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Jax
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#1
17th April 2003
Old 17th April 2003
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Question Guitar Amp Mods

I figure we might as well continue talking gtr amps til we're blue in the face. I sho am learning alot about it.

There's a local fellow with an ad for amp repair/mods, part of which reads: "... a very popular mod I do is to convert a Fender, Traynor, or whatever tube amp you may have (preferably 50 watts minimum) to a Dumblesque amp.(You know, the high priced boutique amp). This will make a mediocre tube amp like a Silverface kick some serious booty."

This is the first time I've heard of Dumblesque. Any info on whether it would be worth doing? Also, whatever mods any Slut knows about (any amp), shed your weight here! I'm all ears.
#2
17th April 2003
Old 17th April 2003
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I dunno about the "dumble" mod, but if you have a decent stock vintage or semi-vintage amp, I would say don't mod it. There are so many newer, cheap amps that can cover a lot of different tones without possibly damaging an otherwise good vintage amp. I dunno, I'm sure people have had good experiences with mods, I'm just bummed cause I gotta rebuild my JCM 800 2203 cause of botched mods...

But that's just me...

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#3
18th April 2003
Old 18th April 2003
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Just about every Fender in here has been 'blackfaced.' I've heard a Dumble, and although a very very good sound, it ain't worth $12,000 (the last one I saw-that was the going price)...

I've always thought that modding guitar amps to be something they are not (IE Fender into Marshall) is a silly thing to do...if one wants the Marshall sound, get a Marshall...want 'chime' get a Vox/Matchless/whathaveyou...

And, FWIW, I think the majority of tone comes from the player...Clapton sounds like Clapton regardless of his amp.

For some really cool amp talk, try Weber VST ... lots of mods/anti-mods discussions, links to schematics, and just about everything else you can think of.
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#4
18th April 2003
Old 18th April 2003
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This is one thing I could talk about for weeks on end.

On one hand I'm all for modding if it's the right thing to do. OTOH, I'm totally against it. There are functional mods and tonal mods and each has it's own evil.

My main instrument is guitar, been playing/hacking away at it for almost 16 years even went to college and took it as a major for a year. Then I got smart and interned at a studio, now I'm here. Anyway, I spent a ton of time in high school and college with a few friends trying everything you could think of guitar wise. Take 4 or 5 guitar players and pile their collections of crap together and you'll get the picture. We also spent lots of time at guitar shops trying stuff out with our own rigs and making those guys nuts. I remember being upstairs in Rudy's and getting calls to turn down from the acoustic room below more then once.

Amp wise we had everything from a 5150, Marshall Major's and a 30th Anniversary, Dual Recto, JCM 900, Twin's, PV Classics, VHT, Vox, Trace Elliot, Rivera etc. different speakers too. Ever try Vintage 30's, Greenbacks, Eminence, Weber's, JBL and EV all in the same cab with 15 different heads? It's loads of fun. Lots of guitars, lots of pickups kinda like a huge swap meet. I lerned a shitload of stuff about guitars and guitar tone which helps me to this day.

Modding amps can be a great thing if your adding features. Need a footswitch to turn the 'verb on your old Gibson amp on and off? Go for it. Same thing with adding a mid-control to the back of a Fender, it usually goes in one of the 1/4" jacks and I see it all the time.

Now, hacking up an amp to get a different sound is a no-no in my book unless you feel like going on an endless search and have deep pockets. The first thing is that if the amp is "vintage" and you start drilling holes in the chassis your sunk because the amp will loose it's value. Also, you'll never get back any of the money you put into the mod regardless of the amps vintage. For the most part people really don't care about your special hip mod unless it's a common one like adding a 4 ohm tap to a Fender Bassman.

And this is probably the biggest reason not to mod. 90% of the time you should really just buy a new amp rather then modding one. I and my friends have chased the holy grail one too many times trying to get a little more ABC out of XYZ amp only to spend a few hundered bucks and still not be happy with it. The case in point was a Marshall Major. This happened about 6 or 7 years ago so my memory is a bit hazy on the exact pricing and details but it's close enough.

My friend Pete was looking for a Plexi or early 70's JMP when he found the Major for chump change that had already been modded with a JMP preamp. So, he bought it then discoverd that it needed to be retubed. After that, the amp still had some issues, one of which was needed to be cranked up a bit before it sounded good. Not to a totally sick volume, but pushing more air then you'd need in a small club. Rather then getting a power break he wanted a bit more gain from it so in goes the Soldano mod at $300 or so. A few weeks later he thought the amp had almost too much gain and when he used the extra gain stage the low end went away. So, he had it modded again with a pull switch for extra low end at another $175. Let's go a few months into the future and he still wasn't all that thrilled with the amp so he had the Soldano mod bypassed but kept the bass boost for $125. But, it still ain't right, he's missing that bit of extra gain and he's already tried the EQ pedal trick and other things. So, he has the Soldano mod re-reversed (no charge, tech buys him a pizza because he's up to 10 "Serviced by" stickers on the back) and dumps the thing off for I think $400 to another friend.

$375 - Original price of Marshall
$250 - Retube
$300 - Soldano mod
$175 - Extra low end
$125 - Additional mods

Total cost - $1125

What he ended up with after a lot more searching was a collection of amps including a Marshall DSL 50 and a real Soldano. Either of which he could've bought for the total cost of the Major Mod and been happier from the start. There are SOOOO many amps out there that you're probably going to find something great that doesn't need any work at all.

More on Dumble when I get a chance...save your pennies until then.
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#5
18th April 2003
Old 18th April 2003
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I find myself in great ambivalence on this topic. On the one hand, I'm all for people making a piece of gear do what they want it to do. On the other hand, I hate to see something that had a certain perfection of it's own changed.

The stuff that's already been said about not trying to get Marshall tone out of a Fender is pretty much spot on. It's far more interesting to have two amps, which gives you lots of options, as opposed to a one amp modded towards a single particular sound. And yes some mods may actually broaden the palette, but that doesn't seem to occur as often.

The there are the mods that correct really stupid choices by the makers. The silver to blackface mods for Fenders seem to fall into this category. I also have a Marshall JCM 90 that has had the diode distortion crap removed from it. That seems to have been a good choice.

One other consideration, if you're the kind of guy that moves from amp to amp, the mods seldom if ever add to the resale value of the amp, and usually detract.
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19th April 2003
Old 19th April 2003
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I would offer that it can be quite appropriate to do a mod that fine tunes the sound of an amp to fit the player better. Little things like fine tuning the tone controls, messing with the r/c coupling in a Marshall if you feel like you're dumping a bit too much bass, tweaking the amount of negative feedback to tweak the "rawness" of the amp's sound. If you like the basic sound of a classic Fender or Marshall circuit, there's so much info out there that a player can easily get it tweaked to better fit his needs without changing the essential character.

The other big thing to consider on two channel Fenders with Reverb is that the Normal channel is generally never used. I consider that fair game if it can be reconfigured to provide functionality. It's easy to route this channel to the reverb as well, so it's easy to set this up as a slightly different sound alternative. Hell, leave the Reverb channel stock and tweak out this one, so you lose nothing you had but still gain a tonal option.

Part of the popularity of using the old amps as the basis of mods was that when the practice started the amps cheap (remember when you could pick up a silver face Twin Reverb for under $500?) and parts for scratch builds were scarce. Chasis and transformers can still often be much cheaper from a donor amp where all the rest is scrapped. At the prices silverface Fenders are comanding now, it IMO only makes sense to buy a Fender to be a Fender. Also, most people are clueless on power supplies (I know I am) so it's often easier to start with a working one.

Bear
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#7
19th April 2003
Old 19th April 2003
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hey, I have an original JMP master volume (late 70's)
2203 chassis.
I want more pre gain for a more metal sound.
any hints on how to mod this beauty, or do I just have to buy me a nice stompbox?
#8
20th April 2003
Old 20th April 2003
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Somthing like that I'd use a stomp box or two...Drop a Tube Screamer in front of it and stand back...
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20th April 2003
Old 20th April 2003
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Marshall's and high gain mods aren't really anything I know too well. You can get to pretty much anywhere from the links at www.firebottle.com/ampage, which is a great DIY forum for anything involving guitar electronics. You could spend a week or two just clicking through all the links they have, never mind asking the locals for tips. (I just posted a question there for an amp I think I'm going to scratch build, so that should convey that I value the place.)

BTW, if it's a 4 input amp with Bright and Normal channels, any easy no-mod trick to push it a little harder is to plug into one channel and jumper the two channels with a patch cable from the second input to the other channel. You're running two channels (which naturally sound a bit different - a lot of people do this not for drive but for tonal balance) and pushing the output a bit harder. It isn't really a high gain modern metal sound, but it is a vintage 70's rock trick that'll get you a bit more raunch and thickness.

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#10
20th April 2003
Old 20th April 2003
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Quote:
Originally posted by andre tchmil
hey, I have an original JMP master volume (late 70's)
2203 chassis.
I want more pre gain for a more metal sound.
any hints on how to mod this beauty, or do I just have to buy me a nice stompbox?
Don't mod it. If you aren't happy with it someone will be more then happy to take the amp off your hands as-is while you go out and get a Marshall DSL, 900, Boogie, Soldano etc. for the high-gain metal stuff.

What I would do is jump the inputs like Bear said. Then use some low-gain stomp boxes to kick the front end in the balls. Zakk Wylde is a huge fan of the Boss SD-1. Keep the gain low and the output high, you could also try a Tube Screamer or a Klon Centaur or the Fulltone stuff. Another favorite trick is the 'Slash' method. Grab a graphic EQ pedal (the Boss is the most popular) but don't boost or cut anything, just raise the output gain. That way you get the same sound that the guitar is putting out, just louder.

If those tricks don't give you enough gain or control buy another amp and keep the Marshall for whatever it's good at or sell it.
#11
20th April 2003
Old 20th April 2003
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Dumble amps.

I'm not quite sure what to make of them, I've played two examples a total of three times and each time I did I was kind of scratching my head when I walked away. For starters, they're totally hand-built. Rather then stamping the chassis out of aluminum like a Marshall or something he takes a solid block of aluminum and mills it. Everything is custom built and mil-spec on those amps. That accounts for most of the price. SRV swore by them for a year or two, so did Eric Johson, Robin Ford and a number of other cats with great tones.

So why the hell didn't I like them? After miuch thought and a few hours playing it next to other amps I came the conclusion that a Dumble is a one-trick pony much like a Plexi, AC-30 or a Champ. But, those amps are like a Pod next to a Dumble. The real deal with a Dumble is that if you dig in and are a muscle player it's NOT the right amp for you. The harder I hit the guitar and the more I dug in the smaller it got. When I backed off and used less pressure from my hands it started to sound HUGE and magical. But you read about the guys who sware by Dumble amps and they all have light touches so it makes total sense. The exception the rule was SRV and even his Dumble period was only a year or so before he went back to Fenders.

If you play with a super light touch it's totally worth checking out, If you use big heavy strings (11 or better) and play hard skip a Dumble.

BTW, one of the coolest modded amps I've ever played was a blackface Deluxe reverb that had been gutted by Ken Fischer and turned into a Trainwreck. Holy crap. Instant goopy sustain, think early Santana. Just ****ing magical if you want that sound. It didn't matter where the knobs were set because they didn't seem to do much but wow man, just magical sound. Is he still around? I know he had some major health problems and had to stop working for a while.
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24th April 2003
Old 24th April 2003
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#13
24th April 2003
Old 24th April 2003
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i ****ed up 2 marshalls and some guitars with adding options i thought they would be cool in the first place but afterwards i figured out , that the sound changed in a bad way .

i think the best sound modification option you can without the need to solder or change the original amp is using different instruments or some stomp boxes .
probably i never heard a " good " modification . i just heard mods which increase the options but killing the basic . even if its just a simple fx send & return . it would be a dream for me finding a amp with lots of flexibilty and still " an original " sound .

i am having an eye right now on those matchless amps .
any infos bout those babys ???


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24th April 2003
Old 24th April 2003
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I've seen the innards of enough Matchless amps to conclude they'd be a PITA to mod, if that's what you mean. I believe there are schematics out for some models and some DIY-ers building copies or derivatives. To be brutally reductive, a Matchless is in essence a Vox made with mil-spec parts and Hiwatt style wire bundling (though not nearly as neat as any Hiwatt I've seen). Some of the designs are in fact fairly original, but the models everyone talks about owe much to their Vox forbears. If you intend to mod a garden variety Marshall or Fender to Matchless territory, I'd suggest you're better off with a scratch build.

Bear
#15
25th April 2003
Old 25th April 2003
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Quote:
Originally posted by 5down1up
i am having an eye right now on those matchless amps .
any infos bout those babys ???
Check out the last few pages of the guitar amp recording thread.
#16
25th April 2003
Old 25th April 2003
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FWIW, I have two older Fender amps that have been modded and sound great.

One is a silverface Twin that I picked up for a song because someone had modded it. It's a wacky thing with pre/post gain, a switchable mid-boost, fx loop, presence, etc, and it's actually got a very cool and unique sound.

The other is a early 70's Pro Reverb that I had restored to Blackface, which because of the vintage and parts was basically swapping some capacitors and a few other small things. I kept all of the parts and it would be easy to switch back.

So I've had great experiences with modding - people love recording through them, and my band uses both of them. The two complement each other very nicely and I don't usually like duelling Fenders amps in a band.

Sometime I'll have to write about the Mullard rectifier tube story in the Pro Reverb. Let's put it this way - I am now very interested in getting some NOS tubes and would be curious about others experiences and where they picked them up...
#17
25th April 2003
Old 25th April 2003
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Mullard rectifiers (I'm thinking GZ-34/5AR4's here) do have a reputation for being nearly indestructible, with service lives stretching into decades.

The most common complaint I've heard about rectifiers is that they will have been abused enough that they rattle. Electronic failures do sometimes occur as well, more readily with most of the Russian of Chinese ones, apparently. One thing to keep in mind with most tubes is they almost always fail mechanically before they fail electronically. It's a strong arguement for not setting a head on the speaker cabinet, or a stack of 412's really hammering away.

Bear
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25th April 2003
Old 25th April 2003
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Excellent! This thread is going exactly according to plan (rubs palms together)...

I appreciate it. This is what I was looking for.
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26th April 2003
Old 26th April 2003
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What are Mullard EL34's going for these days? I have some in my Sound City 120 and I didn't know it when I bought the amp.
I know they're expensive but how much are we talking?

See, I wouldn't hack up an amp like that Silverface Twin but if I came across one that someone else had mucked with and it sounded good I'd consider buying it.
#20
27th April 2003
Old 27th April 2003
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Jay, Mullard EL-34's are well over $100 a pair for NOS. Used and tested will probably draw some cash as well. As replacements for tubes that need that Mullard sound, I like the Svetlannas a lot. (People will also mention NOS Siemens, but I think the Svet's hit it much better.)

Bear
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27th April 2003
Old 27th April 2003
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Quote:
Originally posted by Gone Fission
Mullard rectifiers (I'm thinking GZ-34/5AR4's here) do have a reputation for being nearly indestructible, with service lives stretching into decades.

The most common complaint I've heard about rectifiers is that they will have been abused enough that they rattle.
Bear
That was what happened with mine. It was the original tube (~30 years old!) and it started to make a physical rattling sound after the amp had warmed up. Not a problem for gigs but it was driving me nuts recording.

After replacing it with a new Chinese tube though the sound lost a lot of it's magic. Brought it into my tech and we did a blind shootout of 12 rectifier tubes (6 new, 6 NOS, rebiasing in between changing each tube). Picked out my six favorites, then out of those four, then two.... and in the end chose a NOS Mullard again!

In each series of tests there was one I always liked the best, and when it came down to the final two all I had to do was hit one note and knew which one I liked (the other was a NOS RCA). So, I ended up buying the tube off of him and my amp sounds killer again.

As I said before, now I'm really interested in trying some other combinations of tubes - I was amazed at how much difference the single tube made, I really didn't expect the rectifier to make that much of a difference...
#22
28th April 2003
Old 28th April 2003
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Does anyone know if there's a quick & dirty method to bias the tubes in an amp? I heard something a while ago that you can watch for the lowest amount of glow or something while the amp is idling. Any ideas?
#23
30th April 2003
Old 30th April 2003
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Quote:
Originally posted by Jay Kahrs
Does anyone know if there's a quick & dirty method to bias the tubes in an amp? I heard something a while ago that you can watch for the lowest amount of glow or something while the amp is idling. Any ideas?
Quicker than using your Fluke at the specified test point
and looking at the voltage (if you're lucky, or current if
you are not)?

Most of the amps' circuits are readily available, many
on the 'net.

Of course, the official factory bias setting was just
one engineer's view of the proper tradeoff between
tone and tube life. Your tone and tube life will....
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#24
30th April 2003
Old 30th April 2003
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Ok, but what if you don't have a fluke meter? Is there a way to "wing" it?
#25
30th April 2003
Old 30th April 2003
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Quote:
Originally posted by Jay Kahrs
Ok, but what if you don't have a fluke meter? Is there a way to "wing" it?
Not something I'd want to "wing" Jay.

Here's a good summary of biasing methods.

http://people.cornell.edu/pages/mt24.../biasmeth.html

Get a tech to bias your amp or get one of those Bias Probes and do it yourself but you will need a meter.

Mark
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30th April 2003
Old 30th April 2003
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I would not try to "wing it"
A really nice Fluke meter will only cost a little over $100.
A good set of tubes can easily cost that much, just
for one amp. Less than even a cheap Chinese LDC mic.

The difference in setting between "great tone" and
"fried tubes" is often too close for winging.

Plus, the going rate for biasing an amp arround here
seems to be $50 to $65 per amp, which has
to help the bottom line.

It isn't hard to do. But be careful in there. Tube amps
have voltages up in the 400 to 500 volt AC range.
They can and will kill you, really, if you are sloppy.
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#27
1st May 2003
Old 1st May 2003
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Yup. I know that the plate voltages are leathel, I ain't no dummy. But it seems rather strange that you can find whole articles on how to setup a guitar and even replace frets but bias an amp? Never. I usually take it to my tech but only when I have the power tubes replaced. Should an amp be biased every so often like a guitar setup?
#28
1st May 2003
Old 1st May 2003
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I've actually seen quite a few articles about biasing but have never gotten into it because the proper equipment to do it HAS been somewhat cost prohibitive. And anyhow it doesn't need to be done that often, so I have a tech do it.

It's a good idea to have the bias checked even if you are just changing the preamp tubes. Tubes do change over their lifetime so even if I keep the same tubes for years (which I do), I have my amps looked over every couple of years just to keep them in top shape - check the bias and overall condition.

As for mods, no thanks - my amps are perfect like they are. My blackface Fender Pro was seriously screwed up by its former owner who tried to mod it. I think it's getting over the trauma finally.
#29
4th May 2003
Old 4th May 2003
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Quote:
Originally posted by Jay Kahrs
Yup. I know that the plate voltages are leathel, I ain't no dummy. But it seems rather strange that you can find whole articles on how to setup a guitar and even replace frets but bias an amp? Never. I usually take it to my tech but only when I have the power tubes replaced. Should an amp be biased every so often like a guitar setup?
Clearly, every time you change something "major" you
need to check the bias. The problem is what
is the proper definition of major. It at least
means everytime you change the power tubes.
Or any of the power tubes.

At VPISU they taught me that a properly designed circuit
should not need alignment even if the active component
is replaced. I have seen this also in Radio Repair
textbooks. For the most part this is good advice.
Especially if you are not confident you can do it,
and it is late Friday night, and the band is ready
to record.

As lflier sez, many folks also check when you change
the preamp tubes. So the definition of major
varies, YMMV, etc.

However, if any of the bias resistors have been changed,
or they are suspected of changing indicated by being 30
years old, charred brown, moldy, or just gunky, an
adjustment might help. The resistors should be checked
and replaced if bad. If the capacitors have aged,
they are probably now capacitors in parallel with
resistors, and they are DEFINATELY affecting
the bias. Bias adjustment should not
necessarily be done here, but capacitor
replacement should.

If you change bad capacitors or a bunch of resistors,
then (a) you are an amp tech, and don't need my
advice and (b) should clearly check the bias.

I'd say check it whenever you buy it, every time
you change a "major" thing, and then every
few hundred hours of use. (which is usually
when the power tubes fry anyway). And
every time it comes out of storage after sitting
for a year or more.

BTW, they sell plastic screwdrivers specifically for adjusting
the bias pots and other dangerous things. That way,
if you accidentally cross the screwdriver against hot
leads, you don't cause an arc. They are cheap insurance.

While everyone here is probably already aware,
it is a good idea to put one hand behind your back
while sticking probes into live tube circuits. So the
power doesn't go up one arm and down the other,
frying a critical muscle (your heart) while it zooms
up and down your arms.

This is not a dumb/drunk/stoned "user servicable part
inside"
#30
5th May 2003
Old 5th May 2003
  #30
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Quote:
Originally posted by fishtop_records
While everyone here is probably already aware,
it is a good idea to put one hand behind your back
while sticking probes into live tube circuits. So the
power doesn't go up one arm and down the other,
frying a critical muscle (your heart) while it zooms
up and down your arms.

This is not a dumb/drunk/stoned "user servicable part
inside"
Totally. I was taught to keep one hand in my pocket at all times. That's a bit better, takes a little more effort to move it fast.
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