Tube Sockets, Part 4. Adapters

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7N7 to 6SN7 AdapterAdapter for:

7N7 to 6SN7
7F7 to 6SL7

Compatibility

Take any 7N7, and with this adapter you have a 100% compatible 6SN7. The same applies for 7F7, which converts into 6SL7, using the same adapter.

Though octal and loctal sockets look the same perhaps, they have very big differences. Here are listed the DISADVANTAGES of Loctal Sockets, but also their ADVANTAGES. Overall however, because octal was more monkey proof, it was the winner. Though that does not make it better. In the following text I will explain the differences between OCTAL and LOCTAL, which is more than just the footprint.

Interesting is, we can find on Ebay some very nice NOS LOCTAL for reasonable prices, That is also one of the BIG differences: NOS OCTAL is extremely hard to obtain, a lot of "used before" NOS is offered in the internet. Whereas LOCTAL NOS is usually indeed virgin. Also, because LOCTAL is an older standard, such NOS tubes are generally of higher quality.

Amazingly, Hi-Fi companies seem unaware of this, and keep on using OCTAL 6SN7. Well, we don't have to understand everything :)

Disadvantages of Loctal Sockets:

  • Can not do 4A heater current, like Octal.
  • Sockets must be precision items.
  • Chinese Loctal sockets will crack the tube base. Do NOT use those. They are a hack, made of contacts, NOT suitable for loctal.
  • NOS sockets are hard to find, but we were able to buy a large lot of TEFLON NOS sockets.

Advantages of Loctal Sockets:

  • Guide pin is metal, so it can not break off.
  • Tube pins are hard metal. They can not bend. (Unlike Noval tubes).
  • Tube base is hard glass. This has less grid leakage at high temperature.
  • Tube base is metal shielded.
  • Small signal tubes can have a metal cap, attached to the tube.
  • Loctal NOS tubes can still be found.

So you see, with Loctal you get a tube with a hard glass base, unbendable pins, and a metal shield around the tube base.

About this adapter

Order Number: 399-125-92

Good adapters were made a while from USA NOS sockets, but these have become unavailable now for low prices. Some sellers use now Chinese Loctal, but these are a hack. Such sockets will crack the pin to glass seal, leading to vacuum loss.

 

 

 


 

 


7N7-Sylvania
Order Number:
114-142-90


Special price!
Five-Pack 7N7 NOS.
Order Number:
114-165-48

 

 

About hard glass

For tube base, there are just two technologies, soft glass and hard glass. Soft glass, is when the wires or pins, going though the glass are made of soft metal, and also the glass is a softer kind. ,This colors the wires red, where they pass through the glass. The metal and the glass match thermal coefficient.

Hard glass can bond to hard metal. Such pins can not not bend easily, and the glass has less grid leakage at high temperature. When hard metal pins bond to the glass, this place becomes grey, not red as with soft metal.

So just by looking inside the tube, is the color red or grey? You can already say it's soft glass or not.

Well, and by trying to bend the pins, you can also see it. Pins of Noval tubes bend very easy. Too easy. But pins of loctal tubes do not bend easy. That needs really great force. Do not try it. The pins of loctal tube are made of Amorphous material. This is an alloy of metal and glass. This has normal, good electrical properties, but it becomes very hard and corrosion proof. It has a thermal expansion coefficient same as hard glass, and due to it's glass content, it bonds very good to glass.

Check here this video about 6C33. These are exceptional. Because 6C33 gets extremely hot, glass content of the pins was made higher, and their pins will break like glass. 7N7 pins do not break, but are very difficult to bend.

7N7 Quality

Prime Quality (*) NOS 6SN7 are now very hard to find. As a tube dealer, you always have to collect them in small quantities. Rather one by one even. The times where you could find factory packs with 50pcs of one kind are definitely gone now, and sure this makes it extremely hard to find two tubes of an optical pair, same date code etc, and not to forget same electrical data. For this we only have the Toshiba 6SN7-GTB for sale, which is a specialty, and worth to check it. A nice alternative, is use 7N7 which costs less than 6SN7. The 7N7 is electrically fully identical to 6SN7, apart from the Loctal base, and the pin out is different.

Versions

For the question of GT, GTA, GTB etc, refer to the 7N7 you take. So a 7N7-GTB will become a 6SN7-GTB. The additions GT means Glass tube. GT is the oldest version. GTA was a tube with shorter warm up time, and GTB warms up even faster. So be sure to get GTB versions for your tube television. For HiFi, it doesn't matter at all. Prime Quality (*) means untouched factory packed boxes of 50 or 100 pcs, and inside are individual boxed tubes, crispy like new. Definitely this cannot be found with 6SN7 anymore.

Pricing

NOS quality is of 7N7 is far better, and still costs less than 6SN7! It does not mean 7N7 is a better tube, just good 6SN7 NOS for decent prices is simply gone, but 7N7 you can still find. Though the situation is not like 10 years ago, when you could get them for 1$ on Ebay. That is over now. Still we have the situation of low price, good availability, and high quality for NOS 7N7. So take advantage of it now, and not wait until it is too late. I write this in 2017, and NOS prices go up 20% every year, and they are doing so since 15 years now. (Yes, that many indeed). 7N7 this tube is discovered only "a little bit", but it is coming.