572 SE1

I am distracted due to higher power filament. At this point I am fixing my mind for HY69 need triode curve for the same to know/confirm that it would not hit A2 at max power (given B+ is 350 volt @50ma current.

Regards

Regards

Regards
Click to expand...

It *Will hit g1=0+ if you try to drive it too hard. Same with any other tube you could possibly put in there, up to and including a 7241.

Even with no curves, it is a small matter to pick an idle point that is suitable. With fixed bias, this is a matter of twisting the bias pot shaft. For cathode bias, just pick the right resistor.
cheers,
Douglas
 
#92
I think too the triode curves of the HY69 are not necessary. As I already posted, I estimated that with 400V on both plate and g2 the bias should be 40-45V for 40-45 mA which should give optimal (or close to optimal) output power in the 3-4W region. Easy to veribfy immediately with 1K self bias and then go for fixed bias.
 
#93
minhaj said:
Thank you everybody for all the interesting inputs, it made the thread quite vibrant.

1. Low cost
2. Output transformer should be 3k or 5k
3. B+ 400volt max
4. Class A1 only (no grid current)
5. Triode or shade feedback output
6. 3 watt output

To meet the above conditions I think Hy69 (in triode connection) is a better candidate.
Plate to Cathode 300 volt, 50ma current, grid voltage -?, 5K opt. Is it good for staying in A1 region? Anybody please give me triode connection plate transfer curve, I will be most obliged.
Click to expand...
As so often happens, threads go off on multiple tangents and the original request gets lost in the ("vibrant") haze.

So far, nobody seems to be able to supply you with triode curves for the HY69. They have probably never been published. Perhaps someone with a curve tracer who happens to have some HY69s will come along.

triode_al said:
There is a group of tubes that maay be interesting.
I have used the 10Y for quite a long time. Output: above 3 watts like many say, equal to 300B and . . . less distortion??

Well the secret is a follows: run it from a 6SJ7 (like a classic WE91A that uses the
  • 6-pin version of that same tube);
  • then as output a 10Y, LONG PLATE version.
  • A 7-10K output transformer.
The 10Y comes in a version that looks like the VT52 (which I never had) and that can be run in series to get 12.5 volt battery operation: 5 V + 7.5V. The anodes and other structures are exactly the same.
There is also a short anode plate version of the 10Y maybe commonly named as 10, that has less power I expect, but I have them not used them.

The plate current of the 10Y is low, say 30 mA. Quite a difference from the 300B.
I bought a cheap 7K/8ohm amorphous transformer on the bay for it.

It is not a pain to drive it, no high input capacitance. It is a transmission valve.

So MINHAJ, looking at your list that reflects your sacred goal:

1. Low cost --> not low any more.
2. Outpout transformer should be 3k or 5k --> is higher but I ran it with 5K for 10 years
3. B+ 400volt max --> I ran it at 380Volt & 30 mA
4. Class A1 only (no grid current) --> no grid current, can accept high value Rg
5. Triode or shade feedback output - --> no feedback needed but can be to input in classical way.
6. 3 watt output --> can get that safely​

I get annoyed at the 300B. High current in class A but I cannot drive it to the bottom. Lots of waste.
The 10Y is a gentleman to drive. Sophisticated.
Click to expand...
@triode_al has suggested using the 10Y/VT-25 which he says is good for 3w. In another thread, you said you've tried that and you were only able to get 1.5w from it, which was not enough for your speakers.

Perhaps his 3w output figure is at a higher level of distortion? Maybe he can elaborate.

Do you think 3w would be enough? If not you'll obviously need to look elsewhere but my totally uneducated guess is that the HY69 in triode will have about the same 3w power output.

But, out of curiosity, is the appeal of using thoriated tungsten tubes simply because you simply want something that glows brightly? If so, why not use the 10Y/VT-25 as an input tube with an output tube that is simpler to use and produces more power?
 
#95
If you run it as a triode and restrict it to low B+ and no grid current, you are going to have trouble making very much power. These are requirements that conspire to make power output small.

If you just run the HY69 as a pentode you can get almost 10W output into 5k with a B+ of ~400V. Of course, you will need some local feedback to get a decent damping factor, but that is doable.

You'd have to trace some triode curves to see if you can make 3W at reasonable distortion with low B+ and no A2. It may or may not be possible with this tube. It all depends on where that Vg=0 curve is and how much usable area there is to the right of it.
 
#96
FlaCharlie...this is from you:

'@triode_al has suggested using the 10Y/VT-25 which he says is good for 3w. In another thread, you said you've tried that and you were only able to get 1.5w from it, which was not enough for your speakers.'

- There are few versions with 10/10Y/vt25/vt25A/vt52/vt62 -some are with thoriated
tungsten filament some are with coated filament. The ones I have and I tried are not
capable of making more than 1.5 watt in se @425 B+ and 18ma current opt 10K se.

'Perhaps his 3w output figure is at a higher level of distortion? Maybe he can elaborate.'

- 3 watt in se is possible with long plate 10Y but they are with coated filament.
801A/vt62 can reach 3watt+ and they are with thoriated tungsten filaments.

Do you think 3w would be enough? If not you'll obviously need to look elsewhere but my totally uneducated guess is that the HY69 in triode will have about the same 3w power output.

- 3watt in SE is enough for me/my speakers/my listening habit

'But, out of curiosity, is the appeal of using thoriated tungsten tubes simply because you simply want something that glows brightly? If so, why not use the 10Y/VT-25 as an input tube with an output tube that is simpler to use and produces more power?'

I am into this hobby for more than 30 years meanwhile I tried PP, SE, choke loading, CCS loading, parafeed, with DHT/IDHT etc. I prefer two stage DHT SE amp with loaded driver. For two stage amp 10/10y does not have enough gain for DHT output tube capable of producing 3 watt. And yes I like the glow. And yes my experience suggests DHT with thoriated tungsten filament outperforms coated filament type.

Regards
 
#98
LordGwyn....thank you for the most generous offer. Alas! I am in Bangladesh.

Palustris...or anybody who has experience using Hy69, what will be life span for the tubes.? I heard that TT tubes like Hy69/865 etc. from old days are not rugged enough. Since I live in Bangladesh I need to import the tubes that's why I am concerned.
 
#99
If I come across a cheap HY69, I might add to my collection and satisfy my curiosity. You might try importing them from Japan, a shorter journey, and given the popularity of tube DIY in Japan there is a large market for American-made tubes there. I have purchased thoriated tungsten DHT from Japan, shipped express international to the USA without issue. But of course anything can happen, I recommend express shipment, more time in circulation is more time for packages to be dropped, kicked, crushed, etc.
 
#100
I have your sample in hand LG, and if I may impose, would you also consider running the experiment on an HY1269?

minhaj, I have run these tubes a few times, and had no issue with their life. Class A PP of course... 🙂
cheers,
Douglas
 
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