Bassmec

I have a very old ABM EVO 115 lead slead combo that I use for practice, a very solid sound for a transistor amp, I find the MAG 300's that turn up in the rehearsal studio from time to time, to be surprisingly powerful for the spec and very reliable, if you don't go silly on the minimum ohms. Of course the more efficient speakers you run within 4 ohms the louder the little amp gets.

Well I have been an amp tech since 1972 and often used Watford Valves and primarily bought matched sets of Svetlana tubes in either EL34 or KT88. If its my amp I will find up nice old tubes, mostly ex equipment off eBay and such like. I tend to look for Brimar, Mullards, RCA and GE. Matching sets of tubes is not so bad with old tubes, as they had such good quality control and spec back then that for instance if you substituted any Mullard or Brimar EL34 they would usually have very similar quiescent current and bias together as nicely as any new manufacture so called matched set. If its a customer amp and they just want it to work properly, JJ is no worse than other cheapish new production tubes brand.

[quote name='Waldo' post='303314' date='Oct 9 2008, 08:40 PM']Changing valves is like changing lightbulbs Oil on your skin can make weakspots on the valves? Is there anyone who seriously beleives that?[/quote] Not oil for tubes but even that is true of some hallogen bulbs. I have seen a hot fender bass man 100 picked up by a sweaty roadie go plink when a drip of his sweat dropped onto one of the hot output 6l6 tubes cracking it and turning it a milky color we just wiped it out and its corresponding pair in the push pull arrangement and he then had the equivalent of a fender bassman 50 for a couple of dates on the tour, as he was a guitard he was as usual normally too loud in the stage mix so we put off getting him a new tube for as long as possible. we gave in in the end but after that he kind of turned down a bit having enjoyed his limited power more than he cared to admit. Output tubes in most amps need to be in matched sets unless there are bias controls for each tube and correct biasing is essential for all output stages. Pre amp tubes are not a problem to just swap without doing anything else and If you are lucky you can get some real great tone from all the usual old suspects like Mullard, Rca, Ge, Brimar, one of my favorite 12 AX7 or ECC83 tubes is the Mullard CV4004 mil spec tube they are hard to find but well worth it. I have an original set of 1970 GEC KT88's that have been in an amp in a busy studio and tested just like new when we recapped it recently, the oldest set of tubes I use every day are a set of rca JAN 1620 valves dated 1938 they are still fine. Those old tubes where made like jewelry, quality is not getting better in new tubes at all.

[quote name='thinman' post='242998' date='Jul 18 2008, 07:26 PM']I think it's fairly common practice - don't people use dedicated bass-specific pre-amp for tome shaping etc and a power amp to drive the cabs? As regards the Powerline I believe it's quite a budget product but it may do you fine if you don't overload it.[/quote] The Powerline 800 is quite rugged road wise and a cut above quite a few similar amps sound wise. If you run it within its ratings it wont thermal out on you like some that shall remain nameless. sh*t! donch'a just hate it when that happens.