F5 power amplifier

[Tripmaster]

On Ebay I found matched JFETS for F5. They are all from China vendors. How can you tell if they are the real thing or fakes?

I'm not sure you can. It would make sense to purchase from a reliable source such as Blues. He and others can be found on this forum, and is base in the US I believe

 

[labjr]

I bought mine from Blues. Great matching.

http://www.diyaudio.com/forums/swap-meet/161366-matched-toshiba-fets-sale-33.html


From ebay: probably real but who knows. And how well are they matched ?

 

[andRookie]

I bought mine from Blues. Great matching.

From ebay: probably real but who knows. And how well are they matched ?

I bought these: 4 X MATCHED 2SK170 2SK170BL 2SJ74 2SJ74BL FET! - eBay (item 350330237411 end time Dec-13-10 17:15:16 PST)

and then I had a friend with more el.knowhow help me check them. They were macthed very good in pairs, but for the F5 pair (k170-j74) the match was a not so good.

 

[jwor]

Great news about the new F5 boards. I have a question about the links on this post. When I try to follow them, I end up at a Polish website, I am unable to navigate that site because of language problems. Any place else I could see these photos? Your layouts are so clean that pictures really tell the story. thanks.

 

[anilva]

My F5 clone effort

Hi,

I have posted completed pictures of my F5 clone here:

http://www.diyaudio.com/forums/pass-labs/166784-pictures-your-diy-pass-amplifier-44.html#post2378878

your comments are most appreciated.

Cheers.

 

[Nikon1975]

Is there any advantage to use non inductive resistors for the 10 ohm ? I see that in the tubes amp is always good not to have an inductive element in the cathodes, I don't know much of Jfet, but this looks similar.


Thanks,

Davide

 

[Nikon1975]

As someone suggested me to use R-core transformers, and living in Japan, I asked Kitamura-kiden a quote for 320 VA R-core transformers. they asked 185 $ per unit. But what are the advantages compared to toroidal transformers ?
At the end for me is going to cost the same either to ship toroid from Canada or to have R-core locally.

Thanks,

Davide

 

[EUVL]

R-core has separate primaries and secondaries on separate bobbins wide apart, and thus very little inter-winding capacitance.

http://www.diyaudio.com/forums/powe...formers-poor-choice-amp-psus.html#post1929906

Otherwise they are very similar to toroids.



Patrick

 

[nicoch58]

R-core sound better

 

[AndrewT]

I read (from a few reliable sources) that at least some manufacturers split the primaries and the secondaries so that each bobbin has half of all the windings. Symmetrical wound.
This virtually demands a screen to minimise the primary to secondary HF transmission via the winding capacitance.

 

[tinitus]

I like UI-core trafos

 

[Nikon1975]

In different schematics I found different values for R21 and R22. On one paper I found 10k in another one 22k.

What's the recommended value for these two ?

I am trying R-core. I ordered only one to test it, as locally they ship almost for free.

D.

 

[nar]

Dear Nikon1975,

I am just back from Japan !!! I was in/ near Nagoya

Here in France we get the Selectronic R-Core, which are great value for the money / they have an electrostatic shield to connect to ground - Once done, all good for audio

Best regards,

nAr

 

[labjr]

use 22K.

 

[Russellc]

In different schematics I found different values for R21 and R22. On one paper I found 10k in another one 22k.

What's the recommended value for these two ?

I am trying R-core. I ordered only one to test it, as locally they ship almost for free.

D.

The actual value is 10K. Some have modded to 22K, discussion is in here somewhere! When I was ordering parts kits from Tech-DIY, they included both values.

Russellc

 

[Chad]

Nikon,

I think Papa stated it best.

They measure better with 10K, but sound better with 22K
or higher.

Chad

 

[Franz Gysi]

R-core has separate primaries and secondaries on separate bobbins wide apart, and thus very little inter-winding capacitance.

Are you sure?

I have some R-cores from China. The primaries and secondaries are NOT on separate bobbins on this trannies!

Franz

 

[merlin2069er]

Hi,

I was just looking at the f5 service guide and saw that .0033 mf? capacitor across the ac line power inputs. Is this necessary?

Thanks,
JG

 

[tinitus]

Are you sure?

I have some R-cores from China. The primaries and secondaries are NOT on separate bobbins on this trannies!

Franz

I would expect its like UI core, each secondary have their own primary

I dont know why they called it R core
But I suppose there's an air gap somewhere ?

 

[tinitus]

man it s freezing cold here I need to build my F5