Amplifier Audio Innovations Series 500
Scroll down about 40% for "Figure 10," the schematic for the PS on my late 80s British tube EL34. I have not opened the amp yet. The main trafo primary has at least 3 unterminated wire leads. Upon request I'll open the amp and report the insulation color of the unterminated leads.
I need to change the wiring from 240V to 120V. If possible, please describe a test method with a simple multimeter to determine the 120V leads.
Scroll down about 40% for "Figure 10," the schematic for the PS on my late 80s British tube EL34. I have not opened the amp yet. The main trafo primary has at least 3 unterminated wire leads. Upon request I'll open the amp and report the insulation color of the unterminated leads.
I need to change the wiring from 240V to 120V. If possible, please describe a test method with a simple multimeter to determine the 120V leads.
First of all, show a puicture or two showing transformer and primary wires exiting from it.
Also "unterminated wire ends"
Are wires different colours?
If not, add little labels "W1 - W2 - etc."
We need that basic data to give straighter truer answers.
I know forum members itch to answer "something" NOW but really we need that data first.
Also "unterminated wire ends"
Are wires different colours?
If not, add little labels "W1 - W2 - etc."
We need that basic data to give straighter truer answers.
I know forum members itch to answer "something" NOW but really we need that data first.
I'm all for caution over speed!
Yes; internet posts specify each unterminated trafo wire has a unique color. ASAP I'll post images as requested displaying each unterminated trafo wire, either with separate colors or labels as requested.
Might take a day or two.
The schematic portrays mains trafo with 4 vertical primary windings in series; from the top down in this sequence:
100V
100V
20V
20V
240V mains drives the two outermost terminals across primary windings totaling "240V."
My 120V mains is supposed to drive the terminals above "100V" and below "20V" in the middle, right? Shorting unused primary windings is forbidden, yes?
The mains input shorting capacitor is specified for 240V (schematic shows no value). Should I change the value for 120V? If yes, how do I calculate the 120V cap value based on the 240V cap value?
Thanks very much!
Yes; internet posts specify each unterminated trafo wire has a unique color. ASAP I'll post images as requested displaying each unterminated trafo wire, either with separate colors or labels as requested.
Might take a day or two.
The schematic portrays mains trafo with 4 vertical primary windings in series; from the top down in this sequence:
100V
100V
20V
20V
240V mains drives the two outermost terminals across primary windings totaling "240V."
My 120V mains is supposed to drive the terminals above "100V" and below "20V" in the middle, right? Shorting unused primary windings is forbidden, yes?
The mains input shorting capacitor is specified for 240V (schematic shows no value). Should I change the value for 120V? If yes, how do I calculate the 120V cap value based on the 240V cap value?
Thanks very much!
Having a look on the PS schematic shows that the unterminated wires are not unterminated at all! The transformer has four independant windings on the primary side. For 240V, all are connected in series - the '100V end' is connected to the '0V end' of the next winding etc. For 120 V operation, you need to wire the trafo so that one 100V is series connected to a 20 V winding each, and these two resulting 120V windings need to be connected in parallel. When knowing the colours of all wires (there should be 8 wires coming from the trafo for the primaries) and with the help of a simple multimeter, you can identify each end of the windings. When rewiring the primaries it is important to make the connection in the right order! If e.g. one winding is connected in reverse order, the resulting voltage will be the difference and not the sum. Therefore, before opening existing connections, you need to document what wire is connected to each other to be able to identify the '0V' terminals and the 'hot' terminals (100V or 20V) based on the existing all in series configuration.
The capacitor over the mains leads is a suppression cap and you do not need to change it. It is installed to supress RF and other noise signals entering the amp from the power input.
The capacitor over the mains leads is a suppression cap and you do not need to change it. It is installed to supress RF and other noise signals entering the amp from the power input.
Yes, that makes perfect sense, my bad! I should have looked at it first, sorry. I wrongly thought I read there were unterminated wires.
OK, images next, thank you very much!
Yes, I see 8 primary leads on the schematic.
Do I have this right?
Isolate top most 100V in series with bottom most 20V
Isolate in series middle 100V and 20V
Then:
Parallel the two 120V sections described above, maintaining original polarity.
OK, images next, thank you very much!
Yes, I see 8 primary leads on the schematic.
Do I have this right?
Isolate top most 100V in series with bottom most 20V
Isolate in series middle 100V and 20V
Then:
Parallel the two 120V sections described above, maintaining original polarity.
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Yes. But there is still a possibility to alter a polarity to a wrong on some winding, so be ready for this. To be sure after all - for example, measure a magnetizing current, etc.
It's still unclear what you mean with 'isolate'.
I would do it as follows:
1. open the connection between the two 100 V and between the two 20 V windings
2. connect the now free '100V' wire of the top most 100V winding with the free '0V' wire of the bottom most 20V winding (if not shure what wire belongs to what winding, use a multimeter to check continuity beteen the free wire in question and the still connected wire to the input power lines)
3. connect the still free '0V' wire of the 2nd 100V winding with the '0V' winding of the top most 100 V winding
4. Connect the last free wire ('20V' of the upper most 20 V winding) with the '20V' wire of the bottom 20 V winding)
I agree with most said.
The tricky part is when wiring in parallel. Here the s*** can hit the fan if things have been done wrong.
First step is to get two 120 volt windings.
They must be both, exactly equal 100 + 20 = 120.
Possible mistake here, is to have one that is effectively 100 - 20 = 80 because of wrong phasing between the 100 and the 20.
Second step is to parallel the two identical windings with the right phasing. If the phasing is wrong the transformer blows up.
As a safety caution, I would do all the critical steps with a light bulb in series
The tricky part is when wiring in parallel. Here the s*** can hit the fan if things have been done wrong.
First step is to get two 120 volt windings.
They must be both, exactly equal 100 + 20 = 120.
Possible mistake here, is to have one that is effectively 100 - 20 = 80 because of wrong phasing between the 100 and the 20.
Second step is to parallel the two identical windings with the right phasing. If the phasing is wrong the transformer blows up.
As a safety caution, I would do all the critical steps with a light bulb in series
Just place a 100W incandescent lamp in series with the line cord, connect to mains and if the lamp lights and remains at full brightness the windings are connected incorrectly. Measure voltage across primary and if not close to zero V and the lamp is not at maximum brightness you have probably got it wired correctly.
Make sure to change the fuse to the value recommended for 120V operation. (Best to do after the test above as the lower fuse value provides a measure of protection against unforeseen mishaps.)
Be careful, remember there is mains voltage and even higher voltages present in the amplifier.
Make sure to change the fuse to the value recommended for 120V operation. (Best to do after the test above as the lower fuse value provides a measure of protection against unforeseen mishaps.)
Be careful, remember there is mains voltage and even higher voltages present in the amplifier.
There must be a fuse. For these experiments, a smaller one can be used. So if there be a much large non-polarity fuse has to blow. With a small (20V) non-polarity - yes, a series lamp of cause is much better. But an AC ammeter will show a problem too.
There is a possibility to power a transformer from a secondary (with another transformer), possibly with a lower voltage. So it can give a possibility to make those HV-connections and measurements a bit safer.
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Ampere measurement is insafe.
Multimeters usually have à 10A input to measure high currents. 10A maximum.
If it happens to take much more current.....the multimeter blows up.
You can bet this will happen when you are not perfectly sure of what you are doing.
Before you ever think about measuring a current you do need to know how much it can possibly be.
Multimeters usually have à 10A input to measure high currents. 10A maximum.
If it happens to take much more current.....the multimeter blows up.
You can bet this will happen when you are not perfectly sure of what you are doing.
Before you ever think about measuring a current you do need to know how much it can possibly be.
Pictured is a 6 conductor screw terminal strip from the mains trafo primary, that was fastened (as shown) to the mains transformer. The white and purple twisted pair shown connect the IEC > power switch. A brown and blue twisted pair leads from the power switch toward the mains trafo, likely leading to the primary for the 8 total primary conductors mentioned earlier.
With shorting jumpers removed and power switch "on" I measured:
White to purple 20 ohm
Orange to black 1.4 ohm
Purple to yellow 1.3 ohm
All else infinity.
I did not measure the brown and blue wires to any of the remaining 6 conductors, but shall do so now and report back.
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The DC resistances don't tell you anything about the phasing. But you might have identified the four primary winding parts. Now proceed as suggested earlier.
Best regards!
Best regards!
What you want is exactly half of the secondary voltages, compared to what the transformer is giving you now (going from 240V to 120V AC).
Disconnect the valve amplifier mains transformer secondary windings, use a smaller transformer (anything really.... for example, 120V AC to something like 15 - 25V AC) to feed this lower AC voltage into the valve amplifier mains transformer primary, and then see what combination AND what wiring scheme/phasing is correct to give you exactly one half.
EDIT: this lower voltage will ensure that you'll be getting no more than 50-ish V AC at the plate winding max (with the transformer still wired for 240V AC)
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With the right tools it is totally safe and nothing blows up - at least in the metering. I have a Fluke clamp
on current probe for my Fluke 8060 (I know it's an antique) that can go up to 400 amps. I have yet to measure
in excess of 100 amps.
Current clamp - Wikipedia.
Personally if I had to identify the phasing I would simply run on one of the 2 primaries and measure the other
one to identify the phasing. A few seconds on only one of two primaries should not cause problems. It's easier
with a scope but not difficult with just a meter.
Happy New Year
G²