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sharing eBay find: OPT from Kustom Double Cross
sharing eBay find: OPT from Kustom Double Cross
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Old 1st April 2018, 06:55 PM   #21
Printer2 is offline Printer2  Canada
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I couldn't pass these up. Need an output transformer though. Or maybe just SS.

Click the image to open in full size.

770 VA at 50 Hz, can't remember what it came out of. The caps from a speed drive.
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Old 14th April 2018, 04:14 PM   #22
multi-volti is offline multi-volti  United States
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As George noted with a different Basler audio transformer dresser in power transformer clothes, this one is not terribly impressive in the inductance dept.

1 V, 80 Hz primary (blue-brown) L = 4.835 H, 53.1 ohms DC. At 20 Hz, 8.945 H.

With blk-grn 8 ohm secondary shorted for leakage inductance measurement, it’s 8.5-8.6 mH at 80 Hz.

Black-green 8 ohm secondary L=74.6 mH? at 1 V, 80 Hz (Can’t read Igor’s handwriting [not my friend’s real name, but he has the equipment access). Leakage inductance at 1 V, 80 Hz with blue-brown secondary shorted = 56.8 uH.

At 80 Hz, full primary Z was 2.43k, 77.5 degrees. Sweep looking for presumed SRF at 0 degree phase angle, found 5 kHz Z = 151.5 k/10 degrees and 6 kHz 138.9k/-27 degrees. So wild guess bandwidth is in that range...or should I have asked for 45 degree point (worse). Does have magnificent BW if it were a power transformer.

I don’t what the Kustom Double Cross sounded like, but being discontinued is not a good sign.

Ya get what ya pay for...some days.
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Old 14th April 2018, 04:36 PM   #23
multi-volti is offline multi-volti  United States
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Quote:
Originally Posted by Tubelab_com View Post
I bought a batch of OPT's from an Ebay seller nearly 20 years ago. <snip>
That eBay listing does have the Schumacher drawing as one if the listing photos...perhaps you already saw that. Seller says why buy expensive teplacement iron when you can have...they don’t look like a huge bargain, but at least the core is more substantial on these.

I’m figuring out that for ~ 40 W & under guitar amps the ClassicTone output transformer options are quite reasonable, and Edcor is too, with options for
home audio grade as well.

Making me think the large M6 laminations I got around 1994(?) [yeah, a but of a procrastinator] are still best left for a project I can’t afford off the shelf parts for..
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Old 15th April 2018, 01:13 PM   #24
Tubelab_com is offline Tubelab_com  United States
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Quote:
Schumacher drawing as one if the listing photos
I didn't see it until you posted this, then I found it. My transformers had a similar drawing with two exceptions. Mine are 6600 ohm to 0-4-8-16, and the frequency response was stated from 80 Hz to 5 KHz. They are still in the same shipping cartons like those shown in this Ebay lot. Mine were addressed to ADA, which folded due to a fire before these transformers were delivered. Maybe this batch were slated for a bass guitar amp.

Quote:
they donít look like a huge bargain
I wouldn't pay $70 each, but I got mine when they were in huge oversupply for $16 each in 200 qty. The single unit Ebay price was $20 to $25 back then.

I have built amps with these running off a 600 volt supply making 125 watts. They hold up fine. I have had two failures in about 20 years of amp building, both my fault.

I was cranking about 150 watts through one on a 750 volt supply made with a 600 volt 500 VA industrial control transformer (lots of available current) when my load resistor blew open. The OPT burst into flames, and tripped the 15 amp bench breaker. It was pretty well burnt, so I took it apart.

More recently I was cranking about 160 watts through one when a plate to plate feedback resistor arced through its insulation from plate to ground. The DC arc was extinguished when I hit the bench kill switch, leaving the OPT severely magnetized (650 V 1.7 Amp HP power supply). I have successfully degaussed it and it lives on. I was pulling 125 watts through it last night at 1.4% distortion from a pair of mid sized sweep tubes.
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Old 15th April 2018, 06:44 PM   #25
multi-volti is offline multi-volti  United States
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The HP supply is really shining through this story.

...and the FET & FER (flame-emitting transformer & -resistor.
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Old 16th April 2018, 02:22 PM   #26
Tubelab_com is offline Tubelab_com  United States
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Quote:
The HP supply is really shining through this story.
That thing is responsible for more exploding parts than anything else I have used except for maybe a direct connection to the line voltage or a car battery. It is an old style 60 Hz "switcher." It has a triac controller on the input side of a 40 pound step up transformer. The output side has a rectifier and 1000 uF of filter caps. There is a LOT of stored energy when those caps are charged to 650 volts. The control loop is very slow to react (about 1 Hz) so it throttles back the power after there is nothing left to protect.

I have a more modern switcher to replace it, but I haven't finished fixing it yet. It was a "parts only" unit that I got cheap on Ebay.
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Old 16th April 2018, 03:56 PM   #27
multi-volti is offline multi-volti  United States
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I think I should stick to smaller projects...

A Yellowfin tuna steak burst into flames under a broiler in the kitchen last night. The resulting networked smoke detector alarms, pets freaking out and all the doors & windows open for a couple hours might be preferable to incinerated electronic fragrance. If my wife does it, it’s because she was saving me the trouble of grilling outdoors in freezing rain.

If have an amp inferno, it’s not the result of me doing her a time-saving favor...
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Old 16th April 2018, 04:14 PM   #28
multi-volti is offline multi-volti  United States
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I made an avatar years ago from an online episode of The PJ’s...a Claymation Eddie Murphy series where he was the voice of Thurgood, the superintendent of a hi-rise housing project.

He was battling an ornery nuclear-powered boiler in the basement, and it looked like what you just described. It was hilarious...an action movie scene in Claymation... I referred to it as ‘Thurgood experiences difficulty with his nuclear-powered amplifier’. Don’t know where I left it..,
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