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Old 25th August 2015, 01:48 PM   #1
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Default When to use artificial center tap

Hi peeps my power tranny blew a little while ago I got a new one wound
With no winding centre taps as I was installing it with artificial centre taps on the pre and power tubes I put one on the rectifier tube filiment but thought I'd better ask if this is possible before I power up I'm not keen to let the smoke out of anything else
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Old 25th August 2015, 01:55 PM   #2
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Default On iPad trying to get pic the right way round

To be clear my old tranny had winding centre taps but my new one doesn't any advice on this matter would be great thancs
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Old 25th August 2015, 03:10 PM   #3
euro21 is offline euro21  Hungary
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Quote:
Originally Posted by Goodlagger View Post
To be clear my old tranny had winding centre taps but my new one doesn't any advice on this matter would be great thancs
The schematic contains some (dangerous) mistakes.
The rectifier heater pins (2 and 8) voltage is about +400V! If you put between this points and the negative point 100R resistors, the resistor's current will be 4A!

Try hibrid rectifier.
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Old 25th August 2015, 03:31 PM   #4
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Quote:
Originally Posted by Goodlagger View Post
Hi peeps my power tranny blew a little while ago I got a new one wound
With no winding centre taps as I was installing it with artificial centre taps on the pre and power tubes I put one on the rectifier tube filiment but thought I'd better ask if this is possible before I power up I'm not keen to let the smoke out of anything else
Don't put these resistors on the rectifiers heater! The heater caries the HT.
If the original tranny had a CT, it was the HT output in the case of directly heated rectifiers (5U4, 5Y3,...).
In your drawing you show an indirectly heated type (GZ34/5AR4, GZ32,...). In that case take the HT from pin 8, which is the cathode.
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Old 26th August 2015, 02:25 AM   #5
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Default Yer I thought it wasn't correct

So I've redrawn it with the two resistors in series am in the right path now. Will the resistor values work for this design,is all for the reduction of hum ? Or not needed at all ? Or is there another way? Ps Thanks for the responses .
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Old 26th August 2015, 08:05 AM   #6
euro21 is offline euro21  Hungary
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5U4-GB filament (from Genereal Electric datasheet): 5V, 3A.
Don't use 0.27R dropping resistors, else your filament voltage will be only 3.38V!

" old tranny had winding centre taps but my new one doesn't"
Your last schematic contains CT trapped transformer. If you have this, this part of schematic is correct.
If you have transformer with 320V (no centre tap), use hibrid (two SS diode and rectifier tube) rectifier scheme.
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Old 26th August 2015, 11:48 AM   #7
DF96 is offline DF96  England
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Can we go back to the fundamental points?
1. Octal base rectifiers usually have a connection between the cathode and the heater (even when indirectly heated) so the heater supply must be independent and not connected to anything else - especially ground! In most cases a 5V supply is needed.
2. Other indirectly heated rectifiers may share a heater supply with the rest of the circuit - in most cases a 6.3V supply is needed. It does no harm to provide a heater supply centre tap, but the rectifiers don't need this. All heater supplies must have a DC reference voltage (which may be ground) which can be connected to one side or a centre-tap.
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Old 27th August 2015, 03:29 AM   #8
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Default Sorry to confirm my 5v 3a filament winding had the centre tap

Quote:
Originally Posted by euro21 View Post
5U4-GB filament (from Genereal Electric datasheet): 5V, 3A.
Don't use 0.27R dropping resistors, else your filament voltage will be only 3.38V!

" old tranny had winding centre taps but my new one doesn't"
Your last schematic contains CT trapped transformer. If you have this, this part of schematic is correct.
If you have transformer with 320V (no centre tap), use hibrid (two SS diode and rectifier tube) rectifier scheme.
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Old 27th August 2015, 03:32 AM   #9
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Default Thanks I think you've answered my question

Quote:
Originally Posted by DF96 View Post
Can we go back to the fundamental points?
1. Octal base rectifiers usually have a connection between the cathode and the heater (even when indirectly heated) so the heater supply must be independent and not connected to anything else - especially ground! In most cases a 5V supply is needed.
2. Other indirectly heated rectifiers may share a heater supply with the rest of the circuit - in most cases a 6.3V supply is needed. It does no harm to provide a heater supply centre tap, but the rectifiers don't need this. All heater supplies must have a DC reference voltage (which may be ground) which can be connected to one side or a centre-tap.
I've put an artificial centre tap on all my other tubes but just wire the 5v winding straight to the rectifier tube no need to do anything else
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Old 27th August 2015, 03:35 AM   #10
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No need to worrie about hum on the rectifier tube
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