how much drive

[1iwilly]

does anyone here knows on a Palomar 300A how much drive is needed on low side drive to equal the same output as when in high drive
with cobra 2k i can do 275rms i now have a Yaesu ft 101e i know i can't use it on the high side with this radio but when i go on low side 10 watts from the radio only gives me 110 watts RMS yes the yaesu is putting out it's normal power output had tubes re-done
how much power do the 2 driver tubes put out to dive the 4 tubes

 

[nomadradio]

Does sound like maybe the 300A is not exactly 50 ohms on the input. The FT101 has been tuned/loaded for whatever your dummy load is. For the moment, we'll assume 50 ohms. If the 300A's input impedance on Low side is too far above or below that, this will reduce the efficiency of power transfer into the 300A's final tubes. There is usually a compression trimmer cap soldered to the rear of the High/Low switch. This is to adjust the High side input impedance as close to 50 ohms as possible. A SWR meter and coax jumper BETWEEN the radio and amplifier will allow you to adjust that trimmer cap for lowest SWR.

Might make a difference you can see. The other solution is to tune the Yaesu, or at least 'touch up' the Tune and Load on the radio with the amplifier keyed. Odds are you will see those knobs peak at a different position than they did when the amplifier was on standby. Peaking it with the amplifier keyed will usually change where the peaks fall on those two knobs. Maybe only a little, maybe enough to explain the difference.

73

 

[1iwilly]

Does sound like maybe the 300A is not exactly 50 ohms on the input. The FT101 has been tuned/loaded for whatever your dummy load is. For the moment, we'll assume 50 ohms. If the 300A's input impedance on Low side is too far above or below that, this will reduce the efficiency of power transfer into the 300A's final tubes. There is usually a compression trimmer cap soldered to the rear of the High/Low switch. This is to adjust the High side input impedance as close to 50 ohms as possible. A SWR meter and coax jumper BETWEEN the radio and amplifier will allow you to adjust that trimmer cap for lowest SWR.

Might make a difference you can see. The other solution is to tune the Yaesu, or at least 'touch up' the Tune and Load on the radio with the amplifier keyed. Odds are you will see those knobs peak at a different position than they did when the amplifier was on standby. Peaking it with the amplifier keyed will usually change where the peaks fall on those two knobs. Maybe only a little, maybe enough to explain the difference.

73

so i had a chance to mess with it when i first got the amp i adjusted the high side one when i was only using my Cobra 2k originally it was like 1.6 and i got it down to 1.1.moving forward to the new Toy 101e radio is tune for best it could do seen normal power as the book states i see the trimmer on the hi/lo switch started 1.8-swr best i can do 1.4swr from 1.6-swr why because i switch the jumpers originally 6ft from radio to meter and 3ft from meter now i reverse them and that's when i got it down to 1.4-swr but still the power out-come didn't change 75 watts dead key talking 100/105 pep close to 500 on bird compare with cobra 2k on high side 180 dead-key talking 240/260 pep 840/850

 

[Dmans]

It is difficult for me to decipher your last 1 sentence response.
But owning a Palomar 300a myself, the High position is for inputs of 1-10 watts. The Low position is inputs of 10-100 watts. It sounds backwards but the Low position bypasses the 2 driver tubes to make the amplifier “Appear” to be an “Amateur Radio” amplifier.

Since the typical Amateur transmitter “should be” a 100 watt transmitter, it is not unreasonable to think that with the power switch being in the Low position (2 Driver Tubes bypassed) and being driven with 100 watts from an “Amateur” transmitter that the final section is being driven with 100 watts.

Conversely with the power switch in the High position (Driver tubes engaged) and being driven with a “Non-Amateur” transmitter with output between 1-10 watts, the output power amplifier between the 2 positions should be close to the same.

I would caution to never drive the 2 driver tubes with more than 10 watts peak. Since all of the tubes are the same, mathematically it would be reasonable to think that in the Low power position (100 watts input from your “Amateur” transmitter) is feeding the 4 final tubes 25 watts each, I think the input matching circuits are somewhat different in components and/or power ratings of those components.
If you accidentally key the amplifier in the High power position with 100 watts input you are smacking your 2 driver tubes with 50 watts each or equal to more than the tubes (6KD6 or 6LF6) Datasheet rated output. Not to mention that there is not a Load and Tune capacitor on the drivers output.

73
David

 

[1iwilly]

It is difficult for me to decipher your last 1 sentence response.
But owning a Palomar 300a myself, the High position is for inputs of 1-10 watts. The Low position is inputs of 10-100 watts. It sounds backwards but the Low position bypasses the 2 driver tubes to make the amplifier “Appear” to be an “Amateur Radio” amplifier.

Since the typical Amateur transmitter “should be” a 100 watt transmitter, it is not unreasonable to think that with the power switch being in the Low position (2 Driver Tubes bypassed) and being driven with 100 watts from an “Amateur” transmitter that the final section is being driven with 100 watts.

Conversely with the power switch in the High position (Driver tubes engaged) and being driven with a “Non-Amateur” transmitter with output between 1-10 watts, the output power amplifier between the 2 positions should be close to the same.

I would caution to never drive the 2 driver tubes with more than 10 watts peak. Since all of the tubes are the same, mathematically it would be reasonable to think that in the Low power position (100 watts input from your “Amateur” transmitter) is feeding the 4 final tubes 25 watts each, I think the input matching circuits are somewhat different in components and/or power ratings of those components.
If you accidentally key the amplifier in the High power position with 100 watts input you are smacking your 2 driver tubes with 50 watts each or equal to more than the tubes (6KD6 or 6LF6) Datasheet rated output. Not to mention that there is not a Load and Tune capacitor on the drivers output.

73
David

i understand what you saying what i can understand 5 watts from the 101e gives me a 75-watt dead key on amp low side the 101e with new tubes is showing about 105 watts pep i thought i would do better with the 101e to drive the 300a and it's not

 

[Dmans]

If you are only driving it with 5 watts, then the High side can be used.
I have used mine with several different “1-10 watt drivers” and see approximately the same output on low that you are seeing.

On the High setting, with the same “1-10 watt drivers” I see approximately 350-375 watts output.

73
David

 

[1iwilly]

If you are only driving it with 5 watts, then the High side can be used.
I have used mine with several different “1-10 watt drivers” and see approximately the same output on low that you are seeing.

On the High setting, with the same “1-10 watt drivers” I see approximately 350-375 watts output.

73
D

for a quick experimental, i did try it on hi total dead key of 180 put the 101e only dead keying 2 watts to give me the 180 dead key, and yes saw the same output as with Cobra 2k i cut back on mic gain so not to drive it too hard

 

[Shadetree Mechanic]

It is difficult for me to decipher your last 1 sentence response.

You found a sentence there?

 

[1iwilly]

You found a sentence there?

i thought i would do better with the 101e to drive the 300a and it's not
i guess i put my foot in that one LOL where did that come from

 

[Dmans]

Try driving the Palomar 300a with 100 peak watts on the Low power switch setting.

100 Peak watts or PEP or “Bird Watts”

Or whatever you choose to call it.
You are seeing approximately 30 watts output per tube with your 2 watt input.

Chances are pretty good that you will see more output from the Palomar with 100 watts PEAK input power in the high position. I only use SSB on my amp so I can’t really comment on dead key numbers. I do believe that intermittent duty such as SSB will make any sweep tube amp last longer. Continuous duty modes like AM and FM are hard on the tubes. Tuning an amp in AM mode should be done with maximum MODULATED input to the amplifier for maximum output from the amplifier. Not as harsh on the sweep tubes.

Using SSB might be the best test for this.

73
David