Home » Audio » Group Build » SE 300B Project, Part 13 - The finished amp
Re: SE 300B Project, Part 13 - The finished amp [message #31942 is a reply to message #31941] Sun, 13 August 2006 16:00 Go to previous messageGo to next message
Damir is currently offline  Damir
Messages: 1005
Registered: May 2009
Illuminati (2nd Degree)

Hi, you can try the (cheap, red colour) LED bias - schematic and wiring details are here. Center of your loctal socket can be a "local" (driver) grounding point, you can solder the minus pole of your last filter cap (from the driver supply) here, too. From that point, one wire to the one and only star (chasis) ground point. R1 and R9 are "stopper" resistors and must be non inductive, HQ (say CC or tantalum), and soldered close to the pins. Two red LEDs are connected in series, their leads must be short, too. Of course, CCS version is showed, for interstage version you must make some minor corrections.
Interestingly, with my speakers I have almost too much those low mids, ha. Deep bass - yesss!
Try this, and please report back...good luck!


Re: SE 300B Project, Part 13 - The finished amp [message #31947 is a reply to message #31942] Wed, 16 August 2006 14:43 Go to previous messageGo to next message
horny is currently offline  horny
Messages: 11
Registered: May 2009
Chancellor
hello Damir
I tryed the led and i like it more then a resistor and 220uf Nichicon Muse capacitor
The thin sound that i write was because the tubes are new
later the sound become fuller and fuller and to full
then the amp was a little to dark the led brings it a little on the back right way the sound get also very very clean i like it but other builder maby find it to clean

i had 3 to 3,2 volt cathode bias with the 280 ohm resistor and 190v on the anode (c3g)
with the red leds i have 3.65 and 210 volt on the anode
have i used the wrong leds?
can i leave it this way or must i chance it?
regards Robert

Re: SE 300B Project, Part 13 - The finished amp [message #31948 is a reply to message #31947] Thu, 17 August 2006 07:45 Go to previous messageGo to next message
Damir is currently offline  Damir
Messages: 1005
Registered: May 2009
Illuminati (2nd Degree)
There`re various red LEDs, and mostly the cheap and simple ones have lower internal resistance (about 4,3 Ohms with 10mA, and U~1,7V - "Valve amplifiers 3" source). This voltage drop depends a little with current through the LED - I suppose that you used CCS with ~11mA, like me? Specs for C3g are Ua=Ug2=220V max., and you are just fine...and probably you used right LEDs, too.
Try to "burn in" your amp a few hours more (a few tens or hundreds h even more desirable:-)) and then decide can you live with this sound like a final version. I`m out of ideas here...you can try various "boutique" cathode resistor(s) bypassed with other types of caps, say 4-5 pcs 22µF MKP in parallel...but for me, red LEDs bias sounds better, and I built the amp (finally) that way - CCS+anode out, g3 on anode, LEDs bias - as I said previously...
Did you try interstage version, too with LEDs bias? (Of course, B1+ must be different, about 200-210V + drop into Rw of ITT).
Of course, please - post us your findings...

Re: SE 300B Project, Part 13 - The finished amp [message #32176 is a reply to message #31912] Wed, 01 August 2007 06:24 Go to previous messageGo to next message
red is currently offline  red
Messages: 2
Registered: May 2009
Esquire
Hi Damir,

I ama also think of building thsi amp as it is VERY well documented and you have obviously spent a great deal of time evaluating the option which really help us folk out here.

I currently have most if not all the parts - althought not exactley the same if you get my drift.

I currently have a version of Thorstens Legacy amp (but using conventional power supply CLC) but have also got some C3G to try out - I have not really gotten on very well with this and I am not sure why? The highs seem a bit grainy and the bass a little bloaty - I am sure it could be the non regulated power supply which I do not feel really confident in putting togther.

Just a quick question before I move to your project - how do you go about determining the value of the grid stopper and do differnt value really have any effect on the sound?

Thank

Red

Re: SE 300B Project, Part 13 - The finished amp [message #32193 is a reply to message #31919] Thu, 01 November 2007 07:12 Go to previous message
duderduderini is currently offline  duderduderini
Messages: 2
Registered: May 2009
Esquire
Hi Damir
I have just discovered this thread and forum. I have stumbled across the concept of driving a 300b with a pentode.
2 questions If I may.
1. Where would i get the 1700 H grid choke? What specs
2. I have the iron for a parallel 300b set ca this driver stage be suitably modified to drive that or do I just use 2 of the 6688 driver stages?
Thanks
Nick

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