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 Post subject: Croft supermicro klone
PostPosted: 16 Jul 2017, 05:05 
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Joined: 23 Oct 2013, 00:36
Posts: 6
Hello everyone!
I needed a preamp with riaa, and I found an article about the Croft Supermicro. To simplify the curcuit I will not use tubes in the power supply. Now I use the summer to collect resistances, capacitors, etc,for the project. I have built the super simple single stage preamp, and ForeWatt: DIY ECC802S SRPP Tube Preamplifier, and some other tube projects with good results.

http://www.cma4ch.org/chemo/attivita/croftsmic.html


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PostPosted: 17 Jul 2017, 20:13 
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Location: Arizona, USA
Hi It seems to be missing a grid to ground resistor on the second stage. As shown it will misbehave.

Good listening
Bruce

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PostPosted: 18 Jul 2017, 02:31 
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gofar99 wrote:
Hi It seems to be missing a grid to ground resistor on the second stage. As shown it will misbehave.

Good listening
Bruce

Hi
You mean from the 47K(between the resistor and the second stage on the riaa?) resistor to ground?


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PostPosted: 18 Jul 2017, 08:02 
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gofar99 wrote:
Hi It seems to be missing a grid to ground resistor on the second stage. As shown it will misbehave.

Good listening
Bruce


Hi Bruce,

I think pin 2 of 2nd tube is drawn strange>>follow the grid through the tube it has a 2.2 meg to ground. :|

Regards
M. Gregg

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PostPosted: 18 Jul 2017, 16:55 
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Hi Yup, need an eye check now.

Good listening
Bruce

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PostPosted: 19 Jul 2017, 12:07 
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gofar99 wrote:
Hi Yup, need an eye check now.

Good listening
Bruce


:D your not the only one, someone asked me what the value of a resistor network was on an exam question.
After a quick calculation its 27 ohms I said what's the query, well the answer sheet says its zero.
I said no its 27 ohms then the other guy said perhaps its this and pointed to a straight wire across the network at the bottom of the page.

Regards
M. Gregg

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PostPosted: 19 Jul 2017, 12:26 
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that grid to gnd resistor, seems to me to be a2.2m resistor
located on the right side of that same grid.


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PostPosted: 19 Jul 2017, 12:36 
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how fleet is the glance of the mind, compared to the speed of its flight.


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PostPosted: 20 Jul 2017, 10:46 
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Joined: 09 Oct 2012, 19:43
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Location: Vancouver Canada
I would wire the tape in and out differently.
1- I would tap the tape-out point from the wiper of the input selector switch. This way the tape will record
whichever source selected.
2- Have one more sw, added to select tape monitor then into the volume pot.
This will eliminate the problem of feedback if tape <record> is on, and one selects to listen to the tape.


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