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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: Ampex 620 - good El Cheapo donor? posted by bean on July 20, 2010 at 07:19:09:
"Is the output traffo good enough to make a GOOD El Cheapo?"
I would think so. The stuff Ampex used is better than that found in guitar amps and we initially called for Fender "Deluxe" replacement "iron". Even that "bottom of the barrel" O/P trafo gave OK results. The better the "iron" the better the finished amp. The signal circuit topology is valid.
Between triode mode "finals" and a 68 nF. cap. in the I/P high pass position, I can't see how you will go wrong. Employing 68 nF. for high pass sets F 3 at 23.4 Hz. The lowest note a double bass produces is 31 Hz. ;> )
BTW, if you have an o'scope, you can get phase compensation "perfection". If not, just connect a 120 pF. mica or NPO ceramic cap. from the "hot" side of the O/P trafo secondary to ground. Inductive wirewound resistors as anode loads in the splitter/driver "peak" HF gain. Natural roll off in the O/P trafo brings things into alignment. The small cap. shorts the NFB loop out above 80 KHz., which keeps the circuit from slew limiting.
Eli D.
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- RE: Ampex 620 - good El Cheapo donor? - Eli Duttman 07/20/1017:16:16 07/20/10 (0)
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