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Old 14th December 2002, 01:35 PM   #1
Fuling is offline Fuling  Sweden
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Default Toroid OPTs

Good afternoon!

Has anyone tried toroid transformers as OPTs in a parafeed circuit?

I ask because I got a package today containing four 6AS7Gs and Id like to build something cheap and simple with them.
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Old 14th December 2002, 01:49 PM   #2
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Default TOROIDS

Hi,

Although I have not tried it myself,I don't see any thechnical grounds why this should not work very satisfactorily.

The 6080/6AS7G is one of my pet output tubes and since it has a low Ri of only 280R/plate any half decent OPT should give good results.

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Old 14th December 2002, 02:10 PM   #3
Fuling is offline Fuling  Sweden
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Im most nervous about the frequency response.

The primary inductance should be quite high due to the parafeed circuit (no DC through the transformer) but I dont know anything about the interwinding capacitances, resonace freqs etc.

I havent deicided what plate load to use yet. Im thinking either DIY plate chokes (alot of work) , CCS (Sand in my amp... or SRPP.
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Old 14th December 2002, 02:31 PM   #4
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Hi,

In case you would choose an SRPP topology,an OPT such as the Hammond 119 DA should do fine.
Poweroutput would be 3.6W before clipping.
If you base your toroid around similar specs it would perform more then adequately.

Are you planning to use an existing power xformer (toroid) and use that as an OPT?

Ciao,
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Old 14th December 2002, 02:50 PM   #5
SY is offline SY  United States
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I'm not familiar with the term "parafeed." From context, it sounds like it might be synonymous with Circlotron...?

In any case, the thing to watch for in 6080/6AS7 based circuits is drift of idle current. What won't bother an EI stack can cause some grief with toroids. Idle current stabilization schemes (e.g., servos) and/or low value grid leak resistors can help a great deal.
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Old 14th December 2002, 03:23 PM   #6
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Default PARAFEED

Hi Sy,

Quote:
I'm not familiar with the term "parafeed."
If you like you can read about "parafeed" here:

Can someone explain parafeed & direct coupled & a.c. coupled?

Quote:
What won't bother an EI stack can cause some grief with toroids.
Since one does not have DC on the OPT it should be a problem.

Ciao,
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Old 14th December 2002, 03:33 PM   #7
Fuling is offline Fuling  Sweden
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Hi guys!

Thanx for the quick replys!

That Hammond 119DA seems like a really nice little transfomer, maybe I should try to get a pair of those instead of paying the same money for power toroids.

Now I feel encouraged to start up this project ASAP, right now Im going for a little cartrip to pick up four 12B4A for another project.
...Or maybe they would work great as driverstage for the 6AS7s?

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Old 14th December 2002, 03:37 PM   #8
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Have a look at the "Cheapskates line amp" here
http://home.t-online.de/home/MHuber/
Phil.
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Old 14th December 2002, 03:37 PM   #9
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Default GAIN.

Hi,


Quote:
...Or maybe they would work great as driverstage for the 6AS7s?
You could use the 12B4A for that if you can live with the fact that the amp would hardly have any gain.

Cheers,
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Old 14th December 2002, 03:52 PM   #10
Fuling is offline Fuling  Sweden
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Thanks for the link, Phil.
Thats very interesting.

And yes, I guess the gain would be a bit low when I think about it...
Ill save those 12B4A for a small poweramp instead, which was my original intent
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