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Old 13th August 2012, 09:41 PM   #1
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Default Recommended 300B SE Amplifier Designs

Hello
Can someone be so kind to send me some 300B schematics please...
I do not want to spend on tubes until I do not have a proven great sounding schematic.
Al do I have the amplifier enclosure, OP transformer, power transformer choke, PS capacitors etc.
Please help me if you can.
Thank you so much!
Greetings Gabor
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Old 13th August 2012, 11:36 PM   #2
kevinkr is offline kevinkr  United States
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Gabor, I moved your post to a new thread as I thought you deserved a shot at getting your question answered. The original thread you posted to has a very poor SNR..
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Old 13th August 2012, 11:41 PM   #3
kevinkr is offline kevinkr  United States
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How about an IT coupled design using the D3A as the driver tube? (Triode connected)

I'd recommend a Lundahl LL1635 for the IT, and an Electra-Print output transformer.. (3.5K:8 110mA/30W)
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Old 14th August 2012, 02:52 AM   #4
tcqanh is offline tcqanh  Viet Nam
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Originally Posted by kevinkr View Post
How about an IT coupled design using the D3A as the driver tube? (Triode connected)
C3g in triode - 300B is on my plan.

some experimentals may be plate choke or IT. I did 1 pair choke of 130H 15mA and hope them are suitable for C3g.

I have IT 5k:5k, but it seems to be a little bit small impedance for C3g.
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Old 14th August 2012, 03:11 AM   #5
kevinkr is offline kevinkr  United States
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I suspect 5K:5K will work ok with the C3G which has only slightly higher rp than the D3A when triode connected, depends on the primary inductance and your target LF -3dB roll off frequency. (-1dB is 2X this)

130H chokes should work well with the C3G, hopefully the inter-winding and capacitance to core is reasonable .. I seem to have trouble getting beyond 60kHz in most choke coupled circuits.

This is going to sound odd, but the filament in the C3G seems to be quite fragile, a number of people have reported loosing hot tubes to minor shocks (like removal) so you might want to keep that in mind while debugging your design.
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Old 14th August 2012, 03:20 AM   #6
tcqanh is offline tcqanh  Viet Nam
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Originally Posted by kevinkr View Post
I suspect 5K:5K will work ok with the C3G which has only slightly higher rp than the D3A when triode connected, depends on the primary inductance and your target LF -3dB roll off frequency. (-1dB is 2X this)
my IT has nearly 20H on manual LCR meter at scale of 120Hz and max current is about 40mA. I think it is enough

Quote:
This is going to sound odd, but the filament in the C3G seems to be quite fragile, a number of people have reported loosing hot tubes to minor shocks (like removal) so you might want to keep that in mind while debugging your design.
Could you say more clearly ?
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Old 14th August 2012, 03:26 AM   #7
kevinkr is offline kevinkr  United States
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Yes, the filaments can apparently break easily when hot if the tube is moved for any reason. Not sure why, have been told this by a number of members here, and by a friend who belongs to the same diy club as I do.
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Old 14th August 2012, 03:38 AM   #8
tcqanh is offline tcqanh  Viet Nam
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Originally Posted by kevinkr View Post
Yes, the filaments can apparently break easily when hot if the tube is moved for any reason.
wow, maybe over heater Voltage is the cause ? . I will be cautious. Tks.

I think those German post tube are type of vibration resistance, also like Ba, Bh, Be tube ...
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Old 14th August 2012, 09:01 AM   #9
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C3g in triode - 300B is on my plan.
Best sounding in pentode mode (on my plan) : 12GN7, 12HG7, EL802, EL183E
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Old 14th August 2012, 10:37 AM   #10
tcqanh is offline tcqanh  Viet Nam
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Originally Posted by PhilippeS View Post
Best sounding in pentode mode (on my plan) : 12GN7, 12HG7, EL802, EL183E
why do you use 10uf Cap connected K to B+ of 300B ?
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