Hi.
I've salvaged a transformer out of a old vcr and I'm wondering if it could be used in a gc amp. I know it's 40VA and seems to have dual secondaries as it has 2x4 leads coming out. How would i have to take measurments? I know these questions maybe stupid but it is better to ask people than to frie it all 😀
PS: Markings on it are:5214411 SOHH ZK and C-222-40VA.
I've salvaged a transformer out of a old vcr and I'm wondering if it could be used in a gc amp. I know it's 40VA and seems to have dual secondaries as it has 2x4 leads coming out. How would i have to take measurments? I know these questions maybe stupid but it is better to ask people than to frie it all 😀
PS: Markings on it are:5214411 SOHH ZK and C-222-40VA.
I'm assuming this T/F isn't some fancy high voltage step-up one with high resistance windings.........
First make sure you've identified all of the windings using an ohms tester, the primary should be obvious from how it was wired in the VCR but it will be the highest resistance winding, probably >>15R. The dual secondaries will likely be a few ohms at most. Check if the 2 secondaries are isolated or not on the low ohms range of a DVM for future reference, both are OK but you need to know. Then, assuming you haven't got a 500v isolation tester, check on a high Mohm DVM range that there's isolation between primary and both secondaries, i.e. no reading or at least higher than 20M.
If the above is OK then power the primary up as safely as you can temporarily, insulating wires and using a 1A mains fuse, 3A at most. Measure the secondary AC voltages on the DVM for reference.
This won't tell you the phasing of the secondaries. If you need to know that (you won't unless they're the same voltages), then if they were isolated, wire them in series and the total voltage will double if the 2 joined wires were out of phase, or drop to near zero if the joined wires were in phase.
First make sure you've identified all of the windings using an ohms tester, the primary should be obvious from how it was wired in the VCR but it will be the highest resistance winding, probably >>15R. The dual secondaries will likely be a few ohms at most. Check if the 2 secondaries are isolated or not on the low ohms range of a DVM for future reference, both are OK but you need to know. Then, assuming you haven't got a 500v isolation tester, check on a high Mohm DVM range that there's isolation between primary and both secondaries, i.e. no reading or at least higher than 20M.
If the above is OK then power the primary up as safely as you can temporarily, insulating wires and using a 1A mains fuse, 3A at most. Measure the secondary AC voltages on the DVM for reference.
This won't tell you the phasing of the secondaries. If you need to know that (you won't unless they're the same voltages), then if they were isolated, wire them in series and the total voltage will double if the 2 joined wires were out of phase, or drop to near zero if the joined wires were in phase.
Watch out if VCR had a gas tube display. May have a relatively HV secondary. Otherwise just issolate outputs and measure between all wires coming out. Write it down. Open leads won't fry things. Shorted leads will. When in doubt attach meter with clips to output leads and start with meter on highest range, then plug in transformer. Take reading, unplug and move to next set of wires.
Doc
Doc
It had a gas tube display if I'm correct, that means that one of the secondaries is unuseable for a gc amp, but the other one may still be useable? One of the bridge rectifiers that it had was 100-800v, and the other 60v. that's what I managed to find out.
also, could this be used for a gc amp?
https://www.elfa.se/elfa3~ee_et/elfa/init.do?item=69-946-85&toc=19593
also, could this be used for a gc amp?
https://www.elfa.se/elfa3~ee_et/elfa/init.do?item=69-946-85&toc=19593
What voltages do you need? What were the readings from the transformer leads? I don't know what a "gc" amp is, but it doesn't matter. You should know what voltages your project needs. Having a gas display doesn't eliminate a transformer, that's just an extra winding you may not need. I would presume the VCR had +/- supply rails. What does your project call for?
Doc
Doc
A gainclone amp. It would need about +-25v after rectifier. I'll take the measurments later today. I've been wondering about one thing between the ac input and the transformer there were two little transformers(atleast i think they were transformerers) arent these supposed to up the voltage?
It's been a while but I seem to remember the output voltages for a VCR power supply to be 12V for motors ( up to 1 amp) 5V ( another amp) for logic and 36V for the florescent display at a few milli-amps.
So the transformer should be unuseable for this purpose. Where could I scavange a transformer for a gainclone amp? Or would this work:
https://www.elfa.se/elfa3~ee_et/elfa...6-85&toc=19593
https://www.elfa.se/elfa3~ee_et/elfa...6-85&toc=19593
From my VCR repair days it was quite common for the display to be driven from its own little invertor.
One way, maybe not the best way, to ascertain the current capacity of the windings of an unknown transformer is to load the secondaries with resistors.
At NO LOAD the secondary will have an excessive voltage. This will quickly stabilise as you add resistors.
What you are looking for is the point at which the voltage starts to fall to about 95% of this stable voltage.
For Example. If you measure Vs at no load and it is 24V. Try adding 240 Ohm 3W resistors one at a time across the secondary.
If one resistor gives you say 22V and the second 22V, you have reached a stable voltage.
Now add more resistors, one at a time until the voltage drops to about 20V.
You will now have an approximate value of load that can be sustained by that winding.
If you have multiple secondaries you might need to repeat the experiment wih all secondaries loaded.
THIS IS NOT EXACT - But it does give you an approximation.
For safety sake you can always down-rate your findings.
At NO LOAD the secondary will have an excessive voltage. This will quickly stabilise as you add resistors.
What you are looking for is the point at which the voltage starts to fall to about 95% of this stable voltage.
For Example. If you measure Vs at no load and it is 24V. Try adding 240 Ohm 3W resistors one at a time across the secondary.
If one resistor gives you say 22V and the second 22V, you have reached a stable voltage.
Now add more resistors, one at a time until the voltage drops to about 20V.
You will now have an approximate value of load that can be sustained by that winding.
If you have multiple secondaries you might need to repeat the experiment wih all secondaries loaded.
THIS IS NOT EXACT - But it does give you an approximation.
For safety sake you can always down-rate your findings.
@ KatieandDad
This is true, but before the switching power supplies were introduced, which apparently he has, they sometimes had a separate winding instead of the inverter . I'm talking late 70's here.
This is true, but before the switching power supplies were introduced, which apparently he has, they sometimes had a separate winding instead of the inverter . I'm talking late 70's here.
Last edited:
Mid 70's VCR ???
My comment is still valid above but obviously you have to scale down the expected load available from that particular winding. A display would only need microamps or one or two milliamps at HV. The filament current would be the higher load.
It's a valve in disguise.
My comment is still valid above but obviously you have to scale down the expected load available from that particular winding. A display would only need microamps or one or two milliamps at HV. The filament current would be the higher load.
It's a valve in disguise.
I was just thinking about buying the switching power supply if i can't use the transformer from the vcr. I would like to build a lm1875 powered stereo amp and I was wondering if I could use the transformer I scavanged from the VCR.
I'm a newbie to diyaudio, and it would be my first project. I have relatively no experience in schematics, I've done a lot of soldering though. I'll post the results of the transformers output tommorow.
I'm a newbie to diyaudio, and it would be my first project. I have relatively no experience in schematics, I've done a lot of soldering though. I'll post the results of the transformers output tommorow.
Build a bulb tester.
Insulate every transformer tapping by inserting each into a separate terminal of an insulated terminal strip.
Find which tappings are on the same winding. Label them.
Power up the presumed primary via the bulb tester.
If the bulb goes OFF, then you do not have a short circuit in the wiring.
Very carefully measure the mains input voltage at the terminal strip. Note reading
Measure the voltage at the ends of each winding. note readings.
Note mains voltage again.
Report your findings.
Insulate every transformer tapping by inserting each into a separate terminal of an insulated terminal strip.
Find which tappings are on the same winding. Label them.
Power up the presumed primary via the bulb tester.
If the bulb goes OFF, then you do not have a short circuit in the wiring.
Very carefully measure the mains input voltage at the terminal strip. Note reading
Measure the voltage at the ends of each winding. note readings.
Note mains voltage again.
Report your findings.
So I Took the measurments on Acv setting with my multimeter from the secondaries. the results were this
(pin)8 - 9 = 15V
8 - 10 = 18V
8 - 11 = 10V
9 - 10 = 5V
9 - 11 = 0V
10 - 11 = 9V
14 - 15 = 32V
14 - 16 = 10V
14 - 17 = 12V
15 - 16 = 0V
15 - 17 = 2,5V
16 - 17 = 3V
The transformer had 8 pins on the secondaries, by groups of four. That is the reason I think there are two secondaries. Now for the second part, How do I measure the ampers of this thing? If the VA rating is 40, then do i divide 40 with the volts and get ampers? and would this suite the needs of a lm1875 stereo amp?
PS. Are the voltage results strange and I'm doing something wrong? cause they seem wrong to me, so many different results.
(pin)8 - 9 = 15V
8 - 10 = 18V
8 - 11 = 10V
9 - 10 = 5V
9 - 11 = 0V
10 - 11 = 9V
14 - 15 = 32V
14 - 16 = 10V
14 - 17 = 12V
15 - 16 = 0V
15 - 17 = 2,5V
16 - 17 = 3V
The transformer had 8 pins on the secondaries, by groups of four. That is the reason I think there are two secondaries. Now for the second part, How do I measure the ampers of this thing? If the VA rating is 40, then do i divide 40 with the volts and get ampers? and would this suite the needs of a lm1875 stereo amp?
PS. Are the voltage results strange and I'm doing something wrong? cause they seem wrong to me, so many different results.
This is not a very user friendly transformer but dont give up yet.
Look at #10.
You can load up each pair of terminals maybe 100mA at a time and see what happens.
Be careful though, as already intimated, there may be some very low current HT windings that are only rated at a few mA each.
If you load each winding at say 50mA and it is significantly different to your original readings, turn OFF immediately and report your results.
Look at #10.
You can load up each pair of terminals maybe 100mA at a time and see what happens.
Be careful though, as already intimated, there may be some very low current HT windings that are only rated at a few mA each.
If you load each winding at say 50mA and it is significantly different to your original readings, turn OFF immediately and report your results.
You can't measure the amperes.
You can estimate the relative current capabilities of the windings by comparing the wire diameters used for each (and every) part of the windings.
One winding, let's say it is 12-5-0-5-12Vac and all the wire in the winding is 0.9mm diameter. then you can estimate that each part of that winding can carry the same maximum current.
If the other winding were say, 10-6-0-6-10Vac and the wire were 0.8mm diameter from 6-0-6 but only 0.6mm diameter from 10-6 and from 6-10 then you can see that the winding has a lower current capability in the middle sections and a much lower current capability in the two outer sections.
Proportioning the VA ratings between all these windings can be done, but there is quite a bit of arithmetic involved.
You can estimate the relative current capabilities of the windings by comparing the wire diameters used for each (and every) part of the windings.
One winding, let's say it is 12-5-0-5-12Vac and all the wire in the winding is 0.9mm diameter. then you can estimate that each part of that winding can carry the same maximum current.
If the other winding were say, 10-6-0-6-10Vac and the wire were 0.8mm diameter from 6-0-6 but only 0.6mm diameter from 10-6 and from 6-10 then you can see that the winding has a lower current capability in the middle sections and a much lower current capability in the two outer sections.
Proportioning the VA ratings between all these windings can be done, but there is quite a bit of arithmetic involved.
Yes, but he cant see the wire diameter.
This is going back to the Black Box approach of the unknown quantity.
This is going back to the Black Box approach of the unknown quantity.
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