Palomar 350Z

[nomadradio]

A 2 ohm in the driver tubes' cathode return, and 1 ohm in the finals provides negative feedback. Typically improves linearity, and serves also as a 'self-bias' function that limits peak cathode current. Never tried jumping a wire around them. Would probably make the wattmeter worshippers happier.

But cooking the tubes at full idle current the whole time the amplifier is in receive mode takes the cake for me.

73

 

[Shockwave]

I'm unable to see where adding this resistor provides any real negative feedback loop. It's simply pushing the bias more towards cutoff as the tube draws peak current and this tends to reduce linearity when driven near full output. The schematic for the 350Z shows a 2 ohm 2 watt resistor on the final cathodes. The 300A omits this resistor and shows more PEP output with the same tubes. Granted, it doesn't cook them in receive either.

 

[CCC GGG]

I'm unable to see where adding this resistor provides any real negative feedback loop. It's simply pushing the bias more towards cutoff as the tube draws peak current and this tends to reduce linearity when driven near full output. The schematic for the 350Z shows a 2 ohm 2 watt resistor on the final cathodes. The 300A omits this resistor and shows more PEP output with the same tubes. Granted, it doesn't cook them in receive either.

I have tried many things to try to bring the 350Z up to what the 300a can do on 10 meters with no luck. The strange thing is I can get about 400 PEP out with the 350Z on 40 meters but max on 10 meters is about 250 or 275 PEP out. But the 300A hits over 400 PEP out both on 40 meters and 10 meters. I tried nearly new 6LF6's, playing with bias and screen voltages and even virtually copied the tank circuit from the 300A in my 350Z but still, no way getting past about 275 with the 350Z. It's been an on again off again frustrating project for me for a couple years but I'm too stubborn to give up. My SB-220 sits nearby watching me like I'm some sort of crazy addict. I can't throw it away. I even bought a second mint condition 350Z to see how they should really do on 10 meters but guess what, yes another 250 out on 10 and 400+ out on 40! 350Z madness! So thanks for pointing out the 2 Ohm cathode resistor. I never noticed that! I'll change that to zero ohms and see if it helps. But it doesn't make sense because the 350Z works fine on 40 and the 2 ohm resistor is in there. How could that be frequency dependent?

 

[kopcicle]

https://pa0fri.home.xs4all.nl/Lineairs/Frinear400/frinear400eng.htm

YMMV

 

[CCC GGG]

I have tried many things to try to bring the 350Z up to what the 300a can do on 10 meters with no luck. The strange thing is I can get about 400 PEP out with the 350Z on 40 meters but max on 10 meters is about 250 or 275 PEP out. But the 300A hits over 400 PEP out both on 40 meters and 10 meters. I tried nearly new 6LF6's, playing with bias and screen voltages and even virtually copied the tank circuit from the 300A in my 350Z but still, no way getting past about 275 with the 350Z. It's been an on again off again frustrating project for me for a couple years but I'm too stubborn to give up. My SB-220 sits nearby watching me like I'm some sort of crazy addict. I can't throw it away. I even bought a second mint condition 350Z to see how they should really do on 10 meters but guess what, yes another 250 out on 10 and 400+ out on 40! 350Z madness! So thanks for pointing out the 2 Ohm cathode resistor. I never noticed that! I'll change that to zero ohms and see if it helps. But it doesn't make sense because the 350Z works fine on 40 and the 2 ohm resistor is in there. How could that be frequency dependent?

Just a quick follow up. I eliminated the 2 ohm cathode resistor by jumpering around it and no help on the output. The resistor is only in there to give the plate current meter a voltage to work off of. Dang it the 350Z low power output on 10 meters lives on. Maybe I should put an old Datsun insignia on the cabinet. Maybe that's all it needs.

 

[Tokin]

Just a quick follow up. I eliminated the 2 ohm cathode resistor by jumpering around it and no help on the output. The resistor is only in there to give the plate current meter a voltage to work off of. Dang it the 350Z low power output on 10 meters lives on. Maybe I should put an old Datsun insignia on the cabinet. Maybe that's all it needs.

Its the 210 wagon of Palomars lol.

 

[CCC GGG]

When you calculate 20xlog(250/400) and see that 250 W is only 2 dB down from 400 W (less than half an S unit) the motivation gets a bit 'squelched'. In fact the 250'ish level is a good practical level for yakking with the group at night that's spread out over a 25 mile radius. Why run a pair of 3-500Z's with 3400 Volts on the plates when you're already15 over 9? But that doesn't take away the enigma of that 350Z. Eventually I'll get the horsepower up on par with the 300A. I just hate it when something doesn't work right. And it becomes an obsession until I solve it! Doesn't matter if it's some intermittent switch in my Chevy, or a leaky P trap under the sink or an underperforming amp; it's all the same. It's on the fix it list bugging me until I solve it.

 

[Tweetybird]

When you calculate 20xlog(250/400) and see that 250 W is only 2 dB down from 400 W (less than half an S unit) the motivation gets a bit 'squelched'. In fact the 250'ish level is a good practical level for yakking with the group at night that's spread out over a 25 mile radius. Why run a pair of 3-500Z's with 3400 Volts on the plates when you're already15 over 9? But that doesn't take away the enigma of that 350Z. Eventually I'll get the horsepower up on par with the 300A. I just hate it when something doesn't work right. And it becomes an obsession until I solve it! Doesn't matter if it's some intermittent switch in my Chevy, or a leaky P trap under the sink or an underperforming amp; it's all the same. It's on the fix it list bugging me until I solve it.

You WILL find it

 

[KN4ZWW Ryan]

Hello, how does the Paloma 300a work on the HF ham bands? I see it is a multiband But it seems they only work well on the CB band and/or 10 meters. Thanks for your help!

 

[nomadradio]

Hello, how does the Paloma 300a work on the HF ham bands?

Very, very poorly.

The band selector and the tapped coils connected to it are a fig leaf over the private parts. An attempt to circumvent FCC rules of the day.

The input circuits feeding drive power to the tubes are tuned for 11 meters only. Or maybe 10 meters if you tweak the input-trimmer caps, one each for high and for low side.

For the 300A to be a true ham-band amplifier, it would have to contain a band switching section on its input circuits, not just the output circuits.

They didn't bother. They knew the market for it would be 11-meter operators, and that's what it's built for.

73

 

[KN4ZWW Ryan]

Very, very poorly.

The band selector and the tapped coils connected to it are a fig leaf over the private parts. An attempt to circumvent FCC rules of the day.

The input circuits feeding drive power to the tubes are tuned for 11 meters only. Or maybe 10 meters if you tweak the input-trimmer caps, one each for high and for low side.

For the 300A to be a true ham-band amplifier, it would have to contain a band switching section on its input circuits, not just the output circuits.

They didn't bother. They knew the market for it would be 11-meter operators, and that's what it's built for.

73

Thank you very much! I’ve been trying to get that answer for weeks now! I’m looking for an amp for the ham bands and not sure why I’m looking for. They all seem to be foe CB band. I’d like to find something I. The 400-600 watt range. Thanks again very much for your response, it was most helpful!
73
KN4ZWW

 

[827 miami !]

I have a Palomar 350z and get 850 watts output w/ 90 watts drive ,I'm using it for more than 15 years and I have no problem so ever ,is the best linear amplifier ever have ,including my 300a that I can get 650 watts output for 20 years !

 

[jtrouter]

I have a Palomar 350z and get 850 watts output w/ 90 watts drive ,I'm using it for more than 15 years and I have no problem so ever ,is the best linear amplifier ever have ,including my 300a that I can get 650 watts output for 20 years !

Spring is here fire up the Blazing BBQ

 

[nomadradio]

,I'm using it for more than 15 years and I have no problem so ever

Gotta say that's outside my experience.

But in the bigger picture, my experience is with stuff that's broke, or not performing. I have almost no experience with a 350Z that exceeds original ratings for decades.

Nobody in his right mind would pack up one of those and bring it to me. If it ain't broke why bother?

Everything negative I know about that model is from first-hand experience since the year it was first sold.

Just because I haven't seen a "miracle" 350Z doesn't mean it can't exist.

Absence of proof does not prove absence.

73

 

[Shockwave]

Gotta say that's outside my experience.

But in the bigger picture, my experience is with stuff that's broke, or not performing. I have almost no experience with a 350Z that exceeds original ratings for decades.

Nobody in his right mind would pack up one of those and bring it to me. If it ain't broke why bother?

Everything negative I know about that model is from first-hand experience since the year it was first sold.

Just because I haven't seen a "miracle" 350Z doesn't mean it can't exist.

Absence of proof does not prove absence.

73

Do you know if they use the same transformer? If not, I wonder if the B+ sags more under load. Just a bit more internal resistance on the windings, could be the difference. I've never seen a 350Z, that could impress a 300A owner either.

To take it one step further, customers were mad at the local business that was selling the 350Z, after they had experience with the 300A. More than one got a refund on the same day.