The new amp boards is the bias set at factory or does it have to be adjusted after hooking it up
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2995dx
- Thread starter my2995dx
- Start date
We have found that it's all over the map from the factory. Sometimes too low, sometimes at near-suicide too high. Beware the surface mount trimmer pot. It has no end stop. So if you turn it towards zero, and overshoot, the bias current jumps immediately up to "fry" category. Gotta be quick and continue to turn it back down to a safe level.
Somebody (else) needs to post a YT video showing how to do this.
73
Somebody (else) needs to post a YT video showing how to do this.
73
New amp in set the gate to 3.80v now went.to check the driver and final bias I'm not getting anything at TP7-8-9
Any time someone says this I have to ask how you hooked up the meter.
I just use the meter's 10 Amp range, so the meter's internal current-mode fuse won't pop if I turn a trimpot the wrong way.
Have you checked the fuse in the meter's current range?
73
I just use the meter's 10 Amp range, so the meter's internal current-mode fuse won't pop if I turn a trimpot the wrong way.
Have you checked the fuse in the meter's current range?
73
I have hooked up a meter checked i tested the AM reg seems fine and it's a pnp transistor now with this having MOSFETs driver and final is the procedure the same as older ones or do you set the gate voltage like you do in the amp.
You remove the jumper plate and connect the meter to feed voltage first into the driver, with one probe on the inner fork the other on the outer one. This passes all the driver's collector current through the current meter. The driver's setting for zero-signal current keyed up in sideband with mike gain at zero is 50 or 60 mA.
The finals get measured using the inboard-most fork and the center one for the meter. Start with both trimpots set for zero current, turn up one of them to 10 mA, then turn the other one until the reading is 20 mA, keyed on sideband with mike gain at zero. The factory recommended this lower setting back around the time they started using IRF520 transistors for RF.
Doesn't matter which sideband you use for this.
But that's the rundown. If you get a zero reading this way, something is wrong, no question.
73
The finals get measured using the inboard-most fork and the center one for the meter. Start with both trimpots set for zero current, turn up one of them to 10 mA, then turn the other one until the reading is 20 mA, keyed on sideband with mike gain at zero. The factory recommended this lower setting back around the time they started using IRF520 transistors for RF.
Doesn't matter which sideband you use for this.
But that's the rundown. If you get a zero reading this way, something is wrong, no question.
73
This leaves open two possibilities. Is the meter reading zero when it should not be?
Or are there TWO faults in the radio, one in the driver and one in the final BOTH causing the zero reading?
Time to hook the meter to another circuit and see that it reads current accurately.
73
Or are there TWO faults in the radio, one in the driver and one in the final BOTH causing the zero reading?
Time to hook the meter to another circuit and see that it reads current accurately.
73
Going to dig in her more in the next day or two and see ordered new driver and final but there a few days out
Just making sure the meter WILL read DC current at all sounds like a good starting point. If it won't, then wasting time on the radio won't improve the meter.
73
73
Then there is a reason the driver stage shows no drain current.
First place to look is the gate terminal of the driver transistor. The bias trimpot should allow you turn the trimpot up to nearly 4 Volts. A good transistor will definitely draw current if it gets turned that high. More-typical reading after setting bias is around 3.5, plus or minus tolerance.
If there's no voltage on the gate, the driver transistor's problem is in the gate-bias circuit somewhere.
As for the finals, same rule applies. Put enough voltage on the gate, and it will draw current. Might look at the voltage on the center drain terminal, and make sure no open circuit has occurred between the bias-test post and the driver transistors' drain (center) terminal.
73
First place to look is the gate terminal of the driver transistor. The bias trimpot should allow you turn the trimpot up to nearly 4 Volts. A good transistor will definitely draw current if it gets turned that high. More-typical reading after setting bias is around 3.5, plus or minus tolerance.
If there's no voltage on the gate, the driver transistor's problem is in the gate-bias circuit somewhere.
As for the finals, same rule applies. Put enough voltage on the gate, and it will draw current. Might look at the voltage on the center drain terminal, and make sure no open circuit has occurred between the bias-test post and the driver transistors' drain (center) terminal.
73
I recently went through one of these 2995dx radios.
The owner let an amateur tech go through it. He had it all outta whack.
Receive frequency was about 4khz off, transmit was about 7khz off, output power was very low (40w pep swing) and would drop lower the longer keyed up.
The guy aligned it with the amp turned off, this radio must be aligned with the amp turned on, it came from the factory with the amp always on.
After I got it, I found why the power was weak and getting weaker. The limiter was defeated, they had 2 swing mods installed, passthrough was getting scorching hot, driver and final bias was cranked all the way up.
I yanked all the swing mods out, re-enabled the limiter, replaced passthrough and AF regulators, reset bias back to specs, complete alignment.
The outcome?
AM Deadkeys 45w exactly, swings to 190w pep, bout 125w peak and swings forward to about 100w average.
SSB swings up to about 190w to 200w.
All modes are dead on frequency now.
He and all his buddies are amazed at how that radio sounds now.
Tip:
2995dx radios must be aligned with the amp on. The amp must deadkey 45w all the way up on RF Power. These rigs do not need any swing mods, just a complete alignment is all that is needed.
The owner let an amateur tech go through it. He had it all outta whack.
Receive frequency was about 4khz off, transmit was about 7khz off, output power was very low (40w pep swing) and would drop lower the longer keyed up.
The guy aligned it with the amp turned off, this radio must be aligned with the amp turned on, it came from the factory with the amp always on.
After I got it, I found why the power was weak and getting weaker. The limiter was defeated, they had 2 swing mods installed, passthrough was getting scorching hot, driver and final bias was cranked all the way up.
I yanked all the swing mods out, re-enabled the limiter, replaced passthrough and AF regulators, reset bias back to specs, complete alignment.
The outcome?
AM Deadkeys 45w exactly, swings to 190w pep, bout 125w peak and swings forward to about 100w average.
SSB swings up to about 190w to 200w.
All modes are dead on frequency now.
He and all his buddies are amazed at how that radio sounds now.
Tip:
2995dx radios must be aligned with the amp on. The amp must deadkey 45w all the way up on RF Power. These rigs do not need any swing mods, just a complete alignment is all that is needed.
Going to check that there is a shipping delay on the transistors I ordered should have them Monday but in the mean time going to check gate voltage
It's up and running here my meter was all screwed up.I got a new one well it was bad so got out my old one re-set amp tested the AM voltage regulator it was bad put in a new one and all is good
- No one is chatting at the moment.
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