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An illustrated guide to building an F5
An illustrated guide to building an F5
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Old 18th September 2020, 11:10 AM   #1491
Zen Mod is online now Zen Mod  Serbia
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An illustrated guide to building an F5
that's rude, calling 6L6 - dim bulb ...

he's our Bright Bulb

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Old 18th September 2020, 12:32 PM   #1492
thomasnadeau is offline thomasnadeau  United States
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An illustrated guide to building an F5
Quote:
Originally Posted by 6L6 View Post
^^ do everything Ben said.

( Using the same color wire for both V+ and V- is a pretty dismal idea as he hinted at, Id make a run to the hardware store and get something different for V-. )
Or at least get some green and red electrical tape and use it as a label for the wires. I'll admit I did that a while back because I didn't want to have to unsolder/re-wire.

--Tom
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Old 18th September 2020, 04:19 PM   #1493
Chiptech is offline Chiptech
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Quote:
Originally Posted by McQuaide View Post
The dim bulb saves the day
I'd say I get the dim bulb award for the week.
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Old 18th September 2020, 04:25 PM   #1494
Dennis Hui is online now Dennis Hui  Canada
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An illustrated guide to building an F5
Great catch by 6L6!

@Chiptech: Does the bulb test now pass and have you started biasing the amp?
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Old 18th September 2020, 07:02 PM   #1495
Chiptech is offline Chiptech
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Default Hey I'm on the West Coast [nearly] Tucson time

I'm just starting to undo the snafu I created.
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Old 18th September 2020, 11:52 PM   #1496
Chiptech is offline Chiptech
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Default How durable are these

I have extracted Q3 and Q4. I'm wondering how durable these units are? /they seem ok and are built for heat. Any thoughts before i put them back in?
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Old 18th September 2020, 11:56 PM   #1497
Zen Mod is online now Zen Mod  Serbia
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An illustrated guide to building an F5
try them with diode/beep test

if they're not beeping between pins, they're most likely OK

regarding heat durability ........ from personal experience, I know that they're most sensitive to stupidity, everything else goes second

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Old 20th September 2020, 09:06 PM   #1498
Chiptech is offline Chiptech
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Quote:
Originally Posted by Ben Mah View Post
Your power supply voltage is good. Your wiring to the amplifier board looks good.

Looking at the P channel Mosfet (right side of board), the thermistor wire may possibly be contacting the washer/screw. Make sure that only the body of the thermistor is in contact.

Once that is done you are ready for power up with the dim bulb tester. Having two meters for the biasing is best, with one meter set to DC Volts on the speaker out and the other meter across R7, also set to DV Volts.

If all is good, the dim bulb tester should dim after intially glowing bright.

The voltage across R7 should be very low (much less than 1V).

If good, then biasing is next.
Well, I undid the errors with the Mosfets on Q3 and Q4. I double checked everything else on the boards.

But once again dim bulb rules and stays on. I did get a -434.2 reading off the speaker out. didn't get a reading on R7.

Appreciate any input.
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Old 21st September 2020, 01:53 AM   #1499
Ben Mah is online now Ben Mah  Canada
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An illustrated guide to building an F5
1. Your Mosfet or Mosfets may be damaged. Did you test them as Zen Mod mentioned in his post #1497?

2. Your -434.2 at speaker out- what are the units?

3. "Didn't get a reading on R7" -do you mean VDC = 0 across R7 or you did not measure?

4. Did you check Resistance between Mosfet pins and screw clamping Mosfet to heat sink? Check if you did not after remounting Mosfets. Should read high or infinite resistance.

5. Check VDC across R8.

Here are detailed instructions for testing Mosfets:

How to Check a MOSFET Using a Digital Multimeter | Homemade Circuit Projects

As I mentioned in post #1460, I'm not knowledgeable in trouble shooting the rest of the circuit. I've gone as far as I can.

Hopefully Zen Mod will step in and help. He can solve all problems.
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Old 21st September 2020, 10:15 PM   #1500
Chiptech is offline Chiptech
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Thanks for the How to Check a MOSFET reference.

Today's measurements:

Regarding #4 above: testing resistance on the MOSFETS I get:

For the right amp P Channel:

Gate OL
Source .047
Drain OL

For the right amp N Channel:

Gate OL
Source .048
Drain OL

For the left amp N Channel:

Gate OL
Source OL
Drain OL

For the left amp P Channel:

Gate OL
Source OL
Drain OL


On R7 I get OL.

On speaker out I get -427.6 mV

On R8 I get OL.

If one or more of the MOSFETS are bad I can replace all of them.

At least I'm learning a lot these days.

And thanks for your interest in helping me debug my handiwork.
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