Palomar 300A Trivia

[NavyVet1959]

While searching for a 10BASE2 RG58 cable the other day, I stumbled across a Palomar amplifier that I had used back in the mid-1970s. It was in a storage box and I suspect that it ended up there when I was cleaning out my parents' place after my father died a couple of decades ago. While searching for info on it online, it appears that it is a model 300-A (no data plate on the back of the unit). I also discovered that there should be a power supply unit with it. I had completely forgot about that being part of it, so I didn't bother to search through any more storage boxes to try to find it. I don't even know if I knew when I was cleaning out the house to even search for it at that time. Things were kind of hectic, I suspect...

So, the trivia questions that I have are:

1. Why was the power supply unit separate? Weight? RF interference? Heat dissipation?
2. What is the name of that 6 blade connector that is on the back of the amp? I remember being able to buy one from RadioShack back in the day, I haven't seen anything use that connector in probably 40 years...
3. Any chance the unit can be used in low power mode without the power supply?

Just curious... I recently passed the FCC General class license, but I have no plans to set up a home transmitter and this is definitely not a "mobile" amp unless your vehicle is an *RV*. I just want to have 10-13m (and a GMRS handheld) in my Jeep for emergency usage since I am sometimes in areas with no cellular service...

 

[Enterprise312ok]

Those 300a Palomars are a great amp, Unfortunatley It will not function without the transformer unit.
Welcome to the forum.

 

[NavyVet1959]

Those 300a Palomars are a great amp, Unfortunatley It will not function without the transformer unit.
Welcome to the forum.

I suspected as much, but I figured I would ask, just in case...

Maybe I'll stumble across the power supply before *I* croak... Times's running out... When I bought my Jeep (JL) a couple of years ago, it was with the full expectation that it will most likely last longer than I will, so no compromises (with the wife) -- I wanted a manual transmission and not a slush box...

 

[DoctorAudio]

6 pin is a Jones connector.

 

[NavyVet1959]

6 pin is a Jones connector.

Yep, that is...

Thanks...

 

[nomadradio]

Ahh, eight pin. The so-called "Jones" plug was originally a product of the Cinch-Jones company, developed in the 1930s, pretty sure. The typical part number would be P308, followed by some letters that indicate which housing it has. A second-source company sprang up in the 1980s named "Beau", and their part number would have been P3308. The external cabinet contains only a transformer and if you're lucky a panel-mount fuse for the low-voltage circuit.

The missing transformer provided low-voltage AC for the tube heaters, pilot light and relays. A second secondary winding provided either 280 Volts AC if the amplifier was wired one way, or 560 if it was wired the other way. Without getting lost in too many technical weeds, you need the correct transformer to match the wiring inside the amplifier box.

Just one problem. They are each marked in an identical way, with absolutely no external hint as to which amp or which transformer you have in front of you.

Consider that if you put the low-voltage transformer on the high-voltage amp deck, the 300A will be perpetually on "Low" side no matter which way you flip the High/Low switch. Operating from only half the high voltage it should, power will be really wimpy.

The other possible mismatch is the high-voltage transformer on the low-voltage amp. This results in "SNAP-POW!" problems.

I started to work up an aftermarket replacement for this transformer box. My box would have two transformers in it, one for the low voltage, one for the high voltage. Figured I could put a switch inside it to select either of the two high-voltage setups. Sure don't want that switch on the outside.

But paying customers just keep waving money at me and I get all distracted. Pretty sure we have the parts, just haven't put the prototype together. Nearly half the expense was for a steel cabinet. Should probably try to track down a more-affordable aluminum enclosure. Empty boxes are not cheap.

Don't see anyone else racing to put this on the market.

Oh, and yeah. Why is it separate? Always made me suspect they planned a 12-Volt DC power pack to run it mobile. Never have seen or heard the tiniest hint that they ever tried to. More than one tube-type ham radio was built with a Jones plug on the back where either a mobile power supply or base power supply would connect. Ham radios with a built-in power supply didn't become common until the hybrid radios came along and only needed high voltage to transmit. A separate AC power supply was common for tube-only transceivers.

Pretty sure it's way too late to ask what they were thinking at the time.

73

 

[NavyVet1959]

Ahh, eight pin. The so-called "Jones" plug was originally a product of the Cinch-Jones company, developed in the 1930s, pretty sure. The typical part number would be P308, followed by some letters that indicate which housing it has. A second-source company sprang up in the 1980s named "Beau", and their part number would have been P3308. The external cabinet contains only a transformer and if you're lucky a panel-mount fuse for the low-voltage circuit.

The missing transformer provided low-voltage AC for the tube heaters, pilot light and relays. A second secondary winding provided either 280 Volts AC if the amplifier was wired one way, or 560 if it was wired the other way. Without getting lost in too many technical weeds, you need the correct transformer to match the wiring inside the amplifier box.

Just one problem. They are each marked in an identical way, with absolutely no external hint as to which amp or which transformer you have in front of you.

Consider that if you put the low-voltage transformer on the high-voltage amp deck, the 300A will be perpetually on "Low" side no matter which way you flip the High/Low switch. Operating from only half the high voltage it should, power will be really wimpy.

The other possible mismatch is the high-voltage transformer on the low-voltage amp. This results in "SNAP-POW!" problems.

I started to work up an aftermarket replacement for this transformer box. My box would have two transformers in it, one for the low voltage, one for the high voltage. Figured I could put a switch inside it to select either of the two high-voltage setups. Sure don't want that switch on the outside.

But paying customers just keep waving money at me and I get all distracted. Pretty sure we have the parts, just haven't put the prototype together. Nearly half the expense was for a steel cabinet. Should probably try to track down a more-affordable aluminum enclosure. Empty boxes are not cheap.

Don't see anyone else racing to put this on the market.

Oh, and yeah. Why is it separate? Always made me suspect they planned a 12-Volt DC power pack to run it mobile. Never have seen or heard the tiniest hint that they ever tried to. More than one tube-type ham radio was built with a Jones plug on the back where either a mobile power supply or base power supply would connect. Ham radios with a built-in power supply didn't become common until the hybrid radios came along and only needed high voltage to transmit. A separate AC power supply was common for tube-only transceivers.

Pretty sure it's way too late to ask what they were thinking at the time.

73

Yep, 8 pin... My mistake... I didn't have my reading glasses and didn't look that closely at it...

If it was just transformers in the external box and AC voltages, then it shouldn't be difficult for me to make up one if I knew the voltages expected on each pin. The schematic that I stumbled across online doesn't list the voltages or pin numbers...

 

[nomadradio]

The low-voltage secondary is about 13 Volts AC if memory serves. The HV winding for the amp in the schematic is 280 Volts AC. The full-wave voltage doubler circuit delivers a DC output equal to 2.828 times the transformer voltage, or roundly 800 Volts DC.

Each series pair of 6.3-Volt heaters draws about 2 Amps. Three of those series pairs in parallel call for at least 6 Amps current rating at 13 Volts.

If we ever sell our substitute transformer, I'll definitely publish the Jones plug pin numbers.

73