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Old 2nd Sep 2010, 8:31 pm   #1
Mike Brett
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Default 6 valve pulse counting tuner

Hi guys
I am going to have a go at building a 6 valve pulse counting tuner that I found on a web site. You can find the schematics at philsvalveradiosite.co.uk, please have a look and give me your opinion of this design.I have tried to contact the author to ask about a few points but without success. My problem is what transformer to order for the main power supply T1 and T2. For T1 Rapid Electronics do a 230v 12va 18v + 18v transformer and for T2 I was going to order a 230v 50va 6v + 6v transformer for the heaters, does this seem ok to you.
Mike
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Old 2nd Sep 2010, 10:44 pm   #2
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Default Re: 6 valve pulse counting tuner

A better link may help, this one is a bit generic..
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Old 2nd Sep 2010, 10:52 pm   #3
AlanBeckett
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Default Re: 6 valve pulse counting tuner

This one?
http://philsvalveradiosite.co.uk/phi...receiver_1.htm
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Old 3rd Sep 2010, 12:24 am   #4
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Default Re: 6 valve pulse counting tuner

Hello,

Looking at the website he specifies a 18v 12VA transformer. However the output has a 100ma fuse which means that it would only take a maximum of about 2VA, although the pulsed nature of the current could require a higher rated transformer, so as far as I can see the transformer you suggest would be more than adequate. One of the 18V windings on its own could be enough or you could put the two 18V windings in parallel.
A better alternative might be a 9V + 9V 12VA transformer and put the two windings in series to give 18V (windings in series are generally better than in parallel).

The 7 valves require a heater current of 2.425A and he specifies a 2.5A transformer. A 20VA 6V + 6V transformer would give a total current of 3.3A so would do, but you would have to split the heaters between the two windings so as not to have more than 1.6A on either, say 3 of the ECC88s on one winding and the rest of the valves on the other. (You could also put the two windings in parallel as above). This is only suitable if you are sure that you do not want to add more than one or possibly two, low consumption extra valves for an amplifier etc.


With the 50VA transformer you could put all the valves on one 6V winding or split them between the two. It would also give you plenty in hand if you wanted to add extra valves. Running a transformer well below full load will usually cause the voltage to be higher than the rating but as the valves have 6.3V rather than 6V heaters this might actually be helpful.

Description of the 6 valve tuner with 7 valves is here:- http://philsvalveradiosite.co.uk/phi...receiver_1.htm

Yours, Richard

Last edited by Mr Moose; 3rd Sep 2010 at 12:47 am.
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Old 3rd Sep 2010, 8:29 am   #5
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Default Re: 6 valve pulse counting tuner

That link is the one, looks like a fun project. Let us see the end result.
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Old 3rd Sep 2010, 9:24 am   #6
Mike Brett
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Default Re: 6 valve pulse counting tuner

Hello all
Thanks for your detailed observations Richard, as you all say it does look a fun project.
If all goes well I will try and post a picture of the finished unit in due course.
Cheers Mike
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Old 3rd Oct 2010, 8:43 am   #7
Mike Brett
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Default Re: 6 valve pulse counting tuner

Hi all
I have wired my 50 va 6v-6v transformer in parallel and the output reads 7 volts, although this is with no load on it. As the eight valves have heaters of only 6.3 v do you think the voltage will drop to a safe limit when the valves are in circuit, only I do not want to risk over running the valves and shortening there lives.
Cheers Mike
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Old 3rd Oct 2010, 9:00 am   #8
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Default Re: 6 valve pulse counting tuner

7V isn't going to blow the heaters, but may be undesireable in the long term. Power up the "set" with the valves in and measure the voltage under load. If it's too high you can drop it using a resistor.
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Old 3rd Oct 2010, 11:31 am   #9
Mike Brett
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Default Re: 6 valve pulse counting tuner

Hi Graham
Many thanks for that,sounds simply, I will give it a go.
Cheers Mike
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