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Lummerland with 2xel84

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Offline Leadman

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Lummerland with 2xel84
« am: 30.04.2020 21:28 »
Has anybody build a TT Lummerland with 2xel84 output tubes? I would like to keep the same cathodyne phase inverter (2x12ax7 and a 2xel84)

I am going to change de power supply section with more nodes for a better filtering but what changes should be done in the phase inverter section to feed the 2xel84? And in the conjuntive filter?

Thank you in advance.

Best regards.

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Offline Leadman

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Re: Lummerland with 2xel84
« Antwort #1 am: 11.07.2020 18:15 »
It seems Lummerland is based on blues express but the phase inverter looks different.

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Offline Dirk

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Re: Lummerland with 2xel84
« Antwort #2 am: 11.07.2020 23:27 »
Hi,

a 18 Watt version with 2 x 6V6 will be available soon.

Best regards, Dirk
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Offline JTM

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Re: Lummerland with 2xel84
« Antwort #3 am: 13.07.2020 14:34 »
Hi,

a 18 Watt version with 2 x 6V6 will be available soon.

Best regards, Dirk

Great news!! :topjob:

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Offline Dirk

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Re: Lummerland with 2xel84
« Antwort #4 am: 13.07.2020 16:02 »
Hier schon mal ein Bild vom Bub
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Offline JTM

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Re: Lummerland with 2xel84
« Antwort #5 am: 13.07.2020 21:25 »
Hier schon mal ein Bild vom Bub

Stark, bin gespannt! Mit NFB?

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Offline Leadman

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Re: Lummerland with 2xel84
« Antwort #6 am: 31.07.2020 16:47 »
2x6v6 Lummerland is here!

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Offline Leadman

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Re: Lummerland with 2xel84
« Antwort #7 am: 18.09.2020 10:43 »
What is the purpose of R14(220k) in the phase inverter of the LummerLand? This resistor don´t exist in the original Blues Express el84 desing.
It´s the first time I see that resistor in a cathodyne phase inverter and I am curious about it.
Maybe it attenuates the signal before de push pull triodes? because the original desing use pentode tubes and not triode....

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Offline iefes

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Re: Lummerland with 2xel84
« Antwort #8 am: 18.09.2020 12:29 »
R14 provides the grid of the cathodyne with a (self-adjusting) bias voltage. Typically the value would be 470k to 1M. Indeed, I would have guessed that the values of R14 and R28 are actually swapped. This would yield a more typical setup but to be honest I'm not very familiar with those small dual-triode push-pull stages and I'm sure Dirk knows his stuff  :topjob:

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Offline Leadman

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Re: Lummerland with 2xel84
« Antwort #9 am: 18.09.2020 20:36 »
Ah! the r28 acts like a grid stopper for prevent blocking distortion in that desing, and maybe de r14 has been lowered to 220k for match with the push pull triode power section.

Thanks!