Haigh (Matthews) Wobbulator

[frsimen]

An old 555 will benefit from a 10k resistor connected from Pin 2 to the positive supply. The application notes for the circuit show the resistor is needed when AC coupling is used, as is the case here.

You may need to reduce the value of the 0.1uF capacitor for reliable triggering.

Paula

[David G4EBT]

As explained in other threads, when I built my sawtooth generator as per the original circuit it failed to work.
Substituting the NE555 for a CMOS LM7555 cured the problem.

The change in value of R5 on the original sawtooth circuit from 10K to 10 Ohms to enable all versions of the 555 to work was suggested by Peter at post #15 at this link:

https://www.vintage-radio.net/forum/...6&postcount=15

Quote:

"Actually if R5 is made 10 ohm the circuit will work with either a normal 555 OR the Cmos version".

Unquote.

For the wide variations of 555 versions, see post 17 here:

https://www.vintage-radio.net/forum/...53#post1296453

Where I stated:

"Regarding reducing the value of R5 from 10K down to 10R, the original circuit which I tidied up but with all the same component values, (albeit I added a voltage regulator), specified a plain NE555 and a 10K resistor for R5. It's no wonder that with a 10K resistor for R5 and a plain NE555, mine didn't initially work. There is quite a list of versions of the 555, each have significantly different parameters, notably the current drawn, the minimum supply Voltage and the maximum frequency at which they'll operate.

NE555 current 3000uA, max frequency 0.1MHz Min supply Voltage: 4.5V. (Max 16V).
LM7555 40uA, max frequency 1 MHZ. Min supply Voltage: 2V. (Max 18V).
LMC555 100uA, max frequency 3 MHz. Min supply Voltage 1.5V. (Max 15V).

(In this application the upper frequency limit is of no consequence, but will be in some applications).

https://en.wikipedia.org/wiki/555_ti...as%20of%202013.

So, given that the NE555 needs 3mA and 4.5V, and the LM755 needs only 40uA and 2V, it's not surprising that with a 10k resistor, mine didn't work.
With a LM7555 the board worked well with a nice sawtooth output of c. 8.3v P-P and a frequency range of 3 to 117Hz (I set it to 50Hz).

In view of this, in 2020, based on Peters suggestion I updated the original circuit by changing the value of R5 from 10K to 10R so any version of the 555 should work, and added a footnote to the circuit to explain.

With unfussy 7555s plentiful at under £1.00 each, I'd be inclined to try one.

Good luck with it.

Pic 1 below is the sawtooth waveform from mine.
Pic 2 is the wobby waveform at 465kHz.
Pic3 is the frequency readout.

(It's more than ten years since I built mine, and 20 years since the original Raymond Haigh article, initially in ETI, then in Radio Bygones).

Given how much effort Peter 'electronpusher0' has put into updating the design, creating the PCBs and making them cheaply available to many forum members, (as with the 'Mini Mod'), and arranging availability of the coils etc via Tony Nailor of Spectrum Comms, it would be nice to see a few more examples of them built and working.

[keland_uk]

Thanks David & Paula,

David, I think the resistor in question is R26 on the new cct, is that your understanding? I will also try a more modern 555.

Scrub that, there is no resistance in for pins 4&8, R26/C22 make it act as a Monostable, where the output pulse duration is t=1.1R26C22, duh....Different cct to the one with R5. I suppose a short description of how the new cct works would be helpful, I've looked and have not been able to find a general description...


And Paula, there is a 12k resistor from pin 2 to the Vcc in the final cct.

[frsimen]

The following explanation is based on the colour version of the circuit that you have posted.

The 555 is configured as a monostable and is used to delay the start of the next sweep, following the completion of a sweep. Its output will be low until it is triggered.

Q21 and Q22 are configured as a current mirror, providing a constant current source from the collector of Q22 to charge C21. The variable resistor in the base circuit of the current mirror allows the constant current level to be adjusted and gives control of the charge time for C21. Initially Q23 is not conducting, as the output of the NE555 is low, allowing C21 to charge.

Op amp U21A is configured as a unity gain buffer, so its output voltage will track the voltage across C21. This voltage is used to feed the VCO circuit. U21B is configured as an inverting comparator. It compares the voltage present on pin 6 with that set by resistors connected to pin 5. I can’t give circuit references, as that part of the circuit isn’t shown.

When the voltage at pin 6 is lower than pin 5, the output at pin 7 will be high. As soon as the voltage at pin 6 exceeds the level at pin 5, the output at pin 7 will drop sharply towards 0V.


This voltage is fed to pin 2 of the NE555, the trigger pin, via C25. Up to now, the pin has been sitting at close to the positive supply rail. The output change at pin 7 of U21B will cause a negative going pulse to be fed to pin 2 of the NE555, due to C25. The negative going pulse is the condition needed to trigger the NE555. The output at pin 3 of the NE555 will go high for the period determined by C22 and R26.

When the output goes high, Q23 will conduct and will discharge C21 via R23. The output of U21A will go low and the output of U21B will go high. Q23 will stay conducting until pin 3 of the NE555 goes low. At that time, the cycle will repeat.

Paula

[keland_uk]

thank you. The full cct is on page one of this thread, post #12. I'm sure the above will help people.

[markfff]

I've been following this project for a while, and now I think I'll try my hand at building one. I assume the kits and pcb's are all gone by now so I started looking for the parts. I'm having trouble finding the KV1256 varactor diode. I can't even find a spec sheet. Can anyone name a source, or a suitable substitute, or at least provide the specs so I can find something that will work? As for the pc board, is there a gerber file available, or a scale drawing, or even a photo with a ruler for scale? Thanks

Mark

[Bazz4CQJ]

Mark, the guy responsible for the boards was Electronpusher (Peter). I think he did a batch, and then a second batch, so not sure he'll want to go there again

The design has gone through a number of variations; I'm sure that at least one or two people used diodes other than the KV1256, but it's now a pretty difficult task to read through the different threads that have been publish over some years to unpick that kind of detail.

Attached are some notes on diodes I found on file; I have no recollection of making them and I'm actually a bit confused by what they say; so don't take them as gospel!
B

[keland_uk]

I may be able to help, I have a spare set. I'll PM you

Originally Posted by markfff

I've been following this project for a while, and now I think I'll try my hand at building one. I assume the kits and pcb's are all gone by now so I started looking for the parts. I'm having trouble finding the KV1256 varactor diode. I can't even find a spec sheet. Can anyone name a source, or a suitable substitute, or at least provide the specs so I can find something that will work? As for the pc board, is there a gerber file available, or a scale drawing, or even a photo with a ruler for scale? Thanks

Mark

[markfff]

Originally Posted by Bazz4CQJ

The design has gone through a number of variations; I'm sure that at least one or two people used diodes other than the KV1256, but it's now a pretty difficult task to read through the different threads that have been publish over some years to unpick that kind of detail.

Attached are some notes on diodes I found on file; I have no recollection of making them and I'm actually a bit confused by what they say; so don't take them as gospel!
B

I know. I've been going through the posts to try and sort out the different variations. I think just sticking to this thread will be enough, it seems to be complete with the most current info. Thanks for the notes, I had no idea what the diode capacitance would be, and now I'm at least in the ballpark.

Mark

[David G4EBT]

Originally Posted by markfff

I've been following this project for a while, and now I think I'll try my hand at building one. I assume the kits and pcb's are all gone by now so I started looking for the parts. I'm having trouble finding the KV1256 varactor diode. I can't even find a spec sheet. Can anyone name a source, or a suitable substitute, or at least provide the specs so I can find something that will work? As for the pc board, is there a gerber file available, or a scale drawing, or even a photo with a ruler for scale? Thanks

Mark

In post #1 you will note that Peter - the originator of this thread, and designer of the updated version of the Wobbulator stated:

Quote:

'For the varicap I used a KV1236 which are still available at reasonable cost'.

Unquote.

There ae several registered well-established UK business sellers offering these at reasonable cost. Here are just two:

Quote:

1 X KV1236Z TOKO VARICAP

PICTURES ARE OF PARTS IN MY STOCK

Unquote.

https://www.ebay.co.uk/itm/225089499920

And:

‘KV1561A-3 AM Triple Varicap Tuning Diode Ap=2 KV1235 KV1236 See Text KV1561 CI32’

https://www.ebay.co.uk/itm/141267959116

The seller is Peter Thomas, JabDog Electronics Components, who will be well-known to forum members and has been serving the amateur radio and vintage radio communities for many years now, originally via mail order, but in recent years via his internet shop:

https://www.ebay.co.uk/str/jabdogelectroniccomponents

(Peter used to be able to supply the sets of TOKO inductors for the Wobbulator, but of course the design was first published back in 1998, 25 years ago, when TOKO were still supplying inductors to retailers and Peter then carried the full range).

The KV1236 Datasheet is here:

https://www.datasheets360.com/part/d...7762398588424/

As an aside, the original designer of the wobbulator was the enigmatic 'R.F.Haigh' (AKA 'Raymond Haigh') about whom nothing is known. For a brief few years, he published many magazine articles with full constructional details of all sorts of projects such as small amplifiers, and multiband radios, all beautifully designed.

For example:

http://www.fracassi.net/iw2ntf/manua...mond-haigh.pdf

Such neat and elegant designs - what an inventive and clever man.

Then he disappeared without trace.

Was 'R.F. Haigh' (AKA Raymond Haigh), a pseudonym perhaps? I guess we'll never know!

[markfff]

Thanks David, I think I have a source for much of what I need now, but this info will be quite helpful if it doesn't pan out. Interesting set of articles, I quickly scanned them and will make time to read them through.

On a side note, Haigh mentions Lee DeForest in the list of important events. One of my uncles was a professional photographer and did some portraits of DeForest in the 1930's. I think I have a copy somewhere around here.

Mark

[keland_uk]

Ok, I have a newer 555, a LMC555, same problem.
The o/p from U21B certainle goes from around 10V down to zero if pin6 > pin5. Voltae across C21 around 6.92V. i/p to pin2 of 555 is 12.101. R25 is 12k. I've checked cap and resistor values. I do get sine waves from cn3/cn4 L1 377kHz/787khz, L2 1.09/2.64Mhz L3 3.03Mhz to 7.94Mhz, albeit peak to peak voltages are 22/13.2/4.8 respectively.

So C21 is getting charged U21 goes to zero volts, but looks like C21 doesn't get discharged by Q23. Therefore no o/p from Cn23 at all. (should show saw tooth?)

Any pointers where to look next appreciated.

[Electronpusher0]

Originally Posted by Bazz4CQJ

Mark, the guy responsible for the boards was Electronpusher (Peter). I think he did a batch, and then a second batch, so not sure he'll want to go there again

B

I have been away so have only just noticed the recent posts on this thread.

If there was sufficient interest I would be prepared to order a another set of boards.
I actually supplied the board, Coils and Varactor diodes as a set, I will contact Jabdog / Spectrum comms and see if the coils I used are still available. The minimum No of boards and parts I can order is 5 so that is the minimum number I would need to be able to sell, I don't make any money from these, I just add £1 for the handling.

Peter

[Electronpusher0]

Originally Posted by keland_uk

Ok, I have a newer 555, a LMC555, same problem.
The o/p from U21B certainle goes from around 10V down to zero if pin6 > pin5. Voltae across C21 around 6.92V. i/p to pin2 of 555 is 12.101. R25 is 12k. I've checked cap and resistor values. I do get sine waves from cn3/cn4 L1 377kHz/787khz, L2 1.09/2.64Mhz L3 3.03Mhz to 7.94Mhz, albeit peak to peak voltages are 22/13.2/4.8 respectively.

So C21 is getting charged U21 goes to zero volts, but looks like C21 doesn't get discharged by Q23. Therefore no o/p from Cn23 at all. (should show saw tooth?)

Any pointers where to look next appreciated.

I will take a look at your reported issues and see if I can figure anything out. It will be after the weekend though.
Peter

[keland_uk]

Mea Culpa. I used a BC183L, different pinout to a BC183. Can't believe I didn't check it , Assume nothing comes to mind. I have a Sawtooth now on the o/p of CN23, from 4Hz upto around 167Hz. Hurrah, now to check the rest....

[mole42uk]

I've been testing mine over the weekend. I get the sawtooth waveform but only with the Sweep Rate pot towards one end, move it to lengthen the sweep and the signal collapses. The other thing I notice is that the sawtoth level at the Sweep Output is only a couple of volts, I note from the circuit diagram that R33 is used to set the sweep p-p to 6 volts, I get nowhere near that. The power supply is correct at 11.9V out of U1. I do get a fairly stable sine wave from the frequency counter output which changes frequency in accordance with the Range switch. Any suggestion of what to check next would be welcome!

[keland_uk]

Originally Posted by mole42uk

I've been testing mine over the weekend. I get the sawtooth waveform but only with the Sweep Rate pot towards one end, move it to lengthen the sweep and the signal collapses. The other thing I notice is that the sawtoth level at the Sweep Output is only a couple of volts, I note from the circuit diagram that R33 is used to set the sweep p-p to 6 volts, I get nowhere near that. The power supply is correct at 11.9V out of U1. I do get a fairly stable sine wave from the frequency counter output which changes frequency in accordance with the Range switch. Any suggestion of what to check next would be welcome!

I found Paula's description of how it worked helped (#44), I managed to get an oscilloscope plot of the Cap C21 and could see it charged and didn’t discharge, which pointed to BC183.
I just reverted to an old 555 that might have been a problem for me, but that still gives me a sawtooth, and have managed to adjust to 6V peak to peak. Ie your problem wont be the type of 555 you are using, probably


I had a similar problem with an oscillator that stopped working when a load was put on it, that was down to a 2n3906 with a significantly lower Hfe than the guy used when he tested it (Nothing to do with the wobbulator).

Recheck the values of the components and check everthing soldered ok, but I bet you've already done that many times, so excuse me for telling you how to suck eggs... Totally fustrating I know....

[mole42uk]

After more careful testing, I have a useable sawtooth adjustable to 6V p-p at U21A/1 and 3V DC at U22A/1. After inserting the varicap the correct way around, I find the RF oscillator does respond to the sawtooth but the output isn't a nice sinewave at all. It was a good-looking sine wave before I put the varicap into the circuit but there seems to be some unfortunate influence between the sweep function and the FET oscillator. No doubt some more investigation will reveal the cause.

Just as an aside - how have you all dressed the wiring between the coils and the range switch? As short as possible or does it not matter?

[keland_uk]

Originally Posted by mole42uk

After more careful testing

Maybe helpful if you told us what you had to fix?



Would also be nice to know how others are getting on.


I'm going to use BNC connectors, Panel pdf example attached, BUT I may not need fine control since I have a 12 turn pot for main tuning. I think the shorter the better ref wires. I haven't got the Higher frequecies working at all.

Moving onto an amplifier fix next week so this project going on back burner

[mole42uk]

Originally Posted by keland_uk

Maybe helpful if you told us what you had to fix?


I'm going to use BNC connectors,

No fixes, I think I just had to test the correct signal at the correct place!

I also have BNC connectors.