Hello guys have a friend who has a audio research sp3 and had a bad electrical storm lightning struck near his home and it took out several of his hifi components including the transformer in his arc sp3. I been trying to help him get his gear back up but I've looked thru the sp3 schematics and they don't have any voltage values for the secondaries from the transformer, judging from the rating of the caps it looks like there's two under 50v supplies and one under 300v? Does anyone know of a replacement or the values of the secondaries (current and voltage) so I can source a replacement one?
Thanks in advance for all the help
Thanks in advance for all the help
Have you asked AR if they might have one, if obsolete, at least they can provide the sec voltages and VA ratings.
Found a schematic that shows some circuit voltages.
For the HV - red wires, the DCV across the caps is shown as 500VDC and then regulated down to 400 odd volts after that, so the sec winding would be around 360VAC at 100mA or so at a guess (say 40VA)
The other 2 windings, yellow and orange provide what looks like 25VDC for filaments where they wire 2 tube filaments in series, So that would equate to around 18VAC secondaries at say 2 amps or so each, (say 40VA each winding)
Total transformer VA rating would be around 120VA approx.
You will need to double check all of that, but it should be close.
Found a schematic that shows some circuit voltages.
For the HV - red wires, the DCV across the caps is shown as 500VDC and then regulated down to 400 odd volts after that, so the sec winding would be around 360VAC at 100mA or so at a guess (say 40VA)
The other 2 windings, yellow and orange provide what looks like 25VDC for filaments where they wire 2 tube filaments in series, So that would equate to around 18VAC secondaries at say 2 amps or so each, (say 40VA each winding)
Total transformer VA rating would be around 120VA approx.
You will need to double check all of that, but it should be close.
This a sp3a-1 model with the 6 can capacitors I believe they used the same transformer on all versions of the sp3 from what I can see on the different schematics unless I'm mistaken. I have attached the schematic for the sp3a-1 so I'm looking for a transformer that has secondaries rated at
Hv red wires at 290 or 360 vac 50 or 100ma
Yellow wires at 18vac at 2 amps
Orange wires at 18vac at 2 amps
I'll reach out audio research and see if they sell or have any info about it other than them does anyone else know where I can look or find such a transformer for purchase?
Thanks again for all the help highly appreciated
Hv red wires at 290 or 360 vac 50 or 100ma
Yellow wires at 18vac at 2 amps
Orange wires at 18vac at 2 amps
I'll reach out audio research and see if they sell or have any info about it other than them does anyone else know where I can look or find such a transformer for purchase?
Thanks again for all the help highly appreciated
Hopefully you might get a positive response from AR, I see the schematic is dated 1974, so I doubt they would have transformers, so I see no reason why they cannot supply the transformer specs at least. You would most likely have to get one made to suit.
Yeah hopefully they reach back with some specs at the very least I will let you guys know what they say. Any recommendations where I can get a custom transformer made?
I assume you are based in the USA - so I will let the other members there offer some advice on that. Obviously, any new one will need to fit in the allocated space in the chassis, so it would be wise to let any prospective manufacturer know the available dimensions. That was an EI lamination tranny back then, maybe a new toroidal will fit, they will be easier to find and also will be cheaper.
So In order for me to make sure what the voltage amp ratings needed to get a custom transformer made how can I check for that? Do I wire in a metered high voltage ac power supply to the unit at 290 or 360ac and monitor the amp draw from the unit that way I can get a better read on the actual amp required on the secondary and then have two other supplies doing the 18vac and check draw?
In your 1st post you said the transformer was damaged by lightning, so if AR cannot or will not supply the specs, then what you suggest is feasible especially if you can adjust the AC voltage till you get the required DC volts on the PSU. You can use a current clamp probe to measure the AC current or if you have access to a fully adjustable and metered AC supply that will be ideal.
You will be looking for 500VDC on the HV supply at the caps, and close to 25VDC on the 2 filament supplies at their caps. Adjust the AC supply till you get these DC voltages, then record the AC volts and AC current, at each of the 3 circuits.
You will be looking for 500VDC on the HV supply at the caps, and close to 25VDC on the 2 filament supplies at their caps. Adjust the AC supply till you get these DC voltages, then record the AC volts and AC current, at each of the 3 circuits.
The only problem is I am not sure if it is wise to apply the HV to the tubes without the filaments energized. It is OK to apply the filament supply without the HV. So if you can supply the 2 filament supplies and then energize the HV supply, all should be OK while you measure AC supply volts and current an all 3 secondary windings - if that is possible.
Yeah I'll have to go that last option I've contacted several companies about it still waiting on their response thanks everyone for all the help I will follow up once I have some more info
If contact with AR doesn't give you what you want then another possible contact might be very helpful member cerrem. He winds transformer reproductions from his company Merren Audio.
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Yes I'm still waiting for arcs response before I do anything thank you for all the info and help you guys have been most helpful!
I will add Merren audio to my list of possible contacts to have a transformer made thanks!
I will add Merren audio to my list of possible contacts to have a transformer made thanks!
Check with Gerry from Transcendar to get it rebuilt. He might be able to do an unwind to remake the exact transformer. He’s doing only rewinds and no new units.
I am not sure ARC will have transformer specs that old. a lot of info has been lost over the years and in 74 that would have been paper files. sadly a few years ago they had a woman there that didn't know WTF she was doing and threw out a lot of historical data! that company has been through a LOT on the last 10-15 years.
If no data is available you can have good rewinder do a forensic deconstruction to learn the windings, gauges, and layering of the original unit.
Schott Magnetics in MN made the ARC transformers back then, and may even still.
Maybe Schott has some old stock around, or at least the original specs.