Adcom GFA535..Bad Transformer? - Page 3 - diyAudio
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Old 10th May 2005, 11:07 PM   #21
anatech is offline anatech  Canada
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Hi EchoWars,
OUCH! $215.00 Someone is on drugs at UL!! I did recommend looking at the amps first, since we may be spinning our wheels for nothing. I wish I had written down the spec. It was on a Yamaha service bulleton.

Okay, did a search on the web and I see the thermal fuse ranges between 100C to 130 C. Copy [+UL +transformer +"thermal fuse"] into Google search. Hope that helps or leads you to the proper document.

The fuse is buried in the winding and stuck with shellac or whatever they impregnate xformers with these days. Carefully enlarge the existing space to the thermal fuse. Move the fuse with a screw driver while gently pulling on the wires. Soon you will know what it looks like. The replacement, if the same, will slide down in.

-Chris
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Old 11th May 2005, 03:29 AM   #22
woodman is offline woodman  United States
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Quote:
Originally posted by K-amps
The little 535 is the only true dual mono power amp adcom made ;-)

It had 2 E+I trafos, rest had single toroids.
Actually, the GFA-2 was Adcom's first dual-mono. 100WPC with dual EI xfmrs.

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Old 12th May 2005, 12:35 AM   #23
anatech is offline anatech  Canada
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Hi Woodman,
I've worked on lots of GFA-1's. Never saw a GFA-2. What was it like? Does anyone have a schematic for this beasty?

-Chris
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Old 12th May 2005, 01:25 PM   #24
woodman is offline woodman  United States
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Hi Chris,

The GFA-2 was a 3x rackmount with the same type of handles used on the 2nd gen GFA-555s. The heatsinks were inside the chassis (like the 535). It used 2 complimentary output devices - the package size/shape was unusual, but they were Toshiba BJT devices.

The GFA-2 was my first "High-End" amp - I bought it shortly after I started working at Adcom (for $100). As I recall, it was very smooth sounding but didn't have the detail and musicality of the 555.

The biggest problem with the GFA-2 was that the xfmrs were mounted on the PCB and would crack the board during shipping. If you ever see one, you'll surely find some PCB trace repairs & extra support under the xfmrs.

Schematic? Geez, I don't think I've ever seen one, even at the factory some 10yrs ago.

I might have some pics I could email you.

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Old 13th May 2005, 12:42 AM   #25
anatech is offline anatech  Canada
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Hi James,
The pics would be cool. What section do you work in? I did warranty through Pro Acoustics in Montreal, then direct with Adcom. The company name was Micron Electronics in Mississauga.

-Chris
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Old 22nd May 2005, 03:51 AM   #26
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Kind of a follow-up...the amp finally showed up, and it does appear that the primaries are open. The transformers don't have a case, so they are easy to examine, but...there appears no way to take them apart further to look for a thermal fuse, and I can't see one anyway.

How about removing the transformers and replacing with a single toroid of appropriate size, like 500VA, 70VCT? There's plenty of room, but I've had bad luck with transformer EMI with the last Avel transformer I got from Parts Express, so I do kinda fear this solution. Otherwise, is there a reason that I shouldn't do this?
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Old 22nd May 2005, 04:51 AM   #27
K-amps is offline K-amps  United States
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IMHO, 500VA is overkill and will not fit into that chassis. 200-300VA is enough, This will let you drive 2 ohm loads without issues (unless you use constant tones ). THe larger GFA-545 had a single 360VA Toroid. I guess the E + I in this are 100-150VA each.
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Old 22nd May 2005, 09:02 AM   #28
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Actually, a 500VA would fit (barely), but if it's that much overkill, I can easily get a 330VA with 35V secondaries, this one here: http://www.partsexpress.com/pe/showd...number=122-650

Tie the two center secondary leads together and I have a 35-0-35V transformer.
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Old 22nd May 2005, 02:02 PM   #29
K-amps is offline K-amps  United States
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Echo this is already a 35-0-35... why are we tying centers? Anyway if this fits... though it looks wider than the space i remember, it will work fine. You can actually measure it as you have the amp, I worked on one years ago.

I have used the Avels, they are great for the money, and induce little or no stray fields.
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Old 22nd May 2005, 02:26 PM   #30
anatech is offline anatech  Canada
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Hi EchoWars,
Have a look near the edge where the wires go in. It may be covered with something - I can't remember. Most commonly you will see three thicker enamelled wires that measure short to the AC leads. One will show the expected primary resistance to on AC lead and open to the other. Temporarily short the open and try the amp on a variac.

Th only times I've seen the primaries open on these are when the amps are run cranked for a long time with a fan on the heatsinks. I have never seen an electrical storm open one. An electrical spike will take out the fuse. Not unless the fuse went and someone stuck a larger size (or foil) in.

Have you checked the price for a new xformer from Adcom, or another EI core? My money is with an EI core for a number of reasons.

-Chris
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