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 Post subject: Re: KT120 Oddblocks
PostPosted: 14 Mar 2011, 10:47 
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Joined: 26 May 2009, 18:51
Posts: 129
Location: Lilburn, Georgia USA
Yes, with the 360v 250ma versions I have 475v on my KT 88 Oddblocks and all is well . Robert P


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 Post subject: Re: KT120 Oddblocks
PostPosted: 14 Mar 2011, 22:45 
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Joined: 04 Jun 2008, 20:59
Posts: 3648
Location: Arizona, USA
Hi, The 180-0-180s will deliver about 450 under the load of a pair of KT120s. Fine and actually a good value. If you go much higher you will need filter caps that are rated more than 500 V and they get rather costly. Right now the prototypes are running at 405 which is a bit low (trannie is a 160-0-160) , but I can bump the current up a bit to get more output. My targets right now are 450-475 B+ and about 300ma per pair. That is as close to max dissipation as I would care to go. I like my tubes to last a while and the few extra watts gained by pushing the limits are unlikely to be audible.

I spent a goodly amount of time listening to the prototypes over the weekend. The tubes are not yet broken in but some things seem apparent. They will probably end up needing output transformers with about 2500-3000 impedance (present one is 4200, but 4 ohm loads seem to work better on the 8 ohm tap). I have to play with them a bit to be sure. It may be necessary to "tame" the bass a bit. It seems as if I get a gentle rise of about 1-1.5 db in the sub 100 HZ range (+about 1.2 db at 20HZ). If you have a system that is a bit shy there, this can be an asset. If you like stuff with a lot of bass the same applies.

More to follow....

(edit) I'll post the schematic in a week or so, I have a few clever ideas for it, but can't try them until I get some better heatsinks that are enroute. The LM317s will shut down if you get them too hot and at full power, the dissipation will get close to 12 watts. Heatsinks with ratings of better than (lower number) 4 degrees C / watt are needed. Most BTW are in the 6-10 range and will not be suitable.


Good listening

Bruce

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 Post subject: Re: KT120 Oddblocks
PostPosted: 15 Mar 2011, 16:07 
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Joined: 06 Jun 2008, 18:23
Posts: 4868
Location: Australia
Bruce: Did you say this is going to become one of your standard kits? It would be good while the tube is still new to the hi-fi sceen.

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Projects: "Sanctum" - 12AU7 and 6AS7 direct coupled headphone amp | "retro-Oatley 6J6" - 6J6 push-pull headphone amp with OPTs | "retro-Hiraga" - Jean Hiraga Le Monster
Website: retro-thermionic


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 Post subject: Re: KT120 Oddblocks
PostPosted: 15 Mar 2011, 16:17 
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Joined: 04 Jun 2008, 20:59
Posts: 3648
Location: Arizona, USA
Hi Mark, yes this will be a kit. 8-) No sales pitch here folks. It will be a number of months out as we can only source and field so many different new kits at one time. I'm thinking of two versions and the project post will probably show both. One, a minimalist version and the other a premium one with things like DC heaters and on board meters and such.

Good listening
Bruce

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 Post subject: Re: KT120 Oddblocks
PostPosted: 15 Mar 2011, 16:28 
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Joined: 08 Aug 2009, 03:11
Posts: 2208
Location: Chilliwack, BC
Slow Geek is slowwwww....

Bruce, you're Oddwatt? I was wondering why we had so many OW projects here... :D

Cheers!

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-= Gregg =-
* Ratings are for transistors - tubes have guidelines*
Home: GeeK ZonE
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 Post subject: Re: KT120 Oddblocks
PostPosted: 15 Mar 2011, 17:23 
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Joined: 04 Jun 2008, 20:59
Posts: 3648
Location: Arizona, USA
Hi Geek, 8-) Yes, I do the design and support and my partner does the sourcing and selling. I intentionally do not push the kits on the forum. I like to design projects and help individuals with audio projects of their own. I down play the connection between me and the company as I feel it is inappropriate in a diy forum. :2c:

Good listening
Bruce

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 Post subject: Re: KT120 Oddblocks
PostPosted: 15 Mar 2011, 21:18 
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Joined: 08 Aug 2009, 03:11
Posts: 2208
Location: Chilliwack, BC
I know the feeling!

I want to just design and build.... I should get someone to do the footpounding for me ;)

Cheers!

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-= Gregg =-
* Ratings are for transistors - tubes have guidelines*
Home: GeeK ZonE
Work: Classic Valve Design


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 Post subject: Re: KT120 Oddblocks
PostPosted: 16 Mar 2011, 22:25 
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Joined: 04 Jun 2008, 20:59
Posts: 3648
Location: Arizona, USA
Hi Everyone, For those of you following this thread, you may wish to also follow the original Oddblock one as there is information there relating to the KT120s as well. It concerned using different grid resistors on the 120s from the 88s. I got the new heat sinks today and they should allow the Thunder Blocks to go to full power. They are a lot more substantial than the ones in the KT88 version. If they work, I'll post a "first" try schematic for you all. It may well end up a little different as I perfect it, but it will certainly make a good amp (it's quite good now) that has lots of muscle. 8-)

Good listening
Bruce

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 Post subject: Re: KT120 Oddblocks
PostPosted: 22 Mar 2011, 12:32 
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Joined: 28 May 2008, 21:53
Posts: 4548
Location: Winnipeg, CANADA
gofar99 wrote:
I down play the connection between me and the company as I feel it is inappropriate in a diy forum.

Hi Guys, plugging your own product is allowed provided that the Forum Rules are followed. In particular:
Quote:
Commercial vendor offerings and advertisements of your own product will not be allowed unless the commercial vendor shares full details of their product (ie. schematics, PCB files ...) and they spend significantly more time contributing to the DIY efforts on this forum than they do trying to sell and promote their products.

Geek and gofar99 are excellent member examples of how we would like the commercial folks to behave on this forum.
Cheers

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[ DIY Mains AC Power Cable Cord ] - [ Gobo LM1875 Amp Kit ] - [ Tang Band D4-1 Horn Speaker Kit ] - [ Monoblock Push-Pull KT88 Tube Amp Kit ]


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 Post subject: Re: KT120 Oddblocks
PostPosted: 22 Mar 2011, 22:51 
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Joined: 04 Jun 2008, 20:59
Posts: 3648
Location: Arizona, USA
Hi Gio, Thanks for the kind words. I still make every effort to avoid pushing the products on the site. I just feel it is rather tacky to post a project and then hope someone will buy it from us. I love diy and really like to explore ideas on the forum and help others in their seeking audio nirvana - hopefully learning a little on the way and maybe even helping others to get involved. :D

BTW on the Oddblock project thread I added some thoughts on how the CCS works and some things that I considered as possible problems. I got my larger heat sinks last week and put them in the KT120 push-pull amplifiers. I'm now running 300 mA per pair of tubes. All seems fine. I want to juggle a few parts and then if there is no smoke, fire, arcs, sparks and nothing just pain blows up - I'll be ready to do serious tests on the amps. My initial thoughts are that they are quite similar in performance to the KT88 amplifiers, but may have a slightly boosted bass in the sub 70Hz range. This - depending on what you like for music, might not be a problem. The amps sure rattle things in my listening area. :o

Good listening
Bruce

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