If you look at VTL schematics you will see they are very simple and intrinsically reliable, operating the output tubes at low current. However they use a high anode voltage and the choice of output tubes is critical - if you take Albert Porter recommendation of Wing C 6550 you will have no problems!
Many cheap 6550 can not withstand these high voltages. Also, when tubes became tired replace them - do not wait until they break!
Many cheap 6550 can not withstand these high voltages. Also, when tubes became tired replace them - do not wait until they break!