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Old 19th July 2006, 11:25 AM   #11
Giaime is offline Giaime  Italy
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That's even better than my idea
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Old 19th July 2006, 11:39 AM   #12
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hehe...glad you like it!
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Old 19th July 2006, 11:41 AM   #13
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Hi Gianluca, What's "choked SRPP" do you have a schema?

Cheers,
Pete
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Old 19th July 2006, 12:04 PM   #14
lndm is offline lndm  Australia
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Perhaps the current should be increased. Running the 46 up seems the first logical step. Adding the extra CF cathode resistor to ground seems to be more than just an extra current path, it appears to somehow make the current more constant. One circuit I have seen has a ccs here instead of the resistors.

The higher current is going to mean a smaller upper Rk. I am concerned this will decrease the signal to the pentode. I have a 90H choke that I made from two small power xfmr's that has a good FR. I fear it will saturate. Is there a way to tell while trying it?

Geek,
DC screen driving sounds like a great idea. I'm set up for triode now and it may need higher rails so I feel I'm more than one step away from it. Maybe if I manage to learn to use the mu stage well, I'll head that way

I have a copy of Morgan Jones' book on order right now so I guess anything's possible.
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Old 19th July 2006, 12:51 PM   #15
Gluca is offline Gluca  Italy
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Pete, here is a link to an italian forum where my project is being documented. Still on the breadboard and still to be tweaked. Unfortunately you'll see only an old version of the schematic

looking at the schematics, note that

-the output is taken from the 801A's anode
-there is no coupling cap between 801A and 807
-the 807 is biased by the choke DCR + that 820 resistor

The 807 is now triode strapped (get rid of that 47kR and connect the screen to the anode via the 100R and forget the 100uF screen bypass cap). The 807/801 are now wired as SRPP but the choke (and the 820R) are biassing and loading the tubes. Thats what I called choke assisted SRPP

http://www.audiofaidate.it/forum/top...24&whichpage=1

Do I like that mu-stage? Yes I liked it. I am considering to use a different driver (eimac 100TH) and IXYS chips to make the whole thing simpler.

I hope it can help.

Ciao
Gianluca
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Old 19th July 2006, 11:01 PM   #16
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Hi Gianluca,

Nice! That looks *very* similar to the "choke assisted mu-stage" published in VTV. I feel it's a very elegant circuit, which removes one of my bugbears with the conventional mu-stage - the coupling cap. (I hate capacitors ;-) ), and provides a very high impedance load ot the lower tube.

So you're saying you're running basically the same circuit, but the 807 is triode strapped? What made you change from pentode operation?


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Pete
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Old 19th July 2006, 11:48 PM   #17
Gluca is offline Gluca  Italy
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I just wanted to try it (LOL). The basic idea was to load the 801A with the highest load ... a ccs possibly. But now I really want to get rid of the iron+heater for the sake of simplicity.

Speaking of "sound quality" ... well if you go for a pentode load take the signal out of the lower plate (I liked it more) ... triode mode ... not such a big difference (cathode/plate).

OH! As Indm was suggesting, an higher mu pentode would work even better than the 807 (mu=8). 807 was just cheap, sturdy and reliable.

OH! If you elect to use the choke ... you need to pay attention to its DCR before buying it as it will bias your tubes.

Ciao
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Old 21st July 2006, 12:18 PM   #18
fred76 is offline fred76  Philippines
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Quote:
Speaking of "sound quality" ... well if you go for a pentode load take the signal out of the lower plate (I liked it more) ... triode mode ... not such a big difference (cathode/plate).
Hi Gluca,

That's a neat schema. For for a mu follower variant or srpp, Paul Joppa also likes it better when the signal is taken from the lower plate. He also cited that a choke at the upper cathode has its advantages too (he listened to this type of set up).

Maybe the new srpp version of the Seth PP (2A3 and 300B) amp could be modified in this way too for the 6H30pi or other good driver tubes with the same heater voltages.

regards,
fred
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Old 21st July 2006, 01:22 PM   #19
Gluca is offline Gluca  Italy
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OH! I made it with a 6H30 + EF184 ... lovely! And I used also the EXO173 to drive the 2A3s. I didnt use a choke ... but it sounded really great ... I could not find any choke with a suitable H/RDC combination. Probably using other penthodes with higher bias (the EF184 was at 2V or so).

Now that amp is dismantled and parts recycled ... but I do miss it.
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Old 22nd September 2006, 03:57 PM   #20
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Hi guys,

Did one of you ever looked on www.triodedick.com?
There are a lot of mu-stage designs availlable, some also with an english project desciption.
The designs use a variation of tubes for V1 in pre-amp and power amp setup.

regrads.
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