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 NEW  Matt presents bias and operation data for the 6V6 tube in SE operation - 6V6 Single-Ended (SE) Ultra Linear (UL) Bias Optimization.

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 Post subject: Re: KT120 Oddblocks
PostPosted: 09 Oct 2018, 07:48 
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Joined: 07 Mar 2017, 03:14
Posts: 92
When you say poly cap, what do you imply? Polypropylene or polyester?


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 Post subject: Re: KT120 Oddblocks
PostPosted: 09 Oct 2018, 09:50 
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Joined: 02 Mar 2009, 12:41
Posts: 1069
Location: Vänersborg, Sweden
For "surge and spike killers" use polyprop as they are self healing.

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 Post subject: Re: KT120 Oddblocks
PostPosted: 09 Oct 2018, 15:02 
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Joined: 07 Mar 2017, 03:14
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As much as I read polyester caps are also self healing.
https://ec.kemet.com/self-healing-capacitors-fix


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 Post subject: Re: KT120 Oddblocks
PostPosted: 27 Oct 2018, 08:14 
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For KT120 heaters which pin should be + and which pin should be -?

What about 12SL7gt heaters


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 Post subject: Re: KT120 Oddblocks
PostPosted: 27 Oct 2018, 08:55 
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Joined: 04 Jun 2008, 20:59
Posts: 3854
Location: Arizona, USA
Hi, Even with all the test gear I have here and my ears, I have not found a significant difference in which ones are + and -. It may (kind of iffy though) make a difference in the phono preamps. In that case it does seem to influence which side an extra capacitor (roughly 47-50uf) to signal ground is attached. Sometimes neither, other times one side or the other. I get really mixed results in this. For those of you unfamiliar with what I am talking about....in the heater circuit for the phono preamp it is 6 VDC regulated. There is no center tap (similar but at 12 VDC for the power amps). Thus whether the +6 is attached to the tube heater centers (pin 9) or that pin gets the negative may have a very slight influence on the S/N. Since the heaters are raised by about 1/3 the B+ voltage to protect them from H-C over voltages there is no low impedance connection between them and the signal ground. About 1/2 to 2/3 of the time I find that putting a 47-50uf electrolytic capacitor between one side or the other to the signal ground will yield about 1-2 db improvement in the "hiss" level. It is already quite low, but being the fanatical hater of hum and noise I can never get stuff too quiet. I want to hear the music not the noise. Back to the power amps....there is no reason not to try this fix on them as well I just find that mine don't make any noise. With nothing attached to the inputs you need to stick you ear on the speaker grill to hear anything.

BTW, since in all the equipment that can use them, I use spiral heater tubes and this may matter in this case. Standard heater designs might behave differently. If anyone has insight on this please let us know. None of the tubes in the power amps using KTXXX and 12SL7 are spiral heater designs that I know of.

Good listening
Bruce

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 Post subject: Re: KT120 Oddblocks
PostPosted: 27 Oct 2018, 09:32 
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Be 100K resistor better close to rca input or close to 12sl7 tube?


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 Post subject: Re: KT120 Oddblocks
PostPosted: 27 Oct 2018, 17:09 
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Joined: 04 Jun 2008, 20:59
Posts: 3854
Location: Arizona, USA
Hi, the 100K resistor is a relatively small grid to ground resistance for a triode. It can go either way, at the tube or at the input. I usually have mine at the tube for convenience and ease of hooking up the shielded cable from the input jacks.

Good listening
Bruce

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 Post subject: Re: KT120 Oddblocks
PostPosted: 28 Oct 2018, 05:07 
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Thank you, Bruce


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 Post subject: Re: KT120 Oddblocks
PostPosted: 29 Oct 2018, 03:18 
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How do you mount LM317HVs onto heatsink? Some part of the heatsink will be outside of the chassis. It might be dangerous if I screw them naked. What should I use for isolation?


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 Post subject: Re: KT120 Oddblocks
PostPosted: 29 Oct 2018, 03:54 
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Joined: 02 Mar 2009, 12:41
Posts: 1069
Location: Vänersborg, Sweden
There are special insulation for power semiconductors. There are often made by silicon or (older) mica.

Looking something like this:

Image

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