Standel Transformer rewind

Jerry Roller · From: Van Buren, Arkansas USA

Can someone tell me a good place to have a transformer repaired? The primary winding is open.
Or, does anyone have a power transformer for a Standel Custom 15? It is approx. 1968 solid state. The transformer has PT620 stamped on it.
Thanks,
Jerry
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Bruce Derr · From: Lee, New Hampshire, USA

Are there any other numbers on it? If there's a 6- or 7-digit number it could be the EIA manufacturer code and date code. The mfr code could help ID the transformer.

If you're feeling lucky... Once in a while a primary blows open where the winding attaches to one of the transformer's terminals or lead wires. When that happens there is a chance that it can be reconnected. A delicate soldering job but worth trying for a rare transformer that's otherwise shot.

Michael Butler · From: California, USA

a good, but, expensive place for rewindings is mercury magnetics. call them just to check, but, you may want to check ebay to see if one is available.

also, i believe that you can check to see what the primary and secondaries are and then see if there is one compatible. some places to check are heybour, triode, mercury, and hammond as they are some of the manufacturers.

good luck.

play music!
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Michael Brebes · From: Northridge CA

Later than '64 because they were still making the transistor tube hybrid amps in '64.
Looking at the available schematics, it looks like most of their amps have +/- 32VDC as their source voltage. This means you will need a power transformer that outputs roughly 60VAC with a center tap. As for current, what is the fuse value for that amp?
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Instrument/amp/ pickup repair
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Dickerson MOTS/Dobro D32 Hawaiian/
Goldtone Paul Beard Reso

Mesa Boogie Studio Pre/Hafler 3000
RP1/MPX100

Jerry Roller · From: Van Buren, Arkansas USA

Michael, it has two internal fuses that appear to be 3 amp. It has an external fuse with 1 amp marking on the chassis but it appears to have a 6 amp fuse in it. None of the fuses blew when the amp quit. There was a loud hum then nothing. The back of the chassis shows it to be a 70 watt amp. Is the transformer you believe it to need readily available anywhere? I took the transformer out of the amp and checked all the connections to the coils get voltage out of the secondary coil but none out of the primary. I also get no resistance reading from the primary. I chased the primary leads down to each end of the winding and scraped the insulation and got no resistance reading thru the coil.
Thanks,
Jerry

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Jerry Roller · From: Van Buren, Arkansas USA

This is a great sounding amp. I really must get it fixed. Can someone help me? I have been talking with Tim Maag in Los Angeles and he has tried to guide me but we are to the point that I have to get another power transformer or have this one repaired.
Thanks for any help,
Jerry
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Bob Carlucci · From: Candor, New York, USA

Jerry, Mercury Magnetics is the place to call... bob
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Greg Cutshaw · From: Corry, PA, USA

I've taken power transformers, solenoids and chokes to my local motor repair shop and they come back just fine. After I tell them them how "specially" wound they are they just laugh and say they can match the winding technique, wire size and shellac. It takes a few days as they have to bake the windings and sometimes they have to make a form to shape the windings on. These motor repair shops repair things a lot more complex than a power transformer. Most are well aware of bifilar and trifilar winding techniques and the need to have the thing come out with the same impedance.

Jerry Roller · From: Van Buren, Arkansas USA

Greg, how can they know what the output should be if the transformer is not working? I don't know if there is such a shop in my area but I will check to see. Could you possibly email me contact info for the shop you use? My email is rollermusic@cox.net
Thanks,
Jerry
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Jerry Roller · From: Van Buren, Arkansas USA

Bob, I have a call in to Mercury and someone is to call me back. Very impressive website. Thanks for the information.
Jerry
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Greg Cutshaw · From: Corry, PA, USA

Jerry, there are motor rewind shops in every major city and even some smaller ones. All they need to do is match the wire sizes, winding method, number of turns and you're good to go. Mercury can certainly do this job as well.

Possibly in your area:

http://www.amoelectricmotorservice.com/

Quote:

" Already have a motor? We offer a wide range of standard services such as rewinding and part replacement", "At AMO Electric Motor Service, no job is too small and no task is too daunting"

Also:

Delta Electric Motors & R
1501 S 28th St, Van Buren, AR 72956
(479) 474-7019

"Rewinding Repairing Rebuilding New Used Rebuilt Motors "

Michael Brebes · From: Northridge CA

Here is a link to a possible replacement from Hammond:
http://www.hammondmfg.com/165.htm
I would suspect the 165P60 would be the correct one. Check the physical size of your transformer against the dimensions on the web page.

And here is the link to the service manual with schematics for the C15R:
http://standelamps.com/support/schematics/documents/1968/reverb_amplifiers_serv.pdf
_________________
Michael Brebes
Instrument/amp/ pickup repair
MSA D10 Classic/Rickenbacher B6/
Dickerson MOTS/Dobro D32 Hawaiian/
Goldtone Paul Beard Reso

Mesa Boogie Studio Pre/Hafler 3000
RP1/MPX100

Jerry Roller · From: Van Buren, Arkansas USA

Michael, this transformer has 8 leads. I can understand the two to power the primary and two and a tap from the secondary but how about the other three leads? One is a ground which I don't know where it would come from and that leaves two more which are connected to much smaller wires than the coil wires I can see. The schematic only shows the two in and 3 out. The Hammond transformer appears to have 5 leads and not 8. Any ideas?
Jerry
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Bruce Derr · From: Lee, New Hampshire, USA

Hmm, a couple of things occur to me... First of all, the 70 watts shown on the amp's panel is the power consumption, or the power that the amp draws from the electrical service. The amp's power output is probably much less, perhaps half of that. Also, for a power supply output of +/- 32 VDC using the circuit in the service manual that Michael linked, the power transformer secondary would need to be more like 44 VCT. This would provide 62 volts peak. (Transformer voltages are specified in RMS volts.) The big filter caps hold the AC peak value constant as DC; that's their job. So that's +/- 31 VDC. Subtract a couple of volts from each side for the drop across the diodes. Then maybe add a few volts to allow for the fact that the transformer voltage rating is typically specified at full current output. Voltage would actually be a little higher when it is supplying less current, as would be the case when the amp is idling. (The voltages shown in the schematic were likely taken with the amp idling.) That would get you in the ballpark of +/- 32 VDC. Line voltages have crept up slightly over the years from the 117 VAC expected by this amp, and that could add another volt or two to the DC supply output. Current rating of the transformer is probably around 1.5 to 2 A. Since 44 VCT transformers are not common (48 VCT is pretty common but that might be a little too much), it's probably best to get the old one rewound as others have suggested.

Bruce Derr · From: Lee, New Hampshire, USA

The extra leads could be primary taps. Could be a 120/240 primary. The back panel says 120/240 with 240 crossed out, so they may have used the same transformer for the export market.

Carl Mesrobian · From: Salem, Massachusetts, USA

Jerry, you might want to check with Classic Tone http://www.classictone.net/

EDIT - Jerry you might want to consider dual primary if you intend to sell the amp "across the pond" Smile

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Jerry Roller · From: Van Buren, Arkansas USA

Carl, I don't want to sell the amp. It is my favorite go to amp. I gotta' get it fixed. I got a call back from Mercury and a rewind was quoted at $400.00 + shipping too and back. I can't afford that route. They can dismantle this transformer and completely build a duplicate from scratch cheaper than they can rewind this one. I need to find a replacement transformer. Please keep ideas coming, I need help.
Thanks,
Jerry
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Bruce Derr · From: Lee, New Hampshire, USA

I wonder if the current Standel company would have any suggestions.

Edit: All of their current offerings use tubes, so maybe not.

Jerry Roller · From: Van Buren, Arkansas USA

Bruce, I did call Danny McKinney at Standel. He referred me to Tim Maag who has been very gracious in trying to guide me to the point I am at presently. You do jolt my mind to recall Mr McKinney told me if I don't get anywhere to call him back. I don't think he would have a transformer but I need to call him and tell him the problem is the tranformer. It is strange that Mr McKinney told me in his over 40 year involvement with Standel he has never seen one of these transformers go bad. Am I not the lucky one? If I were younger I would order a new Standel amp.
Jerry
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Bruce Derr · From: Lee, New Hampshire, USA

Jerry, it's likely that another component failed first, causing excessive current demand on the power supply, which caused the transformer to blow. I'm basing that on your description of "a loud hum, then nothing." A sudden component failure (shorted filter cap or output transistor maybe) caused the loud hum, and then the transformer opened from excessive current. Had the fuse on the back panel been a correct 1A unit instead of a 6A, it may have blown first and protected the transformer from damage.

I hope I'm wrong but I suspect you've got more to replace than just the power transformer.

Hammond has a 42 VCT 2A transformer, #166L42, that might be a suitable substitute for yours.
http://www.newark.com/hammond/166l42/bobbin-transformer/dp/10M5334

Please ask Danny or Tim to check this info - I may be all wet.

The 1968 schematic has different transformer numbers and primary fuse rating, so your amp's circuit may be different, perhaps an earlier version. Hopefully it's close enough to use as a repair guide.

I assume you made careful note of where your transformer leads were connected. That would help when figuring out the purpose of each lead.

Another thought: Check your speaker with an ohmmeter. Hopefully it didn't blow. That can happen when a direct-coupled solid-state amp's output stage shorts and places full rail voltage across your voice coil. (I'm saying that from personal experience; when my Webb blew it took a nice D-130F with it.)

Henry Brooks · From: Los Gatos, California, USA

This maybe a dumb question, but are you sure that transformer is the power transformer? The colors on the wires in the photo match the inter-stage transformer secondary windings on the schematic.
Henry

Bruce Derr · From: Lee, New Hampshire, USA

I wondered about that but then noticed that the interstage transformer numbers are OTxxx vs PTxxx for the power transformers. Still it's definitely worth checking out to make sure. I hadn't noticed the wire colors matching.

Jerry, is sending the amp to Tim an option? Probably expensive but it sounds like he's the right guy.

Looks like a sweet amp. I sure hope it gets repaired and back in the game soon.

Bruce Derr · From: Lee, New Hampshire, USA

By the way, if the S2773 output transistors turn out to be gone, here's a thread that mentions some suitable replacements:
http://music-electronics-forum.com/t12117/

It says that Standel part number S2773 is a SDT9203.

In the NTE line (which are relatively expensive aftermarket replacements marketed to repair shops) the SDT9203 cross-references to a NTE284.

The thread suggests that the MJ15003 is a cheaper and readily available equivalent.

Original SDT9203 transistors may still be available though.

I can't vouch for any of the info in the thread but it's the only search hit I found.

I just wanted to mention all this to capture the information. I'm not suggesting or jumping to conclusions about the transistors in your amp. Hopefully they are still good.

Jerry Roller · From: Van Buren, Arkansas USA

Bruce, I had help checking the transistors and they are good.
Thanks for this information,
Jerry
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Bruce Derr · From: Lee, New Hampshire, USA

That's a relief. Speaker'll be ok too, then.

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