Palomar elite 450 HD keying circuit problem

[Drradio61]

Hello all,
I have a Palomar elite 450 HD with four SD 1446s it has a burnt resistor that can't be identified except for the silk screen on the board that says r19. Does anyone have one of these amplifiers or a schematic that could give me an idea of what the value is of that resistor?

 

[Lost Ram]

Without digging into my amp notes I would say its a 33 ohm 1/2 or 1 watt carbon film resistor. Likely had to much drive into the amp. Also replace that diode by it, likely a 1N4007 will do just fine, this is likely bad too. Anyone correct me as I am just going from memory.

 

[SuperLid]

It looks like R19, is tied to the base of the keying transistor. Not the best photo, not too revealing. I would try a 220 ohm there.

 

[9C1Driver]

So an AI google search said this. So I guess you have a range of suggestions to help get it up and running. Good luck.








The stock value for R19 in the standard Palomar Elite 450HD input padding circuit is 100 Ohms (typically rated at 2 Watts, non-inductive). [1]
However, its functional value often depends on the specific modification or version of the schematic you are tracing:

• Stock Attenuator / Padding Network: It serves alongside a 27 Ohm resistor to form the High/Medium/Low power input drive selection.
• The 5-Ohm Bias Circuit Modification: In community-modified versions of the Palomar bias schematic (such as the popular WorldwideDX Regulated Bias Tracing), techs frequently replace the stock 100-Ohm resistors in the branch lines with 5-Ohm resistors. Leaving them at 100 Ohms severely restricts the current, preventing the TIP-31C pass transistor from supplying enough forward bias to the gates/bases of the pills. [1, 2]

It also came up with this older thread on this amplifier.

Thread 'Palomar Regulated Bias Schematic Elite 450HD'

May 26, 2020

Was reading over posts here about simple amplifier biasing to otherwise AM/FM only Class C amplifiers, by adding big resistors and reverse diodes, the normal, easy, but works, way to do it. So I thought I'd contribute this, for opinions, options, upgrades and applications.

This is a crude schematic I drew up from an amplifier I had here at my shop, it's an older, but later model, Palomar Elite 450HD (NOT the FET version). It originally came with 2SC2290A's x 4. The Bias is switched on at Transmit by an extra set of contacts on the TX/RX relay, a 4PDT being used as a 3PDT with two...

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