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 Post subject: Re: KT120 Oddblocks
PostPosted: 29 Jul 2016, 14:29 
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Joined: 04 Jun 2008, 20:59
Posts: 4285
Location: Arizona, USA
Hi, :bawling: From your description it sounds as if one tube lost vacuum. Physical damage is the usual cause. This would cause the issues you described. You should verify the resistance to ground from each signal grid on the output tubes as a fault there will cause a tube to draw excess current and if it is sufficient cause LM317 failure. The 100 ohm resistors are a fail safe built into the amps that protects the amp in case of catastrophic B+ related failure. Apparently they worked. Before you power it up again verify also that there are no shorts in the LM317 circuit and check the value of the sense resistor.

Good listening
Bruce

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 Post subject: Re: KT120 Oddblocks
PostPosted: 08 Aug 2016, 13:27 
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Joined: 05 Aug 2016, 11:28
Posts: 1
Location: Sweden
Hi!

I'm about to order transformers for the KT120 Oddblocks and though I'd get a second opinion before I place the order.
My plan is a stereo amp on one chassi (17x14"), so far I've planned on using two PTs.
The power transformers are Toroidy:
TS 300VA PRI: 230V SEC:
190 - 0 - 190V @ 600ma
11V @4A

...and the output transformers that(if I remember correctly) someone else already brought up:
http://sklep.toroidy.pl/en_US/p/TTG-KT88PP-Tube-output-transformer-4kOhm-2xKT88-2x300B-Push-pull-or-similar/563

Is there anything special i should take into consideration with these transformers?

Thanks for the help!


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 Post subject: Re: KT120 Oddblocks
PostPosted: 10 Aug 2016, 14:49 
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Joined: 29 Oct 2014, 12:32
Posts: 95
Location: Russia Komi republic
Stereo amplifier will be a very heavy weight, should take this into account!
If I understand correctly, the power transformer is 2. If so, 600mA - a good number for each. Here are just a voltage 190-0-190 it seems very large. After straightening it will be more than 500 volts. Much more. This will certainly destroy the capacitors. As the tube, I guess. You'd better go on the road 180-0-180.
As the output transformer - I will not say anything. But the figure is 4 kΩ confuses me. It is better to wait for the views of Bruce.

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 Post subject: Re: KT120 Oddblocks
PostPosted: 10 Aug 2016, 17:09 
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Joined: 04 Jun 2008, 20:59
Posts: 4285
Location: Arizona, USA
Hi, 190-0-190 might be pushing it a bit. I use 180-0-180 and get about 425-450 VDC going to the outputs under load. If you find the B+ to be too high then you can put a series resistance in front of the first filter cap to bring it down. One thing I would recommend is to delay the voltage going to the filters until the output tubes are warmed up. Not to protect the tubes, but to be sure the B+ without a load does not get too high and put the filters at risk. With your transformers it could get to about 530 VDC. Most caps rated for 500 will tolerate it as it is short duration, but it would be better to not do it. The value I use 180-0-180 is pushing the limits as is without a load. It could just hit the 500 mark. It is a compromise as I want the tubes to operate at a relatively high voltage, but not so high as to need expensive filter components.

The relatively high value for loading on the output trannies (3400-4000 ohms) is related to the class A operation of the amp. For other classes (like AB1) it would be too high.

Good listening
Bruce

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 Post subject: Re: KT120 Oddblocks
PostPosted: 15 Aug 2016, 13:44 
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Joined: 29 Oct 2014, 12:32
Posts: 95
Location: Russia Komi republic
I restored my monoblock. At the same time I bought four gold lions kt88. One monoblock listening to kt120 second with kt88. In listening no winner or loser. kt120 - dynamics and power. Gold Lions - rich velvety sound. Now I'm confused, what is to listen :lildevil:

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 Post subject: Re: KT120 Oddblocks
PostPosted: 25 Aug 2016, 06:35 
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Joined: 18 Jun 2016, 06:52
Posts: 28
Hi. I'm not sure what the DC rating of the switch between 6R8 and 14R (KT88/KT120) should be. I bought RS Components 316-973 (AC rating 6A 250V, DC 4A 30V) but I'm getting cold feet. I don't know much about switches and I wouldn't want to see it go up in flames. Some advice would be welcome.

Jan


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 Post subject: Re: KT120 Oddblocks
PostPosted: 25 Aug 2016, 09:58 
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Joined: 04 Jun 2008, 20:59
Posts: 4285
Location: Arizona, USA
Hi Jan, The switch you bought is fine. Anything over about 2 amps DC is fine. It only needs to actually pass about 1/10 amp. It really should not actually be switched when the amp is running so resistance to arcing and such is not an issue.

Hi Zyu, yes the GLs have a nice sound, but the dynamics of the KT120s are more to my taste. Both play well in the amps (as do many other tubes). BTW the GLs were an early option in the KT88 kit amps. That is until we got some bad ones and went back to only JJs. They are neutral and dependable and sound quite nice on many systems.

Good listening
Bruce

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 Post subject: Re: KT120 Oddblocks
PostPosted: 27 Aug 2016, 15:26 
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Joined: 18 Jun 2016, 06:52
Posts: 28
Thanks Bruce, that put my mind at rest.


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 Post subject: Re: KT120 Oddblocks
PostPosted: 27 Aug 2016, 19:01 
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Joined: 05 Nov 2015, 01:57
Posts: 9
Does anyone have a recommendation for a DIY speakers that would be a good match for the KT120 amps?

Thanks for your help.

Greg


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 Post subject: Re: KT120 Oddblocks
PostPosted: 30 Aug 2016, 21:30 
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Joined: 03 Aug 2016, 19:28
Posts: 2
Ok, thinking about building two based off the schematics. Does anyone have a BOM for the amps? Mainly I am wanting to know exacts or recommendations on capacitors, down to brand if possible. Also, I am looking at adding another circuit I am working on to do a turn on from 12v amp turn on plugs and check AC mains voltage for high or low voltage conditions. Does anyone have a recommendation on an IC for DC voltage monitoring. It should never come into play, but I wouldn't want to push the B+ too high or power on the amp if input voltage was low. Lastly, any recommendations on frames?

Adam


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