Additional Preamp Tubes

I went and looked at my tube collection, and forget that I have a pair of RCA JRC 6189/12AU7WA dated 8/62. These are a ruggedized tripple mica black plate tube. I had them in my Rogue RP-1, but went on to the Tekefunken G73-R’s as they were what I was looking for. But in retrospect of this conversion and peoples suggestions, I thought I’d mention them. My pair came in pristine condition from “ The Tube Museum “. Here’s the AI sound description-  Warm , articulate with a punchy midrange and a tightly defined low end compared to standard 12AU7’s. Regards, Mike B. 

The M8137 valves you are interested in are ones I own, where all retained Valves from purchases made, have all been tested and are comfortably within factory specification.

I did not achieve this simply by purchasing valves and relying on the measurements provided by vendors. I only proceeded with purchases when sellers agreed to the testing criteria outlined in my previous post. For clarity, all measurements were taken using a calibrated AVO valve tester.

Over several months, I purchased more than 12 valves sold as matched pairs. The advertisements included attractive measurement data for each valve and half valve section.

However, when I had the valves tested, some of the valves' actual measurements differed significantly from those stated in the ad.

Following a number of returns and further purchases, I eventually assembled a set of six valves that are effectively interchangeable, closely matched, and all meet or exceed factory specifications on both half valve measurements.

Note: A valve specialist who is visited to carry out independent testing, explained that most valves will still function and produce sound even when their performance is well below factory specifications. He also noted that many valve owners do not know their valve's condition regarding factory spec and continue to use low spec valves without concern.

The advice I received was that a valve's published test results shown in an ad are just as important as the photographs used for the ad showing the valve's physical condition. A buyer may decide not to purchase a valve that appears to be in poor condition, and they may also reasonably question the asking price if independent testing shows that the valve's actual performance differs materially from the specifications advertised. In my arrangements, I do not negotiate the asking price when the spec is proven to be concerning; I already reserve the right to return a valve. 

@pindac Great advise & process! 
@buellrider97 Mike! I should have known. This gentleman was kind enough, (a few years ago when I was brand new to this hobby), to loan me several sets of tubes to try. Other than meeting on Audiogon, I was a complete stranger & he shipped me a couple $K worth of tubes (Mullard, Siemens, RCA, Tele’s), not trying to sell them, but to try in my RP1. I ended up buying my Siemens & Tele’s from another source as a result of Mike. What a gentleman! Thank you again Mike! 

buellrider97,

8/62 seems pretty late for a triple mica blackplate tube.   I think both GE and RCA phased this design out around 1958 or 1959.  It might have been stored without printing or possibly re-printed at the time.  Regardless, it is a very good tube, although not in the same class of some of the others mentioned above, IMHO.  Just for the record, my opinion doesn’t count.  Plug them in and see how YOU like them.  Best of luck.

@bbroussard , I’m not an expert but they shipped in their original box’s. They are not rca logos but a light brown military JRC box with the production date below the other info. The tabs fell off the second time I opened them. I did try them then went on to 5-6 other pairs settling on  the black coated Tekefunkens. Regards , Mike B. @signaforce , Ha Ha , I still have the RP-1, I aquired a Rogue Hera and a pair of M-180’s that I had upgraded to Dark. Got ‘em done last fall and it’s all in the closet until I wall mount a yet to purchase TV, new rack built and a loom of balanced IC’s. Hopefully in the new couple months. Happy Hunting.