[Csericks]

On the base is the number 5105

 

[Xcalibur255]

Any chance for a close up photo?  If they're from the 50's or maybe very early 60's they very well could be Hytron, anything later than that is very likely to be a re-branded RCA.

 

[Skylab]

On the base is the number 5105

Well, that is a date code, not an EIA manufacturer code.

http://www.triodeel.com/eiacode.htm#tubes

 

[Ultrainferno]

Just got these NOS, quite happy!
 

 

[Skylab]

Two of the very finest there are! Congrats.

 

[grokit]

I just tried a pair of those GEC's for the first time, really nice. From my correspondence with the seller:
 
They really open up the Sophia, not so much the 596 which was unexpected because the 596 has always had the bigger soundstage. With the HD800 and the Sophia the soundstage is unbelievable, really defined. I am guessing but it would probably be too much with the EML 5U4G, it is already too much with certain recordings. The overall sound is pretty refined though, much more so than the 7236. The 596 brings some punch back but the soundstage is lesser. Will compare more combos later but I really like these tubes, and stopped cursing about the price as soon as I heard them.
 
I am running the Shuguang Treasure drivers with the above in my WA22.

 

[imckt]

I just ordered pair of IBM brand 5998A in USD 46. Does anyone tried it before?
 
Just do a quick googling, seems not many post related to it.
 
http://www.diytube.com/phpBB2/viewtopic.php?t=3663

 

[Skylab]

5998A tubes I have seen are just a 6AS7GA, relabeled.

 

[hodgjy]

Very true with two exceptions.  I have the Sylvania 5998A, which has the typical 6AS7GA bottle, but it has the Sylvania 7236 plates.  The plates look and sound the same between the two. Also, I have the Tung-Sol 5998A,which is the Tung-Sol 7236 in the 6AS7GA bottle.  But as far as IBM and GE 5998As go, they are just rebadged 6AS7GAs.
Quote:

5998A tubes I have seen are just a 6AS7GA, relabeled.

 

[09Challenger]

I have a Bottlehead Crack on the way.
 
In anticipation of it's arrival, I have already started collecting tubes to roll.
 
So, far I have a GE 6AS7G and a Mullard 6080.
 
Anyone have any experience with these tubes?
 
Dave

 

[imckt]

1) Eventually the IBM 5998A is shipped. Let's compare with my RCA 6AS7GA ...
 
Light brown base is IBM. Black base is RCA.
 
Bottom part is similar, but the top part is difference. Square getter for 5998A, while circle for 6AS7GA.
 
Any expert can double confirm IBM 5998A is identical to RCA 6AS7GA?
 
2) Moreover, I have find a dealer selling National 5998, get a pic from them. This is my first time to know 5998 can be straight bottle. But it really look like IBM 5998A / 6AS7GA.
 
I have ordered a pair to verify whether this is 5998A instead. Will post the details once delivered.
 
Comparsion
 

 
National 5998 pic from seller
 

 

[hodgjy]

The National 5998 plates are just 6AS7 plates.  The only "real" 5998 is the Tung-sol.  After that, the numbers get confusing.  Here is my understanding of all the tubes, based on my looking at the plates and hearing them.
 
Plates only, not necessarily bottle shapes:
Tung-Sol 5998 stands alone.
IBM 5998 = Tung-Sol 5998
Chatham 2399 = Tung-Sol 5998.
Chatham 5998 = Tung-Sol 5998.
WE 421 = Tung-Sol 5998.
Arcturus 5998 = Tung-Sol 5998.
Tung-Sol 5998A = Tung-Sol 7236.
Sylvania 5998A = Sylvania 7236.
IBM 5998A = 6AS7 plates.
GE 5998A = 6AS7 plates.
National 5998 = 6AS7 plates.

 

[Skylab]

Nice summary. Looks right to me based on my experience. I would only add that I have Tung-Sol 6520's that are clearly Tung-Sol 6AS7G's, but I also have some that are clearly 5998's.

Oh and it's 2399, not 2339

 

[Beefy]

The real confusion comes from the fact that the 5998A, while having 6AS7 plates, also has:
 
* The lower heater current of the 5998; 2.4A for 5998(A) vs 2.5A for 6AS7
* The higher amplification factor of the 5998; 5.4-5.5 for 5998(A) vs 2 for 6AS7
* The higher transconductance of the 5998; 14000-15500 for 5998(A) vs 7000 for 6AS7
 
References for Tung Sol versions of all tubes:
http://tubedata.tubes.se/sheets/127/5/5998A.pdf
http://tubedata.tubes.se/sheets/127/5/5998.pdf
http://tubedata.tubes.se/sheets/127/6/6AS7G.pdf

 

[hodgjy]

Good catch!

Oh and it's 2399, not 2339