The Canadian Guitar Forum banner

1 - 20 of 22 Posts

·
Registered
Joined
·
365 Posts
Discussion Starter #1
I'm interested in some simple amp mods for a '70 Traynor head I just got. I don't have much experience with soldering, but I would definitely like to change the power cord to a 3 prong one.

Does anyone know what the ground switch does/is for?

:food-smiley-004:
 

·
Registered
Joined
·
274 Posts
-the three prong cord is pretty standard and not too hard. (black and white go where they were before, and green goes to chassis if possible, some other ground if not)

-One thing I thought helped a lot was to pull the treble pass cap off my volume pot. The active treble and bass pots have huge range anyway.

I have heard of a few people changing the main volume from 4megs to 1meg (again to help with the harshness)
 

·
Registered
Joined
·
365 Posts
Discussion Starter #4
I really don't know anything about electrical stuff, but the amp has a 2 prong power cord, then a ground switch. what could potentially happen if I didn't replace it?
 

·
Registered
Joined
·
1,381 Posts
I'm guessing that it lifts the connection to the chassis ground, but I'm not sure.

I know that some older two pronged stuff had a polarity switch, that did the same thing as turning the plug around in the socket.

Better wait for somone that knows for sure.
 

·
Registered
Joined
·
3,220 Posts
with an older 2 prong cord i think it is polarized to work only one way- one prong is supposed to be bigger than the other so you dont plug it in backwards- however it wasnt standard for buildings to have all the same type plugs. if you plug an older tube amp into a wall socket, perhaps you have it backwards, and face a shock. the three prong ensures that you plug it in the right way around, and also the extra ground helps.
seemed to me that on an older 2 prong amp you used the ground switch to reverse the signal, you knew the correct setting to use because the hum was less.
 

·
Registered
Joined
·
1,154 Posts
Make sure that if you open it up to remove the charge from the caps first. There's enough voltage in there to make you adamthedead. Check online to see how it should be done safely.
 

·
Registered
Joined
·
737 Posts
I really don't know anything about electrical stuff, but the amp has a 2 prong power cord, then a ground switch. what could potentially happen if I didn't replace it?
Hey Adam; If you don't replace it you can get a shock when you get between the amp and ground, if the 'hot' is connected to the chassis. So, I think it's when you get a shock, simply switch the ground and then you won't, or maybe a bigger one. Best to change it and disable the grd sw.

As for mods, depends on what model it is. Some have an un-used tube section that you can hook-up for more gain/dist. If I wanted to, I could re-wire the tremelo tube in mine for additional gain stages, add a master volume. But I'm leaving it 'stock'.

+1000 to NB-SK's comment, be careful, go in there with one hand behind your back.
 

·
Premium Member
Joined
·
17,444 Posts
Adamthemute: Take your amp to a tech !!

It is not just about learning how solder (and that takes some practice as it is) but also knowing how to identify the components, how to discharge the caps (as mentioned) and how to wire the components together correctly so that you don't end up creating a dangerous situation for yourself and potentially damaging your amp.

The responses you have been given so far in this post are meant to be helpful. I don't think some of the responses are very accurate (I'm feeling the heat of the flames now).

IMHO, making an amp safe and getting the best tone from it is not a task for a beginner.

Dave
 

·
Registered
Joined
·
2,665 Posts
I really don't know anything about electrical stuff, but the amp has a 2 prong power cord, then a ground switch. what could potentially happen if I didn't replace it?

Adam, you shouldn't get a nasty shock with a 2 wire cord. Despite the implications of all the tips to the contrary, people were not electrocuting themselves daily before the 3 wire cord was adopted!:smile:

This is the REAL story!

There are 2 different categories of power systems in old radios, amps and other vintage gear. Really cheap stuff did not have a power transformer. The line voltage was rectified into DC power for the tubes directly. All circuits must have a ground return. With the cheap gear the chassis was NEVER connected DIRECTLY to the line voltage "ground"! The circuit may have used the chassis as a return but then they used a big capacitor to connect to the AC power as a ground return.

If you had a cheap radio and one of the knobs had broken you might have been turning the radio volume by gripping the bare shaft of the pot, which of course was grounded to the chassis. That chassis was grounded to the circuit through a capacitor, as I had said. One of the two line power lines was always "neutral", or grounded already. The other was "hot" with respect to ground. If you were washing dishes at a metal grounded sink and reached up to adjust that bare volume shaft you had a 50:50 chance that you might get a little tingle shock and NOT a total electrocuting zap!

That's because it depends on which pins on the plug at the wall were lined up with the power line neutral. If things were the wrong way then yes, the chassis was "hot" to ground but THROUGH A BLOCKING CAPACITOR! That capacitor was only big enough to allow signal ground currents to flow through it. Big scary currents saw the cap as a big limiting resistor, that let enough through to give a bit of a "tingle" (not pleasant but not really dangerous) but not enough to be life-threatening.

More expensive equipment had a power transformer. This provides total isolation between the unit and it's chassis and the wiring in the wall.

So far I've been talking only about safety concerns. The other factor is grounding as shielding from stray hum and noise pickup. Using a cap and/or a transformer for isolation still leaves the problem that hum can get into your amp or radio circuits and end up in the speaker audio. If the chassis is grounded through a cap and/or coupled through a power supply transformer then the metal of the chassis acts as a shield to keep that nasty stuff out. However, if the plug pins are reversed so that the "ground" side is on the "hot" wire and not the ground neutral then the chassis is not grounded through the power line system and rather than acting as a shield it actually becomes an antenna for hum! Every guitar player has found that at times his guitar and cord seems to be picking up hum, changing as he moves around.

Every radio owner in the old days knew that his radio,record player or amp would have less hum if he flipped the plug at the wall the right way. With guitar amps the makers put in a "ground reverse" switch. It worked by grounding the chassis to the power lines through a capacitor, but the switch would toggle from one power wire to the other. That way if the plug was the wrong way or if the wiring in the wall was not consistent ('cuz someone let their idiot brother-in-law do the wiring) the switch would flip things for you and let you choose the position that killed the hum best.

Where the scary stories come in is that the only safety feature was the quality of that blocking capacitor. It came to be known as the "death cap" because if it shorted then you DID have a 50:50 chance that the plug would be inserted in such a way that the "hot" side of the power line would appear on the chassis of the unit! If you stood on something grounded and touched the metal chassis of the unit then you would get the full force of the power mains flowing through you! This hurts and in some cases can even kill.

"Death cap" shorts were relatively rare. Manufacturers knew that even though the system was legal nobody would want to buy a unit with a reputation for shocking the customers so they used good quality capacitors. Besides, the law through electrical wiring codes said they HAD to! Failures were rare and odds were 99% that nobody got killed! They just got a bad shock that caused them to say some naughty words and then took the unit to the repairman.

The 3 wire system just added a common ground wire to everything. The extra prong on a power cord is connected to an actual grounded wire in the wiring system in the walls of your house. This prong is also connected to chassis ground in your amp. If something ever did go wrong inside your amp then the hot wire would be grounded if it wound up connected to the chassis. This would immediately blow the fuse!

The best use of 3-wire cords is with power tools. Who wants to use a power drill on a damp construction site when the metal housing has developed a short to the power line? :eek:

So don't worry, be happy! I would get the cord changed but wait until you're paying a tech to open the amp up anyway. The extra time to change the cord will be less, which means a smaller bill.

The change is a good idea but the danger is nowhere near as high as some folks have been suggesting. Still, people do win lotteries and they do get struck by lightning. That's why I'm NOT saying don't bother! Just don't lose any sleep if it's not changed by tomorrow...:smile:

:food-smiley-004:
 

·
Premium Member
Joined
·
2,086 Posts
Adamthemute: Take your amp to a tech !!

It is not just about learning how solder (and that takes some practice as it is) but also knowing how to identify the components, how to discharge the caps (as mentioned) and how to wire the components together correctly so that you don't end up creating a dangerous situation for yourself and potentially damaging your amp.

The responses you have been given so far in this post are meant to be helpful. I don't think some of the responses are very accurate (I'm feeling the heat of the flames now).

IMHO, making an amp safe and getting the best tone from it is not a task for a beginner.

Dave
I have to agree...there's just too much potential for something to go wrong. If you have no technical experience, the amount it will cost to send it to a qualified tech will potentially save you a lot of headaches and maybe even a shock or two...or worse.
Remember...it's only an amp. Your health is worth far more...(fanning the flames for you Dave)...
 

·
Registered
Joined
·
2,665 Posts
Adamthemute: Take your amp to a tech !!

It is not just about learning how solder (and that takes some practice as it is) but also knowing how to identify the components, how to discharge the caps (as mentioned) and how to wire the components together correctly so that you don't end up creating a dangerous situation for yourself and potentially damaging your amp.

The responses you have been given so far in this post are meant to be helpful. I don't think some of the responses are very accurate (I'm feeling the heat of the flames now).

IMHO, making an amp safe and getting the best tone from it is not a task for a beginner.

Dave
Your answer got posted while I was composing mine and Dave, that's good advice to Adam! I should have picked up on that.

Adam, listen to Dave! Your posts make it obvious that you don't have nearly enough experience to safely work on amps. You've got a lot to learn first.

Amps have voltages that sometimes are more than 500 volts! If that doesn't KILL you it WILL HURT LIKE A SONOFABITCH!

I don't mean to sound patronizing but your questions are like someone who has never even started a car asking how to handle it in a NASCAR race! We do NOT want to help you with obtaining a race car's ignition keys!

It's a pleasure to have someone interested. It would be nice if you lived long enough to ask more questions!:smile:

:food-smiley-004:
 

·
Registered
Joined
·
365 Posts
Discussion Starter #13
Awesome responses, thanks. That's why I like this forum!

Yeah I'll probably lug it over to Long & McQuade. I was trying to find a local amp tech in Winnipeg but couldn't find one.
 

·
Registered
Joined
·
1,531 Posts
Got any friends heading to the western part of the province? I won't be in Winnipeg for a little while, but I most certainly could do it for you and give it a good check over at the same time to make sure all the caps etc are okay.
 

·
Registered
Joined
·
561 Posts
I'd highly recommend getting a couple of BYOC pedals from Scott...you can get initiated to DIY with no risk to either your health or your wallet (in a big way) before tackling an amp.

Andy
 

·
Premium Member
Joined
·
17,444 Posts
I'd highly recommend getting a couple of BYOC pedals from Scott...you can get initiated to DIY with no risk to either your health or your wallet (in a big way) before tackling an amp.

Andy
+1 ..try building some small circuits (pedals are an excellant suggestion) with 9V supplies, if electronics interests you.
 

·
Registered
Joined
·
1,909 Posts
as I remember it, the easiest way to tell if your guitar amp had the ground switch out of sync with the ground switch on the PA was to touch the mic with your mouth while playing the guitar. ZAP.

ah, the 'good' old days.
 

·
Registered
Joined
·
1,154 Posts
as I remember it, the easiest way to tell if your guitar amp had the ground switch out of sync with the ground switch on the PA was to touch the mic with your mouth while playing the guitar. ZAP.

ah, the 'good' old days.
On purpose or accidentally?
 

·
Registered
Joined
·
1,048 Posts
I can relate

Hey,
I have a 70s Traynor, and my mouth has been zapped like that, but we always blamed it on the PA system that is at least as old. So perhaps I should have been flipping the ground lift switch on the back of the amp. It doesn't seem to make any sound difference when I switched it so far... but a 3 prong chord was installed on the amp by the previous owner.
Anyways, I've been wrestling lately as well with what sorts of mods I might like to do to my Traynor. After playing with quite a few (some fairly expensive) pedals, I have come to really like the distortion I get when the pre-amp is pretty much around 8 or 9 and the the Master is set to a very precisely acquired spot around 1 3/4 with deafening volume. So, I've been considering whether it's possible to change channel 1 to an additional gain stage, or perhaps even cut the power of the amp in half to 50Watts. I know it seems silly to reduce power (especially for someone like me that loves to rock hard sometimes), but this is also to do to with wanting to have a new speaker cab with only 2 12"s instead of a big single 15". Reducing the power increases the number of choices of what those 2 speakers could be.

I have a Celestion G12H left over from a pair that I bought for my first DIY amp build that I just did. So, I thought of being able to use that. Oh ya, I'm already being long-winded so I might as well get it over with and tell my whole life story. I just built a clone of a Matchless DC-30 and it sounds amazing (although it's not in it's combo cabinet yet because my retired father is still building one for me). Anyways, I'd encourage anyone who really wants to work on amps, but has no experience. I don't mean just start poking at caps and getting yourself killed. But if you really are interested to learn and would rather do 80 hours of slow work yourself than pay a tech 70 dollars, you can learn all this stuff. I'm still a noob, but come on, give me some credit for my amp working perfectly on the first try. (of course I was following diagrams and some photos the whole time.)
Anyways, about my Traynor, I'm still deciding what to do. An amp tech at a store in Calgary told me to bring it in to him and he will suggest whether I should try to keep it stock or whether to let him mod it up for me. I kind of feel bad about that because if I do mod it, I might like to do it myself, now that I'm so cocky about not killing myself yet. Ok, I'll shut up now. I sound so lonely and desperate to talk about amps. (My girlfriend never lets me talk about amps to her anymore)
 

·
Registered
Joined
·
1,531 Posts
If someone is interested in learning about building pedals or amps etc, before you buy any kits or anything, buy some books and learn about the theory and function of basic electronics and basic circuits. It's all well and good being able to follow the bouncing ball and wire resistor R1 into the board where it is supposed to go, but that doesn't really help you understand how the circuits work etc. Once you understand how the parts functions, and then how they function together, it makes the building and repair process easier and more enjoyable.
 
1 - 20 of 22 Posts
Top