Valve junior filter cap help

[grandmasterflash213]

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

[Amp Kat]

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.

[steve]

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

If you have the newer version of the PCB, there is already a resistor in the PS to drain the caps. Look for a 220k, 3w resistor marked R11 on the PCB.

steve

[grandmasterflash213]

Thanks for that! i didnt even notice this resistor. Mine is the newer version as it has 4 filter caps, and doesnt hum !

[davethehat]

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.

[Enzo]

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.

[davethehat]

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.

[Rick Erickson]

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.

Sure, but didn't most of those radios & TV's have tube rectifiers? The Valve JR has a SS rectifier which dumps full B+ to the tubes the minute it turns on. I suppose it's no big deal if you shorten the life of a single 6V6 and one 12AX7....

RE

[Enzo]

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.

[pvsage]

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.

I'm an absolute n00b when it comes to tube amps (I was only converted from the Church of JFET last week), so I know virtually nothing about this triode/pentode mod. However, here are some pdf's of various editions of the stock schematic that I've been able to track down:

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!