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I'm back from a (rather long) vacation and have resumed collecting more parts for my PP DHT (2A3) project. I already have the OPT (fisher 500 / 800 ) and a pair of electra-print phase splitters.I'm now looking for a power transformer
1. I have a 400V transformer rated at 300mA ,I don't know if this would be ideal for a PP2A3
2. I also have the big fisher 800C power transformer (about 200 something volts on the secondary) which is meant to be used with a voltage doubler. I'm not so sure about voltage doublers being the best thing, based on my reading.
3. Would the linked toroidal power transformer be ideal (with dual rectification)? See link below.They also have another model with dual 150V secondaries. I'm assuming I could use this too (bhttp://cgi.ebay.com/300V-CT-150V-150VA-Toroid-Tube-Power-Amp-Transformer_W0QQitemZ270066715861QQihZ017QQcategoryZ4665QQcmdZViewItemy tying the secondaries together) with a single rectifier. It's also somewhat cheaper.
4. Any preferences? Should I just stick with good old EI types.
Thanks
Follow Ups:
I totally agree with Jeff Medwin about toroids. But there may be another reason for the inferior sound quality. The noise issue is not only a factor for the device where the toroid is supplying power, it also allows noise to go the opposite direction, namely, noise caused by the diodes can pass into the room's electric wiring and enter other eqpt.I have experience with this effect, and it's easy to demonstrate. Just wire up a DC supply (transformer, diodes, cap) amd attach a dummy load. It doesn't get conected to your hifi gear in any way except that it gets plugged into a wall socket. Then listen to some music while the DC supply is plugged in and while it is not. Can you hear the difference when the DC supply is plugged in? In my experience, the effects are quite noticeable and they are more so when a toroid is used.
nt
nt
I used a pair of these when I built my very first 300B monos (overkill) about ten years ago.It's a heavy duty unit and has a 120V/240V primary, 380-320-55 (bias tap) -0-320-380 at 200mA, 6.3V at 3.5A for power and input tube filaments, as well as 5V at 3A for rectifier tubes and a 5VCT at 1.5A for a 300B filament. It is also noiseless (no faint hum or buzz. Good Luck, wpod
I bought transformers from Antek -- John Ngo -- last week. I had a good buying experience. Ordered on Mon., arrived in NH on Friday. Toroids generally seem to be pricy (e.g., Plitron), but his prices were pretty low. He was not able to give me technical information for wind-your-own purposes.I am not at the moment using mine for B+, only filaments, so cannot comment on the noise and hash. Some folks have built amps with toroids for HT, so I do not think its out of the question. The toroids used were Plitron, as I recall some write-ups. Search on "Plitron" and "tube amp" and you might find some description of real life experiences.
Hammond has one model in their 300 series that is designed for 2a3 projects, having a 300-0-300 sec., 5v rec, 6.3, and two 2.5 volt windings. IIRC the HT secondary is rated at 200 ma, which, depending on the draw of the driver stage, should be adequate for a pp 2a3 monoblock.
Hi,For audio, avoid toroidal PTs, they couple very high frequency noise into the supply.
No real need for custom wound, either.
Go on-line and order a Hammomd Catalog, they got whatever you need, there, at decent prices, and they are made well !!
As Jeff says, toroids have a very wide bandwidth, which is exactly what you don't want in a power tranny, because HF noise from the mains can be an unwanted 'feature'! You can get them with an electrostatic shield between the windings but I don't know how effective that would be. The advantages of toroid trannies are compact size, high efficiency and relatively little hum irradiated to the rest of the circuit.
Thanks for jogging my memory. I recall reading an article about this particular disadvantage of toroids.I wonder, though, if the PS filtering won't eliminate HF noise.
To quote from a site I read up on sometime ago (http://members.tripod.com/~gabevee/mypwrsup.htm ) where the author was talking about SS diode induced hash in a power supply...
"
A 3 henry choke at 120 hertz has a reactance of about 2300 ohms. The same choke at 10 to 20 kilohertz, the region where hash likely is, will have a reactance of:Xc=2PiFL=6.28x10 000x3=188400
A whopping 188 Kilohms!, How the heck can hash get past that
"
A 3 henry choke at 120 hertz has a reactance of about 2300 ohms. The same choke at 10 to 20 kilohertz, the region where hash likely is, will have a reactance of:Xc=2PiFL=6.28x10 000x3=188400
A whopping 188 Kilohms!, How the heck can hash get past that
By capacitive coupling.
But I agree, with proper layout and perhaps throw in an extra small choke for filtering it should be possible to get rid of the noise. If it's possible with a transformer (as claimed) than it should be possible with a filter as well.
Hi Zobsky,Why have to correct a problem - when one can easily AVOID it all together?
Besides, who wants a 3HY choke anymore?? Certainly not I !!
exactly.I'm not convinced the toroidal transformer or the rectifier hash issues are anything other than theory. I have amps utilizing both, and there is no audible effect. I would not hesitate to use toroids or SS diodes again. "dr"lowmu, above, may also tell you to use transformers with no more than 2ohms DC resistance or your amp will suck... so theres that.
Ask Gary Gallo, Walt Jung and his crew all about standard versus toroid PTs. They even had graphs of HF response, vs a standard one, published in a Dell magazine ten years ago.Pooh pooh on toroids they all said .... and showed the data.
You, Jeff, are the one who proposes, listen and you will belive.
Untill you have heard a torid powered amp how can you put them
down?
No TextJeff Medwin
I promised myself that I would not respond to your follow-up post.
Why? Because I do not come here to argue, I am here to discuss
diy tube audio.However, since you don't seem content with that here we go.
First of all, I did not say that torids are the best solution to
amplifier design. In fact, I don't belive that they are at all
the best solution. I simply said that they can and do sound very
good.Unlike you, I have an open mind when it comes to designing and
building amps. I build it, I listen to it, then I decide if I
like it or not. And I do not limit my possibilities to what I
have read or heard.If I (we) had listened to the so called experts about how tubes
vs transistors measure, I (we) would be still listening to SS amps.Think about it Jeff, just because you don't agree with something
doesn't mean that it is wrong.But then, maybe in your world it does.
Cal
But not on Power Transformers, but Greg's 245 amp uses Plitron SE toroidal output trannies and they are really realy nice sounding and wideband.
What makes them good as outputs makes them bad as power transformers.Why would I want to listen to them on the other end of the amp, where I know from articles I've read and graphs I've seen that toroids allow high frequency line hash to pass into the B+ filters. ... I don't see any logic at all. So your amp has em, BFD. That doesn't mean its the best solution to the amplifier design problem. Sorry.
Jeff. Could I not use the same arguments with regard to your power supply theories?
Touche'. You are right, you could. Nice point !!But you will be missing out one heck of a good power supply implementation that simply sounds way superior. The difference in sound between a toroid PT and a regular PT will not be anywheres NEAR the magnitude of importance.
Why argue over anything??
Just spend under fifty dollars and get the L1/C1/L2/C2 power supply parts I outlined and hear and enjoy it for yourself. It is REALLY good !! All who have implemented it as suggested - just LOVE it !!
I also have built several amps useing toroidal transformers. They all sound very good. World class sound? Mabye, maybe not, and certainly not Dr lowmu approved, but they can and do work well.Also the seller you mentioned provides an excellent transformer (standard disclaimer here) I have bought many from him and am
very satisified.
I had Jack at Electra-Print wind me a power transformer exactly as I needed for a stereo PP 2A3 amp. Very good quality work. You get exactly what you need with the simplest implementation. Keeps the dropping resistors away and you can choose the form of rectification.
_______________________________
Long Live Dr.Gizmo
I second Electra-Print. Jack is great for custom work. He makes horizontal mount M6 power transformers for me and can provide chrome transformer covers. It gives a very nice finish to amps. Jack likes to run the solid core filament wires straight out (one less connection), which can be difficult to work with so I ask him to tap with more flexible stranded wires. See the 6BQ5PP amp photo for the power trans.
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