First project (mini mod)

[baza100]

Trying to build a mini mod got no experience so from the picture I can put the resisters on any way. Any advice on how the other components go on? Never done any electrical work like this.
Thanks

[Radio Wrangler]

Resistors can go either way.

Many capacitors can go either way but you'll come across plenty that can't. Look for a plus or minus sign to tell you which lead must go where. Aluminium electrolytic capacitors normally get a - marking by the negative lead. For some reason I've never found, Tantalum electrolytic capacitors are normally marked by the positive lead.

Watch out because some makes of transistor have the leads coming out in different orders to other makes!

Until you've found your way around the differences in components, it is perfectly normal to feel that the people who created these inconsistencies should be boiled alive in oil.

If in doubt, post a photo and plenty of people on here will help identify what goes where.

David

[Al (astral highway)]

Originally Posted by baza100

Any advice on how the other components go on? Never done any electrical work like this.

Hi and welcome. Just to add to what David says:

--pay attention to the stripe on the body of the diode, which marks the cathode (negative).

--also note the drain, gate and source markings on the FET, Q1. (D, G, S). These are marked on your diagram from the top of the component and you should make sure you align the straight side as shown on the diagram, viewed from above. Easy to confuse when soldering .

--and similarly, note that the emitter of the transistor is marked by a little tab.

--the IC (LM386) also has a notch, here shown at the top of the board. If you haven't soldered much before, I would recommend using a socket.
Once the rest of the construction is in place, you can then install the IC. It will likely arrive in a tube with a load of others, or in some polystyrene. When you remove it, you may find that the pins are just slightly too wide to fit into the socket. You can carefully give them a small squeeze to get them to fit, but easy on it when pushing it into place as you can easily bend the pins.

It might be easiest to follow a set order. Just as a suggestion, install all the resistors, then the capacitors. With the capacitors, place the largest electrolytic capacitors, which are C11 and C4 first, because you might otherwise not have space for them. Then (this isn't critical) the coils, then the diode, Q1 and the component marked e, b, c, on your diagram

That way you will also be less likely to overheat the 'active' component (the transistors and diode) when soldering.

Take your time because when you are working like this, you keep flipping everything upside down (not recommended) or left to right. It is easy to make an error. For this reason, carefully check the placement of each component when you think the leads are in the right place -- but before you solder.

Good luck and let us know how you get on! It's an lovely project, although for skill level in construction and troubleshooting, not the obvious choice for first steps... but achievable.

[David G4EBT]

I've built several mini-mods over the years which have worked very successfully, though initially, the first one didn't. That turned out to be because the pinouts on the BF256 FET didn't conform to the data. Initially the transistor wouldn't oscillate but on changing the drain and source connections over, it worked fine, with a nice clean sine wave about 10 V p-p.

Attempts to test the FET were problematical, in that a current model Peak Atlas DCA55 transistor tester would only identify the gate - not the source or drain; an earlier DCA50 thought a BF256 was a diode, and a Chinese cheapo multi-tester correctly identified that it was an N Channel J-Fet, but would obligingly call any lead anything, according to which test clip went where! Below are some notes I made at the time.

Hopefully you won't have these difficulties, but I thought it was worth echoing what's already been said by David & Al.

Good luck with this well tried and tested very useful little gizmo and an enjoyable project to build. Have fun!

There have been several threads and countless posts on the forum about the Mini-Mod going back to 2015 and beyond.

A scary reminder of how quickly time passes.

All our yesterdays!

[Nuvistor]

If you have not soldered this type of circuit before, use a piece of scrap Vero board and wire and practice soldering.

[60 oldjohn]

Is this built on .1" or .15" Vero board? Am I right i thinking the square cross hatch marks are where a section of the copper strip is to be removed ? Easily done with a drill bit between the fingers? If so there looks to be a lot removed from under the coils. Thing like these are easy to work out when the circuit is to hand, and component pitch, coils in particular can be measured. If you get a "solder bridge", it is easy mopped up with solder wick. If you use an IC socket DIL--Pin It will also have a notch indicating which way to fit it and to fit the IC "Highly Recommend" Also polish the copper track with 1200 grit wet and dry or Braso or pan scrubber then IPA or soap and water, the cleaner it is the easier it will be to solder. Sorry if you had realised all this, Hope it helps save a mistake.

John.

I second Franks idea above.

[Kentode]

I'm using two Minimod's built by John (60 oldjohn) and David (G4EBT) which are excellent! Thanks John and David!

If you look at the picture below, I've highlighted some, but not all, of the breaks that have to be made on the veroboard.

The second picture shows how you can break the copper strip with a drill to match the red hatch-marks on the diagram.

Don't be afraid to ask more questions...

[Kentode]

A quick question for Baza, where did the diagram come from? Is there one of the cutouts required?

[60 oldjohn]

Hi Ken, I have never made the Mini Mod featured. I made the FM / DAB to AM convertor in different versions.

Looking at the coils on this project seem the centre pins fall between two tracks, Are these pins actually used?

John.

[baza100]

I also got this bottom picture for the cut outs which will help a lot Just bought my solder today so hopefully starting it at the weekend.

Thanks

Barry

[Timbucus]

One thing to watch out for is that all the tracks under the LM386 are likely to need to be cut not just the two peeking out from the top and the bottom...

[TonyDuell]

One thing I don't think has been mentioned yet is that the components are mounted on the side of the board without the copper tracks. You poke the wires though the holes, turn the board over and solder them.

This must be 0.1" stripboard because of the IC (LM386). The pins of that are spaced at 0.1". Quite apart from the fact that 0.15" (and 0.2", which I saw once) stripboard is very hard to find now.

I am sure all 4 tracks under the LM386 have to be cut. I normally do a zig-zag pattern, cutting next to pin 1, then next to pin 7, then next to pin 3 and finally next to pin 5. It doesn't matter with a small IC but I once had a column of lots of ICs on a bit of stripboard (Veroboard), cut all the tracks in a vertical line and the board was weakened enough to crack in half when I was doing more work on it.

A 3.5mm twist drill is a good tool for cutting tracks. Hold it in your fingers, not in a hand or power drill. Make sure the tracks are fully cut, check with the ohms range of your multimeter (an unbroken track will read 0 ohms, a cut one will be over-range.

[Kentode]

Originally Posted by 60 oldjohn

Hi Ken, I have never made the Mini Mod featured. I made the FM / DAB to AM convertor in different versions.

Whoops, my mistake John.

[baza100]

Originally Posted by Kentode

A quick question for Baza, where did the diagram come from? Is there one of the cutouts required?

https://www.vintage-radio.net/forum/...d.php?t=133001

Hi this is where the pic is from

[60 oldjohn]

What resistors are you going to use ? If they are the "metal film" ones I would strongly recommend checking each one with a multimeter before inserting in the board. In case of it not working first time it will be nearly impossible check after insertion due to the interaction with other components. The blue body and indistinct colours make distinguishing between red and brown or blue and green very difficult. I received wrong value from Ebay due to this, the pack was wrongly marked. I hope you have bought Lead Tin solder, not the new lead free rubbish.

Wishing you good luck with your Mini Mod, John.

[Al (astral highway)]

Originally Posted by baza100

Hi this is where the pic is from

Hi Baza, how are your plans going?

[baza100]

Hello, had a try fitting the resistors only broke one by the solder sticking to the resistor and me pulling the wire away. Really struggled to see it with my glasses on. What do you think to he soldering should I give up and leave it to the experts? Don't know if i got the resistors too hot as well. All in all I do think I have got the confidence to finish it off.

Thanks Barry

[Al (astral highway)]

Originally Posted by baza100

What do you think to he soldering should I give up and leave it to the experts? Don't know if i got the resistors too hot as well. All in all I do think I have got the confidence to finish it off.

Hey Barry, it looks ok but the photo isn't very high res. so hard to see properly. I can see a small square of stripboard is missing on the left, about fifteen rows up - was that intentional?

If your soldering iron is ony in contact with the board for a second or so you should be ok. That means a hotter iron for a little while rather than a cooler one for longer.

Can you show the component side of the board?

I'm glad you're feeling confident!

[60 oldjohn]

Hi Barry, did you clean the board before you started to solder? and keep the iron tip clean. There is plenty about TTH soldering (through the hole) on You Tube, worth watching one or two and seeing the experts technique. Resistors will take more heat abuse than the transistor and other plastic parts. If possible check each component before soldering. It is not unknown for components to be wrongly marked or be fake parts. The experts will be pushing Soldering Stations, I and many others on here have managed for years without one.

John.

[baza100]

Originally Posted by baza100

Hello, had a try fitting the resistors only broke one by the solder sticking to the resistor and me pulling the wire away. Really struggled to see it with my glasses on. What do you think to he soldering should I give up and leave it to the experts? Don't know if i got the resistors too hot as well. All in all I do think I have got the confidence to finish it off.

Thanks Barry

Made a mistake in my previous comment, i do not have the confidence to finish it off. My eyes are just not good enough for he small work. Anyone interested in building one for me please? Thanks Barry