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Old 4th May 2008, 05:08 AM   #1
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Unhappy Help with dead Jadis Defy7 Amp

I have a Jadis Defy 7 tube amp that today will not power on. WHen I turn the on switch, the front panel light does not turn on, the tube filaments do not light up. Any help or ideas appreciated. I am relatively handy with electronics, have the requisite meters, etc... Where should I start to debug?

THX
Warren
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Old 4th May 2008, 05:39 AM   #2
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fuse?
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Old 4th May 2008, 06:53 AM   #3
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uh, let me be more specific. First, fuse is OK. Next, check continuity of the power switch: OK. Just in case, checked each individual tube for filament shorts - OK. Checked components for bulging caps, burnt resistors - none. hmmmm
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Old 4th May 2008, 07:33 AM   #4
korey is offline korey  United States
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Check power transformer primary for an open winding??? Just another guess, is it plugged into a power strip with its switched turned off? lol, I've done that before!
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Old 4th May 2008, 04:04 PM   #5
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power transformer is fine. I read somewhere that Jadis amp have some relatively common power supply failures due to some cheap parts. Anyone know what theses are? THX to all
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Old 4th May 2008, 07:40 PM   #6
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Does anyone know how the filaments are typically wired on tube amps?

Are they wired in series or parallel? Does the AC typically come off a winding from the transformer? is it AC or DC?

THere doesnt seem to be any voltage on the filaments, trying to figure out why.

THX
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Old 4th May 2008, 08:47 PM   #7
pchw is online now pchw  United States
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AC, DC, regulated DC, parallel, series are all possible. Without a schematic, it is had to tell. Are you able to get one? If you follow the trace, you probably can find out which
is the case. Make sure you disconnect the power before dong the trace.

Anyhow, I will first try to locate the secondary of the filament.
Make sure you get AC there, it s going to be 6.3VAC and above, depending on
AC, DC, or regulated DC heater supply. I suspect a regulated DC, assuming it is genuine Jardis Defy7.
If it is regulated filament supply, measure the voltage before and after the regulator. Based on your description, there is probably no voltage after the regulator. If you do measure voltage before the regulator, then you know what is toasted .......
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Old 4th May 2008, 09:44 PM   #8
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Unfortunately I do not have the schematic. More precisely I have found a web link to one by Paoletti that purports to be a schematic; it does not say what version of the Defy 7 it is.

I pulled all the tubes out. With them out, when the unit turns on, the panel light turn on. The panel light is powered by the filament voltage. The resistance of the 2 wires powering the filaments (with the unit off of course) is 47 kohms with no tubes. That seems high if that is directly connected to the windings. (If true, does that mean something broke with the transformer?).

On the Paoletti schematic, there is a 12V DC bridge and filtering and a voltage regulator to supply 12VDC to something that is not identified. However, I cannot find anything on the circuit board that has any of those components. All I see are the 2 wires powering the filaments to a hole on the chassis that looks like it hooks to the transformer. Here's where a Jadis expert could help - do they bury the rectifiers and voltage regulators on the bottom of the transformer? Or are the filaments powerered by AC?

Its a big pain to take the transformer off so I would like to know before doing so.

THX.
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Old 4th May 2008, 10:10 PM   #9
korey is offline korey  United States
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If you say you get power without the tubes, then it sounds like one of your tube filaments is shorted. Try plugging in each tube at a time and see what happens. Of coarse we can't do much without the schematic! Most tube amps require 6.3 volts to the filaments if the tube numbers start with a 6. I.E., 6L6GC, 6CA7,etc.
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Old 4th May 2008, 10:18 PM   #10
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I checked each tube and the filaments are fine. (Checked them in a tube tester, each tube draws the correct amount of current in the heater.) Without tubes, the heater/filament supply reads 5.2VDC on the amp. With a tube, it drops to zero. it doesnt seem to matter which tube it is. The tube complement are 6550's and 12AX7, 12AU7.
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