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Tubes Asylum Questions about tubes and gear that glows. FAQ |
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Tubes Asylum Questions about tubes and gear that glows. FAQ |
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In Reply to: Bogen DB20 - junk? posted by FuddyDuddy on November 18, 2013 at 00:32:39:
Ditch all those pre-amp tubes AND upgrade the splitter driver stage with a 6CG7 or a 12FQ7 in LTP mode and a single FET CCS to load it. You might still need a single twin triode gain tube in front of it an the simplest and best sounding would be a good 12AY7. NOT a 12AT7, IMO.
Upgrade the PSU
- with parallel SS diodes (soft recovery type) around the valve rectifier which then become less $$$ to buy new ones (ELI D has posted here about this a LOT,)
- and put in bigger (> uf) PSU caps, 100degrees c rating and by pass the last two
This will give you a bit more B+ and a bit more power (<3db though!). the amp will be a lot quieter.
For the power amp circuit you now have, upgrade all the small signal R's - double the wattage at least - and use MF resistors - a mix of brands, but the same make/model in each particular spot. This will audibly lower noise.
Use a mixture of good-sounding MF plastic caps. Sprague Orange drops are fine as IMO are WIMA MKPs. again IME double the voltage rating helps relax things sound wise, and use at least two brands -one dullish and one a bit brght. If you must use an oil-filled cap somewhere use a plastic type and for the cathode-bypass on the output stage.
This IS an NFB amp so don't spend $$$$$$$ on parts. EXCEPT for the caps and R's that set the NFB loop/s, where Holco / bulk foil Rs and teflon (commercial ones) caps are worth the money.
Do try less and more NFB. IF you can play with separate NFB on the input and LTP stages - less will likely sound better. esp if you CCS both input tubes, paralleling the gain tube. A bit more around the output stage and transformer might sound better but do experiment.
Warmest
Tim Bailey
Skeptical Measurer & Audio Scrounger
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- If it were me ...... - Timbo in Oz 17:58:30 11/21/13 (0)
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