VE301W Radio help

[PJL]

To avoid extra heat, I still think the bucking transformer is the way to go. You only need a very small transformer, 6VA would be more then enough. There are plenty on ebay or maybe a wanted request would get you one.

[Station X]

The OP has a limited budget and I agreed to do this job for a fixed price. The cost of all parts has to be met by me. There is limited room on the chassis, so any bucking transformer would have to be mounted externally, which means additional costs for an enclosure etc.

I've had the set running for several days with a 2W 390R wire ended resistor connected in series with the flying lead going to the mains transformer's voltage selector. The resistor is situated adjacent to the voltage selector in free air. The resistor gets warm, which is what it's intended to do. There's room on the chassis for what is effectively a heat sinked 15W resistor. It will dissipate far less heat then the dropper resistor in an AC/DC receiver. It will also provide a rigid point on which to terminate the wiring and make the mod easily reversible.

[HamishBoxer]

Great write up Graham and loads of good common sense.

[Station X]

One post moved to a new thread here:-

https://www.vintage-radio.net/forum/...d.php?t=161378

[Courtney Louise]

Don't suppose you fancy doing another?

[Station X]

Sorry, but no. I might make a decent set of capacitor block removal tools and make them available to forum members on loan.

[Station X]

In view of this thread I've suspended work on this radio while I decide what to do next.

https://www.vintage-radio.net/forum/...d.php?t=161378

[mister valve]

Fortunately these receivers are very simple 'TRF' sets with a single tuned stage leaky grid detector valve with reaction, an o/p valve, and of course, a rectifier valve.

I do recommend you replace all the paper capacitors (condensers), they are bound to be very electrically leaky and re-form (or replace) any Electrolytic capacitors (if fitted). Check any mica or ceramic capacitors particularly for shorts or damage. Check resistances are within tolerance, pay particular attention to the 2M ohm grid leak resistor on V1. if that has gone high it can introduce poor sensitivity and distortion.

Before using the set do check the mains voltage tap is on the 220 volt setting you may need to add a resistor in the mains connection to safely use on the UK 230V (normally 240V) line system.

[Station X]

Have you actually read this thread?

[HamishBoxer]

I do not think so! Good idea what you have done Graham and a safe one in my books.

Of course this opens a whole new can of worms about any old set now as the best way to go.

[ex 2 Base]

All very interesting Graham, I like your safe methodical approach.

[HamishBoxer]

The safe way is always the best.

I have a AC/DC Ekco AD75 for restoration and wondering what the best way is with this.

[Station X]

In view of the safety concerns expressed elsewhere regarding the mains transformers in vintage radios I decided to try an alternative dropper resistor arrangement.

Having already drilled two additional holes in the chassis to accommodate a 15W wire wound resistor, I was reluctant to drill any more. Therefore I made a custom terminal strip to suit the existing holes. Mounted on this were 200R and 180R 2W flameproof resistors in series.

On powering up the radio worked as expected, but I was not satisfied with the new arrangement. Despite being well within their rated power dissipation I could smell the paint burning off the resistors and they were too hot to touch, with the power off of course!

I took a good a look at the mains transformer. Was it really likely to self destruct emitting vast quantities of acrid smoke and starting a fire? I didn't think so. The transformer is well made with proper cheeks on the former and no sign of tar impregnation.

I decided to revert to the original arrangement with a 15W resistor bolted to the chassis. It runs as cool as the proverbial cucumber and I'm perfectly happy to leave the set powered up in my own house or anyone else's.

[HamishBoxer]

Spot on Graham.

[Station X]

The next step was to reassemble everything. The tuning scale was attached to the tuning capacitor's shaft and engaged with the "pulley" on the tuning control knob's shaft. This slow motion drive made tuning a lot easier. The position of the scale relative to the tuning capacitor was adjusted so that the 0 and 100 markings corresponded with min and max capacitance.

I ran into problems after refitting the chassis into the cabinet. One of the three knobs was different to the other two. It was larger in diameter and used a different fixing method with the fixing screw being much nearer to the front of the knob. The result was that the fixing screw barely made contact with the tuning control's shaft The fixing was very insecure and the knob could easily be pulled off the shaft.

I solved this problem by extending the shaft at the outboard end. The method of doing this was as follows. Sorry for the lack of pictures apart from that of the finished result.

Mount the 6mm dia shaft in lathe, drill to 1/4" depth and tap 6BA, then lightly countersink.

Turn a 3/16" long by 0.126" diameter stub on a 4" length of 5/16" diameter brass rod. Thread 6BA cutting as close to the shoulder as possible.

Mount the brass rod vertically in the vice and wrap a ring of soft solder round the stub. Screw the shaft onto the brass rod until it contacts the solder.

Use a propane torch with a small burner to heat the brass rod about an inch below the joint. The reason for doing this was to avoid melting the solder holding the pulley to the original shaft. Once the solder melts screw the shaft down onto the brass rod and allow to cool.

Saw off most of the brass rod, return the job to the lathe and turn down the brass rod to the same diameter as the original shaft. Face and chamfer the end.

It takes longer to describe the process than it does to do it!

I then refitted the shaft to the chassis.

[Station X]

The chassis and speaker were then mounted in the cabinet. The two anachronistic, brightly plated posi-drive screws holding the chassis to the cabinet were replaced with cheese head types.

The knobs were fitted. This time I had no problem getting the tuning knob to grip the shaft securely.

After fitting the valves to the chassis it was time for the final job refitting the back panel.

I observed that this set uses M4 threads throughout, whereas mine has M3.5 screws securing the back to the chassis and cabinet.

The repair is now complete. I'll use the radio as a workshop set for a few days and so long as it doesn't burst in flames, or develop any faults, I'll return it to the OP next week.

[Station X]

I've repaired two of these sets now and made a couple of observations.

These sets suffer from mains hum. It's audible on switch on, increases in level as the valves warm up, then drops back to an acceptable level where it's masked by the received program. What I call "The Dansette Effect". It's not caused by faulty smoothing capacitors as they have been renewed. I put it down to the fact that the indirectly heated valves have their filaments fed with AC. The LT rails have a virtual centre tap ie a low value resistor is connected across them with the midpoint connected to the chassis. This does not completely eliminate the hum though and the tap isn't adjustable.

The weak point in the reproduction chain is the high impedance speaker. Presumably the armature which drives the cone via a connecting rod has a lot of inertia. Bass reproduction is good, but treble response runs out at 6kHz. Good for speech, but not so good for music. The DC feeding the output valve's anode flows through the speaker's coil biasing the armature one way. I found that the speakers worked better with the leads connected one way round when compared to the other. As a test I tried using a set with an output transformer and low impedance speaker. The sound quality was much better.

[Lloyd 1985]

Excellent work, I’ll keep the resistor mod in mind for my set, which I must do something with other than keep it as a static display piece. I’ve also got one of the smaller sets too, which I’ve also done nothing with!

Regards
Lloyd

[Station X]

This set is now back with its owner.

[JUSTDAMO]

Indeed it is.

I don't mind admitting I was a bit skeptical when sending the radio to Graham, I didn't know him and had no idea what to expect or even if the radio would be damaged etc.

However, Graham was very professional, i tried following the thread but on many occasions it felt like reading the instruction manual for a space rocket. In the end I was amazed at what had been done, I thought Graham would simply get the radio 'up and running', thats it..... However there were so many extras he did that I was really grateful for and really didn't expect.

The return of the radio was wrapped brilliantly, I warp many items as I buy and sell on ebay as a part time job as well as looking after the little one but that packing really was amazing.

instructions and even an aerial was given, extremely thoughtful and professional, so instead of calling him Graham I might just call him 'Scotty' from now on from Star Trek Thanks again

So now I have two more questions for anyone to answer... what would happen if you plugged in all the short wave slots with 4 aerial's? would it give a better signal or gain more stations or simply cause confusion.....

Also, for outside aerial wire does the thickness make a difference?