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Old 6th May 2017, 8:11 pm   #1
AndyG6OHM
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Default Tait T525 68-88 conversion to 6m

Hi Everyone.

Looking for conversion details to convert a 68-88mhz Tait T525 to 50mhz.

The Tait i have already converted to 70mhz.

Can anyone help with conversion details to 50mhz.

If so please drop me a line.

We have a new 6m repeater coming on line soon GB3EC at Bury St Edmunds.

So want to get the rig up and running A.S.A.P.

Thanks Andy G6OHM

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Old 6th May 2017, 11:29 pm   #2
Biggles
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Default Re: Tait T525 68-88 conversion to 6m

Converting to 70MHz on a 68-88MHz set isn't really much of a conversion but to get the rig to perform outside it's design limits is something else, but I suspect you already know this! I would expect to have to change the front end coils and the VCO or multiplier stage coils if it's a crystal. I'm not sure if you would get away with just changing the capacitors to get the tuned circuits to resonate that low. I use a Chinese Wouxon quad band set which covers six metres and it's pretty good. I know this is cheating but it sounds like a lot of work to convert your set to 6. Sorry, not really answering your question...
Alan.
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Old 7th May 2017, 12:25 am   #3
Steve_P
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Default Re: Tait T525 68-88 conversion to 6m

I used to convert these as at one stage there were repeaters in Band I and we had to convert these to work down there.

The VCO coils are underneath the metal section that was screwed to the main board. We used to put a small capacitor across the colis - under the metal panel and soldered to the board. Only a few pF as I recall.

The RX and TX will go down there no problem as far as I recall.

I wonder also, thinking back into the dark corners of my mind, if the If injection can be changed - I remember doing that on a Kenwood.

Wish I could be more help.

Cheers.

Steve P.
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Old 7th May 2017, 8:28 am   #4
AndyG6OHM
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Default Re: Tait T525 68-88 conversion to 6m

Hi Steve

Many thanks for the info.At least it's a start.I was reading the Tait t525 manual last night.
I see there are links in the PA section to make it work below 70mhz.

If you think of anything else please get in touch.

Thanks Andy G6OHM
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Old 8th May 2017, 12:41 pm   #5
Omegaman
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Default Re: Tait T525 68-88 conversion to 6m

I'm sure there was an article in one of the magazines a good few years ago on putting these on 6M. Maybe Ham Radio Today?
It could have been Chris Lorek's second book?
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Old 8th May 2017, 7:50 pm   #6
Jon_G4MDC
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Default Re: Tait T525 68-88 conversion to 6m

Haven't done a 525 Andy, but GB3AM is a T355 ( I think it is anyway) xtal controlled base station predecessor. I did that. RX of late is something else but the 355 was fine back in the day.

You can choose how hard you want it to be. For RX you can just pad tuned circuits with capacitors to where you want them (at the expense of switching bandwidth most likely) or you can scale the whole thing L and C. That is more effort.

For the TX power amp and low pass I recommend scaling reactances of L and C if you have no better way - simulator or similar.

I have done MC Micro LB>6m, MX295 (200MHz)>6m and almost got there with an FM914 this way. I got bored with the front end of the FM914 - too hard to dismantle, but the rest worked - including the synthesiser hardware hack to subtract 20MHz from the programmed value. Program as 70MHz but get 50MHz (blocked) - well I thought that was sneaky. (also works for programming 430MHz as 450 MHz - Aussie CB channels are also blocked)

I still have it somewhere.
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Old 10th May 2017, 6:50 pm   #7
G6Tanuki
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Default Re: Tait T525 68-88 conversion to 6m

Part of me is wondering if you could spare hassle padding the receive LO-multiplier chain by using 'high-side' LO injection.
[this was a classic way to easily get 450-470MHz ex-MetPol Pye Pocketphones to work on 430-odd MHz]
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Old 10th May 2017, 7:55 pm   #8
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Default Re: Tait T525 68-88 conversion to 6m

On 'U0' High-UHF (440-470MHz) Pye / Philips MX296s the VCO often could not naturally track down low enough, even when adjusted, for the preferred low-side injection to be used at the lower end of the amateur 70cms band.

Chris Lorek's solution to this involved modifying a couple of coils in the VCO, but some people just altered the channel programming code to use high sided LO injection and left the VCO as-was.

On 'T4' Low-UHF (420-450Mhz) versions which were obviously perfect for 70cms use, low sided injection always worked.
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