RCME simpletone. 27 MHz transmitter

[Pchristy]

Funnily enough, I spent a couple of hours on the 'phone with an old friend yesterday. He was trying to fault find on a brand new Remcon Quantum 6 he'd built from a NIB kit!

The fault turned out to be VT3, which served an identical function to the VT3 in the Simpletone we are discussing here! The oscillator was running, the encoder was running, but there was no RF output as VT3 was open circuit!

I'm hoping he'll sign up to this forum, as he has a nice collection of vintage radio gear, all in excellent condition!

Cees: Yes, all valid points, but I'm assuming that the circuit was tested "as is" before being published, and should work without modification. Before tweaking component values, I think the OP should go through the fault finding sequence that I detailed, otherwise there is a chance of adding faults rather than reducing them!

Once working, there may be room for improvement, but get it working first!

--
Pete

[Taurus Flyer]

you're absolutely right Pete.
I have built several transmitters and converted an original one of my own to silicon transistors (2) because the original germanium transistors (1) are very scarce, this was an AF118 antenne signal transistor. I still have the last two in the world and can be blown up very easy!
What struck me is the date of the schematic, that must have been in the beginning of the silicon transistors, hence some ideas from myself to try to optimize the output power, partly that I read from several modellers from that time and heard that they had insufficient range. These were other circuits but simular.
I follow the topic with interest.
Cees

[bluejets]

Plenty of AF118 on Ebay mostly in and around UK and Germany.

https://www.ebay.com.au/sch/i.html?_fro ... ansistor

Also this........... The best replacement for the AF118 is the 2SA358, I have never had one affected by whiskers (unlike the AF118). I have replaced all the AF118's in my germanium TV sets with the 2SA358. They do have unique specs for a germanium, both in the voltage rating and combined high frequency capable department. They also make a very robust output stage for a small AM transmitter.

https://www.vintage-radio.net/forum/sh ... ?t=157782

[Taurus Flyer]

Thanks for information, never too old to learn. I looked for a supplier in the Netherlands, thanks,
I also remember there were Japanese transistors of which you could place two in parallel but a single AF118 performed better and in the past costed me 12 guilders, so a lot of money.
I remember the 2SA158 but can be wrong. 158 .......358?
..
Cees

[MJF]

Here is a source located in Canada for a very wide assortment of old radio parts. I purchased some transistors for a Bonner Transmite Servo from him at a reasonable price. From what I have heard he used to frequent (before Covid) Ham Radio swap meets and has a huge selection of old electronic goodies.

http://nettyelectronics.com/

[Pufango]

Hello lads ,
Thanks again for the information .Geting the original components is not a problem thanks. Have been trying to contact Flea flyer and stormer 254 via private email but to no avail ! If you still want to contact me see email below
Best regards Tony

thepufango@gmail.com Please note the spelling.

[flea_flyer]

Tony (and possibly others)
Finally fixed up my profile with correct email address for PMs!
I have just found some 1.0mm aluminium sheet to start the transmitter case.
Gerry

[stormer254]

Email sent.
Steve

[Pufango]

Hello lads , update on the TX .
Thanks to the genorosity of stormer 254 who kindly sent me an original TX (thanks again) hopefully I have found the problem.On my tx the oscillator coil is wrong ,the primary turns are correct but the output coil was wrong! I had made it with five turns instead of the three turns of stormer 254s original ! Haven’t altered the coil on my tx yet but hopefully it will work! Do you experts think I’m on the right track ?

[flea_flyer]

Pufango
It sounds hopeful. The number of primary turns is all about resonance. Secondary turns will be all about impedance matching and power transfer. If secondary turns are too high the primary (oscillator) stage may be overloaded to the extent of killing oscillation altogether. Just my thoughts....
Gerry