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EL84 Amp - Baby Huey
EL84 Amp - Baby Huey
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Old 7th December 2011, 01:52 PM   #1121
Brouilly is offline Brouilly  United Kingdom
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Just let the smoke out of a 150R 2W screen resistor, so that would mean the bias is drawing too much current?

Little bit worried about doing any damage to the output transformers, will they be ok as long as ive got the dummy load connected?
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Last edited by Brouilly; 7th December 2011 at 01:57 PM.
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Old 7th December 2011, 01:56 PM   #1122
TheGimp is offline TheGimp  United States
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Yes, sqrt (2W/150R) = 115mA screen current!

Short term this won't damage your opt, but if left running it would.
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Old 7th December 2011, 02:13 PM   #1123
Brouilly is offline Brouilly  United Kingdom
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I replaced it, and powered up again and it blew a second time. The LED array lit up straight away so there is obviously an issue. The array itself is fine, so what might be the causes of the sudden inrush of current?
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Old 7th December 2011, 02:26 PM   #1124
TheGimp is offline TheGimp  United States
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I"d check the grid resistor connections and and coupling caps to the output stage. Something has to be biasing it wrong to pull that much current. Also double check your OPT wiring.

If the LEDs light up, you know the cathode connection is there. You might measure the cathode voltage on power up to see if it reaches the expected bias voltage.
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Old 7th December 2011, 02:38 PM   #1125
Bas Horneman is offline Bas Horneman  Netherlands
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Quote:
should 0v at ecc803 be grounded
The "bottom" of the CCS's of the driver/splitting stage should be wired to their respective "CCS power" connection. (Which are actually -12 to -13V or something like that).

The + part of the bias supply is connected to "ground". I.e. you should connect your CCS to a negative bias voltage.
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Last edited by Bas Horneman; 7th December 2011 at 02:40 PM.
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Old 7th December 2011, 02:50 PM   #1126
Brouilly is offline Brouilly  United Kingdom
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Thanks, I was initially just connecting the '0v at ecc803' to the '0v at ecc803' without grounding it also. At CCS power I was reading -13V but only reading about -0.5v at the cathode of the ecc803.

Ive replaced the resistor and powered up, and this time the dropping resistor in the power supply blew on the same channel. In rush of current again as the LEDs all lit up.

The wiring to the OPT is fine as is the grid connection and coupling cap. There's got to be something going on...
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Old 7th December 2011, 02:54 PM   #1127
Bas Horneman is offline Bas Horneman  Netherlands
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Quote:
and this time the dropping resistor in the power supply blew on the same channel
Wow. Do you have a fuse in your amp somewhere? Does that not blow first?
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Old 7th December 2011, 02:55 PM   #1128
Brouilly is offline Brouilly  United Kingdom
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Quote:
Originally Posted by Bas Horneman View Post
Wow. Do you have a fuse in your amp somewhere? Does that not blow first?
1A time lag fuse on one half of the mains
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Old 7th December 2011, 03:10 PM   #1129
GloBug is offline GloBug  Canada
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Should be on the hot side of the mains?
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Old 7th December 2011, 03:15 PM   #1130
Bas Horneman is offline Bas Horneman  Netherlands
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Should be on the hot side of the mains?
I don't think it matters. Since the current is everywhere . Please correct me if I'm wrong.
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