I highly recommend the conversion to the GI7B or the EL-509/6KG6 tubes. I prefer the GI7B myself but the EL-509's (russian sweep tubes) work ok to. Both are Russian military surplus tubes and are excellent for conversion in any Dentron GLA-1000 series amplifier.
Look on my web site:http://www.geocities.com/ko4nrbs
Look on the N2DX web site as well.