CJ also made another unit, I believe the Evolution pre, that used nuvistors. I had one and was glad to get rid of it because the nuvistors constantly went noisy.
That was the one drawback with nuvistors....microphonics. When Ampex designed the MR70 electronics they mounted the nuvistors in modules that are essentially isolated and vibration free. The electronics use 3 modules,bias,reproduce and record for a total of 10 nuvistors, each shielded with large brass block heat sinks. There are also 6 nuvistors on the main board for a total of 32 nuvistors per stereo pair. The very few companies that pursued the nuvistor other than Ampex failed to design for the nuvistor properly. Also the nuvistor's introduction was at the beginning of the transistor introduction and economies of scale took hold....the rest is history.
I have a custom-made preamp as a backup, sounded quite decent off the shelf and some months later I decided to upgraded it with Mundorf caps, the mod brought it three steps back in sound quality.
I recapped my Ampex 350 with Mundorf supremes,silver oils,and SGO's. I also used Mundorf electrolytics in the power supply. I lost count of the hours it took for the gain to settle and reach maximum. The Mundorfs are a interleaved design and are like 2 caps in one enclosure. My experience is that they are among the best sounding caps made. If I had to guess how long it took for the recap to come up to speed I would guess 1,000 hours,but the size of the capacitors used in my Ampex 350's is about 3 times what the originals were. YMMV
p.s. The mundorfs yielded the most controlled bass I have ever heard in any preamp.
I recapped my Ampex 350 with Mundorf supremes,silver oils,and SGO's. I also used Mundorf electrolytics in the power supply. I lost count of the hours it took for the gain to settle and reach maximum. The Mundorfs are a interleaved design and are like 2 caps in one enclosure. My experience is that they are among the best sounding caps made. If I had to guess how long it took for the recap to come up to speed I would guess 1,000 hours,but the size of the capacitors used in my Ampex 350's is about 3 times what the originals were. YMMV
p.s. The mundorfs yielded the most controlled bass I have ever heard in any preamp.
CJ also made another unit, I believe the Evolution pre, that used nuvistors. I had one and was glad to get rid of it because the nuvistors constantly went noisy.
Their premier Seven four box preamplfiier also used nuvistors in the phono input - two per channel. I think I still have a few 6CW4 somewhere in my garage. I could get the RCA and GE ones, and remember that I had a preference for one of the brands as it was statistically less noisier, but can not remember which anymore.
