Hi, can someone help me out with a problem I have with my Airzone 605 tombstone radio, the problem is when it is going the reception isn't that strong when the aerial is connected but it's when I touch the top of the Frequency mixer tube 6A7 the reception becomes stronger.
Could it be a weak tube or maybe something else.
Any help would be appreciated.
Thanks.

That's pretty normal actually. That's why so many radios get butchered where Mr Someone permanently joins the antenna direct to the mixer tube. You'll probably notice a large increase in noise when you do that.

Firstly, make sure the radio is earthed either with an earth wire or preferably via the earth wire in a 3-wire mains cord.

Make sure you give your radio a long antenna, the bigger the better.

It may need a tuneup but you need to know what you're doing.

I've had a couple of rare cases where connection of the antenna actually makes things worse. Turned out one side of the aerial coil was wired around backwards.

I've had a couple of rare cases where connection of the antenna actually makes things worse. Turned out one side of the aerial coil was wired around backwards.

Struck that exact problem with an Airzone that had been "repaired by a professional".

That is not normal. The finger on the grid normally throws it off.

Radio Museum shows a 6D6 pre-amp then the 6A7. That means that there are tuned circuits either side of that 6D6.

In order for the signal to get from the antenna to the grid of 6D6 and then to the signal grid of 6A7 those two resonant circuits must track together on the same frequency. Should this not be the case then the signal will be severely attenuated.

What has not been done to the set? Has it been overhauled? If it has, then once you have changed parts in the RF section you need to re-calibrate it from start to finish, this is recommended by virtually all manufactures. Changing parts throws things off frequency and poor alignment & not doing it properly, are the greatest causes of deaf sets.

I would seriously look at the alignment. In order to do it properly that needs a signal Generator that has some semblance of accuracy.

As I fix them, I have a semi-permanent setup just for that purpose (One forum member has actually seen it) {Generator, Frequency Counter Attenuator & Oscilloscope}. Normal length for most domestic sets was 25 feet and there is such a thing as too long an aerial (RCA antenna chart).


Marc

Just want to say a big thanks to GTC and Marc for your help👍it's amazing when a very long antenna is attached and all seems ok😊
Leon.

If you dare construct a long wire antenna approaching, half of a wave length on BC band, you have to be able to control it. Taken out of service when I moved house & yet to be reinstated away from the RFI from the NBN box, was a 50m long one feeding a FRG-7700.

The major difference here was that FRG-7700 has the attenuator & matching box for that unit. So with a local station I could cut the signal strength by up to 60dB. The point being, that there is more than one way to get a set to perform badly: Overloading the front end with signal is, but, one of them.

I have an FRG-7700 myself, but no room for a 50 metre long antenna!

Leon, is 👍 meant to be a pair of eyes?

I can go bigger: There is a 70m one here not being used. One spur of my private power line is 460m & the distance, garage to road gate, 700m: The joys of space.

The biggest potential radiator of the lot when things go wrong, is the electric fence, at around 3km.

Marc

Leon, is 👍 meant to be a pair of eyes?

It's a thumbs up icon in my browser.

It looks like a hand with a thumb sticking up. I assumed it was a handshake.

It's just a square with hex code in it here, in Firefox.

I can see one of those in the thread's title: 😕

^ That's how they all appear to me. I don't experience it anywhere else.

Brad: does your forum code alter these things in some way?

Forum code won't over-ride any icons typed in by members who are (most likely) using phones or tablets.

That said, to be honest I can't see these other icons very well. They are smaller than the ones included with the forum software.

Okay, I didn't have the appropriate font on my PC.

Having installed it I can now see tiny, faint icons of a confused (?) face and what I'm told is a thumb up but I wouldn't have been able to determine the latter one without being told what it is.