There is a common misunderstanding in the internet called TESLA-JJ tubes.   I don't know which duck invented this word,  but such tubes don't excist.     There are TESLA tubes,  and there are JJ tubes,  both made in different factories, by different people, with different technologies.  Only the machines are the same. The used materials definitely are not. For instance TESLA has used the cathodes from the former TESLA Rosnov factory, but this factory is closed now.  So Tesla gets them somewhere else.  Cathodes are elementary  for tube performance.  

May be you know that Yugoslavian "EI"  ECC-series tubes are made on old Philips machines.   This is EXACTLY the same situation, but I hear nobody talk about  EI-Philips tubes.  They are regarded something different, which is correct. 

Until 1997,   the world market  prices of tubes of the  ECC series  were relatively low. There was enough NOS around. Many people thought this situation would allways stay that way, and the TESLA management thought so too.  

The Russians sold NOS EL84 for 400$ per 1000,  and from China you could buy good EL34 and ECC83 for increadible low prices, if you knew the way.  It was b ythat time that Tesla decided to sell off their line of  Audio tubes to JJ.  In the last years,  the TESLA ECC83 was sold for only 2Euro in OEM quantities,   by company in Austria, who claimed to be their exclusive distributer.   From this you can see that the factory price must  have been very low.  After selling off the audio line,   TESLA went on making transmitter tubes, and other devices like vacuum capacitors, and military devices,  which they considered more profitable.

So the TESLA ECC-series, EL34, and KT88 was out of production now.   The machines were moved out of the building and re-enstalled at the JJ factory.

Unfortunally for TESLA, this was a big mistake.   In the  years after that,  Ebay made the NOS prices soar,  and today in 2004 they still rise 20..30% per year.  NOS is practically unavailable in  quantities.  Russians and Chinese tube factories raise thier prices twice a year due to higher energy costs and higher cost of all kinds.   It  appears that JJ made a perfect buy!

Since most JJ  tubes are mader with old TESLA tools,  differences are small.    They do use a different cathode, because the TESLA cathode factory in Rosnov is closed now.   Both TESLA and JJ used to get their cathodes there.    So NOS  TESLA tubes have cathodes from Rosnov,   and where JJ has their cathodes from today,  I don't know.  This is one difference.

Indentical tools are used

Another difference is in the part numbering.    E88CC originally is a long life version with gold plated leads,  but the TESLA version has only normal leads.   In the below picture you can see this difference clearly.

Gold pin TESLA tubes.

The next differnce I noted, are some costs savings on the shielding.  With this tube there is a shielding plate between the two triodes.  With the TESLA tube, they did someting nice.  The shielding plate was coated black, and is used to transport the heat out of the tube center.  So is is used a cooling fin.  This is great, because the center anode plate is already hotter than the outside anode plate.

With the JJ tubes, exactly the same shielding plate is used as with the TESLA tube.  Only  JJ uses lower cost, untreated white nickel, so the cooling fin function is not present any more. This will give the old TESLA tubes a better lifetime expectation.  In vacuum,  only black material will radiate heat very good.

For the Czech Post, a GOLD GRID version was made.  These are little jewels.   Highly underestimated.  Most of them have yellow printing.    These are from the 1960's.

Here you see a close up of the gold plated grid bars coming out of the mica. So obviously they did not use just gold plated grid wire, they gold plated the complete grid after it was made.  What a quality this is!