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PALOMAR TX-5200 QUESTION

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Old 12-23-2008, 07:33 PM
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Default PALOMAR TX-5200 QUESTION


I try my QRP 5200 on 2 different radios and it works on 11 meters but when I hit the other ham bands I unkey and the damn thing takes a second to key then it stays keyed kind of the key like stays lit and recieve drops down then I turn of the amp and then back on light goes out and recieve coms back.

The amp is staying keyed I guess now would this be due to a tune some one did to run it out of band would I have to reset the variable pot at the front by the band selector while in each band or is there a happy medium I need to find but then not beable to run it on 11 meters which I actually dont and it wouldnt matter anyways.

Heres a link to a site with pics of my exact amplifier notice in front by band selector theres a silver variable I guessing this is what needs adjusting?
Palomar TX5200 for sale pictures from hobbies & interests photos on webshots
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Old 01-05-2009, 06:58 PM
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Yes, it is a multi-band "Amateur" amplifier but, it does not have tuned input for each band, to run that thing, you need a tuner between the radio and the amp.


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Old 02-02-2010, 12:06 PM
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Im thinking about actually digging this out and playing around with it. I need to find specs on what input drive power it reccomends. I guess I can use one of my radios with a internal tuner for input tuning but I will have to setup another tuner for inbetween the amplifier and the inverted antenna.
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Old 02-15-2010, 05:56 AM
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Tony, here is the answer to OUR question about why our Palomar 5200s occasionally hang up (Thaks Bob).

Quote:
Originally Posted by bob85 View Post
paws,
you see different values of cap/resistor to give a certain amount of feedback at a certain frequency without coupling collector dc to the transistor base, there are other ways to do it but the cap resistor is most commonly seen in cb amps,
the .1uf you see in dave clones and the .01's seen in many others give very little reactance @27megs, you are mainly dealing with just the resistance,

capacitive reactance ( xc ) = 1/ 2*pi* f* c , caps also cause current to lead voltage by 90 degrees of phase,
cap/resistor feedback circuits are ok for single band amplifiers but not for broadband amps which usually add an inductor in series with the cap/resistor,
inductive reactance ( Xl ) = 2*pi* f* L, inductors cause current to lag voltage by 90 degrees of phase,

the result of the series connected capacitor/inductor is reactance X = Xl-Xc , plus the resistor gives you a impedance Z which determines the level feedback at any particular frequency,
the reactance of the cap/inductor in series with the resistor gives you a feedback curve that if designed correctly will flatten the naturally rising gain of bipolar transistors as frequency is decreased,

amps that dont use an inductor in the negative feedback such as rmitaly have a rising gain as frequency is reduced, the cap does little and what it does do is the opposite of what is needed in a negative feedback circuit if you hope to use the amp over a wide frequency range,
they are also often unstable under certain drive/load conditions and frequencies, you can make them self oscillate, even the ones they sell as hf amplifiers with filters vswr and overdrive protection bling,
better designs use L/C/r networks and should not start break dancing when you hit a sweetspot,

negative feedback has other effects, it closes an open loop, reduces gain, extends frequency response, lowers effective input and output impedance, improves damping, lowers distortion and can improve stability,
the designer must calculate the best tradeoffs based on the transistor characteristics hes going to use and the intended frequency and/or bandwidth of operation amongst other things,

i have repaired many 1446 amps that have got so hot the feedback components are fried or dropped out of the board and they dont self oscillate @27mhz like a palomar which makes me think the people behind the palomar ripoffs dont have a clue what they are doing, they are far from alone,

68ohm in series with .01uf cap is typical for cb amps using 1446 transistors, its a carryover from the days when the same amps used mrf455's which have a less enthusiastic character than 1446's but those values seem to work @27mhz, its when you go well below 27mhz and gain gets hairy that the shit can hit the fan with a big swing on your current meter and a puff of smoke,

the maths behind it all when using reactive components applied to real amplifiers are pretty complex,
if you can get your head around it thats great, if you can't then its your choice of what to try next,

i agree with boo, 1/2watt is not nearly large enough wattage, even 2w is marginal,
Maybe if we add negative feedback (my amp does not have it in there from the factory) it might affect that "un-keying" issue.

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Old 03-15-2013, 09:38 PM
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I still have to hook my 5200 up and run it a little. Mine has 4 x 2SC2290 Transistors in it and was like that when I got it. I know they are not the original transistors that came with these amplifiers the ones that are supposed to be in the amp I am not the least bit familiar with.
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Old 07-09-2013, 06:56 PM
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Tony, if your still checking this link here is my experience.

the 2290 takes less drive than the stock transistors so what I would do is hook the thing up to a dummy load and give it some low drive. adjust the input 16-150pf cap for your lowest SWR on the rig at the highest op freq. and adjust the 16-150pf cap on the 10-15M band pass for the maximum output.

Next you could design a 50 Ohm 3DB input attenuator out of some 3 Watt metal film resistors and insert it on your input in place of the 27 ohm 5W, if that doesn't drop the output enough go 6db. This will lower the SWR to the rig and make the amp more stable.

I would probably remove the fixed caps on 20-80 the band pass filters and install trimmers like there is on the 10-15M filter.

Lastly you could install trimmers across the output transformers but without the proper test setup they are a bitch to balance in a multiple push pull config.

Good luck and thanks for the schematic links!

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