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KT120 Oddblocks
http://diyaudioprojects.com/Forum/viewtopic.php?f=9&t=3089
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Author:  ozapaydin [ 03 Dec 2018, 17:05 ]
Post subject:  Re: KT120 Oddblocks

:)

Author:  ozapaydin [ 03 Dec 2018, 17:42 ]
Post subject:  Re: KT120 Oddblocks

Cathode current of kt120s is 137 mA and 138 mA. Oh man, this thing is really getting hot.

Author:  ozapaydin [ 05 Dec 2018, 02:03 ]
Post subject:  Re: KT120 Oddblocks

Is it normal to see 76 volts above the ground on the positive leg of the heater of the first kt120 tube after relay is closed? The potential difference between the positive and the negative legs of the heaters (both KT120s included) is 13 volts. Nothing wrong there. But 13 volts potential difference is maintained with 76 volts on the positive leg and 63 volts on the negative leg (measurement reference is the ground) if I remember correctly.

Author:  TIJ-NIKI [ 05 Dec 2018, 02:11 ]
Post subject:  Re: KT120 Oddblocks

That is done on purpose. Bruce always uses a reference voltage on the heater to avoid possible arcs and shorting inside the tubes especially on the SRPP stage. In the SRPP circuit it is easy to exceed the heater to cathode voltage ratings of the tube, causing an internal short. You should never ground the heater circuit on such design, doing so defeats the purpose of elevating the heater voltages

Author:  ozapaydin [ 05 Dec 2018, 14:15 ]
Post subject:  Re: KT120 Oddblocks

Thank you. The interesting thing about this problem is that it does not occur everytime the amplier is turned on. Should I suspect 0.2 uF cap between pin 1 and 2 of lm555? Cause, mine is a very tiny one. If it is short, is it possible to see this problem?

ozapaydin wrote:
Houston, I have a problem. The relay is closing after about 50 seconds but opens again after a few seconds. What might be the problem?

Author:  ozapaydin [ 06 Dec 2018, 05:59 ]
Post subject:  Re: KT120 Oddblocks

Congratulations... :up: I'm also very close to getting some sound out of my prototype :) I can't see the pictures you shared though. Led touch is a very handy feature. Can you share how you did it?

TIJ-NIKI wrote:
I decided to add a little touch, the power button led breathes while the tubes are warming up, once the relays turn on the main the led stands still

https://i.imgur.com/jXYO9Oz.gifv

Author:  TIJ-NIKI [ 06 Dec 2018, 08:46 ]
Post subject:  Re: KT120 Oddblocks

Hi, I used a dual pole double throw relay on the timer circuit. One pole switches on the b+ the other is connected on no on a lm358 breather circuit, the other side to cathode. So when the timer is still counting the b+ is not connected and the led is connected to the breather, once the timer reaches one minute the b+ is connected and the led bypass the breather so it stands on still.

For the pictures the hosting website must have removed it, gonna upload some in a sec

Author:  TIJ-NIKI [ 06 Dec 2018, 10:19 ]
Post subject:  Re: KT120 Oddblocks

For some reason on mobile I keep getting logged out before being able to load pics.. Have some links
Image
https://i.imgur.com/QqZTe8b.jpg
https://i.imgur.com/9jYNMJR.jpg
https://i.imgur.com/tRvQKWS.jpg
https://i.imgur.com/DRsZgsM.jpg

I absolutely love how these 12sl7 sound. They are an Italian clone of old RCAs. New old stock, i wish I could find more

Image

Author:  gofar99 [ 06 Dec 2018, 21:29 ]
Post subject:  Re: KT120 Oddblocks

Hi, Did you solve the relay problem?

Good listening
Bruce

Author:  ozapaydin [ 07 Dec 2018, 11:59 ]
Post subject:  Re: KT120 Oddblocks

Hi Bruce,
I was away from home. So, I couldn't deal with the problem. I'll hopefully take care of it in the weekend.

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