modding tube amps without killing oneself/amp (1 Viewer)

[JohnnyRaz]

right, couple of months ago got a valve junior amp. Have recorded and gigged with it, and am very happy with it considering its low price. As its the version 3 model, a lot of the orriginal design flaws/ommissions (including only having a 4 ohm speaker out) have been corrected.

however, having been the sort of kid that took his toys apart, and having read loads on the web about how easy this amp is to mod, Im curious to give it a go- at the very least change the valves or buy one of those paint-by-numbers mod kits to stick in a standby switch and a tone knob...

one thing that seems to come up again and again in (the largely ammerican) web waffle about this is the danger of shock from un-discharged tubes. so, how does one safley discharge valves, or is this as much of an issue in a country where the plugs have an earth?

sorry if this seems incredibly dense, but I reckoned the thumped guitar wizards would have an idea.
yours vaccumly
j. raz

 

[chutneyfarmer]

pm your man paoloJM he's always posting about this sorta stuff

 

[tommytrousers]

First off -it's not the valves that need to discharge it's the capacitors- obviously don't touch it just yet!.

 

[JohnnyRaz]

First off -it's not the valves that need to discharge it's the capacitors- obviously don't touch it just yet!.

aye..just been reading about that!
Ive no intention of going near it till I have some notion of what im about! hence this post!

 

[JohnnyRaz]

aye..just been reading about that!
Ive no intention of going near it till I have some notion of what im about! hence this post!

for my fellow tube spas; this is a good website explaining how tubes actually work;

http://www.vacuumtubes.net/How_Vacuum_Tubes_Work.htm

 

[tommytrousers]

I tried a home repair job on a valve amp before and discovered my soldering skills weren't up to scratch, the connections need to be immaculate or you lose performance. I'm personally out of the tinkering game these days and glad for it. I wouldn't personally recommend it.

 

[JohnnyRaz]

I tried a home repair job on a valve amp before and discovered my soldering skills weren't up to scratch, the connections need to be immaculate or you lose performance. I'm personally out of the tinkering game these days and glad for it. I wouldn't personally recommend it.

hmm..fair enough, i do have fuck all soldering time under me belt. any other experiences/advice??

 

[GeneralMapache]

To discharge those big @ss smoothing capacitors safely this is what you do:
1. The quick way: You take a plastic covered wire with the plastic covered crocodile clips at both ends (i.e, no exposed wire or clip, available in Maplins, etc) and attach one crocodile clip to the ground end of the cap and the other crocodile clip to the other plate voltage end. This must be done with only one hand and one crocodile clip at a time!!! and you should have the other hand behind your back so you don't accidently rest the spare hand on something that might cause a shock, it is dangerous stuff. If you use one hand and do get a shock the shock will go up your arm down your side and safely to ground is the theory too, if you have both hands mucking about in the amp chassis trying to connect the two clips at the same time most likely the shock will go up your arm through your heart and down the other arm to ground and you might not be around to joke about it so always one hand behind the back to be safe and one crocodile clip at a time!!! By attaching the wire you are just giving the current stored in the cap a route to get to ground and dissapate away. Leave it for a minute until the plate voltage has dropped to 1 volt or less.
2. The proper way: You take said plastic covered wire with plastic covered crocodile clips and cut it in half and solder a 100 Omh 1 or 2 Watt resistor in the middle and cover the resistor and exposed wire in heat shrink and blow dry it so you have a safe wire with no exposed bits and do the same as in 1. This way allows the current to discharge slower across the wire (cause of the resistor) and avoids any possibility of the wire melting from too high a current discharge etc. I've never had a wire melt on me but this is the safer way. Leave it for two minutes until the plate voltage has dropped to 1 volt or less.

ps. It also helps to have one of those rcd's in your house's fuse box which will detect the surge in current due to a short and might just save your life. How I remember fondly that day I melted a metal pliers while cutting live mains wire, what a giggle I had.

Ruairi.

 

[PaoloJM]

My advice is look up some soldering guides on-line. There's loads of demo vids on uTube and plenty of step-by step-instructions.
Once you're happy with that I'd say make a trip to Maplin or use their on-line store. Get a cheap 25W soldering iron, a small tube of solder, a bit of perf board, a small bag or resistors and a few stakes. Keep practising until you can make a shiney, clean joint every time.
If you're happy with that then get a cheap multi-meter and get good with using it, learn how to read resistance, voltage etc. properly. Again there's plenty of on-line guides.
Then once you're happy with that look up a guy called Alnicomagnet on eBay. He does a mod kit for the VJ that includes detailed instructions with easy to understand technical explanations of what each step does and why.
Feel free to post or pm me any questions. I'll be happy to help if I can.

Meant to link this as well.

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[JohnnyRaz]

sound man, thanks! I'll be back with more stupid questions anon!!

My advice is look up some soldering guides on-line. There's loads of demo vids on uTube and plenty of step-by step-instructions.
Once you're happy with that I'd say make a trip to Maplin or use their on-line store. Get a cheap 25W soldering iron, a small tube of solder, a bit of perf board, a small bag or resistors and a few stakes. Keep practising until you can make a shiney, clean joint every time.
If you're happy with that then get a cheap multi-meter and get good with using it, learn how to read resistance, voltage etc. properly. Again there's plenty of on-line guides.
Then once you're happy with that look up a guy called Alnicomagnet on eBay. He does a mod kit for the VJ that includes detailed instructions with easy to understand technical explanations of what each step does and why.
Feel free to post or pm me any questions. I'll be happy to help if I can.

Meant to link this as well.
YouTube - Journey to the Center of a Tube