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Old 17th Oct 2007, 7:04 pm   #1
ColinB
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Default Bush VHF 70 with new relay

Hello everyone;

After a break from repairs, I am working on a Bush VHF 70. The wavechange switch in this is OK, having removed the HT from it (tracking and smoking). What I want to do is to use the contact to switch a relay.

Where in this set could I get the 6 or 12 volts that the relay would need - ideally without having to install a transformer just for this....?

Any suggestions?

Thanks in advance

Colin
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Old 17th Oct 2007, 7:19 pm   #2
Steve_P
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Default Re: Bush VHF 70 with new relay

The problem here is how to drive the relay (i.e. get 6v) without affecting the performance of the set.

Can the VHF90 mod be used?

http://www.vintage-radio.com/recent-...h-vhf90-1.html

Or, take the volts from the Dial Lights via a small diode....

Trader Sheet 1419 refers.

Cheers,

Steve P
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Old 17th Oct 2007, 7:47 pm   #3
paulsherwin
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Default Re: Bush VHF 70 with new relay

You can leave the HT connected to the VHF front end permanently, even when the radio is switched to AM. The only downside is that the valve life will be reduced if the radio is mostly used on AM.

This is the normal workaround for these wavechange switch problems - fitting a relay is a sledgehammer to crack a nut

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Old 17th Oct 2007, 8:11 pm   #4
Leon Crampin
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Default Re: Bush VHF 70 with new relay

The last time I repaired one of these, I used a miniature microswitch which was tripped by the end of the switch slider. These are rated to take mains voltage and work well.

Leon.
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Old 17th Oct 2007, 8:15 pm   #5
ColinB
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Default Re: Bush VHF 70 with new relay

Yes, that was what I did in the end, remove the switch and join the HT feed to the AM and FM sides. However, I wasn't sure this wouldn't give worse performance on FM - they must have put in the switch in for some reason.

Probably as you say though it's more in the way of powering the FM front-end down when not needed.

Cheers for the advice folks, I think it will stay as it is (hotwired!)

Regards

Colin
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Old 17th Oct 2007, 8:22 pm   #6
paulsherwin
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Default Re: Bush VHF 70 with new relay

Quote:
Originally Posted by ColinB View Post
I wasn't sure this wouldn't give worse performance on FM - they must have put in the switch in for some reason.

Probably as you say though it's more in the way of powering the FM front-end down when not needed.
The cost of switching the HT was very small (the wavechange switch was needed anyway) and it maximised valve life. I don't think performance was an issue.

Paul
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Old 17th Oct 2007, 9:26 pm   #7
Ed_Dinning
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Default Re: Bush VHF 70 with new relay

Try a small capacitive dropper (say 10 to 100nF) and a bridge rectifier to give the DC for the relay coil.

Ed
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Old 18th Oct 2007, 8:31 am   #8
Studio263
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Default Re: Bush VHF 70 with new relay

How about the cathode of the output valve? This is the traditional place to "borrow" a small DC voltage from. If you choose a relay with a high resistance 12V coil (with resistors in series to make up the voltage) then the change in bias would be minimal.
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Old 18th Oct 2007, 2:48 pm   #9
Tim
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Default Re: Bush VHF 70 with new relay

Nice elegant solution Leon, nearly tried once or twice!!

Nice to hear from you again.
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