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EL84 Amp - Baby Huey
EL84 Amp - Baby Huey
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Old 8th December 2011, 01:05 PM   #1151
Brouilly is offline Brouilly  United Kingdom
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These values do not change when adjusting the pot though. I have checked thee ccs and it is wired correctly as far as I can tell. I left out the ropt and copt.

Power for ccs is -12V, output of ccs is 0.25V, anode1 314V, anode2 74V.
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Old 8th December 2011, 01:05 PM   #1152
Bas Horneman is offline Bas Horneman  Netherlands
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And did you check and double check the pinout?

1 and 8 (cathodes) to CCS

3 and 6 (anodes)

2 and 7 (grids)
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Old 8th December 2011, 01:08 PM   #1153
Brouilly is offline Brouilly  United Kingdom
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I did yes. I am searching and searching for a wiring error to justify all this, but I am yet to find one.

Is +0.25V correct for the output of the ccs?
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Old 8th December 2011, 01:35 PM   #1154
Bas Horneman is offline Bas Horneman  Netherlands
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Quote:
Is +0.25V correct for the output of the ccs?
I'll have to measure this evening. (Unfortunately I don't know what it should be)
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Old 8th December 2011, 01:40 PM   #1155
Brouilly is offline Brouilly  United Kingdom
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I mearsured my other one when I was at home last night and I recall it being something similar. Im going to put a 1R resistor in series and see what current it's drawing and report back.

Thank you
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Old 8th December 2011, 01:49 PM   #1156
Brouilly is offline Brouilly  United Kingdom
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About 1mA drawn from the ccs.
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Old 8th December 2011, 02:22 PM   #1157
Brouilly is offline Brouilly  United Kingdom
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It seems very strange.

I measured the voltage of the ecc83 anodes at turn on

Anode 1 - Starts at about 500V and ends up at 314V when the el84s start drawing current.

Anode 2 - mirrors that but ends up at 73V when the el84s start to draw current.

If I tap any rail with DC on the '314V' half the LED bias blinks, but when I tap any rail on the other side the LED array doesnt change. It still is drawing about 90ma which is obviously too high.

This is the first time ive delt with a bias techneque like this, can someone suggest some actions to lower the current through the array and maybe suggest some fault finding steps?

Many thanks
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Old 8th December 2011, 03:54 PM   #1158
Brouilly is offline Brouilly  United Kingdom
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I really can't understand why im getting such different readings.

The 220K plate resistor on the lower half of the driver is dropping nearly 150V, where the other plate resistor is dropping 5V.

I have swapped everything over that I can, check my wiring again. Checked the ccs again. Anyone got any bright ideas, I am all out.

Cheers
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Old 8th December 2011, 03:55 PM   #1159
Soonerorlater is offline Soonerorlater  United Kingdom
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EL84 Amp - Baby Huey
If this was my amp I would like to know that all is well apart from the ECC803s ccs and the RLD bias scheme for the EL84's. I had similar problems with the ccs's in the basic BH version. I simplified the amp by replacing the preamp ccs with a 675R resistor ( IIRC ) and biased the EL84's separately with 270R resistors. Happily this gave me a working amp with all the proper voltage values. I then reintroduced the ccs's one by one solving any local faults as I went along.

HTH Bill
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Last edited by Soonerorlater; 8th December 2011 at 04:12 PM. Reason: spelling
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Old 8th December 2011, 04:01 PM   #1160
TheGimp is online now TheGimp  United States
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I recommend removing both output tubes and resolve any LTP issues before going back to the output tubes.
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