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Palomar Regulated Bias Schematic Elite 450HD

Why not just sense with a part that was specifically designed to precisely change its voltage drop, in proportion to temperature? Like, a Thermistor? They are available in a wide range of resistances with both positive and negative temperature coefficients. This makes them readily adaptable for use in many 3 terminal regulator circuits. By simultaneously adjusting a parallel and series resistance used with the thermistor, you can adjust the rate at which it tracks, without disrupting the desired output voltage. That can be easier than trying to find a specific P-N junction, that matches the thermal characteristics of your output device.

To decrease the thermally tracked voltage change, you decrease parallel resistance while adding series resistance. The effect is to maintain the same overall resistance and "starting voltage", while the thermistor carries less of the current path and causes less of a thermal voltage shift. Increasing or removing parallel resistance while adding a similar amount of series resistance, would have the opposite effect and causes a larger voltage change, for a given temperature change. Dialing these two resistances in, allows perfect thermal tracking for a wide range of output devices.
 
The approach seems to be more focused on how the semiconductor junction would use the bias in their DUT, so really much of what is being done to "bias" the device is aftermarket, we're doing the research for them.

At least that's how HG and other Chinese look at it. Give the FCC a datasheet and let their ignorance and inability to translate from their language becomes their bane.

So Motorola and Toshiba - even though competitors, worked together to formulate the very information on the Datasheet that even the Chinese don't seem to quite fully grasp all that data - at least they copied it and seem to know what they're doing - just we're doing the legwork the Former makers of these now-cloned parts - did.

So Carbon Composition versus the Thermistor - whether being similar to a PIN diode or cruddy intrinsic layered device - we also must realize that as we're looking for Diodes that work as Bias devices, let alone the Thermistor and it's composition - many are not getting the "profile just right" I'm seeing it being due to one thing...

We're being fooled - seriously.
Look here, and to me, what the world has done, this is where it starts...

https://www.worldwidedx.com/threads/mike-debunks-shottky-diode-receive-mod.236937/

The above? It's the thread I got bashed about as Reinventing the wheel for Mike Radio Review is a good example of how the newer makers are cheapening up the diodes and flooding the market with these newer replacements.

Everyone's being led (seems to) believe that they are better, only to find out - once installed, they were better off keeping it STOCK with the older USA made carp - it's their money - yeah, it hurts us all when people want more and try to make the old Model-T a Formula 1 .

upload_2021-1-26_8-38-15.png

Look Ma!
It's the
Made In Michigan Man!
Why? Well, there is a BIG difference in junction performance profiles between of Schottky diodes versus the keeping with the OEM germanium or even the Doped Silicon design of the radio - per the 2SC2999 Receive mods that plagued the net and still do.

Why does this matter? Well, you used to have 3 layers, now we're lucky to just have two...for many a upstart semiconductor manufacturer (Read: Overseas) - the Schottky is far easier to make than the two layer P - N - then Meld - PIN-type (PN Junction) of junction component.

At least the old days, the Germanium types had the Galena-Crystal and Cats whisker which had inherited impedance and resistive trait that had it's own built in high-cut roll off filtering that made that radio have the warm sound.

upload_2021-1-26_9-0-20.png

When you look at it,
The Galena - Cats' Whisker onto the Foxhole Radio - both construction types ARE
similar to the now adopted Schottky design - single junction and heat applied under pressure
it was inevitable that the PN junction types would eventually be re-replaced by the older design
- now new again...

upload_2021-1-26_8-48-14.png

Not to be outdone,
In earlier models - the detector was a tube...​

Now? That isn't happening because of the Schottky design is NOT the same junction nor even the same material...the Pellet is singular, and the Weld to the now-beholden bonded metal is where that junction now occurs, no longer pure doped or otherwise...

upload_2021-1-26_9-12-52.png

So that changes everything when it comes to biasing the PN types.

We're missing the other half...we are biasing PN junctions being that they are Dual-Layer single junction devices, but Schottky designs have SINGLE LAYER using single junction devices,

upload_2021-1-26_9-55-31.png

The voltage drop - there's your problem; from ~1 to 0.7V now gone down to 0.3V or LESS Forward Voltage Drop.

Or at least we should review the PN profiles versus the Schottky we seem to evolving to -the PN had it's intrinsic barrier of two layers and the intrinsic bond - Schottky's barrier is different - so the performance between the two is now different = temperature or performance changes.

So I love your idea of the Thermistor - but the Diode it replaces can still be "used" you just have to change your approach from Parallel or Both Series and Parallel - so, Yes, I agree!
 
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Hello 443, could you repost the schematic? I have a 450 elite HD that is playing up and can not find a schematic.
The one you posted is not accessible now.
 
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Hello 443, could you repost the schematic? I have a 450 elite HD that is playing up and can not find a schematic.
The one you posted is not accessible now.

Yeah the server I had it on is not same. I cannot edit the original post (or I couldn't figure out how) this is my schematic I posted a user had just added the part about adding in the 100 ohm resistors in the bottom right of the image: Sorry I hadn't been here since last year. I'm bad, I know.
upload_2020-5-26_16-25-22-png.37616
 
Hello 443, could you repost the schematic? I have a 450 elite HD that is playing up and can not find a schematic.
The one you posted is not accessible now.

Reading back over this, sounds like maybe you needed the full amp schematic, I do not have that. The one I posted is just a quick drawing of the "Regulated" Bias circuit used in the later model Elite series Palomar amps. A full schematic might be found by searching heavily with Google or others, and cycling through the images section till you find one that is similar. I doubt you'll find the exact schematic.
 
Finally Received the MQ of MRF422 from PRC. Hua Gao the wafers are etched with 78 but my tester reports 56, 56, 47, 48. I understand a lower result from my Peak Atlas but I did not expect a 10 point spread. Is this something worth complaining about?

My intended PSU (28vdc @ 30A) blew one of the new 2n3772 I paid dearly for only 2 years priors. It's only been exposed to very light usage since I completed over a year ago so I've got to go over it again. voltage higher than the typical 14-20vdc is another ballgame it seems.
 

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Still moving forward on replacing the 2879's in a Palomar Elite 900HD with MRF422's. PSU threw me into 723-land for weeks. In frustration, I ordered a replacement 28v Astron board but got the TH-land 723 board working the day before Astron delivered. I'll use it eventually. Every Ham should build a regulated PS at least once I suppose.

I'm using an outboard OVP module from AliExpress instead of standard SCR crowbar. Only $22 and it's adjustable! Made a separate unit by bonding it to the 80A relay. Keeping it external, can use on bench like this. So this is my update, got 28v PSU in order so I can return to Bias circuit on amp again.

Also got an FT-891 and removed the HBTV vertical (it never worked right) Erected 2 new antennas: A 20m rotatable alum dipole & a 40M EFHW sort-of (22' counterpoise, OCF? IDK, it's high and nearly straight, 70' off the ground and I get 1:3 without ATU on 80; 10-40 all <2) I was surprised. It's my first wire antenna and it often out-performs the 20M dipole (on 20M!) which is 4' higher. Been using an mfj antenna analyzer also for the first time. It is a time saver and eliminates OTA tune ups.

BTW: Can I use it to check impedance on broadband amp transformers by using a known value Resistor on the output??

Pandemic was good for me, hope everyone here and their loved ones are safe and healthy. I will post update on amp as I progress.

Neil , NY City
 
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