Ok so for my quest of a BIG tube amp I am still searching an thinkering about the available options.
I've maybe found a company who can make custom OPT's and possible also for Higher Voltages.
As I was searching the 572b tube caught my eye.
Big triode and the needed anode voltages are (still dangerous) but possible.
One of the things I see everywhere is people using those transmitting triodes on to low voltages in SE.....
I think they would be very nice in pushpull and at a voltage they where meant to be used at (1500 to 2000v)
A pair of these in a load of around 12k5 to 15k can do 300w + using 1500v and going to 2kv can make 500w+ without a problem.
Svetlana makes them and Shuguang also.
First looking at the curves gives a load around 12500-15000ohms for the OPT.
A little bit high but can be done.
Also the tube has a nice look.
So a few questions:
-Would it be safe to use 2kv on the tubes produced today?
-I was thinking about a load of 15k giving around 500w using 2kv. other suggestions are welcome.
-It doesn't need extreme voltage swing as drive but it needs grid current as it is a zero grid bias tube. Operations is also class AB2. So best solution is to use some mosfet followers I think.
-As the tube is a zero grid bias tube it doesn't need a negative bias but some datasheets show a few volts negative when using it at 2kv (or more). so best to include soms small amount of bias ?
I do know it is high voltage and dangerous so I will take precautions when testing. Will still be a few months till I figure everything involved in the design.
I've maybe found a company who can make custom OPT's and possible also for Higher Voltages.
As I was searching the 572b tube caught my eye.
Big triode and the needed anode voltages are (still dangerous) but possible.
One of the things I see everywhere is people using those transmitting triodes on to low voltages in SE.....
I think they would be very nice in pushpull and at a voltage they where meant to be used at (1500 to 2000v)
A pair of these in a load of around 12k5 to 15k can do 300w + using 1500v and going to 2kv can make 500w+ without a problem.
Svetlana makes them and Shuguang also.
First looking at the curves gives a load around 12500-15000ohms for the OPT.
A little bit high but can be done.
Also the tube has a nice look.
So a few questions:
-Would it be safe to use 2kv on the tubes produced today?
-I was thinking about a load of 15k giving around 500w using 2kv. other suggestions are welcome.
-It doesn't need extreme voltage swing as drive but it needs grid current as it is a zero grid bias tube. Operations is also class AB2. So best solution is to use some mosfet followers I think.
-As the tube is a zero grid bias tube it doesn't need a negative bias but some datasheets show a few volts negative when using it at 2kv (or more). so best to include soms small amount of bias ?
I do know it is high voltage and dangerous so I will take precautions when testing. Will still be a few months till I figure everything involved in the design.
Modern 572Bs should take 2 kV without any trouble- the SB200 runs them around that point, and when detuned with the key down that is far more abusive than any audio amplifier will be.
Keep in mind that a 12k primary, insulated for what would realistically have to be somewhere between 6 and 10 kV, will be one seriously tricky transformer to make perform well, especially at the power levels we are looking at here.
If a good output transformer solution can be figured out, then it would be a great project. The plate and filament transformers are really no big deal. Antek has a few options that would probably do the job, and you could always use a 120 : 600 control transformer if you had to.
The biggest downside is that this thing will be enormous and ridiculously heavy- no way around it.
Obviously a project like this is deadly in a big way. That said, you sound like you have some idea as to what would be involved (which is more than can be said for many people who want to build amps around these tubes).
I'll be very interested to see what you come up with for output transformers.
1500-2000V is pretty dangerous.
If you cant get the power put more valves in parallel and use same voltage.
If you cant get the power put more valves in parallel and use same voltage.
It's no more dangerous than any other amp running those kinds of voltages. There is more than one way to skin a cat. Lots of hams build much scarier linear amplifiers with 3 kV power supplies and a pair of 3-500Zs. This is still a dangerous project, but that's not to say that it can't be done.
Some people are crazy enough build linear amplifiers around a 4-1000A running 4 kV on the plate. That is a much scarier project than this.
All of this depends on the OP's experience level. If he/she has the experience to do this kind of project without getting themselves killed, then they just need to get a small overhead crane installed at their bench to move the thing.
The Svetlana 572B's were actually made by Ryazan; they may or may not be manufactured currently. The Svet is not quite the same as the old 572B's, some amps need some minor mods to use them. I have quite a few of them that I got to replace 811A's, but my Svet 811A's are still in good shape
The audio SV572-160 are really cheap right now ( I've bought them for $50/pair NOS at hamfests ). I've used the SV811-10, and it is a real nice tube
The audio SV572-160 are really cheap right now ( I've bought them for $50/pair NOS at hamfests ). I've used the SV811-10, and it is a real nice tube
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Anyone thinking of running some amp for Home Use using rediculous killivolts is asking for trouble.
If you want high wattage - use solid state for lords sakes.
Come on now.
If you want high wattage - use solid state for lords sakes.
Come on now.
I guess I'm going to make the same argument I did in my last post- Hams have been doing it for decades in the form of 1500W RF amplifiers using pairs 3-500Z tubes. You still have to be extremely careful, but this isn't exactly "new territory" so to speak. Lots of people build 845 amps, and I've seen a few push-pull amps with 304TL tubes or SE 833 amps.
Really the only thing stopping me from building one is that the output transformers are very, very expensive. I could wind my own, sure, but I don't have the design skills to design one that will perform well over the entire audio spectrum at 100W with a 10k primary impedance and 10kV of isolation.
572B in push-pull, sure, how much power do you actually want/need? Running less than 1kV, you could certainly get 100W without having to deal with the class B nasties (feedback of course will be required for something like this).
800V/150mA into a 10K transformer would be good for 100+W. That's still a painful output transformer to wind/source, but the core size won't be so outlandish and the insulation issues are somewhat mitigated.
800V/150mA into a 10K transformer would be good for 100+W. That's still a painful output transformer to wind/source, but the core size won't be so outlandish and the insulation issues are somewhat mitigated.
In the past I have been involved with some high power grounded grid RF finals.
Power supplies of 5kv and 1A maximum => very dangerous and very heavy.
First thing I would do is to make sure the top caps of the tubes are not accessible.
Using some plexi or glass so the tubes are still visible.
The bias adjustment I would make easy accessible with a build in meter (they also did this for the mcintosh mi350)
So under normal operation there is no need to be under the chassis where the high voltage is.
If I really needed the power for PA or something I could just go out and buy something Class D......
This is more of a fun project of something different. Putting lots of tubes parallel has been done.... SVT bass amp etc.....
The high impedance is indeed tricky... I could of course parallel 2 pairs and be done with a primary impedance of 6k5 and lower the voltage to around 1,5kv.
Makes it a little bit easier for the OPT
This can still make around 500w of power.
I am waiting the quote from the transformer winding company.
Another thing that got to me is the fact that this tube is most of the time used in grounded grid. So maybe it would be an idea to try this for audio...
The driver would need to be a small power amp of it's own but this could be achieved using a smaller power triode in SE. Could sound very nice I think.
Power supplies of 5kv and 1A maximum => very dangerous and very heavy.
First thing I would do is to make sure the top caps of the tubes are not accessible.
Using some plexi or glass so the tubes are still visible.
The bias adjustment I would make easy accessible with a build in meter (they also did this for the mcintosh mi350)
So under normal operation there is no need to be under the chassis where the high voltage is.
If I really needed the power for PA or something I could just go out and buy something Class D......
This is more of a fun project of something different. Putting lots of tubes parallel has been done.... SVT bass amp etc.....
The high impedance is indeed tricky... I could of course parallel 2 pairs and be done with a primary impedance of 6k5 and lower the voltage to around 1,5kv.
Makes it a little bit easier for the OPT
This can still make around 500w of power.
I am waiting the quote from the transformer winding company.
Another thing that got to me is the fact that this tube is most of the time used in grounded grid. So maybe it would be an idea to try this for audio...
The driver would need to be a small power amp of it's own but this could be achieved using a smaller power triode in SE. Could sound very nice I think.
Yes, the driver will need to deal with significant grid current.
Going from 100W to 300W will more than double the cost of the output iron (and weight).
I would recommend setting an approximate budget or a desired level of power, then working backwards from there.
Going from 100W to 300W will more than double the cost of the output iron (and weight).
I would recommend setting an approximate budget or a desired level of power, then working backwards from there.
I think the thing to do is to figure out what output transformers are available and within your price range.
For the budget that is just a matter of saving up money for this project.
Not that I am going for exotic silver expensive stuff but I do know it is gonna cost me some money.
If I see what kind of things some HIFI people buy...... I would rather put it in a nice amplifier.
If I would want something cheap I wouldn't go for tubes but just a chip amp.....
Neurochrome made a very nice chip amp..... it's plenty for normal Hifi listening.
So back to the topic.
For the power transformer I was thinking indeed for a toroidal from Antek.
Something like this AS-8T650 - AnTek Products Corp could be something to start.
It has 2 windings of 650v using them in series will give around 1.8kv after rectification.
It has 2 windings of 6.3v @ 5A so they can be used for the filaments.
If I would use 2 pairs in parallel to lower the needed primary impedance I could use 2 of these transformers.
That way I have the needed filament power and more power reserve for the HV.
Capacitors will be in series with bleeder resistors. That way the voltage will discharge when the amp is off and the voltage is divided equally over the capacitors.
Was thinking of making a PCB for this but 1.8kv on a PCB could be asking for trouble.
Also an indication using a neon bulb and a series string of resistors that will light as long there is voltage on the capacitors.
For the diodes I haven't made up what to use. Maybe some HV Tube rectifiers.
Btw something to think about. I know this can be dangerous but..... what about a microwave oven? If I remember correctly this is around 5 kv using a voltage doubler.....
It's used in a kitchen where there is water etc..... as long it is enclosed in a earthed metal frame this doesn't give any problems....
First thing would be getting the quote for the output transformers indeed
Not that I am going for exotic silver expensive stuff but I do know it is gonna cost me some money.
If I see what kind of things some HIFI people buy...... I would rather put it in a nice amplifier.
If I would want something cheap I wouldn't go for tubes but just a chip amp.....
Neurochrome made a very nice chip amp..... it's plenty for normal Hifi listening.
So back to the topic.
For the power transformer I was thinking indeed for a toroidal from Antek.
Something like this AS-8T650 - AnTek Products Corp could be something to start.
It has 2 windings of 650v using them in series will give around 1.8kv after rectification.
It has 2 windings of 6.3v @ 5A so they can be used for the filaments.
If I would use 2 pairs in parallel to lower the needed primary impedance I could use 2 of these transformers.
That way I have the needed filament power and more power reserve for the HV.
Capacitors will be in series with bleeder resistors. That way the voltage will discharge when the amp is off and the voltage is divided equally over the capacitors.
Was thinking of making a PCB for this but 1.8kv on a PCB could be asking for trouble.
Also an indication using a neon bulb and a series string of resistors that will light as long there is voltage on the capacitors.
For the diodes I haven't made up what to use. Maybe some HV Tube rectifiers.
Btw something to think about. I know this can be dangerous but..... what about a microwave oven? If I remember correctly this is around 5 kv using a voltage doubler.....
It's used in a kitchen where there is water etc..... as long it is enclosed in a earthed metal frame this doesn't give any problems....
First thing would be getting the quote for the output transformers indeed
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I wouldn't use tube rectifiers for this- that's quickly going down the rabbit hole of insanity. You could use Hg vapor rectifiers like the 866, but that would make this a pretty dangerous amp. Putting 1N5408s in series is pretty standard, cheap and effective.
IIRC, Microwave ovens use some sort of "half-wave voltage doubler" to get their high voltage supply. One side of the secondary is tied directly to the transformer core.
This project can be made "adequately safe" for HiFi use. Just try to keep things enclosed enough that nobody can get anywhere close to those plate caps, even if they are insulated. It doesn't have to be completely idiot-proof like a microwave does since it won't be going on the market.
+1 on the Antek toroid- they're great transformers. A single one will not have enough filament current for a quad of 572Bs (though I think monoblocks might be wise here). You can always add another filament winding though since Antek doesn't fill the center of their toroids with epoxy.
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4 pcs 2CLG 20KV 3A High Voltage Diode HV Rectifier Tesla Ham 852664621790 | eBay
I own a Henry amateur amplifier that uses something similar to these.
The PS produces around 4KV at .5A
The chokes used in it pop up on eBay occasionally.
Chokes use a tuning capacitor in parallel.
I own a Henry amateur amplifier that uses something similar to these.
The PS produces around 4KV at .5A
The chokes used in it pop up on eBay occasionally.
Chokes use a tuning capacitor in parallel.
We use similar rectifiers at the lab on occasion. IIRC, they are just a series diode string (possibly with equalizing resistors?) cast in an epoxy block. I personally think they're too expensive for what they are.
MFJ lists the replacement power transformer for the AL572 at about $140. That's good for a quad ( I think ) of 572B.
Maybe an old modulation transformer could be modified or rewound. They probably only go to 7 or 8 KHz, though.
Maybe an old modulation transformer could be modified or rewound. They probably only go to 7 or 8 KHz, though.
I have built lots of 811A-572B amps, but never more than 100-150 watts.
I used 600 volts for 100 watts.
I used the circuit used for record cutting. uses an out put transformer 1500 ohms to 2000 P-Pull
I used 6BL7's as cathode followers to drive the 572b's, but you can use Mosfets
There is circuit in glass audio for a 300 watt 572 Amp with multiple tubes.
I used 600 volts for 100 watts.
I used the circuit used for record cutting. uses an out put transformer 1500 ohms to 2000 P-Pull
I used 6BL7's as cathode followers to drive the 572b's, but you can use Mosfets
There is circuit in glass audio for a 300 watt 572 Amp with multiple tubes.
Good 572b tubes (the original ones with the plate cap terminal) are pretty much gone, except for remaining stocks which are getting thin and rising fast in price. The Svetlanas are out of production. Because the 572 has been popular in ham amplifiers, both unto itself and as a drop-in upgrade for 811a-s, various companies keep bringing 572b-s back to market but quality and longevity of the Chinese ones seem poor. Too bad, it is a truly great tube and kind of a 'sweet spot' of simplicity, price, and performance. The steal of a deal right now is the GU-81M, if you don't mind using a pentode.