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Old 19th September 2006, 02:46 PM   #1
jarthel is offline jarthel  Australia
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Default dropping heater voltage

My secondaries for the heaters are high even with load.

5.6V for the 5V secondary. and 7V for the 6.3 secondary.

I can go the cheap route and use .1ohm on 1 secondary wire and a .22ohm resistor on the other wire. But I've seen replies saying the resistor values must be the same but I'm not sure if this applies to my situation.

The tubes connected to the heaters are for the power supply. the 5V secondary going to the 5*4 rectifier and the 6.3 secondary going to the 6as7/6sl7 tubes used for the voltage regulation.

thank you for the help
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Old 19th September 2006, 03:31 PM   #2
poobah is offline poobah  United States
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You're on the right track Jarthel,

If these were center tapped secondaries, and the CT was "referenced", one could make a small case for balancing the resistors. In your case though, it shouldn't matter. You can even use ONE 0.33 Ohm if it makes life simpler.

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Old 19th September 2006, 03:46 PM   #3
jarthel is offline jarthel  Australia
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Quote:
Originally posted by poobah
You're on the right track Jarthel,

If these were center tapped secondaries, and the CT was "referenced", one could make a small case for balancing the resistors. In your case though, it shouldn't matter. You can even use ONE 0.33 Ohm if it makes life simpler.


both secondaries are CT secondary and I intend to reference the CT to 1/2 B+.

And unfortunately, I cannot find any .33ohm resistor locally. I need to go to Farnell or RS for such a value.
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Old 19th September 2006, 03:48 PM   #4
poobah is offline poobah  United States
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I don't think you reference the CT on your rectifier heaters.

Can I see your schem?

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Old 19th September 2006, 03:59 PM   #5
jarthel is offline jarthel  Australia
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Quote:
Originally posted by poobah
I don't think you reference the CT on your rectifier heaters.

Can I see your schem?


you're right. my mistake. only the 6as7/6sl7 would've referenced CT.

so can I use different value resistors on the secondary wires to drop voltage?

thanks again
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Old 19th September 2006, 04:57 PM   #6
poobah is offline poobah  United States
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Yep,

It could be argued that this might induce some hum... very doubtful, although in principle the resistors should be matched.

Why not go ahead and get things moving with the resistors you have... leave the resistors easy to remove... don't wind the leads around the eyelets 5 times... just poke 'em in and so9lder them. Order the correct resistors next time you place an order... so you don't have to spend $15 for 2 ******* resistors.

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Old 20th September 2006, 06:53 PM   #7
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Default Heater voltage..

I have a similar problem, and a 'different' cure....

I have a Toroid that is supposed to be 25V @4.5A loaded O/C volts is 27.8 and loaded by 3.5A is arond 27.5.

Im using it to supply two series wired 6C33C-B heaters.--27.5 is too much.

A simple 'mod' I did was to measure the turns/volt by looping test-lead through toroid core and back to meter. It was .5Vac or thereabouts....

I wound 6 turns More on the core, and connected it in Anti-phase to the original secondary. It was all insulated after with good quality tape. This dropped the voltage to 24.5, which Im happy with.

Its been working well for many months with no heating or other issues.

--No hot resistors or hard to find values, or waste of power. Easy with a toroidal Tx, but maybe not possible with an E I type Tx as there may not be room on the bobbin and sometimes hard to insulate if there is room for an additional couple of turns....

For your centre-referenced Tx, you'll need to join two coils of half the number of turns each to each end of your existing secondary, Both in Anti-phase. Use wire the same thickness as the secondary coil wire OR slightly thicker....
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Old 20th September 2006, 11:34 PM   #8
jarthel is offline jarthel  Australia
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Default Re: Heater voltage..

Quote:
Originally posted by Alastair E
I have a similar problem, and a 'different' cure....

I have a Toroid that is supposed to be 25V @4.5A loaded O/C volts is 27.8 and loaded by 3.5A is arond 27.5.

Im using it to supply two series wired 6C33C-B heaters.--27.5 is too much.

A simple 'mod' I did was to measure the turns/volt by looping test-lead through toroid core and back to meter. It was .5Vac or thereabouts....

snip....
except that I'm using an rcore and more importantly, I do not think I'm competent enough such a modification

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Old 20th September 2006, 11:38 PM   #9
poobah is offline poobah  United States
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Actually Jarthel,

An R-core would probably provides the simplest way just to remove some turns!

Has your trans been dipped in varnish?

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Old 21st September 2006, 12:01 AM   #10
jarthel is offline jarthel  Australia
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Quote:
Originally posted by poobah
Actually Jarthel,

An R-core would probably provides the simplest way just to remove some turns!

Has your trans been dipped in varnish?


I have to look if it has been dipped in varnish. but in any case, can you tell me how it's done?

not sure if it's important but here's 2 pics of the transformer:

http://img156.imageshack.us/my.php?i...ict0004ty5.jpg

http://img82.imageshack.us/my.php?image=pict0005ne7.jpg
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