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Linear Amp UK 'Ranger 572' HF Amplifier.


Thought i would share my finding on a problem i 'had' with my Ranger amp, First of the amp isnt even two years old yet and its not had a lot of use, Mine is the Ranger 572, It uses 4 '572B' tubes instead of the 811 tube.

Anyway ive noticed problems with the Input matching on 15 and 10 mtrs, The vswr that the radio is seeing has been very high and most of the time end stopping and this makes it unusable on these bands, Yet on 20 mtrs and lower all is fine, So no real problem with the actual tubes and such as its doing about a Killowatt on these bands into a dummy load with no faults.

10-15 mtrs is were the fault is so i guessed its down to the input matching for these bands, The input matching is a conventional 'PI' match, it uses a small coil of about 4 turns connected to input and the output, from each end of the coil and running to ground is a capacitor two in total, Both are 100 pf and rated for 2 killovolts ( nice ) you would think so. but all is not well, for the capacitors are getting 'Hot' with only 80 watts of drive and as such i think the capacity is changing wildly, The capacitors are small disc ceramic and for this power level they use a 'Y5U' dialectric this is very unstable with small changes in temperature, hence my problems with tuning..

Ive been intouch with Paul from Linear amp uk and he's stated that he no longer uses these capacitors anymore ( maybe he or some of his customers have had the same problems as me, so ive changed the capacitors in my amp for 'silver mica' capacitors although these are expensive compared to the ones that were in there, there also very stable with a stable dialectric..... And at prsesent ive not had any problems, the amp is working as it should, im seeing about 900 watts on 10 mtrs with a stable input vswr so the radio is happy..

Paul from Linear amp UK has also said he NO longer uses tuning coils that have a ferrite core as this in some instances can become 'Hot' and this makes the inductance of the coil change, putting it out of tune.

So if anyone else is having problems with the input vswr on there Ranger amp maybe this is the cause.

Marc
 
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Last edited by madmark1, 4/Nov/2011, 12:03 pm


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yamanx1 Profile
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Re: Linear Amp UK 'Ranger 572' HF Amplifier.


Hi Marc, interesting, there are FB ops using this PA 

I’m using an old Heathkit 2 x 3-500z valves atm, this has ferrite style tuning coils. The main issue I have with this amp is there is no stand by feature, its on or its off. Not too big a problem as the 3-500z’s don’t require too much warming.

But the even with the PA off it still seriously affects the tuning from the auto ATU on the radio, when using differing bands without the amp, the auto ATU doesn’t like the amp in line at all.


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madmark1 Profile
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Re: Linear Amp UK 'Ranger 572' HF Amplifier.


Hi Dave, I take it the amp is hard switched and its either switched via the ACC on the radio or your using a footswitch ? or simular..

What you can do in that case is put a switch in-line with the PTT/ ACC from the radio to amp.

This is all thats done on amps like the FL2100 series or the Ranger i have.

You could install the switch on the Amp if you wanted to.

Mark



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Re: Linear Amp UK 'Ranger 572' HF Amplifier.


Ah, thanks for that Mark, good idea, I will do that cheers emoticon

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Re: Linear Amp UK 'Ranger 572' HF Amplifier.


Hi mark did you change the caps for a like for like in the values ie. 100pf and 2kv
5/Jan/2013, 3:55 pm Link to this post Send Email to Gary m1rec   Send PM to Gary m1rec Blog
 
madmark1 Profile
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Re: Linear Amp UK 'Ranger 572' HF Amplifier.


I did, Yes.... Ive the schematic for the amp... so i just went of the standard values... Its been running now for quite sometime without problems...


Mark

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