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Old 2nd Aug 2020, 4:01 pm   #1
Scotorvm
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Location: Falkirk, Stirlingshire, UK.
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Default Graves Vulcan II tuning help

Guy's, have successfully powered this unit up with a battery eliminator and horn speaker.

Have a 2m earth rod hammered into clay soil, 10mm earth cable to an earth bar, tapped of this with 2m of 1.5mm earth to radio.

approx 40m of bare copper wire on insulators along the top of a 6' fence, then up the outside of the house into the attic attached to a digital TV aerial.

Trouble is only 1 station seems available, it is loud and clear, horn speaker able to adjust volume via knob on base.

Absolute radio is the station I can receive.

When either the earth or aerial cable removed, radio is silent. Short wave and long wave switch change plays the same station.

I think there is at least another 1 station trying to break through when turning the tuning capacitor.

Does all this sound normal for this type of set? Do I need a better aerial? I live in a modernish housing area so my options are limited for height.


Thanks.

Lee


Ps had another post re a Columbia 357, managed to get this working too after replacing all the condenser block caps for polyester film caps and 6 open circuit resistors, only 1 station available with another ghosting in the background.

Subsequently changed another two paper caps, a 0.25uF and a 0.035uF for polyester film caps, then received nothing
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Old 3rd Aug 2020, 10:29 am   #2
Herald1360
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Default Re: Graves Vulcan II tuning help

From that description I would say there's a problem with the tuning/reaction circuit which has resulted in no actual tuned circuit being active. Absolute is probably just the strongest signal at your house and is being received by an effectively untuned detector followed by an audio amplifier stage.
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Old 3rd Aug 2020, 3:07 pm   #3
Scotorvm
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Default Re: Graves Vulcan II tuning help

Thanks Chris
Going to double check everything, just in case I've missed something.

The transformer windings are to spec.

Apart from the 0.0005uF tuning cap, there are two other caps, 1 next to the PM1 valve is 0.0003uF.

On the circuit diagram this shows a 0.0002uF cap with a 2Mohm resistor in parallel. The resistor in parallel with my 0.0003uF cap is measuring at 3.2Mohm.

The only other cap is on the underside and is 0.0005uF which seems the correct value.

All other connections check out ok.

Thanks.

Lee
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Old 3rd Aug 2020, 6:20 pm   #4
Herald1360
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Default Re: Graves Vulcan II tuning help

Transformer windings? Is that the audio coupling TX or the tuning unit coils?

The circuit relies on dc continuity through the aerial coils and the wave change switch for the tuning condenser to resonate the circuit. The reaction feedback coil needs to be correctly phased in its coupling to the aerial coils for positive feedback to occur. All the connections need to be good and low resistance.

The grid capacitor and its parallel grid leak resistor are probably near enough to their values to be OK but it could be worth trying a couple of modern components instead to see if they help.
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Old 3rd Aug 2020, 9:01 pm   #5
Scotorvm
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Default Re: Graves Vulcan II tuning help

Quote:
Originally Posted by Herald1360 View Post
Transformer windings? Is that the audio coupling TX or the tuning unit coils?

The circuit relies on dc continuity through the aerial coils and the wave change switch for the tuning condenser to resonate the circuit. The reaction feedback coil needs to be correctly phased in its coupling to the aerial coils for positive feedback to occur. All the connections need to be good and low resistance.

The grid capacitor and its parallel grid leak resistor are probably near enough to their values to be OK but it could be worth trying a couple of modern components instead to see if they help.
Hi Chris, yes the audio coupling TX.
Will check the reaction feedback coil and resistances, thanks for your help.

Cheers

Lee
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Old 3rd Aug 2020, 10:17 pm   #6
Mr Moose
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Default Re: Graves Vulcan II tuning help

Hello,
According to Wikipedia Falkirk is only 3 miles from the Westerglen transmitting station so I would expect your aerial to be OK.

(https://en.wikipedia.org/wiki/Wester...itting_station).

It gives the following stations broadcast from the transmitter;

BBC Radio 4 198 Khz LW at 50 Kw
BBC Radio 5 909 Khz MW at 50 Kw
BBC Radio Scotland 810 Khz MW at 100 Kw
Talk Sport 1089 Khz MW at 50 Kw
Absolute Radio 1215 Khz MW at 50 Kw

You only appear to be able to pick up the highest frequency medium wave station (Radio Scotland at 810 Khz is the most powerful with twice the power of Absolute Radio) so it could simply be that for some reason your set will not tune low enough to to get the other stations.
This could suggest a problem with the tuned circuit possibly the coils or tuning capacitor .
Yours, Richard
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Old 4th Aug 2020, 9:04 am   #7
Scotorvm
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Default Re: Graves Vulcan II tuning help

Quote:
Originally Posted by Mr Moose View Post
Hello,
According to Wikipedia Falkirk is only 3 miles from the Westerglen transmitting station so I would expect your aerial to be OK.

(https://en.wikipedia.org/wiki/Wester...itting_station).

It gives the following stations broadcast from the transmitter;

BBC Radio 4 198 Khz LW at 50 Kw
BBC Radio 5 909 Khz MW at 50 Kw
BBC Radio Scotland 810 Khz MW at 100 Kw
Talk Sport 1089 Khz MW at 50 Kw
Absolute Radio 1215 Khz MW at 50 Kw

You only appear to be able to pick up the highest frequency medium wave station (Radio Scotland at 810 Khz is the most powerful with twice the power of Absolute Radio) so it could simply be that for some reason your set will not tune low enough to to get the other stations.
This could suggest a problem with the tuned circuit possibly the coils or tuning capacitor .
Yours, Richard
Thanks Richard good info there, didn't know the transmitting station was so close, the coils all appear to be OK on continuity and produce low ohms readings. You maybe correct re the tuning capacitor, I did notice yesterday that touching the bakelite knob for the tuning capacitor seemed to help reception. I might strip it out and check the insulators.

There's not many parts to this set, hopefully get it fixed, cheers

Lee
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