Toroid OPTs

Fuling · 14th December 2002, 01:35 PM

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 I´d like to build something cheap and simple with them.

fdegrove · 14th December 2002, 01:49 PM

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.

Ciao,

Fuling · 14th December 2002, 02:10 PM

I´m 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 haven´t deicided what plate load to use yet. I´m thinking either DIY plate chokes (alot of work) , CCS (Sand in my amp...

or SRPP.

fdegrove · 14th December 2002, 02:31 PM

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,

SY · 14th December 2002, 02:50 PM

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.

fdegrove · 14th December 2002, 03:23 PM

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,

Fuling · 14th December 2002, 03:33 PM

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 I´m going for a little cartrip to pick up four 12B4A for another project.
...Or maybe they would work great as driverstage for the 6AS7s?

phil · 14th December 2002, 03:37 PM

Have a look at the "Cheapskates line amp" here
http://home.t-online.de/home/MHuber/
Phil.

fdegrove · 14th December 2002, 03:37 PM

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,

Fuling · 14th December 2002, 03:52 PM

Thanks for the link, Phil.
Thats very interesting.

And yes, I guess the gain would be a bit low when I think about it...

I´ll save those 12B4A for a small poweramp instead, which was my original intent

14th December 2002, 01:35 PM	#1
Fuling diyAudio Member Join Date: Aug 2001 Location: Sweden (Mora)	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 I´d like to build something cheap and simple with them.

14th December 2002, 01:49 PM	#2
fdegrove diyAudio Senior Member Join Date: Aug 2002 Location: Belgium	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. Ciao, __________________ Frank

14th December 2002, 02:31 PM	#4
fdegrove diyAudio Senior Member Join Date: Aug 2002 Location: Belgium	TOROIDS 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, __________________ Frank

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14th December 2002, 02:10 PM	#3
Fuling diyAudio Member Join Date: Aug 2001 Location: Sweden (Mora)	I´m 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 haven´t deicided what plate load to use yet. I´m thinking either DIY plate chokes (alot of work) , CCS (Sand in my amp... or SRPP.

14th December 2002, 02:50 PM	#5
SY diyAudio Moderator Join Date: Oct 2002 Location: Chicagoland Blog Entries: 1	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.

14th December 2002, 03:33 PM	#7
Fuling diyAudio Member Join Date: Aug 2001 Location: Sweden (Mora)	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 I´m going for a little cartrip to pick up four 12B4A for another project. ...Or maybe they would work great as driverstage for the 6AS7s?

14th December 2002, 03:37 PM	#8
phil diyAudio Member Join Date: May 2001	Have a look at the "Cheapskates line amp" here http://home.t-online.de/home/MHuber/ Phil.

14th December 2002, 03:52 PM	#10
Fuling diyAudio Member Join Date: Aug 2001 Location: Sweden (Mora)	Thanks for the link, Phil. Thats very interesting. And yes, I guess the gain would be a bit low when I think about it... I´ll save those 12B4A for a small poweramp instead, which was my original intent

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