John Truba's Blog

Catch up with my musings on music and everything else in the world of Valve Amplifiers

New Ideas , concepts .

I have'nt had much to say about valve amps for the last many months , but the braincell is at work all the time trying to come up with something novel  , Pause , back in 94/95  I came up with a design for a 50 watt head with 6 EL84's in Push-Pull  at the behest of a guitarist friend in Co Cork  ( now emigrated from our shores ) . I believe it was a first , a Hex84 cct.  . The EL84 valve is my favourite valve , if you use one in single ended Class A  say 4 to 5 watts  , you've got an ideal practise/ recording amp  , without being too loud .  2 EL84's in Push-Pull can give you 10 to 15watts of lovely guitar tone depending on type of cct employed .and of course 4  EL84's are the classic power stage of many an amp. notably the AC30  arguably the best guitar amp ever !  I took it a stage further in 94/95 with  6  EL84's  , it put out a clean 50 watts thru' a self designed output transformer that took a day to wind all the bifilar windings , I say it myself that was a good amp , wonder if it's still somewhere in Co Cork ? . Which brings me back to the current time . The autumn months were'nt wasted  ,  I was working on a new development  which appears to be fruitful  , A Dual output mode amp which uses a common pre-amp. voicing  But is selected to 2 different output stages  using a common output transformer  with only minor trade off's  as regards optimum matching .

So far I've built  a 100/30w valve head EL34's (4) and EL84's (4)  to give the respective 100watts and  30watts  , also a lesser powered 15" combo amp  using  2 5881's (30watts) and 2 EL84's (15watts) and they both sound great  . They are complicated beasts  and it cannot be used in channel switching modes , But actually deciding which power or tone you want to play with , ie , the larger power suiting a larger venue , the smaller power for a smaller place , this is assuming sensible pairing with appropriate spkr cabs , ideally a 4x12" for larger venues (100w)  and 2x12" for lesser places (30w) .  I dread the the thought of single 12" large power  cabs being used , as some major manufacturers do  " Infinate Sustain Boxes "  I call them , eg  ,  turn the contols up and hold the note  and three days later the same guitar note is still feeding back  . Powers in the region of a 100 watts need to breathe thru' multiple 12" spkrs  such as 4x12" cabs , long live " Marshalls"   . I personally cannot see the logic in making these very small 300watt speaker loaded  100watt valve amps  (which also belie their weight)  .

 This is all assuming you are lucky enough to be playing large venues where you can turn it up !        That's ROCK N ROLL  !!!   .

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