The Amp Garage

also to be noted that GM from old tubes don't decrease linear with use, many tubes hold GM at maximum values until the end of life...i measured (visible, very used) EL34, which were used maybe 30 years in guitar amp, GM was on max.. new ones (modern production ) dont have this behaviour (JJ EL34 aft...

I have three NOS GE 12AX7WA and a quad of NOS Mullard Xf4 just bursting to sing their little hearts out in it and I don't want to disappoint them! :idea: xf4 tubes are so god, that you can put them in cheap and anemic amp to make alive quickly. when you put them in excellent amp, they have 3D effec...

Thank you bepone, that is very interesting! I'll definitely compare 12AX7 and 12AT7 in the loop and post what I find here. Once I get the footswitch done! Is that a function of plate resistance limiting bandwidth? yes please, let us know diferences :wink: i dont know for sure, but ECC83-12AX7 has b...

fantastic and rich tubes/ experience from soldano hot rod 50

Structo wrote:Gottcha

Can anybody tell me the difference in using different value resistor for the artificial center tap for the heater winding??

no, it doesn't matter, while resistors value are the same, i put 470R when dont have 100R near

hello david, i build many fx loops in the past, mainly for soldano type of amps (all DIY) with 12AX7, 12AT7, 12AU7, 5693, mosfets, subminiature tubes, and for every tube i picked working point from the graph.. i have no experience with "dumble type " fx loops.. from my experience bigger current loop...

bepone, not sure I follow you on "smoothing effects" with the buffered loop. Are you referring to possible capacitative high end losses from interaction with adjacent components? If so, I'll soon find out, but I have used the very same loop twice before in a 2nd gen build and a Bluesmaster w/HRM wi...

very nice.. one question, how FX loop interacts with other circuits inside (do you have "smoothing" effects also when fx loop is built inside?)

simple, when anode resistor goes up (cathode res. follow also), more "glassy" tone you can expect in (lead) overdrive. because ECC83 in OD section, is overdriven hardly and more higher harmonic develops in tone spectrum.. i had in one experimental version of #183 amp 68k resistors in V2 anodes, 5751...

checked schematic and there is no grid resistor EL84 to the ground in design?? [IMG:160:112]http://i284.photobucket.com/albums/ll34/bepone/th_86SpecialVoltages_cr.png[/img] i don't think that this can damage EL84 tube soo much, but there was moments in action, like switching channels maybe or puttin...

What you need to do now is some forensic examination of the circuit to find out what caused such massive overload on the PT. The diode failing open circuit wouldn't alone do it. Check the ripple filter caps. Check also loop jacks for intermittent opens. This could have caused EL84 grid to lose dc p...

also, schematic will be helpful.. which amp, which pt, etc etc
how i follow this board, this is some 5 Watter with EF86?

Any further advice or checks would be really appreciated! Damn shame as I was going to take the amp to a jam tomorrow night, oh well... :oops: hello rogb, step by step, you will find and fix the fault. 1) disconnect PT from the circuit, (all leads, heaters too) and change the fuse. power on and mea...

when you simple disconnect two tubes in PP amp(or put 10K in cathode), primary impedance will be the same, BUT YOU MUST REARRANGE OUTPUT SELECTOR FOR HALF POWER option. this means if 4 tubes works with 4K impedance ratio and you disconnect two of them, remaining two of them will be connected also wi...

I used a super six chassis (essentially a twin reverb) and bought the boards from one of the chaps on the forum and they fit well - it's not finished but there are no issues at all with noise. The paper boards in old Fenders are where most of the noise seems to come from - if you have one that's no...