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 Post subject: Re: KT120 Oddblocks
PostPosted: 17 Sep 2018, 06:03 
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Joined: 07 Mar 2017, 03:14
Posts: 75
Thank you, Bruce.

Jantzen cross caps and Audyn Q4 look like 400VDC rating. Any problem with them? The circuit scheme shows it should be used 500V rating caps. I'm asking because I also use 450V rating electrolytic caps as bypass in the main power supply. Do I face problems in the long run? Should I change them with higher voltage rating caps?

My bests,
Ozan

gofar99 wrote:
Hi, They should be fine. Since it is only a precaution to eliminate noise in the circuit I use low voltage polys from any good brand. Vishay, Kemit, Panasonic, really probably nearly any would do. 25 volt rating or more. In the main power supply the bypass ones should be good quality and any of those brands, and my preference is audio grade Jantzen (cross caps) , Audyn Q4 or Solen. In that application they can make a difference.

Good listening
Bruce


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 Post subject: Re: KT120 Oddblocks
PostPosted: 17 Sep 2018, 09:38 
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Joined: 04 Jun 2008, 20:59
Posts: 3814
Location: Arizona, USA
Hi, Across the filter cap you need 500 volt polys or higher. The working voltage there (depending on your AC mains voltage) can be anywhere from 425 to 475 volts. 400 volt caps might hold that, but for the few cents cheaper they are I would not even consider them. Panasonic, Vishay, Kemit, and lots of others are not costly.

Good listening
Bruce

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 Post subject: Re: KT120 Oddblocks
PostPosted: 17 Sep 2018, 15:45 
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Posts: 171
markos58M wrote:
Hi,i'm planning to do two KT120 monoblock,i have a question,is Edcore XPWR264 right for this project? has only 2A at 10.9 so two KT120 running in series at 12v aren't rated to 1.9A + 1.9A?i need 4A 12V to run two Kt120 or i'm wrong? Any of you is buiding with some modding KT120 stereo with integrated ecc802 SRPP tube preamp? can XPWR264 run at 12V two KT120 and two preamp tube?

My best
Marco


Hi, I'm just bumping the above post because it fell behind in the moderation queue and got buried in the previous page of the thread when approved. Marco, your account is verified now.

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 Post subject: Re: KT120 Oddblocks
PostPosted: 17 Sep 2018, 16:13 
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Location: Arizona, USA
Hi, It is fine. You need 1.9 amps at 6 volts for each tube so in series (not parallel) you will need 1.9 amps at 12 volts. BTW I believe the question was also sent to Edcor and I confirmed that the order was correct. The preamp tubes do not need a lot of heater power and will work fine at the same time. Typically Edcor transformers are listed well below what they can handle. Other brands may not be. The demands on the heater circuit (in this case a little over 24 watts) are largely insignificant compared to the B+ demands. I like to be sure the total heater and B+ demands are below the ratings by a comfortable margin. It helps to insure long life in the gear.

Good listening
Bruce

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 Post subject: Re: KT120 Oddblocks
PostPosted: 18 Sep 2018, 00:38 
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Joined: 07 Mar 2017, 03:14
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Voltage rating of electrolytic caps I used is 450 volts. I don't believe I'll face a problem in the short run. But, using them on the limit or just over the limit will wear them down in upcoming years. Maybe 3-4 years later they will break down and I'll have to fix.

gofar99 wrote:
Hi, Across the filter cap you need 500 volt polys or higher. The working voltage there (depending on your AC mains voltage) can be anywhere from 425 to 475 volts. 400 volt caps might hold that, but for the few cents cheaper they are I would not even consider them. Panasonic, Vishay, Kemit, and lots of others are not costly.

Good listening
Bruce


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 Post subject: Re: KT120 Oddblocks
PostPosted: 23 Sep 2018, 14:40 
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Joined: 23 Sep 2018, 11:43
Posts: 2
Hi,

I'm considering a oddblock kt120 with a revised, common power supply for both channels on a separate chassis.

I have a 400-0-400 600mA transformer that i would like to use for both channels.

To drop the voltage to acceptable levels a 100ish ohm 50w resistor will be used after rectification. The rest of the power supply for the B+ will be the same.

I have a few VR tubes that i've been itching to use but could not find a good project. To supply the SRPP I'm considering a supply similar to this(link) but with the VR tubes in place of the zener diodes of course.

To the questions:
For a common B+ supply how much should I increase the electrolytics?

As you can see in the link above the VR tubes were replaced with zener because they were too noisy, will this be audible?

Since the regulated supply will feed both SRPP channels should I separate the channels with RC filters after the 6AS7?

I appreciate any feedback and tips!


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 Post subject: Re: KT120 Oddblocks
PostPosted: 23 Sep 2018, 20:41 
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Location: Arizona, USA
Hi, Nothing wrong with a common supply, just put wheels on the chassis..it will be heavy. 100 ohms will drop the B+ about 40-50 volts. I estimate you need to drop about 80. I would probably split it into two resistors. Maybe a 150 and a 50. One (the 150) before the filters and the other between them. That way the second filters would not need 600 volt ratings and maybe not the first one either if you have a delay B+ start up. If not then the B+ can get to around 560. When you get over 500 things can get costly. The thing to watch is the maximum dissipation of the tubes and the voltage and dissipation of the LM317s. The tubes can handle the higher voltage easily as long as you watch the current level, but to maintain a safe current level the LM317s will automatically increase the drop across them. The HV versions are rated at 57 volts but really you need to keep it below 45 to allow for the AC voltage across them. Yes the peaks are well over the 57, but it turns out that doesn't matter greatly. Don't ask, because I don't know why they can do that...they just do. I have put as much as 60 volt peaks on some test samples that already had 40 VDC on them and they were not bothered by it. They are apparently better than rated. But putting 70 VDC kills them every time. Most curious.

For the filters...Larger might not be needed, but it certainly would not hurt. If it were mine I would go to 200uf as a precaution. It is a class A design and the current demand is constant. I would be sure to put a larger poly at the connection to the output trannies as it forms a low impedance path return for audio. A 20uf poly or pair of 10s would be my choice.

My experience with VR tubes has been they add noise. YMMV. LR8s are not costly and the K4 ones are fairly healthy. You are only using about 0.7 ma per driver stage so they are easily able to take that. The ones in the commercial amps have a drop across them varying from 125 to 175 volts. No sweat. I would use separate ones for each channel though.

Be sure to heat sink the LM317s and with insulators and heat sink compound all 4 could be mounted on the same heat sink if it is large enough.

Good listening
Bruce

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 Post subject: Re: KT120 Oddblocks
PostPosted: 26 Sep 2018, 15:00 
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Joined: 23 Sep 2018, 11:43
Posts: 2
Thank you Bruce for the pointers!

Still trying to decide on some component choices from mouser.. too much to choose from can be a bad thing.

At least i can't jump the gun and order before late october when they have stocked a viable bias pot (here).
For the filter caps, KEMET's series ALC10 are available in 180uF and 330uF rated at 550 volts, ought to be good enough with a soft start.

It is tempting to just go for the established LR8s and skip the VR tubes... I will have to ponder over that one a bit.

Speaking of heatsinks, if anyone has any tips for ones that can mount all 4 LM317 they are more than welcome!


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 Post subject: Re: KT120 Oddblocks
PostPosted: 07 Oct 2018, 10:50 
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Joined: 07 Mar 2017, 03:14
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Hi Bruce,
There is a 1uF poly cap (SRPP) on the power supply schematic. Does it have to be a special cap like Solen or Audyn?


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 Post subject: Re: KT120 Oddblocks
PostPosted: 08 Oct 2018, 17:18 
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Joined: 04 Jun 2008, 20:59
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Location: Arizona, USA
Hi, No. Use any decent poly there. I like to use audio grade ones though. Dayton, WIMA, Panasonic, Sprague, etc.

Good listening
Bruce

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