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Old 29th October 2009, 04:29 PM   #81
CFT is online now CFT  United States
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Location: Hong Kong
Having this thought here....

What about using a cascode ccs right after B+, then a single ccs to the plate, but instead of connecting the plate to the coupling cap, get the output at the source of the FET (the mu follower), that way, the output z will be small enough that there is no need for an output transformer (?) (see, I am trying to avoid one here)

And by this way it preserves the isolation of the output signal path from the power supply path, and it becomes an SRPP amp but with nice PSRR?

Any comment?
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Old 1st November 2009, 12:08 AM   #82
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I've been juggling around with glow tubes and voltages, and the nearest I've come is the following:
HT = 360v
Glow tubes - 150+105 = 260v
IXYS sense resistor = 485 ohms
Plate voltage = 168v
Cathode resistor = 1.91k
Cathode voltage = 10.6
Current = 5.6mA

No doubt it could be tweaked to get 6mA out of it, but it took me a while to arrive at all this!

andy
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Old 1st November 2009, 04:49 PM   #83
CFT is online now CFT  United States
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OK, I see, GP has done it:
http://home.comcast.net/~pimm1028/we..._linestage.gif

Can someone point out any pros and cons on the mu follower in this case? : )

Or anyone has put together this circuit or similar using IXYS? (Can I replace the VR tubes with a resistor and a bypass cap ?)
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Old 3rd November 2009, 05:44 AM   #84
fingerx is offline fingerx  Hong Kong
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Default I am Alvin.

Hi all, here is my 27 not 26

this is my olderly project when I was crazy for tube

Umm...Parafeed config(cascode DN2540) with tamradio(tamura) 10K : 600 & 1.33uf*2, LED cathode for biasing.

power : 270V*2, 80 retifier, LCRCRCRC, and about 25V inject to the filament to elminate AC filament noise.

Good sounding, still love it much

Cheers.

Last edited by fingerx; 3rd November 2009 at 06:10 AM.
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Old 3rd November 2009, 05:47 AM   #85
fingerx is offline fingerx  Hong Kong
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Oh, pic..
Attached Images
File Type: jpg IMG_9879.JPG (35.2 KB, 1435 views)
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Old 3rd November 2009, 06:02 AM   #86
fingerx is offline fingerx  Hong Kong
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Quote:
Originally Posted by CFT View Post

Can someone point out any pros and cons on the mu follower in this case? : )

Or anyone has put together this circuit or similar using IXYS? (Can I replace the VR tubes with a resistor and a bypass cap ?)
Hi CFT, just go for it, BBCCCSS quiet a good idea, invite me to have a look when you are finished
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Old 3rd November 2009, 06:40 AM   #87
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Quote:
Originally Posted by fingerx View Post
Hi all, here is my 27 not 26

this is my olderly project when I was crazy for tube

Umm...Parafeed config(cascode DN2540) with tamradio(tamura) 10K : 600 & 1.33uf*2, LED cathode for biasing.

power : 270V*2, 80 retifier, LCRCRCRC, and about 25V inject to the filament to elminate AC filament noise.

Good sounding, still love it much

Cheers.
Very nice! Did you ever try battery grid bias? (I suppose 9V would work fine.)
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Thanx!
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Old 3rd November 2009, 08:10 AM   #88
fingerx is offline fingerx  Hong Kong
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Quote:
Originally Posted by bequerel View Post
Very nice! Did you ever try battery grid bias? (I suppose 9V would work fine.)
yes for sure, both sound good, battery grid bias, cathode direct to ground, even less hum noise compare with self-biasing.
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Old 3rd November 2009, 08:50 AM   #89
CFT is online now CFT  United States
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Nice 27 fingerx!

A tube veteran indeed!

Your Symmetry DCB1 on the Pass thread is something I will long for next, say perhaps as a buffer to the RC coupled 26 version. (Together with Lightspeed too, you bet

Yes, I am getting a pair of 20k:600 this week for the transformer loaded settings.

Will order some IXYSs too for putting together that Gary Pimms-like circuit as well. That could be a flexible platform to also play around with 01A and PTT2s, PTTx, etc.... at the mu follower or high Z outputs....

Many options to have fun
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Old 3rd November 2009, 11:40 PM   #90
Richard is offline Richard  Australia
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Hi Guys,

Iíve been following this thread with great interest for a while as Iím building my 26 preamp. I have the separate power supply built and just have to wire up the preamp this weekend.

Power supply is 285CT Ė AZ1 Ė CLC split into right and left, then LC Ė VR tube regulation. VR tubes are 190V (0C3 and 0B3).

For the preamp Iím initially using 2 Hammond 150H chokes in series as plate load, with cathode bias, but have some Hashimoto 20k:600 transformers to try.

I would like some advice regarding grounding, I have followed Kevinís suggestions in his 26 article, using star grounding in the power supply chassis, but Iím not so sure about the preamp chassis.

I have the VR tubes in the preamp chassis and all CLCLC parts in the psu chassis. Should I:
a) join all grounds, (RCA in/out, cathode R & bypass cap and VR tubes to a common star ground an then return this to the psu star ground? Or
b) separately return i)VR tube grounds and ii) RCA in/out, cathode R & bypass cap grounds to the psu chassis star groung?

Any advice would be appreciated

Cheers,

Rich
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