Can this amp be made to be safe?
Don't know, can you link us a schematic? I don't see a 1330 in my listings.
What generally is unsafe is the ones with no power transformer, and we call them "hot chassis " amps. If you have that, what you do is add an isolation transformer in front of it to isolate it from a direct connection to the mains.
It does not have a power transformer so you would need an isolation transformer.
Because it uses a half-wave rectifier you would probably want to use something rated for about twice the power that the amp uses.
Tubes are 50L6, 12SJ7, and 35Z5.
Quote from: memoryman on July 21, 2013, 09:59:25 PM
Can this amp be made to be safe?
It can,
but an isolation transformer and a mains safety ground on the chassis are an absolute "must". Before you do that...
Quote from: J M Fahey1) This amp is a KILLER !!
No kidding.
It sure has no power transformer, meaning the chassis or ground is tied to one side of the power cord.
Keep it strictly as a collector's item (that means never plug it), or use an 1:1 isolating transformer. No kidding.
(
my emph.)
And we ain't joking about that - the chassis, and therefore your guitar strings, are connected to one side of the mains supply. If that happens to be the Active side you are going to have a very short and exciting musical career. {I have to wonder why
Sears had it in for guitarists producing an amp like this, and seriously wonder how many people these transformerless appliances actually killed over the years.}
There are a mess of
Silvertone circuits here;
http://www.webphix.com/schematic%20heaven/www.schematicheaven.com/bargainbin.html (http://www.webphix.com/schematic%20heaven/www.schematicheaven.com/bargainbin.html)
...but not the 1330, however the 1430 should be fairly representative of this particular horror show.
Due to this being such a low power consumption amp, the Triad N68X would probably work fine and is cheap.
http://www.mouser.com/ProductDetail/Triad-Magnetics/N-68X/?qs=%2fha2pyFadugi%2fv1eXR%2f0AiEO2zaUAkSRWI2ho6ZXYjA%3d
Looking some more, some people have said the N-68X gets quite warm (even with an amp this small) due to the half wave rectification.
You could try it to see how hot it gets, or use the next size up:
http://www.mouser.com/ProductDetail/Triad-Magnetics/N-77U/?qs=sGAEpiMZZMvwUzoUXIIvydH8%2fj5UF54y5znvSd0cAC0%3d
It's hard to know how to express this with sufficient force. :grr
Your options are;
1) fit an isolation transformer which it should have had from the outset, then you will have a cool looking amp that is safe to use, or
2) lock it in a glass case - literally, or
3) take it out into the back yard and burn it before it kills somebody, maybe you.
This is like keeping a live WW2 hand grenade around the house coz it "looks cool". It is very aptly dubbed a "Widowmaker" and it now falls to you do make it safe, one way or another.
Fitting a stepdown in the bottom of the case so it can be safely used is hardly the same as drilling new holes in the front panel.
A
We don' want no dead guitarists 'round here
A E
no, we don' want no dead guitarists 'round here
A A7
guitarists come, guitarists go,
D Dm
amps smoke, and amps blow
A E A
but we don' want no dead guitarists 'round here
(c)R.Roper 2013
QuoteWill it destroy its value if I modify it.
What value ? :lmao:
In fact,*if* you properly add an isolation transformer, now it will have
some value.
Figure out its maximum power consumption. Add a margin for error (say plus 50-100%), obtain a suitable isolation tranny of that power rating and secure in the bottom of the case. :tu:
What do you think of this? http://www.clarkhuckaby.com/AmpMods/Silvertn.html
{are you deleting your posts? If so, don't, it makes this thread nonsense and no help to future readers.}
QuoteGood tone isn't very useful to dead musicians
I like it already.
Having read to the bottom, bloody excellent, a great example of what
JM alluded to above; the amp is a deadly horror show as it is, and here is a road map with transformer part numbers &c that shows you how to make it into the amp it should always have been (before the bean counters got to the parts list). After this mod the amp is actually worth something.
QuoteThe amp now has very little background hum, and a bright responsive tone with beautiful clean ring-outs.
The Silvertone 1330 is a great amp if you know what your doing with it (like most any other amp).
the first thing to do is install a grounded cord.
I would yes recommend a isolation transformer (not absolutely needed though)
change out the speaker with a good Celestion or Jensen Speaker.
the tweak for tone from this point.
Quote from: Jack1962the first thing to do is install a grounded cord.
I would yes recommend a isolation transformer (not absolutely needed though)
Sorry
Jack, ground the chassis then plug the cord in so the active is on the chassis (e.g. a transposed outlet) and you'll blow the mains circuit protection, or maybe start a fire. Encounter an outlet which is both transposed
and has an open earth (not unknown, and particularly at venues) and you're
dead.
As a tech with over fifty years experience I flatly reject your advice as dangerous - an isolation transformer is
absolutely needed to
safely operate this amplifier, otherwise a guitarists is quite literally taking their life in their hands every time they touch their guitar.
So called "universal" appliances of this sort are abominations that should never have been built or sold in the first place, and in many parts of the world are now rightly illegal. Adding an isolation transformer will not alter the tone in any way and will make the amp what it should always have been.
Quote from: Roly on August 04, 2013, 01:11:36 PM
Quote from: Jack1962the first thing to do is install a grounded cord.
I would yes recommend a isolation transformer (not absolutely needed though)
Sorry Jack, ground the chassis then plug the cord in so the active is on the chassis (e.g. a transposed outlet) and you'll blow the mains circuit protection, or maybe start a fire. Encounter an outlet which is both transposed and has an open earth (not unknown, and particularly at venues) and you're dead.
As a tech with over fifty years experience I flatly reject your advice as dangerous - an isolation transformer is absolutely needed to safely operate this amplifier, otherwise a guitarists is quite literally taking their life in their hands every time they touch their guitar.
So called "universal" appliances of this sort are abominations that should never have been built or sold in the first place, and in many parts of the world are now rightly illegal. Adding an isolation transformer will not alter the tone in any way and will make the amp what it should always have been.
As a tech for over 35 years myself , I have grounded these amps , a real tech ALWAYS , finds a way to ground ANY piece of equipment they work or they will wind up DEAD
As a tech for over 35 years myself , I have grounded these amps , a real tech ALWAYS , finds a way to ground ANY piece of equipment they work or they will wind up DEAD
[/quote]
Well, if you are grounding these kind of amps (widow makers) without using an isolation transformer that is just not safe. Roly has explained why.
You said that an isolation transformer is "not absolutely needed". That is wrong and unsafe.
Maybe you could explain why you would want to short cut around the safety that an isolation transformer provides? I'm sure you are aware that such an amp would be illegal to build and sell today due to safety reasons.
^^^^^^^ Agree
From my days of playing with ac radio sets I have an 'isotap' isolation transformer. Does anyone use those anymore?
I think you self answered ;)
Meaning they are *essential* for working on AC/DC radios and "widowmakers", which come from the same era.
Maybe not many use them today, although I think the idea of having an isolated workbench power strip is excellent.
Isotap. Is that the blue one with six outlets on top and a voltage switch, RCA brand?
I have one of those. It is across the room or I'd go look. I also have several different iso transformers that are just the transformer, for various uses. I think a bench is not complete without an iso available.
Quote from: J M FaheyI think the idea of having an isolated workbench power strip is excellent.
With one caveat; they defeat the operation of a switchboard Earth Leakage Breaker/Core Balance Relay/Safety Switch, where fitted. These have become very common over the past few decades in Australia.
Quote from: Enzo on August 26, 2013, 02:45:00 AM
Isotap. Is that the blue one with six outlets on top and a voltage switch, RCA brand?
Yup. Mine was made by "Viz" but I think they are copies of RCA. It even has the schematic silk-screened on the bottom.