Though there were long black-plate 7025 made by RCA, the ones you are talking about would be short gray-plate. The black-plate and gray-plate RCA 7025 sound quite different from each other.LerxstLee said:I bought a repair mans NOS box of five. They were from 1967 date code BL.
Timbre Wolf said:Hi Crane!
Mavguy knows those tubes well. Watch for microphonics (or use as phase-inverter if microphonic). If not microphonic, they do have very clear cleans. Nice fat lows, good, robust mids, bright highs that stay articulate - excellent valves. I actually am learning to prefer these to long-plate Mullard 12AX7, since the RCA carry the heavier lows without accentuating nasal low-mids that the l-p Mullards do (I'm more sensitive to that now, and the Mullards are back in storage). In certain amps, the early breakup of the b-p RCA can be too raw and thick. They've given me an icky feel, kind of like ripping thick construction paper, when driven hard in certain amps. So try in several positions in different amps. You'll find a place for them, no doubt.
Now those are mid-'50s black-plate RCA. There are also RCA 12AX7 from the late-'40s (RCA produced the first 12AX7) that have a really wide D-shaped getter wire; almost as wide as the mica disk. They have thinner lows, don't break up as easily, and are very, very clear/articulate. Excellent tubes, but a different sort of character. Another identifying feature of these earliest versions is that the black plates are not dull/flat finish, like the '50s version. Nor are they shiny, like Sylvania and Raytheon black-plates. These earliest RCA 12AX7 have a semi-gloss finish (or is it eggshell? :wink: ) that is unique.
- Thom
You'll be able to tell a difference if you use it in your phase inverter. That's the most sure position that won't exhibit microphonics, but there may be others, between V1 and the PI. Just try your RCA there, and let your ears (and sense of touch) tell you all you need to know about whether it is right for you.Tmuggie said:So.... If I put the RCA in the phase inverter slot, it won't squeal? How much does the phase inverter slot effect tone? Is it the only slot that isn't affected by a microphonics tube?
crane said:Oups... never gave a feedback about those fantastic tubes !
It was a long time .... :wink:Timbre Wolf said:crane said:Oups... never gave a feedback about those fantastic tubes !
That was a long pause between breaths! :wink:
- T
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