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Old 18th March 2013, 11:41 AM   #11
MartinR is offline MartinR  Germany
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Hello Alberto,

you should also consider the usage of a anode stopper (22-47R) with such long leads to the anode resistor and coupling cap. Also the usage of ferrite beads on g1, g2, anode and cathode is highly recommeded with a tube like the D3a. To make things even better you can connect a 1nF ceramic cap from the each heater pin to the chassis.

Best regards,
Martin
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Old 18th March 2013, 12:38 PM   #12
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Hi Alberto!

great that you can move ahead now. I would really consider the recommendations given by the other members, like the precautions against oscillation and reducing the heater voltage on the D3a.

saludos Brasileños de Moçambique! Erik
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Old 18th March 2013, 03:41 PM   #13
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Ceramic resistors in cathode of 300B is not good idea. You can try to change to Mills resistors- 12 W and sound will be really great. Mills resistors page
Better You can use shunt el. caps Black Gate , Elna,
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Old 19th March 2013, 10:22 AM   #14
MartinR is offline MartinR  Germany
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Hello,

Quote:
Originally Posted by azazello View Post
Ceramic resistors in cathode of 300B is not good idea.
Of course, you shouldn´t use them if the heaters between 300B and D3a are shared. Only if the D3a has its own heater.

By the way, the best way to get a solid rock operating point of the D3a is to follow the datasheet by using a positive grid voltage (about 10V) and a higher value cathode resistor. But this requires a coupling cap between input and grid.

Best regards,
Martin

Last edited by MartinR; 19th March 2013 at 10:24 AM.
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