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Old 16th August 2012, 10:53 PM   #1
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Default Help needed for tube power supply design with unknown choke..

Hello I am trying to use 2 unknown chokes I have in the power supplies for a pair of monoblocks using 4 6f6g each in the power supply section in ppp. I was thinking choke input but have no idea the rating or inductance of the chokes. These amps came from baldwin tube organs, the chokes measure 200 ohms dcr and are about the size of a 30 watt pp output transformer and look to be air gapped. Using a full wave bridge ss recto, I get about 600 volts and the want to use the center tap for a 300 volt point I havn't decided where to put ground either on the bottom or in the middle.. My questions are is 200 ohm dcr too high for the current I need? And do I have to use snubbing caps to protect the ss diodes from the flyback voltage at switch off? Am I better off just putting a filter cap first and the choke second? Thanks you guys
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Old 18th August 2012, 01:42 AM   #2
ChrisA is offline ChrisA  United States
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Originally Posted by Austin Translation View Post
..... My questions are is 200 ohm dcr too high for the current I need? And do I have to use snubbing caps to protect the ss diodes from the flyback voltage at switch off? Am I better off just putting a filter cap first and the choke second? Thanks you guys
Your trouble is that you don't have any specs on the choke other than DCR. You really should measure it.

The capacitor input supply is MUCH more forgiving so you can use any choke you like so long as it can take the current. With n un-measured choke this is really the only way.

It is not hard to test a choke. Place it is a representative circuit and measure the AC "reactance" at 120 Hz. Then use a bit of algebra to solve to inductance. The best way to measure reactance is to find a resistor that gives the same voltage drop. You MUST use a representative circuit that places DC through the choke.

Then to measure current handing ability you can use DC and a resistor dummy load. Run a test with a small current for 30 minutes and check the choke's temperature. thenraise the current and wage. Move it up slowly until the choke gets as warm as you want. then measure the current and that is the limit.

Now that you have the inductance, current handing limit and DRC you know enough to make a choke input PS.
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Old 18th August 2012, 03:42 AM   #3
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Quote:
Originally Posted by Austin Translation View Post
Hello I am trying to use 2 unknown chokes I have in the power supplies for a pair of monoblocks using 4 6f6g each in the power supply section in ppp. I was thinking choke input but have no idea the rating or inductance of the chokes. These amps came from baldwin tube organs, the chokes measure 200 ohms dcr and are about the size of a 30 watt pp output transformer and look to be air gapped. Using a full wave bridge ss recto, I get about 600 volts and the want to use the center tap for a 300 volt point I havn't decided where to put ground either on the bottom or in the middle.. My questions are is 200 ohm dcr too high for the current I need? And do I have to use snubbing caps to protect the ss diodes from the flyback voltage at switch off? Am I better off just putting a filter cap first and the choke second? Thanks you guys
size and dcr of the chokes implies lots of turns and high inductance....a 200ohm dcr and 100mA drain is just 20 volts, i'd say you can use it....

if you put the 0ground ref in the middle you end up with +-300volt rails, so for tube amp 0 ground should be at the bottom....

600volts unloaded drops like a stone you will find out...are you using choke input? what is the speck of your power traffo? i bet that it is 440volts centre- tapped, how big is it?
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Old 18th August 2012, 04:25 PM   #4
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Using an unknown choke in a circuit is about the same as using an unknown resistor; you have no idea what will happen. It's a waste of time, and could cause things to be damaged.
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Old 22nd August 2012, 04:39 PM   #5
palmas is offline palmas  Portugal
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Originally Posted by sawreyrw View Post
Using an unknown choke in a circuit is about the same as using an unknown resistor; you have no idea what will happen. It's a waste of time, and could cause things to be damaged.
But as a resistor, you can just measure it, and it does't have to be accuratly measured.
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Old 23rd August 2012, 11:52 PM   #6
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Originally Posted by Tony View Post
size and dcr of the chokes implies lots of turns and high inductance....a 200ohm dcr and 100mA drain is just 20 volts, i'd say you can use it....

if you put the 0ground ref in the middle you end up with +-300volt rails, so for tube amp 0 ground should be at the bottom....

600volts unloaded drops like a stone you will find out...are you using choke input? what is the speck of your power traffo? i bet that it is 440volts centre- tapped, how big is it?

Thank you all very much for the replies!

These are two unknown spec really large power transformers, they supplied about 50 small signal tubes on an external board and on this panel two 6L6 power tubes with several oddball 5 pin 7 pin tubes along with 4 nine pin sockets. No idea what model organ or what tubes came with it but I have replaced all of the odd tube sockets with octals so I have total of 7 octal sockets and 4 9 pin sockets now to play with. I don't have alot of experience with the negative power supply but after reading some stuff on the tubecad website I am thinking of trying the negative supply with the ground at the middle for some of the different things you can do with it. I have decided to try using two 6L6 for a power section and use two 6f6 tubes for drivers and one 6f6 for a cathodyne phase inverter maybe some more 6f6 as voltage amps for each amp for all octal, since I have collected so many of these cool looking 6f6g tubes. There are three heater windings, the 5v recto supply, a 12v supply for all the signal tubes and a 6.3 volt on each amp.

I have wired my filters up CRC since I couldn't decide what to do with the choke.Click the image to open in full size.
new tube project There are paper layers in between the layers of wire like an output transformer, could it be an audio choke? Like for a plate load or cathode load? There is another choke as well, with 2.86k dc resistance end to end and a tap at 1.98k that surely would be an audio choke it seems, like maybe could be used on one of these pentodes as a plate load with the tap going to the screens or as a cathode load for a cathode follower and the tap used for bias, I don't know. I am having alot of fun just deciding what to do with it already and don't even have it working yet.. I am trying to decide how to wire the heaters to make sure I don't put too much load on the 6.3v winding and I am thinking I should wire in series the power tube heaters and run them from the 12 volt though. If I can just get it working with the positive rail that is almost 400 volts unloaded and play with the negative rail later that will be fine, I made a frame from wood that lets me turn it upside down to solder on it with all the tubes in it. Fun stuff!
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Old 24th August 2012, 12:02 AM   #7
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you have a big traffo there that's for sure....i'd say more than enough for a 2 channel power amp and a preamp....

if you can list down the windings on the secondary with their dc resistances, then that will be useful.........there could be more than one 6.3 volt winding there....

Quote:
There is another choke as well, with 2.86k dc resistance end to end and a tap at 1.98k that surely would be an audio choke it seems, like maybe could be used on one of these pentodes as a plate load with the tap going to the screens or as a cathode load for a cathode follower and the tap used for bias, I don't know.
you can supply the outer ends with say 12v ac and measure the centre tap wrt to either end, if it measures 6 volts as i think it would, then you can use that for many things...

Quote:
I have wired my filters up CRC since I couldn't decide what to do with the choke
if you are scared to use those chokes, send them to me i will use them, promise....
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Old 24th August 2012, 02:26 AM   #8
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Quote:
Originally Posted by Tony View Post
you have a big traffo there that's for sure....i'd say more than enough for a 2 channel power amp and a preamp....

if you can list down the windings on the secondary with their dc resistances, then that will be useful.........there could be more than one 6.3 volt winding there....



you can supply the outer ends with say 12v ac and measure the centre tap wrt to either end, if it measures 6 volts as i think it would, then you can use that for many things...



if you are scared to use those chokes, send them to me i will use them, promise....

More than enough for a two channel amp for each transformer? Should for make some nice monoblocks then. I bought both of them from the same guy in my home town here for $60 thinking I could make a circlotron one day and just use them to learn on.
7.3 volts measured from one end to the middle tap and 3.7 volts measured from the other end to the middle tap for the little choke with 11.5 volts from the 12 volt winding with the slight voltage drop because I am using a series light bulb. So I guess not a center tap. None of these heater winding have center taps and they all measure about 1.2 ohms on my cheap vom. They don't seem to be connected to each other at all either by checking for continuity between them.
Click the image to open in full size.


You can see the chokes in this pic.

Click the image to open in full size.
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Old 24th August 2012, 03:41 AM   #9
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you hit the jackpot....congrats....
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Old 24th August 2012, 11:15 AM   #10
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Suppose I connect both the amps power supply transformer secondaries in series for 1400 volts and then to drop the voltage back down to 700 volts I run the power transformer primaries in series with each other. Seems like a great idea but if it were, surely everybody would be trying to do it. I could get four voltage referances.

Last edited by Austin Translation; 24th August 2012 at 11:37 AM.
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