| Author | Message | ||
| georgie_boy
Senior Member Username: georgie_boy Post Number: 1094 Registered: 8-2005 |
I've got the original blue box with my 76 Series 1, which I'm pulling out of the case after 3 or 4 years to enjoy her again!! Someone keeps telling me that it is dangerous because it has no ground wire, yet I used it for years without looking like a well done steak. Anybody help me to save my life??!! G | ||
| adriaan
Moderator Username: adriaan Post Number: 3168 Registered: 6-2002 |
Most electric guitars and basses are shielded by having the ground connected to the bridge and strings. Not Alembics ... I'm no EE, but I seem to remember you're pretty safe when there's a transformer between you and the high voltage. | ||
| rustyg61
Senior Member Username: rustyg61 Post Number: 1375 Registered: 2-2011 |
Don't play barefooted in a puddle of water! :-) | ||
| jimmyj
Senior Member Username: jimmyj Post Number: 545 Registered: 8-2008 |
I'm no EE either but I think Adriaan is correct; the "chassis" ground for the old blue box psu is established by a center-tap on the low-voltage side of the transformer. So you are essentially isolated from the dangerous current. If you are still concerned you can always test for potential with a volt meter before you connect it to your other gear. There is also a "thermal" fuse on the high voltage side of the blue box which would blow if the transformer shorted or tried to draw too much current. Anybody know if 30 years is an issue for those large voltage-regulating caps? Jimmy J | ||
| peoplechipper
Senior Member Username: peoplechipper Post Number: 500 Registered: 2-2009 |
Depends on the cap; I've got amps with 40+ caps and they're fine and others that have had to be replaced far sooner than that...generally you can tell with power caps as they start to swell when they're about to go...it's actually amazing how long some of these components last...Tony | ||
| georgie_boy
Senior Member Username: georgie_boy Post Number: 1097 Registered: 8-2005 |
plugged it in this morning, and it's just great. Pure clean sound, no noise......bass sounds great! | ||
| jazzyvee
Senior Member Username: jazzyvee Post Number: 4282 Registered: 6-2002 |
Good news all round then. | ||
| keith_h
Senior Member Username: keith_h Post Number: 2106 Registered: 2-2005 |
Jimmy - In answer to your question. Generally as long as electrolytic capacitors are used on a regular basis they will be ok. The problem is if they sit unused for a long period of time they lose the internal chemical state that allows them to function and can result in failure when voltage is applied. It is seeing a regular voltage that keeps the internal chemicals in the correct state and maintains the factory conditioning. There are ways to recondition the capacitors by slowly applying voltage but this is usually beyond the ability of everyday folks and it is usually cheaper to just replace them. Keith | ||
| jazzyvee
Senior Member Username: jazzyvee Post Number: 4283 Registered: 6-2002 |
I have a fender twin amp in a flight case that has not been plugged in or used for about 5 years is that long enough for me to have problems with the capacitors also? | ||
| sonicus
Senior Member Username: sonicus Post Number: 3721 Registered: 5-2009 |
jazzyvee , perhaps my friend . On your Twin ___, if you hear a constant low frequency tone then for sure .50HZ or 60HZ depending on your AC . Sometimes you can even hear harmonics of that low frequency. What Keith writes of " recondition the capacitors by slowly applying voltage" is done with a Autotransformer . Variac is a brand of such a device. I have a few of them. In theory if you apply a greatly reduced AC potential (voltage) say about 60 volts AC for 12 hours or so and then bring it up to 80 and in another hour or so slowly to full rating of the equipment requirement and then just leave it powered on . The capacitors MIGHT reform . I do this often with old pro audio gear that someone has stored for many years . It would be part of the procedure to do a physical inspection of the individual capacitors for leakage. In old AMPEX tape transports and electronics this is a common . The Ampex machines were very robust but you can not expect all the electrical parts of a 1950's /60's &70's machine to not require service as is the case in all equipment . Not all capacitors are of a type that can reform and just need to be replaced How I have approached some issues is ; In the case of your blue box you can just plug it in with your bass NOT connected and the next day check the voltages) check with a volt meter. I have also checked for ripple current with an Oscilloscope . Here is the PIN OUT ; Voltage; +/- 15V DC to aprox 22V DC ,but check With Mica 1 ground 2 neck pickup 3 bridge pickup 4 + volts 5 - volts Even if the voltages are steady and correct the filtering capacity of the capacitors could be compromised and as Keith writes replace them. Best bet in my opinion would be to see if Alembic will recondition and upgrade your power supply if you have any doubts. | ||
| gtrguy
Senior Member Username: gtrguy Post Number: 802 Registered: 9-2004 |
There is a gizmo you can make that has a lightbulb in the circuit that will start up your cold amp a bit slower than normal and it will also let you know if there is an open circuit if the light stays bright. I built one and it works well. Fender amps are pretty rugged and it should not be a problem. | ||
| keith_h
Senior Member Username: keith_h Post Number: 2107 Registered: 2-2005 |
Wolf, Not everyone owns a Variac hence the use of "everyday folks". I don't own one although I do own bench top DC power supplies. A couple even have built in AC filament supplies. My feeling is it is best to just replace most electrolytic capacitors when they are in question. For the most part they don't cost that much compared to potential repair costs should they fail and are very common. The exception is some of the old ones like you find in old audio equipment or old radios/TV's. In these cases it is not uncommon to need a certain footprint that just isn't available today. My old 1940's Zenith console radio is an example where as my early 1950's GE radio could use just about any off the shelf component. The DS-5 schematic can be found in this thread about midway down the page. Keith |
