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New 6JT8 build working
http://www.diyaudioprojects.com/Forum/viewtopic.php?f=9&t=3177
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Author:  billyboy [ 03 Jun 2011, 08:34 ]
Post subject:  Re: New 6JT8 build working

Yes, this is true. I wish I had an ST-70 amp left to try this out on. Except for noise figures, 6GH8A is an absolute match for 7199....Check pinouts, though. The ST-70 and, the former Mark III, were my 'amps of choice' back in the day. They were by far , the best amps on the market. Cheap, and great sound.

Author:  Scrounger [ 21 May 2020, 11:37 ]
Post subject:  Re: New 6JT8 build working

ferronier wrote:
It was made as a TV tube. It contains a hi-mu triode and sharp cuttoff pentode so it's ideal for audio use as a one tube amp (like the 6T9, but in a 9pin package). Here's my working schematic.
I have tested it with 6JT8, 6KT8 and 6LY8 tubes. You will get different results depending on brand too, I've tried RCA, Sylvania, GE, Magnavox and Westinghouse. All resistors 1/2W unless noted. Input resistor 4.7K works for CD input, leave out for ipod input. There is room to experiment on this resistor according to your input source...also the .0033 cap from input to ground is optional; I use it on one channel. I found the circuit to be unstable if both channels are identical. After reading a lot about this I found stability by adding the cap on one side. Note this is setup for 100K pot, if you change that you will have to modify input section; it's pretty sensitive.
B+ can be from 200-250v, I shoot for something in the middle; each tube type and brand will pull a different voltage and current but the three I mentioned all work in this circuit.

Shouldn't the .0082 cap be tied to ground and not the plate of the input stage?

Author:  Scrounger [ 21 May 2020, 11:41 ]
Post subject:  Re: New 6JT8 build working

ferronier wrote:
It was made as a TV tube. It contains a hi-mu triode and sharp cuttoff pentode so it's ideal for audio use as a one tube amp (like the 6T9, but in a 9pin package). Here's my working schematic.
I have tested it with 6JT8, 6KT8 and 6LY8 tubes. You will get different results depending on brand too, I've tried RCA, Sylvania, GE, Magnavox and Westinghouse. All resistors 1/2W unless noted. Input resistor 4.7K works for CD input, leave out for ipod input. There is room to experiment on this resistor according to your input source...also the .0033 cap from input to ground is optional; I use it on one channel. I found the circuit to be unstable if both channels are identical. After reading a lot about this I found stability by adding the cap on one side. Note this is setup for 100K pot, if you change that you will have to modify input section; it's pretty sensitive.
B+ can be from 200-250v, I shoot for something in the middle; each tube type and brand will pull a different voltage and current but the three I mentioned all work in this circuit.

Also what about the plate on the output section?

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