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Old 1st May 2019, 4:58 pm   #1
Avid_Nerdlinger
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Default Pilot T854

Got this dead valve table radio Pilot T854 circa 1956. It requires an external aerial, having just black (gnd) and red (aerial) wires sticking out of the back. According to the dial it receives Long wave from 150kHz to SW2 up to 20MHz but only has one aerial input. What kind of aerial were these people using? Perhaps it was a dedicated complicated companion aerial with a band selector switch or were users required to change aerials between AM and SW? Anyone know?
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Old 1st May 2019, 5:24 pm   #2
crackle
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Default Re: Pilot T854

Normally a "long wire" was used, as long and as high and as far from other sources of electrical interference the better. But 12 or more feet should produce some results, but 30 feet is better.

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Old 1st May 2019, 6:49 pm   #3
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Default Re: Pilot T854

Quote:
Originally Posted by Avid_Nerdlinger View Post
What kind of aerial were these people using? Perhaps it was a dedicated complicated companion aerial with a band selector switch or were users required to change aerials between AM and SW? Anyone know?
The majority of people wouldn't have been technical enough to do that....setmakers tended to make things as simple as possible...and in most cases, make the sets as non-critical of aerial types as practical. As Crackle says, just a longwire as high as possible, away from interference sources. You should get good results with that.

If you want something a little more sophisticated you could go as far as stringing a 30ft wire as high as possible horizontally across the garden if you have the room and then taking the connection to the radio via a 'downlead'. You could also add an earth in the form of a copper rod buried in the earth and take that to the earth socket of the radio. 90% of people would just have a longwire though and probably not more than 5 feet hanging from a picture rail.....

There is plenty of info on the internet regarding AM aerials if you want to learn more. You really only need a more sophisticated aerial if you are doing serious shortwave listening and need 'tuned' aerials.
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Old 1st May 2019, 8:36 pm   #4
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Default Re: Pilot T854

I thought I would just add in case you were not aware. There is a capacitor which connects to the grid of the output valve from the preceding stage. These often go "leaky" with age, and allow a positive DC voltage to build up on the grid of the valve.
If this happens then you can sometimes say goodbye to one or more of following, the output valve, output transformer, rectifier and the mains transformer.
If in doubt it is advisable to change the capacitor, they only cost a quid or so.
If you need any more information about this just ask.

Mike
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Old 2nd May 2019, 1:15 am   #5
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Default Re: Pilot T854

Yes, long wire. Thanks. After a lot of googling I can't find much else besides one or two obscure old active "room aerials" which could sort of work over all bands. Wikipedia has a Random Wire Antenna page which refers to a whole chapter (9) on it in Practical Antenna Handbook (widely available free in pdf). Still hard to take in that the manufacturer must have had something like this in mind.
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Old 2nd May 2019, 8:39 am   #6
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Default Re: Pilot T854

Radio Amateurs would usually have opted for a military surplus communications receiver but one step back from that short wave listeners and hobbyists might have gone to the trouble of building an aerial tuning unit such as this http://www.zen22142.zen.co.uk/Circuits/rf/atu.htm which would have improved the matching of a long wire over a wider frequency range. Cheers, Jerry
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Old 2nd May 2019, 11:38 am   #7
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Default Re: Pilot T854

Don't get bogged down with aerial types.....not necessary for a domestic radio. Tuned aerials and elaborate arrays were specialist types used for much more serious work...particularly in the Amateur Radio field where accurate matching of receiver and transmitter aerials was essential.

Domestic radio's were different and built with the ordinary user in mind....a piece of wire strung along the picture rail or hanging out the window was about as 'elaborate' as most people got!
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Old 2nd May 2019, 12:32 pm   #8
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Default Re: Pilot T854

I agree, though back in the 30/40's there were houses which had a long wooden pole at the bottom of the garden. That of course is when you got more than a postage stamp size garden like now.
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Old 2nd May 2019, 12:35 pm   #9
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Default Re: Pilot T854

A good earth is worth the effort of arranging. Simply a 1Metre long piece of copper water pipe tube driven well into the ground and connected to the radio by the shortest route with thick multi-strand wire can often boost signals considerably, and reduce static interference. Longer, thicker, deeper rods are even better.
Dont overlook Crackle's wise advice in post #4. Many a potentially restorable and desirable radio has been rendered useless in minutes by not changing the capacitor referred to in his post. Please excuse that comment if you are familiar with the ageing coupling capacitor problem, but it is important.
Potentially a nice radio. Tony.
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Old 2nd May 2019, 1:16 pm   #10
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Default Re: Pilot T854

Adding a radio earth is not as simple a matter as first thought.

Here are a couple of threads that discuss possible safety issues related to the building earthing arrangements.

https://vintage-radio.net/forum/showthread.php?t=71422

https://vintage-radio.net/forum/showthread.php?t=75844

Al
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Old 2nd May 2019, 11:08 pm   #11
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Default Re: Pilot T854

It's alive! It wasn't actually dead, just missing its mains selector plug, which is new to me. Thanks for the advice about caps, measured well enough in circuit for switching on. Ran an extension lead up the stairs for an aerial and listened to some faint SW stations. Happy days.
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Old 3rd May 2019, 8:29 am   #12
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Default Re: Pilot T854

Quote:
Originally Posted by Avid_Nerdlinger View Post
Thanks for the advice about caps, measured well enough in circuit for switching on.

Great news it is working. Welcome to the fascinating world of vintage radios and bringing them back to life after many years laying dormant. But a word of further advice re the capacitors.

You cannot tell if a capacitor is "leaking DC" by measuring it with a multimeter.
The only way to measure the leakage is to connect the capacitor to a DC supply of the same voltage as the capacitors marked working voltage and connect a sensitive micro amp meter in series to see if there is any DC current flowing. But it is not quite as straight forward as that, because the initial surge of current to charge the capacitor my damage the meter.
You need to arrange for a switch to short the meter terminals whilst the capacitor is charging, then open the switch once the capacitor is charged so that any current still flowing flows through the ammeter and can be measured on the meter. I use a home made electrolytic capacitor reformer which in effect also has a 15k resistor in series.
Or alternatively you could start with the meter in series switched to 10 amps and then switch down through the ranges to uA. But the problem with this is you often have to re-plug the meter leads into a different socket to measure the very small currents involved. At this point the capacitor will need to charge up again.
Any leakage at all on the audio coupling capacitor, which passes the signal to the grid of the OP valve, can be disastrous.
A small leakage in a few other capacitors can be tolerated depending on their position in the circuit and what they do.
The smoothing electrolytics can often still perform a useful function with a leakage figure of as much as 1mA or so. Just so long as there is no sign of them getting warm after use.
Too many capacitors all leaking a couple of mA will cause the voltages to drop and the radio to underperform, and can build up and eventually cause the mains transformer or rectifier to fail.


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Last edited by crackle; 3rd May 2019 at 8:36 am.
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Old 3rd May 2019, 9:13 am   #13
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Default Re: Pilot T854

A further note on the subject of the grid coupling capacitor.
You can often tell if the grid coupling capacitor is leaking badly by measuring the voltage between the cathode and the grid of the OP valve. The grid should almost always be a negative voltage (less than zero) in relation to the cathode. The nominal value of the grid voltage is often given in the specifications for the valve.
The service sheets often give this voltage as a value for the voltage on the cathode in relation to the receiver chassis. Under ideal conditions this would be the same as the grid to cathode voltage. But leakage through the coupling capacitor will still bring the grid voltage up, from a negative one towards zero and even in bad cases to positive, or in other words the same voltage as the cathode. This is when the valve will pass excess current and can cause damage.
I hope you don't think I am trying to tell you you are doing things wrong, you may already understand all this, but it took me a long time to appreciate the effects of leakage in these audio coupling capacitors.
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Old 3rd May 2019, 6:38 pm   #14
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Default Re: Pilot T854

Mike, thanks for your persistence, I measured about 4Vdc on the wrong side of the cap, a Hunts. On desoldering I could see the (heat?) damaged side of the package.

Loft long wire aerial works very well. I'll try my FM radio on it later and maybe start a new thread.

Andrew
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Old 3rd May 2019, 9:36 pm   #15
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Default Re: Pilot T854

All of those resin covered caps will be faulty....the resin cracks and that is the beginning of the end.
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Old 3rd May 2019, 10:00 pm   #16
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Default Re: Pilot T854

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Originally Posted by Avid_Nerdlinger View Post
Loft long wire aerial works very well. I'll try my FM radio on it later and maybe start a new thread.
You will doubtless get some FM reception on a long-wire but it isn't ideal for VHF FM. You would get better results stringing up a dipole of the appropriate length in the loft for FM. Cheers, Jerry
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Old 3rd May 2019, 11:20 pm   #17
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Default Re: Pilot T854

That capacitor is knackered.

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Old 6th May 2019, 12:32 am   #18
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Default Re: Pilot T854

Quote:
You will doubtless get some FM reception on a long-wire but it isn't ideal for VHF FM. You would get better results stringing up a dipole of the appropriate length in the loft for FM. Cheers, Jerry
Thanks Jerry. The FM test was surprisingly good considering I'm well outside the coverage area but still not quite as good as it should be for FM. It's probably not worth bothering with a proper aerial for FM. I was getting Faroe Islands Utvarp Foroya 531kHz on AM clear as a bell though.
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