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PostPosted: August 2nd, 2016, 1:05 pm 
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J-ROB wrote:
The old rule of thumb of drive impedance 5-10X lower than load is a good one, but you have to look at the specific case to understand what the tradeoffs are.

e.g. When driving reactive loads, it may help to have some series impedance to reduce/eliminate ringing.

I have seen this with silver wire amorphous core 10k input transformers. Those suckers wanted to take off and fly. 100 ohms in series and they calmed right down.

Transducers, transformers, etc. are a more complex situation than driving a resistor.

I don't know if this is a problem with the autoformers in question. Probably not. I think if the drive Z is 20% or less of the specified impedance then you should be cool.

Note that the autoformer will step up any impedance connected to the secondary, it is a TRANSFORMER, so the actual load might be higher than the impedance on the label.

A 6SN7 cathode follower should drive the snot out of most audio inputs, I should think. Just fire it up and rock on with your bad self!


All good advice, thanks. But I don't own any autoformers (if your post was directed at ME, which I assumed since you mentioned the 6SN7 follower. My line stage is an LDR input (around 7kΩ) to a grounded cathode 12B4 with LEDs in the cathode for bias and a 10M45S in the plate circuit. That's it. Current source'd (cascode DN2540s) and shunt reg'd with gas tubes.

David M's line stage is a pair of parallel connected 20kΩ stereo P&G pots.


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PostPosted: August 2nd, 2016, 1:10 pm 
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OK, you should be good with a plate follower 12B4 into 7k resistive.

Rock on with your bad self using that. Free Bird! Free Bird!!


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PostPosted: August 2nd, 2016, 1:24 pm 
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J-ROB wrote:
OK, you should be good with a plate follower 12B4 into 7k resistive.

Rock on with your bad self using that. Free Bird! Free Bird!!


Yeah Buddy! :character-beavisbutthead:


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PostPosted: August 2nd, 2016, 3:24 pm 
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I use an autoformer preamp. I also have a single stage VT137 preamp that I screwed up when I removed the nice old 4uF 600V oil caps and substituted a pair of Jupiter Copper caps (which cost me $300 so they must be better right?). But the Jupiter caps sound not very good and that bummed me out so much that I can't even look at the preamp but at some point I will return the old oil caps to their proper place in that preamp.

I think the autoformer preamp, 12' long interconnects are not ideal for JRob cables (or any cable really) although my amps are ~100k input.


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PostPosted: August 3rd, 2016, 11:44 am 
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FYI -- the Gore cables utilize silver clad copper conductors with a high polish because of the extreme frequencies they're used for. Additionally, the center conductor both solid and the stranded version, is wrapped in micro-porous Teflon tape not unlike the stuff used for sealing threaded pipe joints. Following that is a silver/copper ribbon spiral wrapped inner shield, then a thin layer of FEP, then a silver/copper braided shield, then spiral-wrapped stainless-steel armor, then a FEP layer, then the outer jacket with the fancy pattern is some sort of fabric that does not respond very well to my thermal stripper.

To say the least, it is very complex, but I guess that's what makes so sublime for 18-gHz. transmission and especially in my case for audio. It is always said that the devil is in the details.

Here is a current listing on eBay for a 35-foot length at about $5.00/foot. Not a bad price at all compared to some of the "scalpers" out there:

http://www.ebay.com/itm/Gore-Phaseflex- ... SwtnpXkt92

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PostPosted: August 3rd, 2016, 12:47 pm 
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I believe this is the stranded center conductor version. Is there a preference for stranded vs solid core?


SoundMods wrote:
FYI -- the Gore cables utilize silver clad copper conductors with a high polish because of the extreme frequencies they're used for. Additionally, the center conductor both solid and the stranded version, is wrapped in micro-porous Teflon tape not unlike the stuff used for sealing threaded pipe joints. Following that is a silver/copper ribbon spiral wrapped inner shield, then a thin layer of FEP, then a silver/copper braided shield, then spiral-wrapped stainless-steel armor, then a FEP layer, then the outer jacket with the fancy pattern is some sort of fabric that does not respond very well to my thermal stripper.

To say the least, it is very complex, but I guess that's what makes so sublime for 18-gHz. transmission and especially in my case for audio. It is always said that the devil is in the details.

Here is a current listing on eBay for a 35-foot length at about $5.00/foot. Not a bad price at all compared to some of the "scalpers" out there:

http://www.ebay.com/itm/Gore-Phaseflex- ... SwtnpXkt92


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PostPosted: August 3rd, 2016, 1:20 pm 
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There is some 24-26ga Gore shielded twisted pr on ebay too. 100 ohms impedance, so maybe 50pf/m.

This stuff uses the special Gore Tex ePTFE for insulation on the silver plated conductors.

This is more like 20 cents a foot and on might even find it cheaper...but it won't do 20 gHz!

Not the same thing as Phaseflex at all but looks useful and high grade.

Yes, it is often said that "the devil is in the details"...but, c'mon, the devil is in US!


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PostPosted: August 3rd, 2016, 2:56 pm 
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I've tried it in the past -- it's OK but it edits -- using it for line stage levels it's kind of a dull sound compared to others I've tried over the years. However, using for an interconnect form a cartridge to your phono stage it can be very musical. Still It is not even close to the phase flex.

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PostPosted: August 3rd, 2016, 5:45 pm 
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TubeDriver wrote:
I blasted the spade with a 100w solder gun for a few minutes and finally got a decent join but that turned me off to high priced cable.


:handgestures-thumbdown: Soldering guns are pretty much a useless device. For big stuff a large iron is infinitely superior. Guns have no thermal mass, as soon as you put them on something large the gun gets cold.... I picked up a real monster at a thrift store today, no label to tell how many watts, but it's huge compared to my 80W iron....

Roscoe

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PostPosted: August 3rd, 2016, 6:25 pm 
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Rosco has the right idea. There is more to soldering than just tip temperature. When there is a lot of metal concerned it acts as a heat sink. I have a soldering iron that was my Dad's and it is rated at 250 watts with a lot of mass storage. That iron together with eutectic solder I can solder anything to anything.

Besides temperature you have to understand that Btu's are what count when you have large pieces to solder together. An analogy would be water flow. You can have pressure like 70 pounds gauge, but if you try to put a fire out with a restricted outlet (2-gpm) you won't get anywhere. You need the volume just you need the Btu's.

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