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KT120 Oddblocks
http://diyaudioprojects.com/Forum/viewtopic.php?f=9&t=3089
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Author:  ozapaydin [ 01 Jan 2018, 14:18 ]
Post subject:  Re: KT120 Oddblocks

Thank you, Bruce. What is the size of the box (chassis) you used in your kit?

Author:  gofar99 [ 01 Jan 2018, 16:32 ]
Post subject:  Re: KT120 Oddblocks

Hi, In inches....13X9X2.5

Good listening
Bruce

Author:  TIJ-NIKI [ 06 Jan 2018, 05:41 ]
Post subject:  Re: KT120 Oddblocks

Hi, it has been a long time... life hasn't been kind

So i find myself finally in the conditions to finally build these blocks. I would like to ask if i can use TO3 steel package LM317HVK as i have some at my workplace that are collecting dust, and what is the little switch adding the 14ohm resistor in parallel to the 6.8ohm one?

Thank you

Author:  gofar99 [ 06 Jan 2018, 08:43 ]
Post subject:  Re: KT120 Oddblocks

Hi, Sorry to hear things didn't go well. If the TO3 version you have is rated at the 57 volts of the TO220 HVs then yes. If they are only rated at 37 like the more common (non hv ones) ones then it is rather iffy. Some will work and some not. The usual mode of failure is shorting through so it is rather obvious when they fail. The switch allows for setting the cathode curent at two levels, one suitable for KT120s and one for KT88/90 and similar tubes.

Good listening
Bruce

Author:  TIJ-NIKI [ 06 Jan 2018, 11:35 ]
Post subject:  Re: KT120 Oddblocks

It's way better now. The poddwatt sits cozy in my new office, now i need some kt120 to warm up the house. Pellet stoves are overrated.

The datasheet of the ones i have states

" 1.5-A Output Current currents over a 1.25-V to 57-V output voltage range."

So i guess i am fine. At least the to3 will have a cool looking heat sink

I guess that the switch needs to be closed for the kt120?

Thank you again

Author:  gofar99 [ 06 Jan 2018, 16:02 ]
Post subject:  Re: KT120 Oddblocks

Hi, they should be fine. Yes the switch is closed for KT120s. You should check the dissipation for the 317s as well. At nearly 300 ma and somewhere in the 30-40 volt range they need to handle a goodly amount of heat. You may be able to get by with a single 317 of the type you have. I use 2 of the TO220 ones to minimize the heating in each. BTW my experience is that they can be used in parallel and they share the power very well. I originally had concerns that one or the other would hog the power. Not so.

Good listening
Bruce

Author:  TIJ-NIKI [ 06 Jan 2018, 18:02 ]
Post subject:  Re: KT120 Oddblocks

I won't risk it, i plan to still use 2 of them in parallel. I mean i am getting them for free so why not. Better safe than sorry.

For the resistors on the power supply section are 5watt ones fine?

For these ones i am gonna get myself some Edcors, i really want to see if they are worth it. Shipping to Europe is notoriously high because of the weight, but i am getting them anyway so if any user is around Italy/Austria/Germany and want to organize a combined order to save some bucks i am ok with it. They would need to be made on order so i think that 8 weeks or more will be necessary.. CXPP70-3.5K for the output and XPWR267 for power correct?

Author:  TIJ-NIKI [ 13 Jan 2018, 18:48 ]
Post subject:  Re: KT120 Oddblocks

Hi guys, almost done ordering all the stuff, since i want to roll around some tubes in this i was thinking about replacing the bias test points with 2 panel meters per block for a quick bias adjustment on the go everytime i try a different pair.

Edit

At first i thought about using ammeters in series with the cathode resistors but i think it would be better to use a voltmeter in paraller to those. What readings am i expected to get?

Author:  gofar99 [ 14 Jan 2018, 15:15 ]
Post subject:  Re: KT120 Oddblocks

Hi, You will not be able to use most meters as they will not have the sensitivity needed. You are measuring about 0.13 volts (130 millivolts). Most stand alone volt meters like you are thinking of won't do that. If you put high current meters in line with the cathodes they will have considerably more than 1 ohm resistance and will seriously degrade the performance. The only possibility is to use meters with separate power sources that can measure isolated voltage points. They need to measure across the 1 ohm resistors and not to ground. The 1 ohm resistors are approximately 35 volts above ground. You could design a circuit that would do the job, but why bother. In normal operation the tubes will stay within acceptable limits for many months after the initial set up. I check them after a week initially to be sure one tube or the other has not deviated from the original settings (usually not) and then about a month later. After that it is every 6-12 months.

Good listening
Bruce

Author:  eshazen [ 14 Jan 2018, 15:41 ]
Post subject:  Re: KT120 Oddblocks

I agree with Bruce's comments, and I would add that it is well worth including pin jacks or something similar on the outside Iof the chassis for easy measurements.

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