mrjones200x Posted August 31, 2008 Share Posted August 31, 2008 Is it possible to say take the Valve junior basic schematic diagram and build a 10 watt amp from it? Still keeping it as similar as possible or would there be to much to work out and easier to use another circuit diagram. Just wondered if it was possible as i like my epi valve junior and wouldnt it be good if there was one at 10 watts excatly the same. (Not the valve senior) i mean excacly the same just 10 watt version!! Link to comment Share on other sites More sharing options...
cGil Posted August 31, 2008 Share Posted August 31, 2008 Sure, slap in a bigger OT and a 6L6 or EL34, or just a second el84 in parallel. We've been doing that stuff for a while over at SEwatt and have it down pretty well. When SEwatt comes back online from its maintenance overhaul, check the FAQ. It basically only requires that you swap out the OT for a Hammond 125DSE or ESE (or other suitably rated OT), add second power tube socket (8 or 9 pin), and adjust the bias and power supply to suit the tube(s) you want to run. But you'll probably want to tweak the preamp to get more out of it to drive the power tube. And you can squeeze upwards of 15 watts out of the VJr with a 6550 or KT88 and the 125ESE. If you want to get the full 20+watts out of the KT88, you'll need a 125GSE OT and 272FX power supply. Build any of these sleepers and you can scare the heck out of all your friends with stock VJr's! No doubt about it! Gil... Link to comment Share on other sites More sharing options...
Jamesrr Posted September 1, 2008 Share Posted September 1, 2008 I'm bored too... :- However !!! I can really recommend the 6L6 Octal route. I have one Epi VJr with the Bitmo Trio mods installed & it's good... but I also have a Legacy Valve Head (Harley Benton GA5 - EVJr clone whatever) which I have gutted & installed a Turretboard Fenderish Octal with a Heyboer OT. It really does sound glorious. I'm still mucking around getting the bias perfect, but it sounds great even so. Highly recommended. Really, really looking forward to the arrival of my "Matt The Tranny Guy" (Musical Power Supplies) OTs for a full 20 watt version OT, which will do a paralleled pair of 6L6s or even a KT88 (not that I could justify the price of one of them !). cheers, James Link to comment Share on other sites More sharing options...
gmm20 Posted September 6, 2008 Share Posted September 6, 2008 or a 6V6 in parallel.. The stock power transformer can handle the 500 mills of filament current for the extra power tube. Also, the Hammond 125BSE for an output O/T would be a better fit for that power range, and for size inside that small of a chassis. -g Link to comment Share on other sites More sharing options...
theteenagegiant Posted April 19, 2010 Share Posted April 19, 2010 So basically if I want to do this with 2 EL84s all I have to do is wire the pin on the original socket to the same pin on the new socket? However what do I change to have 1 EL84 and 1 6V6, because the pinout is different? Also could I switch the original tube to a 6P1P if I can find one? Link to comment Share on other sites More sharing options...
jefrs Posted April 27, 2010 Share Posted April 27, 2010 If you use 2xEL84 then you have to change the output transformer. You do have to understand the pin-out differences between the Octal and B9A bases. If you do the octal mod and use cathode biasing then you do not /have/ to change the transformer because the Ra for EL84 and 6V6/5881/6L6/EL35/KT88 is similar enough to get away with using the existing one. You can leave the EL84 socket in place (separate cathode resistors) so you can swap to almost any bottle without re-biasing, if you use a suitable cathode bias that more-or-less suits then all. With a bit more of jiggery-pokery (like separate cathode resistors) you can run both EL84 and a 6V6 in parallel. Seek ye the EVJ Octal Mod... Link to comment Share on other sites More sharing options...
theteenagegiant Posted April 28, 2010 Share Posted April 28, 2010 I have a 10 watt capable O/T so would the valve side impedance still be 5k or would it be 2.5k? Link to comment Share on other sites More sharing options...
m-theory Posted April 29, 2010 Share Posted April 29, 2010 I have a 10 watt capable O/T so would the valve side impedance still be 5k or would it be 2.5k? Look up the specs for that OT. The manufacturer will have technical specs available online. Link to comment Share on other sites More sharing options...
theteenagegiant Posted April 29, 2010 Share Posted April 29, 2010 My tranny has 2.5k and 5k taps but I need to know which to use. Does adding another tube bring the primary impedance down? Link to comment Share on other sites More sharing options...
theteenagegiant Posted May 15, 2010 Share Posted May 15, 2010 BUMP! Link to comment Share on other sites More sharing options...
m-theory Posted May 15, 2010 Share Posted May 15, 2010 My tranny has 2.5k and 5k taps but I need to know which to use. Try both and see what happens on the scope. You'll probably find that the amp seems very happy with one and not so much so with the other. Does adding another tube bring the primary impedance down? I'd say that probably depends on the whole of the amp. Sometimes, even a minor change can cause some pretty dramatic things to happen. Experimentation can be very good. Or not. Link to comment Share on other sites More sharing options...
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