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6J7-EF36 in phono stages
Dear RATS,
I just finished a phono preamp using a 6J7 as first amplification stages, followed by a passive RIAA, followed by a 6F5 as a second amp stage, and finally by a DC coupled 6J5 CF as "output" tube. It sounds great (who ever said "my project is bull.."?) but it is noisy, even with DC filaments. OK, it has a lot of gain, but something is definitely wrong. I swapped different pentodes and it seems that most of that noise depends on tubes. If anybody is interested in using these tubes in low noise application, here's what I found: - the less noisy are the metal envelope ones (6J7M, Svetlana) - a bit worse are the European painted-glass shouldered bulb type (Brit military CVsomething, supposedly Brimar) - the more noisy so far are the the painted-glass, big bulb, straight-sided EF36 (US/Canada type) I suppose I have to work a bit on the "grounding" scheme of my unit, but the noise I found is not only 50Hz hum. Conclusion: 6J7 is surely a great tube in other applications (see Leak "point one" gain stage) but not in this case. In fact, it was not described as a low noise pentode like the EF86. Suggestion appreciated. Ciao to all Fabio |
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