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 Post subject: Re: MCA - Son of ZCA
PostPosted: 22 Dec 2012, 13:44 
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Joined: 22 Dec 2012, 11:01
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Hi Mark : I had a chance to look over your MCA prototype circuit looks just like the FET one except you forgot to set the input impedance, in your original you had 47k, which would be fine here too. I haven't done any projects for two years now ,but this does look like something I might try this winter.Did you try any other tweaks since the original experiment? Merry Christmas Jim Orend.


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 Post subject: Re: MCA - Son of ZCA
PostPosted: 22 Dec 2012, 20:30 
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Joined: 06 Jun 2008, 18:23
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Location: Australia
tubem wrote:
Hi Mark : I had a chance to look over your MCA prototype circuit looks just like the FET one except you forgot to set the input impedance, in your original you had 47k, which would be fine here too. I haven't done any projects for two years now ,but this does look like something I might try this winter.Did you try any other tweaks since the original experiment? Merry Christmas Jim Orend.

From the original proto I down graded the input cap (0.1uf). I also tried larger output cap but not required. As it is it will play well though low on power. I think you can increase the PS to 48V and drop the load to 8ohm but I haven't tried it. This may extract more power. The 2N3055 runs cool but with the greater B+ this may change.

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Projects: "Lagoon" - tube preamp with cathode follower | "retro-Oatley 6J6" - 6J6 push-pull headphone amp with OPTs | "retro-Hiraga" - Jean Hiraga Le Monster
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 Post subject: Re: MCA - Son of ZCA
PostPosted: 22 Dec 2012, 22:54 
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The 2N3055 was commonly used in high current power supply's, and is capable of running very hot even for extended periods without failing. They are very cheap and seem to be found just about every where, so there's no harm in pushing it a lot harder.


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 Post subject: Re: MCA - Son of ZCA
PostPosted: 22 Dec 2012, 23:03 
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tubem wrote:
The 2N3055 was commonly used in high current power supply's, and is capable of running very hot even for extended periods without failing. They are very cheap and seem to be found just about every where, so there's no harm in pushing it a lot harder.

When I ran the prototype the 2N3055 barely got warm. If I was to build the MCA, based on my original prototype right now, I would only use a small heat sink. One of the main criteria when designing the MCA I wanted it cheaper to build then the ZCA and to use the same PS. I have seen 2N3055 for 50 cents each. The jFets I get for less than $1 each when I buy 50.

With the ZCA and MCA sharing a similar PS and load you could build an amp which has both ZCA and MCA builds and have a switch which switches from one amp to the next. Just tap off where the bias pot is so each amp has its on pot and set bias.

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Projects: "Lagoon" - tube preamp with cathode follower | "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: MCA - Son of ZCA
PostPosted: 20 Feb 2013, 17:02 
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I'm just wondering in my final drawing of the schematics for the MCA that I may have the drain and source wrongly named. I think the drain should go to the 2N3055 emitter????

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Projects: "Lagoon" - tube preamp with cathode follower | "retro-Oatley 6J6" - 6J6 push-pull headphone amp with OPTs | "retro-Hiraga" - Jean Hiraga Le Monster
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 Post subject: Re: MCA - Son of ZCA
PostPosted: 27 Nov 2013, 23:04 
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mwhouston wrote:
I'm just wondering in my final drawing of the schematics for the MCA that I may have the drain and source wrongly named. I think the drain should go to the 2N3055 emitter????


Hello Mark, I have a few 3055's, will be getting parts together for your MCA build. Have you sort out the correct connection of the FET?

I'm fully aware the MCA/ZCA is designed with 28V in mind, what is the lowest acceptable B+?


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 Post subject: Re: MCA - Son of ZCA
PostPosted: 28 Nov 2013, 15:45 
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wtxs wrote:
mwhouston wrote:
I'm just wondering in my final drawing of the schematics for the MCA that I may have the drain and source wrongly named. I think the drain should go to the 2N3055 emitter????


Hello Mark, I have a few 3055's, will be getting parts together for your MCA build. Have you sort out the correct connection of the FET?

I'm fully aware the MCA/ZCA is designed with 28V in mind, what is the lowest acceptable B+?

I think the FET is drawn correctly. Not sure how low the B+ can go? Just experiment and let us know.

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Projects: "Lagoon" - tube preamp with cathode follower | "retro-Oatley 6J6" - 6J6 push-pull headphone amp with OPTs | "retro-Hiraga" - Jean Hiraga Le Monster
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 Post subject: Re: MCA - Son of ZCA
PostPosted: 18 Dec 2013, 17:59 
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Last time I tried this build, there was some thermal runaway problems ....maybe because I were using wrong components = BS170 and PN4302 ( N-channel FET's ) instead of K170 ( J-FET's ). It could also have been to long wiring or maybe to high voltage = 55 VDC ...anyway I will try this Darlington build form Mr. Houston again some time. I've found some 2N5302, these should go without any problem instead of 2N3055.

OT:
First I have to finish up my NADoz build ( Night And Day of zen ), which shall be a match for my new NAD M51 DAC ( my christmas gift ). The NADoz has mounted a switch so it's possible to switch between halogen lamps ( day ) and resistors ( night ) and another switch function, to choose between choke and resistor ( CRC vs. CLC ). I've found out after tons of listening sessions ( some would say it's just my imagination ), that some music is presented best with lamps as load/CCS and other kind of music is nice through resistors as load/CCS. There's in my opinion a kind of soft vs. hard sound, as well as the difference in sound, between resistors vs. chokes for filtering ( CRC vs. CLC ).

See ya guys !


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 Post subject: Re: MCA - Son of ZCA
PostPosted: 20 Jan 2014, 13:10 
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Joined: 22 Nov 2013, 15:58
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Hello Mark, getting close to having all the parts. The LSK170 at the DIY Store has multiple grades, which one do you recommend for the MCA?


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 Post subject: Re: MCA - Son of ZCA
PostPosted: 20 Jan 2014, 17:59 
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I'll assume you meant the 2SK170. I use the "BL" version for all my projects. Let's know when the build is up. It sounds like you may be officially the first to build the MCA.

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Projects: "Lagoon" - tube preamp with cathode follower | "retro-Oatley 6J6" - 6J6 push-pull headphone amp with OPTs | "retro-Hiraga" - Jean Hiraga Le Monster
Website: retro-thermionic


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