THIS LISTING IS FOR:
ONE PAIR OF 6SN7-RFT, TESTING AS NEW.
So in total 8 tubes.
Some years ago, I found one NOS Telefunken 6SN7, and now I have those RFT 6SN7. They share something curious in common. The plate current is somewhat lower than normal, but within tolerance, and at the same time Transconductance is above 100%, also within tolerance. I have tested several RFT 6SN7, and they all have this property. So far I have seen this only with RFT, Telefunken, and the TOSHIBA branded Telefunken. Though the datasheet is a clone of the USA datasheets, electrically they are not. Here you can see the original RFT datasheet, but as this is a "clone" datasheet, you will find nothing in there with a clue. Here is the test data of the RFT
Also it can be seen, gain of the RFT is higher than normal, which you pay with every tube with higher plate impedance. All in all, this is a compatible 6SN7 still, any changes are within tolerance. Likely this explains the characteristic sound of those, and the reason why they are quite sought after.
The Toshiba are believed to be made by Telefunken as well, so this makes sense. I would say, these are three brands, which have a 6SN7 that is remarkably close related to each other. (Here is the TFK data)
The fact that have also the designation 6H8C, shows they were intended for export, and they haver better specifications that than standard 6SN7. (as 6H8C is an upgraded 6SN7. So you can replace 6SN7 by any 6H8C, but not replace 6H8C by any 6SN7) . The RFT tube fulfills both specifications.
They share something else in common, which is the dimensions of the very large Plates. The difference though is, RFT uses smooth plates, and TFK + Toshiba have ribbed plates.
The RFT have a construction inside which appears like Ceramic.
On the bottem of the RFT socket it a triangle inside the center plug, which has some resemblance with the Telefunken <> diamond, but it is a triangle with the RFT's.
Datecode is "604" and on the side is something which obviously week 41, year 1954. So 604 is a datecode for 1954. And that again is a Telefunken resemblance, because with Telefunken, the datecodes is a CODE indeed, only giving the lest significant digit of the year. So the last digit here is the "4" of 604. Same as with Telefunken.
This pair has excellent test data, it is printed and supplied with the tubes.
ADDITIONAL ITEMS SUPPLIED WITH THIS PAIR: