EL84 Amp - Baby Huey - Page 116

CSlee · 8th December 2011, 12:05 PM

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.

Bas Horneman · 8th December 2011, 12:05 PM

And did you check and double check the pinout?

1 and 8 (cathodes) to CCS

3 and 6 (anodes)

2 and 7 (grids)

CSlee · 8th December 2011, 12:08 PM

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?

Bas Horneman · 8th December 2011, 12:35 PM

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)

CSlee · 8th December 2011, 12:40 PM

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

CSlee · 8th December 2011, 12:49 PM

About 1mA drawn from the ccs.

CSlee · 01:47 PM

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

CSlee · 8th December 2011, 02:54 PM

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

Soonerorlater · 03:12 PM

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

TheGimp · 8th December 2011, 03:01 PM

I recommend removing both output tubes and resolve any LTP issues before going back to the output tubes.

8th December 2011, 12:05 PM	#1151
CSlee Clueless diyAudio Member Join Date: Mar 2009 Location: London	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. __________________ Broke solderer with delusions of grandeur

8th December 2011, 12:05 PM	#1152
Bas Horneman diyAudio Moderator Emeritus Join Date: Apr 2002 Location: The Netherlands Blog Entries: 18	And did you check and double check the pinout? 1 and 8 (cathodes) to CCS 3 and 6 (anodes) 2 and 7 (grids) __________________ Boatanchor amps forum My "adventures" in audio

8th December 2011, 12:08 PM	#1153
CSlee Clueless diyAudio Member Join Date: Mar 2009 Location: London	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? __________________ Broke solderer with delusions of grandeur

8th December 2011, 12:40 PM	#1155
CSlee Clueless diyAudio Member Join Date: Mar 2009 Location: London	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 __________________ Broke solderer with delusions of grandeur

8th December 2011, 12:49 PM	#1156
CSlee Clueless diyAudio Member Join Date: Mar 2009 Location: London	About 1mA drawn from the ccs. __________________ Broke solderer with delusions of grandeur


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8th December 2011, 01:22 PM	#1157
CSlee Clueless diyAudio Member Join Date: Mar 2009 Location: London	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 __________________ Broke solderer with delusions of grandeur Last edited by CSlee; 8th December 2011 at 01:47 PM.

8th December 2011, 02:54 PM	#1158
CSlee Clueless diyAudio Member Join Date: Mar 2009 Location: London	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 __________________ Broke solderer with delusions of grandeur

8th December 2011, 02:55 PM	#1159
Soonerorlater diyAudio Member Join Date: Jul 2008 Location: Belfast	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 __________________ When white moths were on the wing, And moth-like stars were flickering out, Last edited by Soonerorlater; 8th December 2011 at 03:12 PM. Reason: spelling

8th December 2011, 03:01 PM	#1160
TheGimp diyAudio Member Join Date: Aug 2009 Location: Johnson City, TN	I recommend removing both output tubes and resolve any LTP issues before going back to the output tubes.

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