It is well known that I am very fond of the 10 and 10Y, as well as all derivatives of this family: UX210, VT25, 801, 801A and VT62. All these tubes have already been extensively covered on this blog. But there is one very special and rare variant which deserves it's own Tube of the Month post: The 1602:
The 1602 is a specially selected 10 for applications which require low microphonics. It was called '10 Special' before it received it's own number.
It shares all the technical parameters of the 10 or 10Y and of course has the same pinout. In my experience the regular 10 or 10Y are already quite reasonable in terms of microphonics and I use them regularly in line stages. Since the 1602 is even better in that aspect it is the perfect choice for preamps of course. I have no information about the intended application for which the 1602s got selected. If anybody has some more information about this, I would appreciate to know more. The tube was mentioned in the May 1936 issue of the All-Wave radio magazine. So I assume it was introduced around that time.
That magazine mentioned it's intended use in audio applications, which is not a surprise given the selection for low microphonics. Although I always had good results with 10Y tubes in line stages, where microphonics are critical, a tube which is even less sensitive is of course always welcome. It seems that the tubes have also been selected for electrical parameters. I can pick pretty much any two 1602 from my stash and they show perfectly identical plate curves on the curve tracer. This is of advantage for usage in differential circuits like my 10Y differential preamplifier. I am getting excellent results from this tube in preamps. It is not a different sound but the basic characteristics remain the same (which is expected) just with an even quieter background and perceived higher resolution. Don't try to hunt for this tube unless you are very patient and are willing to spend significantly more than is usual for a regular 10 or 10Y. I have been looking for these since well over 10 years and managed to acquire only a few of them.
Apparently the 1602 was only offered by RCA and General Electric the latter under the designation GL1602:
Here a close up of the base:
The tubes are identical to regular 10 tubes from GE.
After the selection process they just got a paper sticker over the number 10. This can be seen here, the paper sticker has been peeled off from the left tube:
The 10 designation also is still visible when the tube is held against a light:
They came in very nice packaging. Oversized boxes with lots of padding material.
Beautiful orange/blue boxes
The GL-1602 with the filament lit up:
Here a RCA 1602 in globe shape:
The other side:
The globe tube from another angle:
Beautifully made with the glass arbor inside which aligns the electrodes.
Unfortunatly I only have one pair of the RCA 1602:
But they are in perfect condition with getter fully intact and matching plate curves.
Not sure if the 1602 was also offered by RCA in ST glass. I have only seen globes from RCA.