RCME simpletone. 27 MHz transmitter

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Pufango
Posts: 7
Joined: 04 Apr 2021, 12:34

RCME simpletone. 27 MHz transmitter

Post by Pufango »

Hello lads,
Has anyone built the simpletone TX rcme may 1968 ? I have and I can’t get it to work! First of I used modern equivalent components no luck what so ever! ( before I continue I made the singlet set TX the radiomodeler equivalent,worked straight away) In the intro to the article it suggests don’t use any alternative components so I made another.using original components Guess what it didn’t work.
I made the oscillator coil at least four times ,tested the components over and over.Still no results apart from the tone signal which is loud and clear.must say it’s got me stumped ! Anyone got any ideas ?
Best regards Tony.
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Mike_K
Posts: 463
Joined: 16 Feb 2018, 06:35
Location: Hertfordshire

Re: RCME simpletone. 27 MHz transmitter

Post by Mike_K »

Hi Tony

Welcome aboard the mode-zero forum!

I'm by no means the most qualified person to help you with the Simpletone Tx and there are many on the forum who are far more knowledgeable, but there are a few things that would help us all to help you.

First, what components have you substituted and with what? As the introduction to the article suggests, coils and transistors were the greatest trouble with the earlier RCM&E S/C transmitter, I would imagine they are the components that you may have substituted with your build? And have you made the pcb in the article or using your own layout? Unfortunately, I'm not a big fan of Rex Boyer circuits and as a young teenager I was told by numerous club experts to steer well clear of his work, so never attempted a Simpletone.

The P346A, 2N4292 and 2N4290 transistors are still available as NOS from Cricklewood (who are highly recommended for obsolete parts, though I haven't used them for a while):

https://www.cricklewoodelectronics.com/P346A.html
https://www.cricklewoodelectronics.com/2N4292.html
https://www.cricklewoodelectronics.com/2N4290.html

The resistors, trimmers, xtal etc should all be available, which leaves the coils. I'm not familiar with any of the Teleradio coils to know what would be a good substitute, do you have the construction details to wind them?

I've attached a pdf of the original RCM&E May 68 article to help those that don't have a copy to hand.

Cheers

MIke
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Taurus Flyer
Posts: 28
Joined: 06 Dec 2019, 11:56

Re: RCME simpletone. 27 MHz transmitter

Post by Taurus Flyer »

Hi pufanco,

The coils normally should not be a problem. However, the corematerial of the oscillator coil must be suitable for the frequency, the material of the core is often indicated with a color dot. In my opinion, a ferroxcube core is always good and perhaps because the exotic materials may have come into circulation later you use a wrong material for that. The cores I am using have a red color dot.
It's strange that identical transistors are used for the VT2 and VT3. If the transmitter does not provide a carrier wave I would in any case replace VT2 with a 2N2219 (A) which I have always used successfully myself. The 2N2218 in the early days.
To determine whether a transmission signal is also generated, you actually also need a field strength meter, I do not know whether you use it or how you can determine that the transmitter is working. You also need a field strength meter for optimal adjustment.

Good luck Cees
Pufango
Posts: 7
Joined: 04 Apr 2021, 12:34

Re: RCME simpletone. 27 MHz transmitter

Post by Pufango »

Hello lads thanks for the feedback.Have used original transistors and components but to no avail.Must say I gave up after attempt number three ( got fed up of making pc boards) Re made the coils several times (to the manufacturers specifications) the only thing I haven’t tried is a different slug ! May have to bite the bullet and fit 2.4 !
Best regards Tony
Taurus Flyer
Posts: 28
Joined: 06 Dec 2019, 11:56

Re: RCME simpletone. 27 MHz transmitter

Post by Taurus Flyer »

Hello Pufanco, VT2 has to be a high frequency transistor, for VT3 it isn't needed.
In the past it was difficult to find optimal results and I don't know the specs of the noted transistor in the circuit. My experience the 2N2219 is absolute good or can give better results, keep that in mind.
The primairy winding of the oscillator coil has to be in resonance with 27MHz parallel with the 22 pF capacitor. I looked in one of my transmitters 20 wdgs // 15 pF , the primary wdgs for 22 pF have to be some less than 20. With a ferrox slug you not only have the right material but also the adjustable range can be more. How many turns is the primary winding? The secondary is the load for the oscillator to activate the antenna amplifier, so 2 a 3 windings. Too much windings will load the oscillator too much, so there is an optimum.
Taurus Flyer
Last edited by Taurus Flyer on 07 Apr 2021, 14:09, edited 1 time in total.
stormer254
Posts: 56
Joined: 03 Mar 2018, 10:08

Re: RCME simpletone. 27 MHz transmitter

Post by stormer254 »

Hi Tony, I have what I believe is an original set, I used to use it in a boat when the kids were little, you are welcome to it if you want!
flea_flyer
Posts: 7
Joined: 16 Mar 2018, 21:14

Re: RCME simpletone. 27 MHz transmitter

Post by flea_flyer »

Hi Tony
I cannot help with your particular query, but I was interested to see that you have built a Singlet transmitter and that it worked first time. I intend to build a Singlet transmitter as well and I'm presently collecting parts. (See thread 'Magazine Tx/Rx plans' under "Single Channel".) I will follow your project with interest.
By the way, is it your Singlet Tx and Pal Joey model (oz4719) on Outerzone?
Gerry
Pchristy
Posts: 243
Joined: 16 Feb 2018, 13:57
Location: South Devon, UK

Re: RCME simpletone. 27 MHz transmitter

Post by Pchristy »

Pufango: You need to be a little more specific when you say you can't get it to work. The circuit breaks down into two parts - the RF section and the tone generator.

The first thing to check is that everything is getting the right voltage. The second is to check the current consumption. If the crystal oscillator is getting the right volts, it should work - even if the tuning is way off. What may not be working is the RF output stage.

So first things first, check for the right voltages around the oscillator, and then check the current consumption. I would expect the current draw to be around 100-150mA if everything is working correctly. If it is drawing nothing, then check for a broken land somewhere! If the oscillator is running, but not the output stage, I would expect a draw of around 10 mA or so (he says, holding a wet finger in the air!).

Do you have an oscilloscope? Even a basic 10 MHz one should be able to "see" 27 MHz, though you wouldn't be able to make any accurate measurements with it. You would also need a X10 probe to avoid loading the oscillator circuit.

As an alternative, you can check for oscillator function using either a short-wave radio, tuned to 27 MHz, or even a VHF-FM radio tune to 27x4=108 MHz. Even if the output stage is not working, you should be able to "hear" the carrier if the radio is close to the transmitter.

If the oscillator is not working, start investigating there. If it IS working, move on to the output stage. Modulation from the tone generator is applied to the output by VT3. If VT3 is switched "on", you should get an output. If it isn't, you will get nothing! As a test you could short the collector of VT3 to the emitter, soldering a short bit of wire in parallel with C6. If this brings the output to life, you have a problem with either the tone generator (VT4 & 5) or VT3.

That lot should get you started on where the problem lies, but always start by checking the power supplies - is power getting to where it is needed?

--
Pete
Pufango
Posts: 7
Joined: 04 Apr 2021, 12:34

Re: RCME simpletone. 27 MHz transmitter

Post by Pufango »

Hello lads ,
Thanks for your help much appreciated .Will let you know how I get on
Best regards Tony.
Taurus Flyer
Posts: 28
Joined: 06 Dec 2019, 11:56

Re: RCME simpletone. 27 MHz transmitter

Post by Taurus Flyer »

Good indications and I have some additions to measure and I have a note for that, please read with me Pchristy.

The voltage of the base of VT1 must 1,1 VDC at 12 VDC supply voltage, (1/11 x 12 VDC). So the voltage across the emitter from VT1 has to be about 0.5 VDC so the current from the oscillator is 0,5/330 1,5 mA. If the oscillator is actually functioning then the voltage of the emitter deviates a bit, may become slightly lower. To test the oscillator separately, the power supply to the other parts of the circuit must be interrupted.


NOTE IS EDITED!!!!!!
The current of the oscillator seems to be pretty low. about 5 mA can give better results, this can be achieved by lowering the resistance value of R3 to 150 a 100 ohm.

The multivibrator consumes approximately 8 mA during operation.
In normal operation, the total current is indeed about 125 mA. If this is significantly lower than VT2 is functioning poorly and a 2N2219 on that location turned out might do better.
When you measure realy output power, some optimization is possible by adjusting account of the secondary windings of L1 or lowering R4 to, for example, 22 ohms, but check the temperature of VT2 that it does not become too high. This transistor VT2 must be provided with a cooling fin.
..
Cees
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