Charging a car battery

In message , "Dave Plowman (News)" writes

Indeed. Car batteries are certainly not 'snowflakes' (if I may be excused for using a presently-fashionable word), and are designed to have a hard life. A quick burst from any charger once in a while should be sufficient to ensure it's OK when you really need it.

Although running them flat is guaranteed to kill them, since they are not designed to survive this. That's why "leisure" batteries exist.

A lot of transformer? Is that code for something?

Just a driver and output, to allow the same transistor to be used.

MW/LW switched both one RF coils AND local oscillator coils

But ONLY those two.

In practice tuning the EF stage in mots conmmnercial grade sets was really veryt briad - the [promary function is image regjection at

With superhets neartl ALL te selectivey is in et pretuned fixed frequeancy IF strip, and thats why they were de regeur. The only tuning as the local oscillator. The RF srages might not even be PRESENT let alone tuned - direct injection into te micxer was not that uncommon spcially on ferrite rod tuned portables but was frowned upon a little as it pumped the oslitaor back up the aerial.

So in essence the RF stage MOSTLY stoppoed te oscillatort being rtertsnmitted , andf provided sa bit of gsaiun., It made very little difference to selectivity and was pretty low Q really.

Ther was no need for two RF coils.

You were quite correct in your previous post regarding the elimination of vibrating variable capacitor vanes.

The tuning and preset tuning arrangements were fiendishly clever and difficult to describe but probably not too expensive to build in quantity. I haven't seen one of these radios for nearly 50 years, so bear with me if this description is not 100% correct!

The cores were connected to a swivelling plate or tuning bar which rotated through about 90°. This was also connected by simple mechanical linkage to the dial pointer. This entire assembly could be moved from one end of the band to the other with very little pressure.

The main and preset tuning were all accomplished by bringing the flat edge of a semi-circular metal disc into contact with the tuning bar which would the swivel until its face exactly matched the angle of the flat.

The disc for the main tuning was normally held in contact with the bar and connected to the tuning kbob via a worm gear. This held the entire assembly in place and ensured that the tuning point was vibration proof.

The discs for the presets were normally held away from the tuning bar. Also, the position of each disc, including the main one, was held in place by a simple friction clutch.

When it was desired to preset a button to the current tuning point, the button was pulled out. This caused the cluth for its disc to be released and the disc moved forwards so that it was in intimate contact with the tuning bar: thus it rotated to match it.

When the button was released, the cluth re-engaged and the disc withdrew.

To return to a stored position, the button was pushed in. This released the main tuning clutch, freeing up the mechanism, and the button's disc was pushed forward onto the tuning bar which promptly aligned itself to the stored position.

The presets also operated the wavechange switch, the righthand button being assigned to Long Wave and the others to Medium Wave.

Correct. Even discharging a deep discharge LA battery to 50% capacity or more will effect it's cycle life.

They are no more able to survive being run flat (especially for a prolonged period) than any other LA battery.

The main difference between an SLI and leisure / traction battery is the thickness of the plates and hence the capacity / kg.

Cheers, T i m

correct yes, just very misleading. The one odd thing about it was that the output tran ran cold. Not what I'd expect for a class A output.

The other end of tv development was when they were all transistor except for the LOPT valve.

NT

Uh?

Well..... quite. That's what superhets do. [When was the last time you used a TRF set ?]

Most house/portable LW/MW radios don't have an RF stage [RF stage? LUXURY!] - but the aerial/mixer input is invariably tuned (as close as possible) to the signal frequency, and the local oscillator runs the IF frequency above the signal frequency.

You don't get much local oscillator radiation if the set has a ferrite rod aerial.

It all depends on the application. LW/MW car radio are VERY short, and I'm pretty sure that many had an RF stage to boost the sensitivity. With those old types (with the 'peak-it-at-the-HF-end' trimmer) it was obvious that the input tuning was quite sharp (and therefore critical if you wanted to optimise sensitivity). However, I have a couple of 'more modern' sets that don't seem to have any provision for LW/MW peaking - and both seem to work OK when fed with a short vertical loft aerial in the loft, via about 15' of 75 ohm coax. With the old sets, this would have been a killer - so I'm not sure what the input circuit is like.

The cable impedance was 75 Ohms, but the aerial would be a total mismatch. The trimmer seems logical, Strange I never really thought about it, but every radio had that little hole inviting the insertion of a screwdriver :-)

Of course! I remember now, all the tuning caps were air spaced. They were damned big.

It was many years later that the addition of a polymer as a dielectric gave them a bigger puffage. Manufacturing techniches probably helped too. I recollect that the early ones needed the skills of the local bike shop to get them "trued up".

I also seem to recall a description of a high Voltage being used to clear shorts when the plates brushed together.

DAB wirelesses don't really make up for all the fun times lost :-)

Incidentally, on the subject of tuning caps, were you aware of any drift related to atmospheric humidity?

Shaw moisture meters were a standard in many industries and laboratories all over the world. The probes were and still are for most manufacturers made from aluminium/ aluminium oxide i.e a capacitor with an oxide dielectric.

There was a photo of "old man Shaw", the company founder outside his wireless repair shop.

I suspect the two enterprises had a link additional to the owner?

Certainly it often crossed my mind over the years.

Wonder if it will be possible to buy a "dash top box" when analogue wireless is phased out :-)

Regards

AB

A nice little double triode, albeit with a heater supply that could trap the unwary.

I had an ambition to build a Mullard 5:10, but like walking the Pennine way, it wont happen :-(

AB

That wasn't the abortion that was produced as a dual standard was it?

I never saw the transistor mod, but the sync was an absolute nightmare.

The amount of line tearing was a complex relationship of image transmitted times mutipath echos. Even with a totally clean signal some tearing would occur.

A transistor would be a good move given the space needed, but deriving the supply must have been interesting.

I cannot think of any other Pye that could qualify for the mod, didn't they become Phillips after that Dual standard model?

AB

No, I think they were EL84s.

I built my first radio using DF96, DAF96, DK96 and DL96 (I think).

The EL84 was a pentode. It was possible to use one of these as a stand alone amp, but it was only really practical with a crystal cartridge, or similar,

A preamp to boost the signal was often developed using an ECC82, with one or both stages being used. The gain would still probably not be high enough for a quality magnetic, so the lineup became Ef86 preamp, ecc82 phase splitter and two EL84s

Happy days!

Sadly the mind is going, at one time I would have known what C13 and R22 did. :-(

AB

It sounds right, with a 90V Ever ready?

Was the heater supply a separate battery? I suppose it must have been.

The Ht battery was made of pp3 type cells. Must have been 60 of them. Damned expensive way of boiling electrons :-)

I used the cases of the commercially available ones as toolboxes for a few years.

I don't think that there were any valve radios produced when I entered consumer electronics.

My first wireless after the almost compulsory xtal set was a TRF with feedback, [regenerative]. It was transistorised, and very good. I can understand why they never were generally available to the public though.

AB

I don't think the theoretical cable impedance was 75 ohms on a car radio aerial. It was peculiar stuff with a spiral inner core. 300 ohms is the figure in my mind - but could be wrong.

IIRC, more modern radios match to the aerial automatically.

How technology has advanced - I once forgot to reconnect the alternator after I'd done some welding on my Mini - it ran fine for a while but then it started to misfire and the lights were dimming. It stalled once and I managed to bump start it, but the second time it just died completely. Fortunately I wasn't far from home so I walked back and got a bike to collect the battery and charge it. I think I still prefer the simplicity of a 1950s car to the cleverness of a modern one, although traction control and ABS are quite good. Replacing the points is a lot easier than troubleshooting an ECU and its attendant sensors, if you only have a screwdriver.

I've taken to buying small "useful" DIY items in Lidl even though I don't need them just now, because I might later. I wonder how many of them will just sit on a shelf unused.

Some batteries for valve portables had the LT and HT in the same unit for simplicity - presumably the LT one was a single zinc/carbon cell rather than the layer construction used for HT.

Kit transistor radios were often regenerative to avoid the difficulty of alignment of a superhet, which would require a signal generator.

Up to about the early 1930s domestic (valve) radios were regenerative with a 'reaction' control (variable capacitor). People just got used to increasing the reaction until it squealed and turning it back a bit. Apparently you could tell when other people were tuning in in the evening by the interference to other sets.

Earlier TRF sets had two tuning controls which you had to turn together as they couldn't make twin gangs that tracked accurately enough.