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Old 7th January 2004, 09:54 PM   #1
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Default I'm starting 300B amp

Hi!!

I want know what you think about that schematic. If there are some mistakes or if I could do something better please give me advise. And that grid resistor is 1k no 1R, my mistake.


THX
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Old 7th January 2004, 10:18 PM   #2
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Hi Metalmaster,

Your schematic does not show...likely because it is to big in pixels...max is 800*600 and should not be bigger than 100k.

If you like you can send schematic to me and I will change and post it for you..

Regards,
Bas
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Old 7th January 2004, 11:07 PM   #3
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Ok the pic.
Attached Images
File Type: jpg 300b.jpg (74.7 KB, 467 views)
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Old 7th January 2004, 11:40 PM   #4
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Hi,

Quote:
max is 800*600 and should not be bigger than 100k.
Actually I think it's 800*1200 and no larger than 100Kb but more importantly, if you preview your post the image refuses to attach.

Cheers,
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Old 8th January 2004, 01:52 AM   #5
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Hi,

If it we're me I'd drive a 300B with a 2A3, trioded EL34 or similar, or take an entirely different road.

Cheers,

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Old 8th January 2004, 01:55 AM   #6
arnoldc is offline arnoldc  Philippines
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Quote:
Originally posted by fdegrove
Hi,

If it we're me I'd drive a 300B with a 2A3, trioded EL34 or similar, or take an entirely different road.

Cheers,

hi frank, can you point me to an EL34-300B circuit that you would likely build.
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Old 8th January 2004, 02:05 AM   #7
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Hi,

Quote:
hi frank, can you point me to an EL34-300B circuit that you would likely build.
Hmmm...memory tape going bzzzzzzzzzzz and bzzzzzzzzzz...

Can be done though....

Came up with zip...but...I do recall the WE91 mods of La Maison de L'Audiophile...Good sounds...

Good recipe too, a penthode driving a triode...Hold on...Ahhh...Thorsten Loesch, our "dondersteen"...

Bingo:

Thunderstone Loesch..........

Hope that helps,
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Old 8th January 2004, 09:41 AM   #8
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Default Re: I'm starting 300B amp

Konnichiwa,

Quote:
Originally posted by metalmaster
I want know what you think about that schematic. If there are some mistakes or if I could do something better please give me advise. And that grid resistor is 1k no 1R, my mistake.
First, you can likely drop that resistor.

Secondly, your +B supply will have some nasty resonances, you probably want either more capacitance or inductance, damping resistors and you really want to tune this, best done in the first place in P-Spice and then finetuned in the Amp.

Thirdly, your gainstructure is a bit problematic. Your input can step up by no more than 1:4 by which time reflected input capacitance is at a srathospheric > 1nF making a seriously meaty preamp mandatory. The 300B Driver has a Mu of around 3.85 and the IT will not do more than 1:2 sensibly, even that should probably not be used. With around 80V Bias you will have 2V input sensitivity for full Output using a 1:4 input and a 1:2 interstage stepup, both of which will limit bandwidth and 4V input sensitivity for no interstage stepup.

Also, for "sound" reasons, you might wish to use a 10/10Y/VT-25 or similar as driver. People who have tried have liked the 10 or also the WE 205 (Sakuma) as driver for a 300B over many other valves. The circuit can remain as before, except the heaters should be around 6.5 - 7.5V DC @ 1.25A. You get a Mu of around 8 and you can use a lower power Interstage Transformer with likely better bandwidth.

If you are going to use DC Heaters, how about making the symmetrical and filtered via emitter follower "gyrators" or inductors?

Sayonara
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Old 8th January 2004, 02:09 PM   #9
mcs is offline mcs  Denmark
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I'm sure Lundahl will like it

Why do you use such a small cap value after the first choke? I would probably use 50F rather than 10F. And if you use such small cap values (10 or 50F), why not use paper or plastic caps rather than electrolytics?

Best regards,

Mikkel C. Simonsen
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Old 8th January 2004, 06:28 PM   #10
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Resistor and +B will be not a big problem. I can give one more voltage on transformer (7V) becouse thats not big cost and it give some possibility to experimentation and education - that is my first tube amp.

Im not sure what should I do with my gainstructure. That is my bigest problem
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