Premier 16ls Transformer Replacement

[Jonnydubu]

Hello,
I purchased a 16ls from an estate recently. It worked excellently and sounded great... for about 2 hours then it died on me. Took it in to my tech locally here in California and he traced the issue to a failed power transformer.
"The power transformer is bad. There are shorted turns which causes the line current to go up to about where the fuse blows after some time. That’s why there was a smell as the transformer heated up. I was able to recreate the failure by starting the preamp at low line voltage. I could hear noises coming from the transformer and then it started smelling. There are no shorts downstream."
We haven't had any luck tracking down the transformer specs to order a replacement and was hoping someone here may happen to know it or have the full schematic. The directory only has page 1 of the 3 page schematic.
CJ has given a quote to replace it and the high cost + concerns about shipping it across the country without the original packaging, I'd rather do it here locally.
Thanks.

[admin]

Unfortunately, I don't have more info about the transformer. If there really are no markings on the transformer and it's broken, you really can't do any reliable measurements.

Are you sure there are no markings on the transformer? By the looks of some "internet pictures" of the same unit, there is a tag on the transformer, but the pictures are not high enough resolution where I can read it: https://ginotrifiro.it/portfolio-artico ... mier-16ls/

CJ's policy is that they do all repairs in-house. No exceptions so ordering parts from them is not going to happen. Maybe if you find an official CJ dealer they can try to order the transformer and do the repairs, but I think even that is a long-shot.

[Jonnydubu]

Thanks for the reply. I opened it up and took a photo of the label on the transformer. I've been googling the different bits, no luck yet but will keep looking around. Do these mean anything to you?

IMG_20231005_152835.jpg

[Jonnydubu]

Looks like it's a Magnetek transformer, made in 1999, which checks out. Trying to dig up some old catalogues but pretty light so far.

[admin]

I think this may be the company that owns Magnetek,... or bought it.

You may want to give them a call. https://www.waukeshatransformers.com/co ... /magnetek/

[Jonnydubu]

I'll give them a call tomorrow when's they're open. I also found Triad Magnetics which, according to their history, were owned by Magnetek at the time of manufacture. I gave them a call and they've passed my info on to the relevant department, waiting to hear back from them.

https://www.triadmagnetics.com/historical-archive/

Unfortunately the catalog archive on that page is broken.

[Jonnydubu]

Some progress, I spoke with Triad Magnetics and they confirmed that they do have the Magnetek records. The very kind rep dug up the old cutsheets for the standard 783P10 transformer they had at the time and the special order 783P12 that they made for Conrad Johnson. The cutsheets appear to only be sheet 3/3 for each but I'm hoping it's enough information to determine an adequate replacement. I'm a mechanical engineer so my electrical knowledge is limited, time to dig up the old textbooks and see if I can figure it out.

2052_001.pdf

783P10.png

783P12.png

[admin]

That's really interesting. Good detective work. I guess the question is whether you can find something compatible. I presume Triad Magnetics does not offer a modern substitute?

[Jonnydubu]

Just wanted to update this thread with my progress. I have not heard back from Triad regarding a modern equivalent offering or additional information on the transformer specs so I decided to go another direction. I downloaded and learned how to use LTSpice, a circuit modeler and simulator. The one page of the 16LS schematics that we do have on the forum is the power supply so I modeled the exact same circuit in LTSpice (all of the resistors, capacitors, etc are called out, just not the transformer) and ran the circuit for a range of input voltages. I found that the voltage supplied to the tubes leveled out at 450V input, supplying ~60V to the plates. Any higher, the voltage doesn't increase due to the zener diodes. The data sheets of 6922's show a plate supply voltage of 90V for class A amplification, so we're not far off. The heaters of the tubes need 6.3V and there is a 6.2V zener diode on the heater circuit so the LV output of the transformer should be 6.3V. So I think a 450V / 6.3V plate - filament transformer, which Hammond makes.

The main concern is that I know just enough about circuits to get myself in trouble here, if I'm wrong I may blow the pre-amp. So I'm going to attempt to re-wind the transformer by hand first and count the turns while I'm at it which should hopefully confirm what I'm finding or I'll realize I've screwed something up in my LTSpice circuit.

Prem16LTSpice.png

[admin]

Let us know how the hand winding goes. I've never done that before. It certainly can be done as many high end transformers are hand wound.

[roberto]

I think you are right. It is good to be safer in about 30% more of the needs regarding Amps consumption. The voltages are OK. I how you finally can have back your preamp. If the power transformer can supply more current than the needed in the circuit, you are totally safe.

Happy listening!

[Jonnydubu]

Doing a bit more digging around, I noticed that the 783P10 transformer was also noted as '9484'

783P10-9484.png

Looking through the available schematics, I found that Conrad Johnson has used the same transformer for a few different components, including the Premier 10, Premier 17LS, and Evolution 20.

Prem10.png

Looking at the EV-20 schematic in the forum archive, I see someone marked the secondary voltage of the transformer as 235V, which would make sense if it's positive voltage +/-235V

EV20.png

I did notice that the Premier 10 appears to use a stock Triad transformer, which typically show the details of the transformer on the side of the case. If someone has a Premier 10 and can find a way to get a picture of the side with the transformer info, it would be greatly appreciated.

Prem10_Xformer.png

TriadXformer.png

[admin]

Good investigation work. I'm not surprised that the same transformer is being used in multiple units. If you find something you like, you stick with it. Also makes stocking extra components easier as your total parts list is smaller.