WOPL 400 Build

MarkWComer

Veteran and General Yakker
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Nov 1, 2014
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Gaston, SC
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Victim of the record bug since age five
#22
Ok, cool. I've got a dim bulb for the initial, but when adding the transistors row by row, 5a will do the job?
Should be fine.

Two things to know: the variac limits voltage, the force of the current in a circuit, but not voltage. The DBT limits current, the amount of electricity going through the circuit, but not voltage. I plug the DBT into the variac for the first startup, the bulb will only glow slightly when you reach 120 volts.
 

Mohawk

Journeyman
Joined
Oct 29, 2019
Messages
62
#23
The bulb is in the circuit in series..... Your gonna limit or split the voltage between the amp and the bulb... If the amp is " shorted" the bulb is bright .... Acting like a pass through leaving the voltage drop for the bulb
Saving the amp from ka boom/fizz ( Diagram below is from Don's protect relay documents )

M

1585225494679.png
 
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MarkWComer

Veteran and General Yakker
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Gaston, SC
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Victim of the record bug since age five
#26
The bulb is in the circuit in series..... Your gonna limit or split the voltage between the amp and the bulb... If the amp is " shorted" the bulb is bright .... Acting like a pass through leaving the voltage drop for the bulb
Saving the amp from ka boom/fizz ( Diagram below is from Don's protect relay documents )

M

View attachment 40766
Series divides voltage, parallel divides current. Yes, I had that backward.
 

swarmin

New Around These Parts
Joined
Mar 24, 2020
Messages
22
#30
When soldering to my fuse posts I pulled the fuses. It appears one of them is toast, but it looks like someone used an 8A 32V. From what I've read, it needs to be 8A 125V or can be 250V. I'm not finding any options on mouser. Does anyone have a direct link handy?

I'm going to head to my storage unit and dig up a box of fuses. If I have it could I use a lower value to get through the testing?
 

Gepetto

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Staff member
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Sterling, MA
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Old 'Arn Enthusiast
#31
When soldering to my fuse posts I pulled the fuses. It appears one of them is toast, but it looks like someone used an 8A 32V. From what I've read, it needs to be 8A 125V or can be 250V. I'm not finding any options on mouser. Does anyone have a direct link handy?

I'm going to head to my storage unit and dig up a box of fuses. If I have it could I use a lower value to get through the testing?
Plenty of options:
576-0312008.MXP
 

MarkWComer

Veteran and General Yakker
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Gaston, SC
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Victim of the record bug since age five
#34
Fuses...
Those tiny little wires...

Do they glow like light bulbs when they’re conducting?
 
Joined
Apr 26, 2011
Messages
288
Location
Central Ohio
#37
When soldering to my fuse posts I pulled the fuses. It appears one of them is toast, but it looks like someone used an 8A 32V. From what I've read, it needs to be 8A 125V or can be 250V. I'm not finding any options on mouser. Does anyone have a direct link handy?
I'm going to head to my storage unit and dig up a box of fuses. If I have it could I use a lower value to get through the testing?
The AGC fuse protects the transformer and bridge rectifier. The smallest fuse that doesn't blow due to inrush current would be fine.

I have inserted a scope photo of the inrush current on a 700II. A 700B would be the same. The amp has 15,000uf caps. The yellow trace is the current at 50A/division. The bluish one is input voltage. Notice how the input voltage collapses at turn on. The peak current on the first cycle is just short of 150A. The voltage recovers after about 4 cycles. Now, is there any question why the switch could fail?

1585274831512.jpeg
 

swarmin

New Around These Parts
Joined
Mar 24, 2020
Messages
22
#39
Progress? How’s everything going?
Initial bring up is good! I'm tickled! Currently soldering everything else in and then on to the 2nd row of transistors.

The fuses I had were 8A 250V, but they were 20mm. I just coiled some wire and packed it in the fuse cap. No radio shacks around anymore, so it will have to do. Had to dig my DBT out of storage. It's been a day. Lots of progress though. I'm feeling pretty good about it.

So yeah, gonna finish up the soldering, vac it out with my hand dandy 3M electronics vac (I love that thing), iso the flux off my solder joints, bang my head against the wall while I put the 4 transistors in and give her another go.

Again, thank you for all the help, everyone. It's much appreciated.
 
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