Resurrecting an oldie

[Earl K]

I damaged the power supply of a preamp doing this... I won't be using a variac to bring up any equipment in the future.


Widget

Thanks for that !

Good to know the procedure isn't accepted on a fully ubiquitous level .

FYI, I searched ( Variac ) briefly over at AudioKarma & DIY ( solidstate ) and from my quick perusals it seems that a Variac is typically used "hand-in-glove" with the ( current limiting ) light-bulb .

Some manufacturers ( such as Adcom ) specifically mention ( in their service manuals ) not to Variac .

[jbl]

I damaged the power supply of a preamp doing this... I won't be using a variac to bring up any equipment in the future.


Widget

What was damaged? Why did you try it with a Variac? What was the original problem?

[Mr. Widget]

What was damaged? Why did you try it with a Variac? What was the original problem?

Not sure if there was a problem, the preamp hadn't been powered up for several years.

As I brought up the power, a rectifier tube blew and I sent the preamp to a tech to repair it.


Widget

[Donald]

Saw one mentioned in my searches regarding old caps. One was on eBay and I won it. May have to fix it before I use it.

http://www.ebay.com/itm/281225554799

[Lee in Montreal]

I think the only prep I would do before turning the on/0ff switch would be to pop the cover and vacuum as much dust and "angel hair" as possible. Then turn the amp on with the cover off and check for smoke ;-) Using cheap drivers would be wise. Even $5 car speakers will do.

[Donald]

It arrived. I checked the circuit side. While the rectifier had not come apart like one blogger's did mine did have a detached lead. Both wires the rectifier were attached with were over an inch long and not insulated. I added some shrink tubing on the leads. Saturday I will clear some bench space and fire up the oldie using this oldie.

Saw one mentioned in my searches regarding old caps. One was on eBay and I won it. May have to fix it before I use it.

http://www.ebay.com/itm/281225554799

[Mike Caldwell]

I would plug it in and turn it on, having said that I would not have it connected to any "good speakers". For amp function testing I have some old junker garage sale speakers as well as a moderately high power dummy load. Sometimes I will not even hook up the junk speaker for the initial power up, I'll first measure the speaker outputs with a meter to see see if there is any deadly DC voltage present and then just quickly touch the test speaker leads to the outputs before making the final connection.

Some electrolytic cap replacement may be in order.

I just did a complete electrolytic re-capped my 80's era Hafler pre amp and it took care of the slight hum I was starting to notice and the mid range graininess I had noticed appearing in the left channel.

[Donald]

Well, set up my new\old electric tester and fired up the Pioneer. No smoke. Neither unit. Measured DC at each of the speaker terminals. Highest was .014 volts. Tuned in an FM station and was getting AC on speaker output A. Have not tried an actual speaker yet. All the toggle switches work fine except the power on. A first I thought it was broken but it turns out the lube has just gone beyond molasses. Will open it up to clean all the pots and switches and lube the tuning system. I feel the 70s coming on.

[Eaulive]

May be wise though to build a Dim Bulb tester that will limit inrush current - if something has or will fail shorted, could save extreme damage and give some protection while everything is starting up and stabilizing. A lot of AK techs use that to bring an old unit up for troubleshooting. And with a unit sitting idle for that long, you don't want to chance turning it into an expensive door stop.

I agree, use a 100W incandescent bulb in series, the purpose is to limit the current in case of a component failure, not to decrease the voltage in a working unit.

I use a 100W bulb on big domestic amps like this, a 60W bulb on smaller (25-35W) units and a big 500W PAR64 bulb for kilowatt commercial amps.