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deluxe hunter
Samba Member
Joined: May 17, 2007
Posts: 42
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 Posted: Mon Oct 15, 2007 11:23 pm Post subject: 6v vdo tach on 12 v??? |
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I have an early 6V vdo tach and want to fit it on my 12 V oval....I am guessing I need more than a volt dropping resistor.
Does anyone know the best (safest) way to do this as I dont want to blow the tach.
cheers |
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Lind
Samba Member
Joined: November 06, 2000
Posts: 9916
Location: idaho
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| Posted: Mon Oct 15, 2007 11:47 pm Post subject: |
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do you have any pictures of it?
the correct oval era vdo tachs don't use the car's electrical system at all. they use a small generator that runs off a cable off the crank pulley nut.
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deluxe hunter
Samba Member
Joined: May 17, 2007
Posts: 42
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| Posted: Tue Oct 16, 2007 1:03 am Post subject: |
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| thanks for the reply. It is not the correct oval tach, rather an early 60's VDO 6v item that does fit into the accessory speaker grille. It has connections like any ordinary 12v tach ( coil, +, -, light) . |
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wimkever
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Joined: July 16, 2004
Posts: 412
Location: Holland (the Netherlands)
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| Posted: Thu Oct 18, 2007 12:16 pm Post subject: |
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| deluxe hunter wrote: |
| thanks for the reply. It is not the correct oval tach, rather an early 60's VDO 6v item that does fit into the accessory speaker grille. It has connections like any ordinary 12v tach ( coil, +, -, light) . |
Use a 7806 voltage regulator IC and two cap's and your problem is solved. For the circuit lay out see (near end of page):
http://www.geocities.com/vk3cz/gauge-repair.html
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Flat4Tom
Samba Member
Joined: March 17, 2005
Posts: 443
Location: Kingsport TN
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| Posted: Thu Oct 18, 2007 12:34 pm Post subject: |
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Don't mess with voltage drops with your tach.
I had my era correct 6vt tach converted / restored to 12vt by Palo Alto Speedometer. They did a great job and it was done fast as well.
Here's their website:
http://www.paspeedo.com/
Here it is in the dash of my '56. Disregard the missing firewall carpet...  It's there now.
Regards,
Tom
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| MEANIRISHMOFO wrote: |
| The whole Patina thing has gone way too far. A beat up piece of shit does not have patina. It's a beat up piece of shit. That car is a good base for a restoration, Not a coat of wax. |
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wimkever
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Joined: July 16, 2004
Posts: 412
Location: Holland (the Netherlands)
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| Posted: Thu Oct 18, 2007 2:10 pm Post subject: |
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| Flat4Tom wrote: |
Don't mess with voltage drops with your tach.
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I agree. But what I suggested isn't an ordinary voltage drop, I mean not a simple resistor. It's a regulated circuit and independent of the current (in Milli Amperes) that is drawn, it provides 6 volt. Converting to 12 volt of the tach is a good possibillity, but will cost you a lot more $$, I assume.
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deluxe hunter
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Joined: May 17, 2007
Posts: 42
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| Posted: Mon Oct 22, 2007 1:17 am Post subject: |
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thanks folks,
wimkever, I understand your voltage reg circuit for the tach power supply- cheers.
Do I need to do anything to the trigger connection to the coil?
cheers |
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wimkever
Samba Member
Joined: July 16, 2004
Posts: 412
Location: Holland (the Netherlands)
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| Posted: Mon Oct 22, 2007 1:10 pm Post subject: |
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| deluxe hunter wrote: |
thanks folks,
wimkever, I understand your voltage reg circuit for the tach power supply- cheers.
Do I need to do anything to the trigger connection to the coil?
cheers |
That's a good question. I'm sorry to say I don't know, I don't like to give you an advice that will destroy your tach. My first thought was : no problem. The trigger connection sends pulses, not something like 6 or 12 volt. In most tach's the DC (Direct Current) component should be blocked by a cap'. But I'm not sure how your tach is built inside. Maybe someone else can tell.
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