Hi everybody, could you confirm if this tube is well for F1-X?
http://www.jj-electronic.sk//pdf/ECC%20803%20.pdf
best regards

Pierre-Yves,  
 
I have a JJ ECC83 in my F1-X.  Recently, looking for a higher-gain tube, I made an inquiry to a reputable company called Eurotubes (http://eurotubes.com/).  
 
They recommended the JJ ECC803 and assured me it would fit within the same metal sleeve as the ECC83.  But I do not have personal experience with the tube, so I cannot be certain.
 
Hope this helps.
--Joe in San Diego, California, USA

JJ ECC83s are one of the smaller diameter current production 12AX7/7025/ECC83 tubes.  Electro Harmonics, TungSols, and Mullard reissues will probably be too large to fit inside the shield on an F1-X.  Just tried all of these in a 70's Marshall with small diameter shield bases and the JJs were the only ones that fit.  I highly recommend getting the Ruby tested 12AX7HG+, which is Ruby's nomenclature for the highest gain/lowest microphonics JJs out of the large batches they get.

But they are ECC 803, not ECC83 ? Possible to compare size of your tubes ? Sorry, I don't have pied ? coulisse:
http://www.temps-et-mesures.com/img/p/218-274-thickbox.jpg  
 Thank's

How about some data sheets for JJ tubes:
 
ECC803:
http://www.mif.pg.gda.pl/homepages/frank/sheets/163/e/ECC803.pdf
 
ECC83S:
http://www.mif.pg.gda.pl/homepages/frank/sheets/163/e/ECC83S.pdf
 
Hope this helps!