[Curtisvill]

My fav tube combo on the Airmid was a pair of GEC L63 and a pair of 5998s. There seems to be a few variations of the GEC l63, but these are the ones I have.

I have a pair of those GEC l63s and they are very nice.

 

[jgwtriode]

My fav tube combo on the Airmid was a pair of GEC L63 and a pair of 5998s. There seems to be a few variations of the GEC l63, but these are the ones I have.


The other tubes I tried, including Bendix 6080s, Ken Rad 6J5, Tung Sol black can 6J5, and Sylvania 6J5s, did not impress me much on this amp.
FWIW, my impressions were based on the Verite open. My VC wasn't doing well when I had the Airmid, and has since been returned to ZMF for some driver replacements.

Ouch, so you may not have been hearing your VC properly on the Airmid??? I had to have drivers replaced on my Auteur Blackwoods after about 2.5 years. Weird buzzing
at high frequencies of a certain intensity. Was only aware of it on certain music. But Zach figured it out and replaced them. Been fine since, albeit i rarely listen to them,
much prefer Leopardwood VC's. Welll hopefully they are returned soon.

Happy Listening,

jgwtriode

 

[L0rdGwyn]

I decided the red Airmid prototype needed a home, so it will be going to @jgwtriode early next year. Personally, I like the GEC L63 and Tung-Sol 5998 combination myself. Expensive these days, but they pair very well in the amp.

 

[jgwtriode]

I decided the red Airmid prototype needed a home, so it will be going to @jgwtriode early next year. Personally, I like the GEC L63 and Tung-Sol 5998 combination myself. Expensive these days, but they pair very well in th

I decided the red Airmid prototype needed a home, so it will be going to @jgwtriode early next year. Personally, I like the GEC L63 and Tung-Sol 5998 combination myself. Expensive these days, but they pair very well in the amp.

So how close do the stick Soviet tubes get. Will probably upgrade in stages. 6j5's first, then 5998's. Do it over a few months time. I trust that albeit pricey this combo really is the way to go. Really looking forward to the Airmid In my system. My late Xmas/New years present to myself!

Happy listening to all,

jgwtriode

 

[Monsterzero]

Ouch, so you may not have been hearing your VC properly on the Airmid???

That's correct.

 

[leftside]

I decided the red Airmid prototype needed a home, so it will be going to @jgwtriode early next year. Personally, I like the GEC L63 and Tung-Sol 5998 combination myself. Expensive these days, but they pair very well in the amp.

Great combo in my 1101 Audio V6 amp as well.

 

[mordy]

Just got a pair of Brimar branded 6J5GT tubes (no visible codes). Based on how they look and internal construction they are Ken-Rad VT-94 tubes from the mid 40s.
After playing for a couple of hours one tube started to develop a greyish shadow on top - I assume that it will turn into a black spot later.

I have been told this is called anode boiloff and is not detrimental to the lifespan of the tube. (If the tube has a cleartop it indicates that it is not new = NOS; with a getter flash on top I don't think that you can see it).
Why does this happen?

Remember these two 40's Ken-Rad tubes labeled Brimar? I stated that there were no codes visible on the base or on the glass envelope. Now, thanks to the efforts of the Antiquities and Preservation Department of Trivia University, date codes were discovered in an unlikely place:

On the glass piece which holds the wires and rods in place under the bottom mica date codes are etched.
The above two tubes look like it says W17 and W32?. On two other tubes it seems to say W44 (but the two 4s are upside down) and Y43.
Since Ken-Rad was sold in 1945 to GE it is reasonable to assume that these tubes are from the 40's. Don't know what W and Y stands for, but it seems logical that the first digit is the year and the second digit is the month.
Thus we have July 1941, February(?) 1943 , April 1944 and March 1944.
I find this interesting since I have not seen codes etched on the glass support inside the tube before. The codes are hard to see unless you angle the tube carefully, but they are there.
Is somebody can supply more accureate information, please do.

 

[triod750]

Antiquities and Preservation Department of Trivia University

Professor Mordy, I presume
These markings have been visible on all of the Ken-Rad 'Brimar' 6J5GT/G I have handled. I think I mentioned this when I first posted about them. My Sylvania 'Brimar' don't have these markings but 'H4' and 'F4' on the glass, below the '6J5GT/G' marking.

 

[mordy]

Professor Mordy, I presume
These markings have been visible on all of the Ken-Rad 'Brimar' 6J5GT/G I have handled. I think I mentioned this when I first posted about them. My Sylvania 'Brimar' don't have these markings but 'H4' and 'F4' on the glass, below the '6J5GT/G' marking.

What are the markings on the Ken-Rads?

 

[Xcalibur255]

My pair of KenRad 6J5G also have these etched codes on the side of their glass stems. One is labeled D42 and the other C53.

 

[triod750]

What are the markings on the Ken-Rads?

The four Ken-Rad 'Brimar's I now could find had the following markings on the glass pinch; A44, A41, A41 and W17. Of these I have passed on, several had either the letter A or W. I have commented on this in a previous post somewhere. (One of these markings was upside down). All of them came from a box of spares from an old cinema - also my Sylvania made 6J5GT/G (with better metal band around the socket).

 

[mordy]

The four Ken-Rad 'Brimar's I now could find had the following markings on the glass pinch; A44, A41, A41 and W17. Of these I have passed on, several had either the letter A or W. I have commented on this in a previous post somewhere. (One of these markings was upside down). All of them came from a box of spares from an old cinema - also my Sylvania made 6J5GT/G (with better metal band around the socket).

The reason I asked was that I was trying to understand the meaning of the first letter in the code. So far we have the letters A, C, D, W and Y but I am none the wiser from knowing this lol....
To play it safe, we'll call it a production code which basically is saying nuttin'.

 

[triod750]

I am no wiser about the code but I now know that it is called a 'glass pinch'; the piece of glass holding the metal innards. I learnt it when reading some history about tubes here: https://www.dos4ever.com/EF50/EF50.html
A lot of interesting reading.

 

[triod750]

This is the kind of information that can be found in the article I linked to: "During the Korean War, in 1951, endeavors were made to standardize the radio tube techniques used by the NATO members. The result was the NOVAL technique (nine pins in a circle providing room for ten). This tube was equiped with three-electrode lead-ins like the ”miniature“ tubes. Philips, however improved the shape of the envelope by sealing the tube base upwards. It is typical of technical progress in mass production that this technique, owing to its simplicity and logic design, has been universally accepted in spite of advertizing arguments such as ”it shows more“, ”it looks stronger“, which could be put forward in favour of other designs. Once this version had been chosen for nearly all types, the only difference being the length of the envelope, mechanization could be furthered. Machines were designed to weld the three-piece electrodes together at a rate of about 10,000 per hour, to press these electrodes into the glass base (Fig. 6.8) and to make envelopes of tube glass and to seal on stems at a reate of 2500 per hour. Thus it became possible to turn out a relatively compact unit for production of about 2,000,000 radio tubes per year. These machines were installed in Philips’ and Philips-supported factories in twelve different countries spread over the world".

Or this:"Klaas Rodenhuis recollects an amusing anecdote from around this period [47]. During the war, a group of engineers at Philips had worked on a competing metal tube concept. In an attempt to eliminate the expensive projection welding, somebody had had the cleaver idea to give both the base and the metal envelope a conical shape in such a way that they would fit snugly over each other. After evacuation the two parts would form a tight fit. Apparently the idea worked, so that a decision had to be made which concept to pursue. This decision was made by Frans Otten, the president of Philips who had just returned from exile. Today it seems unimaginable that the president of Philips should be involved in a decision on such a technical detail! The meeting was held, and Otten entered. After a short technical explanation by both camps, Otten asked ‘And gentlemen, which concept is cheapest?’ Everybody had to admit that the glass concept was cheapest. ‘Fine,’ Otten answered, ‘in that case we will drop the metal tube concept, good afternoon gentlemen!’ That is how decisions were made those days"!

 

[triod750]

"At the peak of production in the fifties, Philips produced about 200 million radio tubes a year. It was an enormous industry, in which thousands of people were employed. Over a period of forty years the science and craftsmanship of radio tube manufacturing had been mastered to the level of perfection. It is almost inconceivable, that apart from half a shelf of books in the library and a few hundred forgotten reports, all this knowledge and craftsmanship has almost vanished today".

Some of them are still out there. Not all of them end up on that bay. Go looking...