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PostPosted: 26 Feb 2012, 20:51 
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Joined: 19 May 2011, 16:20
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Location: Somewhere over the rainbow, Cali
Great tips! When I plugged my first amp in (k-12g), I literally just jumped for cover with a wish and a prayer. After about 20 seconds, I felt semi-safe and walked back to the amp and checked for voltage on the chassis, and found everything to be a-ok.

Cheers!

-AJ

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PostPosted: 20 Jun 2012, 12:14 
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Joined: 20 Jun 2012, 11:46
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I suggest using a variac to power up a device that uses vacuum tubes. It will potentially save the vacuum tubes if a wiring error exists. I suggest monitoring the filament voltages (as well as the B+) as you slowly adjust the variac output. If the filament voltages are not the correct percentage of the required value you can quickly shut off the power to the device and check for a wiring error.


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PostPosted: 22 Jun 2012, 00:40 
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Joined: 05 Nov 2010, 21:07
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Location: South East US - Tennessee
Here's a simple one that has eluded some amp builders:
DO NOT POWER IT UP WITH OUT AN OUTPUT LOAD!!! Never,EVER power that amplifier with out either an 8R resistor (or what ever speaker load you've designed for) OR the speaker. That is, unless you like to hear oscillation and see smoke coming from your just completed, blood, sweat and tears hard work!

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We cannot solve our problems with the same thinking we used when we created them. - Albert Einstien
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PostPosted: 09 Nov 2012, 15:36 
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Joined: 29 May 2011, 12:24
Posts: 49
Location: Netherlands
Some good tips here!

For a first time I always use a variac on 10% of the AC line voltage, so that would be 23 volts in my case (Europe). I don't install the tubes but measure all voltages in the amp to see if they are +/- 10% of what they should be if the amp were to be connected to 230v ac. Obviously it's not about accurate readings, but if I get no voltage at a certain spot where I should get a reading I will know that I have a short, or made a mistake in the wiring somewhere. Like this it's easy to trace where the problem is without risking any components.


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PostPosted: 05 Mar 2013, 21:27 
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Joined: 26 Oct 2012, 21:00
Posts: 194
Location: ontario canada
anyone around here ever hear about "dim bulb tester" or homebrew current limiters in my years as a service tech my bench is never without one!


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PostPosted: 05 Mar 2013, 22:57 
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turk 182 wrote:
anyone around here ever hear about "dim bulb tester"....



That's what we called the hazing we gave the new tech's in the TV shops I apprenticed at :lildevil:

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PostPosted: 05 Mar 2013, 23:12 
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turk 182 wrote:
anyone around here ever hear about "dim bulb tester" or homebrew current limiters in my years as a service tech my bench is never without one!


Never heard it referred to that way, but yes. It's a cheap easy way to check for initial shorts on the primary AC side. If it glows dimly, no shorts.

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The key to a successful build is to keep the smoke IN the circuit.
-Les

We cannot solve our problems with the same thinking we used when we created them. - Albert Einstien
_________________________________
LM380 Bridged Guitar Amp, Oatley K301 Phono Pre-amp, Oatley K272 Headphone Amp, Tube proto-board


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PostPosted: 06 Mar 2013, 00:17 
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Location: Winnipeg, CANADA
Dim bulb tester is what I call them too: viewtopic.php?f=5&t=1051

Cheers

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PostPosted: 23 May 2013, 07:08 
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Joined: 30 Apr 2013, 13:24
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Alexg says he has a friend who uses a variac. Go along with that completely especially if you have designed your own circuit. I have been using one for over 30 Yrs the carbon brushes do wear down over the years so you have to watch that or goodbye variac-windings fused/blown but that takes a long time to happen I used to leave 2 Multi-meters attached to monitor the AC voltage and the DC voltage in the unit being tested as well as an amp meter. till I bought a variac with both meters built in. Helped greatly in many situations [no more bangs]


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PostPosted: 03 Sep 2013, 21:49 
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Joined: 20 Sep 2008, 19:49
Posts: 171
Location: Montreal, Canada
The following is a precaution when powering down your amp.

Not sure if this was mentioned previously but if building a DIY unit, PLEASE add a bleeder resistor across the big reservoir electrolytic capacitor (ex 100uF, 450Vdc), value for such a resistance could be around 300Kohm, 2W.

Upon powering down the big cap will discharge into this resistors, after 5 -10 minutes (check B+ voltage first) you should be able to continue with your work...trouble shooting or making adjustment.

Adding that bleeding resistor can save your life..it's a good habit to always use or add one.

Rgds,
Iso

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