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Old 21st July 2007, 12:53 AM   #11
jnb is offline jnb  Australia
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Sorry, are you talking of input or output transformers, still the same though whichever.

As a general rule of thumb, consider the impedance across the other side of the transformer. Multiply it by the square of the turns ratio, as you do, to find what it looks like on the side of interest. When the winding impedance there is lower than the reflected impedance from the other side, it will begin to short that impedance and this frequency represents the lower usefulness of the transformer in that particular application.
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Old 21st July 2007, 01:00 AM   #12
nhuwar is offline nhuwar  United States
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I thought the priciple was the same if my driving stage is a push pull stage?

Am I in error?

Nick
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Old 21st July 2007, 01:10 AM   #13
jnb is offline jnb  Australia
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My last post may have been a little awkward but I didn't mean to convey that your transformer was any different. The principle is the same.
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Old 21st July 2007, 01:17 AM   #14
nhuwar is offline nhuwar  United States
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It's no problem. The way I look is no matter what it's all a learning experience.

The interstage transformer I am using is the universal interstage transformer that triode electronics sell's

Nick
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Old 22nd July 2007, 11:44 AM   #15
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Depending on the grids that you will be driving after the interstage, the job of the driver is a very tough one. This is especially true if you are using anything less than a very expensive interstage transformer (which I suspect you are not).
The load on the driver triode is a combination of the miller capacitance of the "two" driven tubes plus the parasitic capacitances of the interstage transformer. In order to give it a fighting chance of sounding good you should be thinking of high standing current on the driver (at least 20mA and preferably nearer 40mA), and with as low an internal resistance as possible. The 5687 makes an excellent candidate for the job. I also think going parafeed is a good idea as it takes the standing current out of the transformer which potentially gives it more inductance to work with.

Hope that helps.

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Old 22nd July 2007, 03:25 PM   #16
nhuwar is offline nhuwar  United States
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Your right it's not an expensive interstage but this is just a starting point. As far as the driving tubes, i'm talking about a 6sn7gt pushpull into a pair of 813.

But all this is the start of my bread board for this amp so I know for a fact these transformers will be relaced with lundahl interstages.

That's what I used for the output transformers.

Nick
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Old 23rd July 2007, 08:29 AM   #17
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Quote:
Your right it's not an expensive interstage but this is just a starting point. As far as the driving tubes, i'm talking about a 6sn7gt pushpull into a pair of 813.
How are you doing your phase splitting. You seem to suggest that it wont be with the interstage.

Edit: Just looking at the spec sheet of the 813 I don't fancy your chances of getting this setup to work as planned. I would suggest that you look at TubeLabs Mosfet powerdrive as a way of driving the 813's. It will take all of the strain off of the interstage and drive the 813's well. Other than that a follower of some type after the interstage would be worth considering.

Shoog
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Old 23rd July 2007, 12:49 PM   #18
nhuwar is offline nhuwar  United States
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Quote:
Originally posted by Shoog


How are you doing your phase splitting. You seem to suggest that it wont be with the interstage.

Edit: Just looking at the spec sheet of the 813 I don't fancy your chances of getting this setup to work as planned. I would suggest that you look at TubeLabs Mosfet powerdrive as a way of driving the 813's. It will take all of the strain off of the interstage and drive the 813's well. Other than that a follower of some type after the interstage would be worth considering.

Shoog

Hi Shoog I am using a interstage but originally I was going to use a input transformer to. As for using a diffrent driver circuit you could definatly be the better option as this is just my starting point.

I have looked at the power driver circuit but I thought it would get a little complicated coverting it to push pull.

Nick
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Old 23rd July 2007, 01:49 PM   #19
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PowerDrive can work for push pull. You need some type of conventional phase splitter followed by two PowerDrive circuits. I use a LTP splitter in the first stage of an amp followed by two common cathode voltage amps with two PowerDrive circuits. This is essentially a completely differential amplifier design, which is more complicated than the usual P-P amp. I have been experimenting with some unusual phase splitter designs, but I have not had time to experiment recently. All will eventually wind up on my web site.

For those that don't know, the Triode Electronics driver transformer has a center tapped primary and four independently wound secondaries. This allows all sorts of unusual output stage configurations. My favorite so far is a complete H bridge using 6AS7's. I have not taken the time to thouroughly test this transformer, but I do know that it does not like ANY DC offset through its windings. I have been using a parafeed connection off of one of my 45 amps using the original OPT as the choke and a 20 uF ASC cap that I got surplus.

With no DC, bass is not an issue, but I don't know about its HF response. I see no reason to believe it couldn't drive P-P 813's in class A or AB1, but then I haven't tried that either.
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Old 23rd July 2007, 02:53 PM   #20
nhuwar is offline nhuwar  United States
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Thanks for the input. I have looked at your powerdrive circuit and have been thinking about playing with it. But as a said to Shoog the basic setup is going to be my starting point and working up from there.

I just don't want to start the bread board process really complexly and not have anything work. I would rather start simple with something functional and get more complex with the circuit.

Trying to keep my self from getting aggravated and over whelmed.

Thanks for the help

Nick
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