I already posted a thread on the filter caps, but i need some specific info on the Valve Jnr. I opened up my combo intending to drain the capacitors, but they are soldered directly to the PCB and no legs are sticking out. Do you have to unscrew the circuit board and turn it over and short across the soldered points of the capacitors? Any help most welcome
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Valve junior filter cap help
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No ! you do not want to directly short those caps. It will pop and could do damage to other components. You need to use a discharge resistor about 10k and one end of the 10k to the positive side of the cap and the other side to ground. You can put your meter leads attached to both sides so you can monitor the drop. It is possible that after 5 to 10 minutes they are drained anyway ,if there is some resistors there as MB stated. You can use the tube socket on pin 3 to do it also if you rig up a connection that is safe. I would monitor that voltage at pin 3 or 4 of the power tube socket to chassis ground and see what you have first. You may not need to discharge them.KB
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Originally posted by grandmasterflash213 View PostI already posted a thread on the filter caps, but i need some specific info on the Valve Jnr. I opened up my combo intending to drain the capacitors, but they are soldered directly to the PCB and no legs are sticking out. Do you have to unscrew the circuit board and turn it over and short across the soldered points of the capacitors? Any help most welcome
steve
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schematic for new version
does anyone have a schematic for the new version of the valve junior. Also am i right in thinking if you put an on/off/on switch for the triode /pentode mod this will also give you a standby switch. been a few years since i've done any serious electronics. also whats sort of (voltage/amp) power rating should the spdt have.
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The amp doesn't really need a standby switch. They made radios and TVs for many years, all full of tubes, and not a one of them with a standby switch.Education is what you're left with after you have forgotten what you have learned.
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thanks for getting back to me. but if i did what i suggested would that be a standby switch? i know it probably doesn't need one but it would save wear on the valve. therfore whats the harm. i think 12 year working in IT has rotted my brain by the way as i qualified as an electronic engineer.
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Originally posted by Enzo View PostThe amp doesn't really need a standby switch. They made radios and TVs for many years, all full of tubes, and not a one of them with a standby switch.
RE
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Not all of them, no. I don't want to sidetrack the thread, but on such small circuits, no tube wear savings will result. If it gives satisfaction installing one, then so be it. The tubes will lose their tone long before any cathode stripping occurs. The 12AX7 is pretty well protected by the large plate resistor anyway, and the power tube I don't worry about.Education is what you're left with after you have forgotten what you have learned.
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Originally posted by davethehat View Postdoes anyone have a schematic for the new version of the valve junior. Also am i right in thinking if you put an on/off/on switch for the triode /pentode mod this will also give you a standby switch. been a few years since i've done any serious electronics. also whats sort of (voltage/amp) power rating should the spdt have.
From Ultimate Guitar magazine
http://www.premierguitar.com/issue/w...it_drawing.pdf
Note the typo on C3 - it is actually 22uF stock. This is the version I had in my combo before upping the input impedance (R1 to 1M) and taking the blat out of the low end (C3 and C4 to 2.2uF) - you know, the "basic" mods.
First version VJrH schematic
http://i166.photobucket.com/albums/u..._stock_144.jpg
Second version VJrH schematic (June 2007 release)
http://i166.photobucket.com/albums/u...ematic_V2b.jpg
Note the HiZ input and the change in cathode resistors R8 & R9!
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