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B1 with Korg Triode
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Old 24th May 2020, 05:02 PM   #4891
ClaudeG is online now ClaudeG
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The output being in the 200R region depending on your output transistors, and this preamp having IMHO an optimal operational range below 2V, I would say there shouldn't be any problem driving such a load (although unusaly low for a power amp)

As a side note, I also drive directly my 600R speaker, through a 100R resistor, so make that 700R load, without any problem and at circa 1V level...

I hope this helps

Claude
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Old 24th May 2020, 05:49 PM   #4892
Nelson Pass is offline Nelson Pass  United States
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B1 with Korg Triode
The distortion does go up with lower impedances, as if you would notice.

I can see the difference at about 5K.
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Old Yesterday, 05:15 PM   #4893
Bjerrolini is offline Bjerrolini
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I assembled the preamp and fired it up. Right side tube seems ok, nice glow. Left side only half the grid glows, I have to turn the potmeter significantly further clock-vice to get the voltage at T7 down to 9.5V. When T7 and T8 both are at 9.5V, the voltage at G1 is 2.66V and G2 is 2.29V.

Double checked everything on the pcb, seems ok. Desoldered the nutube from the board and hooked it up with wires, left to right and right to left. Glow/voltage issue remained on the left side of the tube. Seems to indicate an issue with the nutube?

Btw, itís also super microphonic. Dont know If it relates to the same issue.

Some advice on this would be much appreciated.
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Old Yesterday, 06:39 PM   #4894
ghitus is offline ghitus  Italy
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Quote:
Originally Posted by Bjerrolini View Post
I assembled the preamp and fired it up. Right side tube seems ok, nice glow. Left side only half the grid glows, I have to turn the potmeter significantly further clock-vice to get the voltage at T7 down to 9.5V. When T7 and T8 both are at 9.5V, the voltage at G1 is 2.66V and G2 is 2.29V.

Double checked everything on the pcb, seems ok. Desoldered the nutube from the board and hooked it up with wires, left to right and right to left. Glow/voltage issue remained on the left side of the tube. Seems to indicate an issue with the nutube?

Btw, itís also super microphonic. Dont know If it relates to the same issue.

Some advice on this would be much appreciated.

I had this apparent issue, too. On one channel the grid did not completely glow and I had to set the trimmers on different positions, but other than this, I had no problem. Beautiful sound! Put a couple of stacked pencil erazers on the nutube and you will almost completely get rid of the ringing. The try to seal every hole on the chassis with adhesive tape. It will help, too. Some posts ago another user showed some isolating rubber spacers to secure the circuit to the baseplate of the chassis, instead of metal ones. I've bought them, but I've still to try. You could do the same!
Best,
Gaetano
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Old Yesterday, 09:17 PM   #4895
Bjerrolini is offline Bjerrolini
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Originally Posted by ghitus View Post
I had this apparent issue, too. On one channel the grid did not completely glow and I had to set the trimmers on different positions, but other than this, I had no problem. Beautiful sound!
I read in the article that the plate voltage measured at T7, T8 sets the distortion level, just figured the higher voltage drop over G1 -> T7 surely would affect the distortion as well. Guess I'll have to box it up and give it a proper go. Thanks for the advice regarding ringing, I have drone gyro dampers that i think will work beautifully for this.
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