Dim Bulb Testing: What to Expect - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State

Solid State Talk all about solid state amplification.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 25th September 2008, 01:40 PM   #1
Plundering the Planet From the Comfort of Home
diyAudio Member
 
DreadPirate's Avatar
 
Join Date: Jan 2006
Location: Northern Virginia, USA
Default Dim Bulb Testing: What to Expect

I finished rebuilding a Marantz 2285B amp. It kept blowing fuses, traced the problem to shorted drivers and outputs. Did not check "everything" in the amp, just the usual suspects. All drivers and outputs as well as electrolytics on the amp section replaced.

I now have it plugged into a dim bulb tester. I started with 20, 40 watt bulbs, not enough to energize the relay. The 60 watt bulb did the trick, relays clicked and the bulb got a tad brighter, but it is still quite dim and has held that way for 10 minutes or so. My questions:

1. Am I out of the woods at this point because my bulb did not go bright or could I still have problems as I move up to 75 and 100 watt bulbs?

2. If my repair would not have been successful and there was still a short somewhere, I'm guessing that the bulb would have gotten brighter and brighter and perhaps eventually burned out, is this correct? Does this happen slow enough that I can catch it and flick off the power before causing damage to the unit?
  Reply With Quote
Old 25th September 2008, 02:13 PM   #2
diyAudio Member
 
Join Date: Sep 2008
Can you specify : Exactly the parts you restore in there ?
And did you check the voltage selector on the back of the amp ?

also you can look at :www.irebuildmarantz.com/ remove-solder.jpg

Sorry bout the link size, but i hope it will help ya
__________________
www.kondenzatori.com - Магазин за продажба на кондензатори.
  Reply With Quote
Old 25th September 2008, 02:26 PM   #3
wg_ski is offline wg_ski  United States
diyAudio Member
 
Join Date: Oct 2007
Once it comes up stable, move up to 100W bulb, and play music at low volume. Then disconnect the speakers and play at full clip. If it passes these tests without drawing high current and lighting the bulb you're probably home free. Even with a 100W bulb, you probably can't hurt anything even if something is wrong. A brightly glowing bulb means little voltage at the amp. Set the bias to where the outputs are barely cracked open (a milliamp or two) because it will go up at full voltage with no bulb. Then hook it up w/o the bulb and set the bias to target (do this slowly, monitoring over the course of an hour or so).
  Reply With Quote
Old 25th September 2008, 02:27 PM   #4
h_a is offline h_a  Europe
diyAudio Member
 
h_a's Avatar
 
Join Date: Sep 2006
Location: Graz, Austria
Quote:
the bulb would have gotten brighter and brighter and perhaps eventually burned out
In case of a shorted amp the bulb would work just as if the amp wasn't connected at all, means it would just glow normally - and give you light to search for the short No burn out.

Have fun, Hannes
  Reply With Quote
Old 25th September 2008, 05:54 PM   #5
Plundering the Planet From the Comfort of Home
diyAudio Member
 
DreadPirate's Avatar
 
Join Date: Jan 2006
Location: Northern Virginia, USA
The extent of my restoration of this unit is described here:

Blow Output Transistors Identified...What Next?

I also replaced the few caps on the amp board with Panasonic FCs. As has been the case with almost every '70s vintage amp I have swapped out caps for one reason or another, they test good with a cap and esr tester. A few grey elnas, mostly chemicons.

The bias voltage is presently set to the absolute minimum. The pot is at maximum, 300 ohm. Interestingly, though both pots look identical and have identical model numbers, one is reading right on at 250 ohm, the other 300 ohm, which is as per the schematic. The 250 ohm pot was on the originally good channel, so I don't think it is a problem.

I'll hook up some speaks and see what happens, go with a larger bulb, and eventually plug it in. This is kind of scary....
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Using Bulb in Place of fuse for testing Zero Cool Everything Else 15 4th May 2008 06:49 PM
Misc. ST-bulb (coke-bottle shape) tubes (and two GT-bulb) FS GordonW Swap Meet 0 4th January 2008 03:14 PM
What to expect? daryll Chip Amps 17 30th November 2004 08:28 PM


New To Site? Need Help?

All times are GMT. The time now is 04:54 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2