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Tube DIY Asylum Do It Yourself (DIY) paradise for tube and SET project builders. |
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Tube DIY Asylum Do It Yourself (DIY) paradise for tube and SET project builders. |
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In Reply to: Re: "Does anyone know what Kurt Strain uses/used for his 27 preamp?" posted by Ronald K. on February 26, 2007 at 14:00:07:
Sorry. But it was real simple. A 5 mA CCS as a plate load, a 1.2K ohm resistor at the cathode bypassed by a 100 uF Black Gate capacitor to ground, a 100K input resistance step attenuator (individual resistors), and a 0.22 uF capacitor on the plate coupled to the 1M output resistor. No buffering was used. Output impedance was about 9K ohms. Good enough to drive a 100K input impedance of a power amp.The power supply came from an choke-input power supply for 250 VDC using a 10 H choke which fed a 47 uF Elna Cerafine electrolytic capacitor and then RC filtered to two different channels with 1K ohms and another 8 uF on each channel (oil caps there). All of this was with one 5AR4 rectifier feeding both channels. The secondary of the power transformer was 275-0-275 VRMS.
The DC supply of the filaments was powered by a programmable voltage regulator used in a constant current arrangement to put out 1.75 A at 2.5 VDC. There were two of those, heat sinked to the chassis.
That should be enough information to make this. It's all the info I can remember. When I troubleshoot it, I just follow the wires while remembering the schematic as I described.
Kurt
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Follow Ups
- My schematic is now just in my head. - kurt s 15:09:23 02/26/07 (1)
- Re: My schematic is now just in my head. - Ronald K. 16:11:41 02/26/07 (0)
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