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previous: rich First off, thanks to all who helped... -- 9/14/2000 9:34 PM

Re: Another SFDR Question!!!!!

10/10/2000 6:45 AM
Bjorn	Re: Another SFDR Question!!!!! Well, FWIW here is what I did to my DR: 1. The DR now carries 2 Svetlana 6L6, biased to approx. 37 mA (1 ohm method), instead of the 6V6 pair. 2. V1 was pulled out 3. PI tube was changed to 12AX7 (12AT7 is nice too). 4. The filter section was changed to SR specs. The “Torres Diode Trick” was performed by the 1K resistor. 5. A 120 pF SM was added across the PI plates (V1) and Grid stoppers (6L6) were changed to 2K2. 6. The coupling cap by the PI was changed from 0.001 uF to 0.01 uF. 7. The NF resistor was changed from 820R to 1K2. 8. I kept the grounded 47R resistor (by the NF resistor) and bypassed it with a 1uF cap (with a 1M Audio push/pull pot; Volume). 9. The tone stack was changed to 0.022 and 0.047 uF (middle, bass) and 390 pF (treble cap, SM). This was done on both channels. 10. The speaker (Oxford) really sucked and two old CTS 10´ speakers from an SR were installed in a new baffle. I was unable to wire the speakers to get the 8 ohms required and settled for 4 ohms instead which was a GREAT mod. 11. The cathodes were separated in V1 and V2. To reduce flatulence the CBC in the first gain stage (V2) was changed from 22 uF to 2.2 uF (the resistor changed from 1500R to 1K) and in the second gain stage to 10 uF, with a very nice result. This was done on both channels. To reduce further reduce flatulence the coupling caps from the driver tube were changed from 0.1 to 0.047uF. 12. The Intensity pot was replaced with a 50K ON/OFF pot. 13. All caps are OD’s (715P) and SM’s and all electrolytes were replaced (Sprague’s). 14. The middle cap (of three) in the vibrato LFO section was increased from 0.01 uF to 0.02 uF. 15. The bias feed cap was changed to 100 uF from 25uF. 16. The 470 ohm screen resistors were changed to 1K, 5W (6L6). Bjorn

10/10/2000 6:45 AM

Bjorn

Re: Another SFDR Question!!!!!

Well, FWIW here is what I did to my DR:

1. The DR now carries 2 Svetlana 6L6, biased to approx. 37 mA (1 ohm method), instead of the 6V6 pair.
2. V1 was pulled out
3. PI tube was changed to 12AX7 (12AT7 is nice too).
4. The filter section was changed to SR specs. The “Torres Diode Trick” was performed by the 1K resistor.
5. A 120 pF SM was added across the PI plates (V1) and Grid stoppers (6L6) were changed to 2K2.
6. The coupling cap by the PI was changed from 0.001 uF to 0.01 uF.
7. The NF resistor was changed from 820R to 1K2.
8. I kept the grounded 47R resistor (by the NF resistor) and bypassed it with a 1uF cap (with a 1M Audio push/pull pot; Volume).
9. The tone stack was changed to 0.022 and 0.047 uF (middle, bass) and 390 pF (treble cap, SM). This was done on both channels.
10. The speaker (Oxford) really sucked and two old CTS 10´ speakers from an SR were installed in a new baffle. I was unable to wire the speakers to get the 8 ohms required and settled for 4 ohms instead which was a GREAT mod.
11. The cathodes were separated in V1 and V2. To reduce flatulence the CBC in the first gain stage (V2) was changed from 22 uF to 2.2 uF (the resistor changed from 1500R to 1K) and in the second gain stage to 10 uF, with a very nice result. This was done on both channels. To reduce further reduce flatulence the coupling caps from the driver tube were changed from 0.1 to 0.047uF.
12. The Intensity pot was replaced with a 50K ON/OFF pot.
13. All caps are OD’s (715P) and SM’s and all electrolytes were replaced (Sprague’s).
14. The middle cap (of three) in the vibrato LFO section was increased from 0.01 uF to 0.02 uF.
15. The bias feed cap was changed to 100 uF from 25uF.
16. The 470 ohm screen resistors were changed to 1K, 5W (6L6).

Bjorn

Replies:

Bruce All that and you are still using th... -- 10/10/2000 2:45 PM