You have received good advice.
NEWCOMERS should AVOID Sweep Tube amps (dead end for plug-n-play operation).
IF you want GLASS RF tubes go for a nice SB-200, Collins 30L-1 or Ameritron that use 811A or 572B tubes.
The Russian EL-509/EL-519 conversion for a GLA-1000 is a short term solution -- that does not address the design shortcomings of the amplifier.http://www.geocities.com/ko4nrbs/http://www.xs4all.nl/~pa0fri/Lineairs/GLA1000/gla1000eng.htm
The Dentron GLA-1000 amplifiers are very good for Russian GI-7b builders for raw parts (a better starting point than CB sweep tube designs that lack HF multi-band switching hardware). http://www2.wcoil.com/~tlee/http://w4emf.gs35b.com/GLA-1000-retro-GI7/http://www.xs4all.nl/~pa0fri/Lineairs/GLA1000/gla1000eng.htm
Tony King, W4ZT and Ron Wilson, K4POZ have Builder's Notes for experienced builders using the GLA-1000 or other HF amplifier as a base for a GI-7b conversion.http://gi7b.com/
They have also built a very nice socket, based upon Lawson Summerrow, W4EMF earlier work.http://gi7b.com/inspiration/index.html