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Modifying a 11 metre amp


I'm after modifying a 11 metre amp to work on 6 metres, you may not think at first that 6m can be freebanded, but it can emoticon UK allocation is only 50-52 mhz, but most of the rest of the world and certainly the US have 50-54 mhz. Many operators freeband the 52+mhz and some also go down to 48 mhz emoticon

I have a 6m radio but its QRP and could do with just a bit more power. Whats the criteria on a solid state amp for operating on a particular band?

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Re: Modifying a 11 metre amp


reckon just a slight re-tuhe.
give me a call on [sign in to see URL], or any freq locally thats not swamped by baby alarms and i reckon we could have a qso!!!

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Re: Modifying a 11 metre amp


It's possible that a valve unit would be simpler to modify than a solid state one. A BRL200 might be a good choice.

You will have to re-wind the tank coil using fewer turns, and the same for the input circuit - trial and error here, along with a bit of common sense. Not done this, but it's simple enough in theory.

One issue you may have is the capacitance of the ouput valves being too high to be able to bring the tank circuit to resonance, in which case disconnect one of the valves at the anode cap and try again.

Good luck!
 Andy.

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Re: Modifying a 11 metre amp


I have'nt had time for this yet, it is a valve amp a single valve produces about 80w with 4 w drive on 11m.

I'm waiting for the 6m loop antenna I've bought from Moonraker to arrive as well, I only have the home made dipole up for 6m and its pants, mind you 6m is deader than 11m atm emoticon

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Re: Modifying a 11 metre amp


I think you'll have problems with the big valves getting them resonant Dave, the beam tube type shouldn't be an issue though, Tranys will be easier just bypass or retune the pass filter. Watch out for parasitic oscillation wich will obviously keep it driving when unkeyed, I had to reposition the whole pcb to get rid of them thus shortening all the wiring. Its not too bad to do just go slow and deliberate. 519's and 509's work well as do 811's, but i had a sod of a job on a 3-500z amp ended up with over 30 decoupling caps in it!! John193 emoticon
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Re: Modifying a 11 metre amp


My first post.

Hi guys,

With a valve amp you may also need to modify the grid circuit for correct drive level.
Output network component values should be calculated to offer a 50 ohm output. There are calc's out there on the web but if you let me know the output valve and the desired freq of operation I'll gladly work them out for you.
You'll need to be able to measure inductance!
The days of six turns on a bog roll are I'm afraid past:-)

With a solid state amp you may have several problems, a sharp falling off of gain if you're using output transistors with a 30MHz cutoff! Also, HF amps tends to use type 43 ferrite material in the input & output transformers whereas type 61 in the norm for 6m.

Just my 2p, your mileage may vary.

Unit 148

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Re: Modifying a 11 metre amp


12Kw before you ask emoticon

Unit 148
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Re: Modifying a 11 metre amp


quote:

Unit 148 wrote:

12Kw before you ask emoticon

Unit 148



Handy way to heat the shack in the winter emoticon



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Re: Modifying a 11 metre amp


Transistor amps can and are modified for 6 mtrs,as others have said it depends on the transitor/s in question, also the ferrite in the input/output matching metworks may not be suitable, this also applies to the input/ output matching.

thers as bit to look into first. possibly a single transitor would be the way to go and do away with the ferrite matching networks. simple pi- matching would do the job then.

also as mentioned a valve amp is normally a lot easier to modify depending on the valve thats used, input output matching would obviously need to be modified and resonances in the anode choke would need to be checked to make sure there arnt any in the 6 mtr band, but there are many who have modified 11 mtr amps to cover the 6 mtr band so information on this shouldnt be a problem.


Mark (Pioneer )

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Re: Modifying a 11 metre amp


Quote:
"The days of six turns on a bog roll are I'm afraid past"

Yep, they don't make bog rolls as sturdy as they used to... emoticon

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Andy - 26 FB107
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