Hi All,

Is it common that Aussie valve radios are somewhat deaf in the lower end of the AM band?

I only have 3 working valve radios, but I notice on all 3 that the stations above 1MHz are loud & clear, while stations below 1MHz are noisy and very low level.


I'm in Melbourne, and find that tuning the following stations have very different results:

693kHz (3AW) -So low I can barely hear it, buried in RF noise.
774kHz (ABC) - A little louder/better than the above.

Numerous stations above 1MHz = VERY loud & clear

Also to note, at the lower freq's, I have the volume turned up to '10' (loudest) just to hear a noisy murmer of intelligence breaking through
At the higher stations above 1MHz I have to turn the volume down to say '3' (out of 10) to avoid overdrive and excessive distortion.


I have a few metres of wire hanging off the ext. Antenna connection, and have also tried moving the radio to face in different directions just to confirm any form of RF interference along with turning off all computers and noisy devices in the home.
I'm not sure how critical it is to need an ext. earth antenna wire too?

The 3 radios are all different brands/models, they *might* coincidentally have the same fault if it's related to an old RF/IF valve causing the problem.

I realise there might also be issues with leaky caps not performing equally well across the bandspread, or is it just a case of needing alignment, maybe the IF slugs are missing or cracked or deformed (damaged) coils etc...


I also thought maybe the radio's are peaked to perform at 1MHz & higher, maybe in the older days radio stations below 1MHz didnt exist? so they're not 'peaked' at the lower end of the dial? - just my guess


Thanx in advance,
Marty.

This is a bit of dart board job but.... The condition of the radio; the type of antenna; and the environment the set is in all effect.

I have no issues with sets here and I service. The two I put across the bench in the last fortnight had no issues: I do have transmitters at both ends of the dial close.

The best reception is always at night and the majority of sets are designed for a 25ft antenna.

If the set is out of alignment they can be deaf. This can be caused by old age & components failing and the set having RF parts replaced and not being re calibrated, or the calibration interfered with (common).

The valve radio is very sensitive to noise that could be coming in via the mains, but being in a city, Switchmode power supplies & Compact Flouro tubes, give them hell.

The regulators have lost the plot & any sort of RFI generating crap, seems to be get into service with impunity.

I get a lot of RF on the mains here & have Mains approved capacitors on the system (and MOV's) to get rid of it.

Rotating the set will do naught. With transformer sets I always fit a grounded cable when refitting a new one.

Thanx Marcc,

You've confirmed the few options I mentioned with old parts failure and/or mis-alignment etc.

You mentioned a 25ft antenna, whereas 1 of my radios has about 2 metres hanging from it, the other 2 radios have 2-3ft.....this may be all it is, just a need for longer wire.

I didnt bother (or think) to add more length on the external antenna as I thought that's what the internal ferrite-rod antenna SHOULD be doing, maybe i'm wrong or these sets dont quite have the type of ferrite rod that a tiny AM tranny would use, and we dont see AM trannies with 25ft wire dangling out of them

I'll go add some wire and come back with results soon.

Thanx,
Marty.

I have the opposite problem with Sydney stations at my location on all my radios. Lower frequency stations under 1MHz such as 2GB, 2KY and 2UE are fine with very little interference. The higher frequencies over 1MHz like 2CH and 2SM are much weaker with more interference although much much better since I discovered an incredibly noisy power board in my son's room above my workshop. I suspect 2CH and 2SM are lower powered stations to start with.

Not many Australian valve radios had ferrite rod antennas before the mid 50's and would definitely need some length of wire, a few feet if you're close to the transmitter, much more as Marcc suggests, if further away.

If you only had this problem on one radio it would sound like an AGC/AVC problem but on all three? I'm not sure that alignment would only affect sensitivity on the upper end of the band so you might actually be chasing a reception problem as Marcc mentioned. If you're not familiar with radio alignment I wouldn't touch much more than the aerial trimmer but once again, the problem is on all three so this may not do any good.

If your interference is local RFI you might be able to do something about it. I waited til everyone was out for the day and turned everything in the house off. I then wandered around the house from room to room with a small AM radio and headphones, turning things on individually. The only things I found making noise were the previously mention multimedia powerboard and the electronically controlled washing machine on spin cycle. Compact fluorescent lights are notorious noise makers as are some types of new LED lighting and small plug pack power supplies. Good luck!

I often wonder why, if it was possible to eliminate noise from the vibrator inside battery powered valve sets, it is not possible to eliminate it from switch-mode power supplies, which are in a way the modern equivalent. Perhaps it would need metal shielding and extra components for filtering like a desktop computer power supply.

maybe in the older days radio stations below 1MHz didnt exist?

Quite the opposite is true. Most of the A-Class stations, those now owned by the ABC, are in the lower half of the dial. For some perculiar reason Radio National's reception from stations like 2FC (2RN) has always somewhat lacked in volume and on air presentation and broadcast quality seems to be also inherited directly from 1922.

Listening in to digital simulcasts cures the lack of volume but not the quality of programming.

I suspect 2CH and 2SM are lower powered stations to start with.

All commercial stations in the state capitals are 5kW. Those in major provincial cities are usually between 2kW and 5kW depending on the size of the listening area and the terrain.

Power output was less back in the valve era though this didn't matter much becase there were fewer stations around then to interfere with each other.

Mind you, on an ideal night it is possible to pick up many stations around the country with five good valves and a half-decent antenna. 5kW goes a long way under the right conditions.

Hi Marty,

I would take the radios to a different location eg. a mate's place ....... and check again for "deafness". Try to use the same aerial/earth system at both locations.

I am also in SE Melb and would hesitate to use 1377kHz as it seems to be a particularly strong signal. You may wish to find out the location and power of the transmitters you are using as 'test' stations.

Cheers,
Ian

Thanx for comments & suggestions so far guys, food for thought...

OK, so, showing my ignorance about valve radios I wasn't aware of the lack of ferrite-rod etc....
Since all 3 radios have a MAXIMUM of 2 metres of wire as an antenna (the shortest one being 50cm's) i'd have to say my antenna is the biggest problem thus far.

I will aim to add a decent length of wire for a start to clear things up.
I also wasn't aware that the antenna-ground wire was actually needed too, not sure if it should be long? or something short that dangles behind the radio? or does it need a definate earth connection?
Probably the quickest way for me to earth it would be to wire onto the earth pin of an unused 240v mains plug to ensure it's attached to 'house earth'. (no, I won't connect it to 'Active' accidently ).


Just to clarify some noise/rfi comments mentioned above, I switched off my entire house during my initial these tests, absolutely NOTHING is running (not even the fridge) during my initial look into the noisy/weak stations I have.


FYI: I have a 25+ year background as TV/Broadcast/Radio(solid state) tech.......so i'm right across alignments and so on...it's just my lack of valve-radio skills & knowledge that sets me back until I play catch up

Regards,
Marty.

As long as you have a healthy respect for 240V AC and up to 800V DC from your work experience then you could do worse than follow the guidance in this link:

http://www.thebakeliteradio.com/page102/page102.html.

Interesting: One of the things we have not established is the history of the radio. If it has old wax paper caps in it, the leakage of these can also impinge on performance.

Often the loop around the ferrite antenna is an individual isolated (from the rest of the set) coil and may benefit from being earthed.

As it has a ferrite antenna, the antenna coil, breaking loose and /or sliding along the ferrite, will de-sensitise the set.

Radio repair here is in a metal shed so an external antenna is needed on most sets. The digital set top box actually gets into the Yaesu 7700. As said I was not having any issues with a 61-51 HMV on 2CH, which according to the GPS is 519Km from me as the crow flies.

Most of the AM stations here in Sydney still transmit on the flat marshes at Homebush Bay adjacent to Olympic Park. There's not as many masts as there was when I was a kid so I assume the stations share some of those that remain.

There is a file on ACMA that will tell you the frequency, power & location of the transmitter.

Just to clarify, the stations that are currently 'weak' are very strong and clear on my solid-state radios...these are the larger commercial based stations such as 3AW (693kHz) etc, not the struggling independant distant stations

I'm yet to drag out the long wire and also earth these radio's to (hopefully) hear a drastic improvement.

Seeing that you have those other little animals. The ferrite rod is directional. If you point is axis (long direction) at the radio station is will null.

The rod has to be broadside to the Xmitter for best input.

If the old sets have problems & there is too much AGC voltage being developed, that will de-sensitise them, which is what AGC does.