Re: Tristar 747 (PTBM121D4X) UK Band Mod

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Phuture
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Re: Tristar 747 (PTBM121D4X) UK Band Mod

Post by Phuture »

Hi all,

I'm looking to do whichever mod is best to access part of the UK band on my Tristar 747. The radio currently Rxs/Txs in the following ranges (with clarifier centred):

HI: 27.415 - 27.855MHz
MID: 26.965 - 27.405MHz
LO: 26.515 - 26.955MHz

I have a Major 588 that has been mod-ed as follows (clarifier centred):

HI: 27.41360 - 27.85360MHz
LO: 26.96370 - 27.40370MHz

On the "HI" band with the clarifier in the 9 o'clock position I can set the radio to Rx/Tx on channel 20 of the UK band (27.79125MHz) and on the "MID" band I can set the clarifier at the 2 o'clock position to Rx/Tx on channel 20 of the mids (27.405MHz). This works well from my perspective and I don't mind having only partial access to the UK band.

So, I've seen the following clarifier mods - the "Factory Clarifier Mod" in Secret CB Vol 19 (page 48 - first image) and two "Slide Mods" in Secret CB Vol 17 (page 35 - second image).

Any advice on which is best for what I want to do? Cheers in advance. :)
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Re: Re: Tristar 747 (PTBM121D4X) UK Band Mod

Post by mrpsychopath »

Would it not be easier with one of Nicks pic uk add ons my 747 is perfect in standard form with uk add on, also gives 10kc switch. Its great like this.
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Re: Re: Tristar 747 (PTBM121D4X) UK Band Mod

Post by 163TM847 »

mrpsychopath wrote:Would it not be easier with one of Nicks pic uk add ons my 747 is perfect in standard form with uk add on, also gives 10kc switch. Its great like this.
I think he just wants UK offset rather than UK channels. ;)

For the Major if you just remove the two components [diode/resistor] then add a voltage from the regulators 10v to the clarifier [Also swap the clarifier control for a 10k it will give an extra little bit of slide], So tune the high band crystal for correct freq at centre for eg 27.415 the unlocked clarifier will then easily drop onto the UK offset, In some 588s it will get to the zeros.

For PTBM121 i just remove the diode/resistor and add voltage [10v] and it gives roughly 3kc which just about gets UK offset.

Personally though if its just UK offset i would prefer to have a offset switch using a 2SC945 [or similar] transistor.
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Re: Re: Tristar 747 (PTBM121D4X) UK Band Mod

Post by mrpsychopath »

Okdokey. My choice would be full 40 and 10 kc in them all.
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Re: Re: Tristar 747 (PTBM121D4X) UK Band Mod

Post by Phuture »

Yep,correct. I'm okay with a UK band offset mod.

Hi Nick, so for the PTBM121, 10V (9.4V BAS) being from the emitter of Q38 (2SD325) to the centre tag of the clarifier? The Factory Mod is similar to what you're describing but without using R18 inline with the 9.4V supply and the additional components and connections on the PTBM011. Picking your brain, if I may, but do you know what the additional components/changes are used for? Looking at "Mod. #2", step F on the slide mods image, I'm not familiar with the term "Super Slide" - any clue?
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Re: Re: Tristar 747 (PTBM121D4X) UK Band Mod

Post by Phuture »

Looks like the mod options in the Secret CB books are non-starters anyway as the varactor diode (ITT310) needed is like hen's teeth and presumably it makes up part of a super diode circuit. Anyway, removed D7 and R18, then connected the unused wiper on the clarifier to the 9.34V supply on Q38 and it slides down to 27.79215 for channel 20 on the UK band (HI band, channel 74 on radio). Swapping in a 10K pot made no difference to the frequency range, which is a bit unfortunate. 90Hz is not far off but I'm wondering if there's anything eIse I can do to drop it a little further? Suggestions from anyone gratefully received.
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Re: Re: Tristar 747 (PTBM121D4X) UK Band Mod

Post by lbcomms »

Replace the varactor with a BB809 to extend the range. Sometimes you can get away with two in parallel, but that often is too much for the oscillator and it will quit at one end of the range or become unstable (warbling). They can be had from eBay:

http://www.ebay.co.uk/itm/BB809-VARICAP ... SwU-pXrFMs

To go down further at the expense of going up, add a 10K resistor from the previously unused terminal (now with 9V on it) to the wiper (centre terminal, usually has a brown wire on it) and recenter the 12 o clock position using the two trimmer caps nearby (first USB, then LSB). This will give you roughly 1K more down and 1K less up.
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Re: Re: Tristar 747 (PTBM121D4X) UK Band Mod

Post by Phuture »

Many thanks for your advice, ibcomms. :thumbup: Will give that a try.

I've ordered three BB809 diodes as I think I'll try them in this "Factory Clarifier Mod" to see it flies. I'll update this thread with the results.

Thanks again. :thumbup:

Attached image of PTOS110A0X circuit for convenience in case it's necessary to refer to.
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Re: Re: Tristar 747 (PTBM121D4X) UK Band Mod

Post by Phuture »

...in progress
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Re: Tristar 747 (PTBM121D4X) UK Band Mod

Post by Phuture »

Hi,

So here's how each test worked out.

The following are all in place of D1 (ITT310) on PTOS110A0X:

BB809 Tests
Test 1: one BB809 only:...........................27.80154 - 27.79378MHz
Test 2: two BB809s in parallel:..................27.78994 - 27.79835MHz (chnl 20 (27.79125) at ~ 11 o'clock on clarifier)
Test 3: one BB809 and one ITT310.............27.78935 - 27.79701MHz (chnl 20 (27.79125) at ~1 o'clock on clarifier)

BB109 Tests
Test 1: one BB109 only:..........................27.79232 - 27.79970MHz
Test 2: two BB109s in parallel:..................27.78884 - 27.7964MHz (chnl 20 (27.79125) at ~1.30 on clarifier)
Test 3 one BB109 and one ITT310.............27.78883 - 27.79613MHz (chnl 20 (27.79125) at ~1.30 on clarifier)

"Factory Clarifier Mod"

I tried this with a couple of BB809s (in place of the ITT310s) but couldn't complete the last step as there is no terminal #10 on the PTOS110A0X sub-board (see above schematic). I assume the "OS011 board" on the Secret CB instructions is an error and actually should be "OS110 board". Could it be terminal #2 or #3?
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Re: Re: Tristar 747 (PTBM121D4X) UK Band Mod

Post by lbcomms »

The best range is BB809 Test 2 (two BB809s in parallel) which gives you about 8.5 KHz of range.

To centre the clarifier from its present ~ 11 o'clock position, add a resistor between the newly wired clarifier terminal and the wiper (centre terminal of the clarifier pot).

You'll need to experiment to work out the value, start with one 10 times the pot value (i.e. if its a 50K pot, start with a 470K or 510K resistor).

The lower the resistor value, the more the 12 o'clock position will be shifted clockwise, without affecting the low and top end frequencies.
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Re: Re: Tristar 747 (PTBM121D4X) UK Band Mod

Post by Phuture »

Hi ibcomms, apologies for the delay replying (had no free time this week). Thank you for your previous reply. Yep, I'll go with two BB809s and find a suitable resistor, as you suggest. Many thanks for your help and advice as always - very much appreciated. :thumbup: :thumbup: :thumbup:
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