Hi All.
Looking for some advice from those who may have worked inside amps.
I have a Mesa Boogie Single Rectifier 50 watt head, which features an effects loop in parallel. This can cause issues with some time based effects creating a helicopter/whomping sound as it feedback into itself (my MXR Carbon Copy delay does just that). An easy fix is to change the effects loop into series, which requires desoldering and moving a couple of wires which I am comfortable with doing.
What I'm a little nervous about is death. That doesn't sound ideal to me and is a risk when working on tube amps!
I've read lots about discharging filter capacitors in amps, but have been unable to find anything specifically on the Mesa Boogie Rectifier. Does anyone have any experience on methods to discharge the voltage so that I don't shock myself and worse, die?!
Appreciate any advice.
Thanks
Comments
ICBM will no doubt give us the benefit soon but, just don't turn the amp on tomorrow! Just fix the FX wires. If you want to be DBSure there is no residual voltage, check pin one of any triode to chassis.
I am assuming you have a meter? If not get one PD bloody Q! NOBODY should contemplate ANY kind of work on any electronic gear without a meter.
Have to say, unless you have a dicky ticker (like me!) the discharge of say 50mfds at 400V is rarely lethal*. BLOODY hurts! I grant you but not likely to kill and you would have to get it hand to hand, across chest.
*Never work on HV kit alone, you really need another adult around because even if you were shocked, basic CPR (+a 999 call) would almost certainly save you. Other vital precautions. ..No kids. No pets. No booze.
Of course, many amp techs here have no choice but to go solo but they and I have learned (OH! How we learned!) and lasted. Old but no longer bold.
Just to add. Some kit is really dangerous. Microwave ovens run 1.5-2kV at about an amp. No chance if you copped that. There are some serious HT voltages in some big amps. SVT 600V+ The early Backstar S1 200 700V later reduced to a pussy cat 600 or so.
Dave.
Yes, I have a meter, alligator clips, one hand in my pocket as I type as practice for when I get in to the chassis!
Just looking for some comfort I suppose. I've read all about pulling the plug out with the amp and standby switch set to the "on" position to help drain the caps (also strumming a guitar whilst the sound fades away), but thought I'd ask the friendly community here for their experiences!
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein
Thanks both.
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein
An old Fender bandmaster once gave me a hell of a jolt when putting the chassis back in the head cab. My thumb slipped inside the chassis onto the switches. Bang! I ended up about six feet back from where I started. 450v DC straight out of the caps is rather unpleasant.
It was a good lesson, but it could have been my last.
I really don't want to feel the voltage passing through my arm if I can help it. I'd rather put up with a problematic effects loop!
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein
There is a nemonic in the heavy electrical industry. Switch off. Isolate. Dump. Earth.
Best to "dump" by crocking a pre amp anode, pin 1 or 6 to chassis then if you DO forget the cable, no harm done assuming the anode loads are decently rated.
Dave.
I did a quick test last night and it appeared to clear up the effects loop actually (which is what I was hoping).
Going to do a proper test today, but so far so good.
I have to be honest that there was a little fear when diving into a Mesa Boogie with a soldering iron!
Many thanks for your input everyone.
Looking at the picture below, desolder wire 1 and tape up (attach securely to other wires with cable tie). Solder wires 2 and 3 together (these are the wires attached to to the send level knob).
This leaves nothing soldered to the pot, so the pot will not work (obviously) and makes the effect loop series (from parallel) and means I can hear my MXR carbon copy delay properly!
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein
Either works though, so good luck if you decide to do it. Loads of info out there on the mod and the benefits of it in certain situations.