Galaxy DX-2547 voltage regulator

[CBerg]

No shorts at all. I'm about to order the IRF520's and was going to get a new AM modulator but the device is marked 2SB827. The schematic says it a 2SB754. I've checked Digikey and Mouser with no luck. Ebay has both. the 827 is sanyo and the 754 is toshiba. Any suggestions on which one to get?
Also can the biasing be done with a good DMM or do I need to take to a shop?

 

[Handy Andy]

So many questions...So little time...

Ebay has both. the 827 is sanyo and the 754 is toshiba. Any suggestions on which one to get?

Ok, the 827 is the OEM upgraded part (Meaning Use it if no other takers...), but take your time. I'm hoping others will chime in and put their two cents in...the Forum is Experienced and Versatile - not necessarily expedient...

Also can the biasing be done with a good DMM or do I need to take to a shop?

You can do it yourself...if you have the schematics - you have MOST of your answer...
I sent you those links to CB Tricks - Two of them - work with them together to answer the MOSFET or Bipolar boards and the conversions...

 

[Shockwave]

The datasheets indicate that you will see no difference in the performance of these two parts since all important specifications are the same. I can say the 754 is a fairly old (1980's) audio amplifier transistor and the 827 may be a newer version with improved reliability for it to be considered an "upgraded" part. A truly improved substitute would have increased breakdown voltage, collector dissipation and current handling while maintaining a similar gain in order to match existing driver circuitry. These parts are the same in all of those areas. That does make one a good "drop in" replacement for the other but the level of improvement appears to be lacking if that was the goal.

 

[Handy Andy]

​

The 827 is what comes with Galaxy radios pretty much standard for that era...

More than likely it was a cost maneuver versus performance - but there's a stat I thought was interesting...

It deals with how well a transistor can deliver regulation under load - dynamic intrinsic or impedance - wise the way the power flows thru the transistor is what gives any transistor it's character.

The 754 and 827 are very close to each other except they switched to a part that seems more "sluggish" - read it has it has a knee, but not like the 754's - so these parts operate differently when under load.

Gain may be higher on the '827, but that doesn't mean much when it comes to Bandwidth product - you have to have a part that operates linearly thru it's Power and Frequency range of operation...stay tuned on that...

That indicates the way they handle Audio drive with DC bias both may be linear, but when under load, their power curves are different.

 

[sp5it]

Just do RWOB and NPC-RC and never worry about AM regulator again.
Mike

 

[CBerg]

new Driver and Final are installed. As a disclaimer I installed EFR2030+ to replace the IRF520. A local repair (all of the local guys respect him) suggested it. Every thing I've read says its a drop in replacement. But I just read an article saying the 2030 will raise the power output. This is not my goal at all! should I pull the 2030's and go with 520's or am I OK?
On to biasing... Cb tricks and tip says to remove the mirror board set the current between tp9 an tp7 to 100ma and the same for tp7 to tp8. Robb stated in a post a while back to leave the board in and set it for 3.7v between the xtal ground and L33 and L37. Any opinion the better procedure? Also I assume these measurements are to be taken in transmit? Neither article says one way or another.
Thanks guys for putting up with me!!!

 

[Handy Andy]

No, Use the Remove Mirror board jumper option - remove it and test for current is the BEST option.

At 3.7 volts - it may latch the parts on from too much Gate voltage and they won't turn off.

You don't know when these parts will start to sink current - best to see the current side and know - rest assured, you're doing it right. You can measure the voltage later when it's properly set, you may have a different reading - in fact if you're so inclined - do this chart for all your different finals you can try in there - using the mA option - you'll see that these voltages can vary to as much as 0.100 (1/10th volt) which does make big differences in the drive level required from the preceding stage to make the device operate linearly.

To set it for 100mA is too much - I derate the mA to lower values - like for 70-80mA instead.

 

[CBerg]

No, Use the Remove Mirror board jumper option - remove it and test for current is the BEST option.

At 3.7 volts - it may latch the parts on from too much Gate voltage and they won't turn off.

You don't know when these parts will start to sink current - best to see the current side and know - rest assured, you're doing it right. You can measure the voltage later when it's properly set, you may have a different reading - in fact if you're so inclined - do this chart for all your different finals you can try in there - using the mA option - you'll see that these voltages can vary to as much as 0.100 (1/10th volt) which does make big differences in the drive level required from the preceding stage to make the device operate linearly.

To set it for 100mA is too much - I derate the mA to lower values - like for 70-80mA instead.

So the ERF2030 is ok to use? and test in transmit?

 

[Handy Andy]

Oh, forgot to cover that...though you'd read between the lines that anything you set Gate drive for, needs to be current monitored - not voltage...

Anything you use MOSFET wise is fine...TO-220 style following GDS pinout (Gate -Drain- Source)

CONDITIONED ON ,

as long as you use the Mirror Board set current option (70~80mA)

- Not responsible for anything more than that - cannot guarantee MTBF will be as long​

You can use 13N10's onto IRF520's and the now-infamous ERF 2030's and their successors ERF 2030+'s
- you can use them in pairs or not
- even mix if you wish for different results.​

Just understand that you are working with an interface layer section where a Bipolar and it's operational character is pushing RF into the MOSFET gates. All it's distortion and spurries are going in to that Gate - so the issue of the Feedback Resistor of 1K and the 102 Disc cap are paramount to keep the Bipolar as clean as possible else you're going to right back into this.

It's all in this thread - review as needed.