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  #11  
Old 29th July 2013, 06:41 AM
robaustralia robaustralia is offline
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Location: Noosa QLD Australia
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Default Re: KEL84 rebuild low HT voltages

FOUND IT!

The minus post on C3 was underneath the C3 so I couldn't see it had lifted. I linked the other side of PCB under C3 to earth.

Hopefully the voltages are within tolerance now.

V2 pin 1 = 219V
v2 pin 2 = 0v
v2 pin 3 = 90v
v2 heater = 6.8v
V2 pin 6 = 68v
v2 pin 7 = 2.08v
v2 pin 8 = 77v
v2 pin 9 = 67v

v4 pin 2 = -.02
v4 pin 3 = 10.8
v4 pin 7 = 322v
v4 pin 9 = 325v

choke 1 = 331v
choke 2 = 326v
R38 = 298v

Thanks again.

Cheers,
Rob
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Kel84 Amplifier
Transcendent Sound OTL 'Son of Beast' Amplifier
TD160 with Ortophon 2M Blue
Australian VAF DCX Gen IV 'time aligned' tower speakers
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  #12  
Old 29th July 2013, 08:38 AM
bob orbell bob orbell is offline
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Default Re: KEL84 rebuild low HT voltages

Hi Rob, been watching this post, I agree with John that the problem is with the HT rectification (the new diodes), a test you can do is set MM to ohms and check each diode in turn with the power OFF, put red lead on one end of diode, black on the other end, note reading, now reverse red and black leads, one way should read high and the other infinity and all four be much the same, also the readings should be uniform for all diodes, ie the same direction. Hope the is of help to you. BOB
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  #13  
Old 29th July 2013, 08:40 AM
bob orbell bob orbell is offline
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Default Re: KEL84 rebuild low HT voltages

Oh well, ignor my post Rob, well done. BOB
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  #14  
Old 29th July 2013, 09:40 AM
John Caswell John Caswell is offline
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Default Re: KEL84 rebuild low HT voltages

Hi Rob et al,
Puzzled, as if the earth of C3 was lifted all that would happen is that you would get hum do you mean C1 ? the one nearest the HT rectifier diodes.
Yes the voltages look fine, the ECF80 voltages are generally all over the shop, but the main give away is the cathode of the pentode pin7 which should read 2V as yours does so fine, and the voltages on the EL84 are well within spec.
Well done!

John

Last edited by John Caswell; 29th July 2013 at 09:44 AM. Reason: additional comments
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  #15  
Old 30th July 2013, 01:11 AM
robaustralia robaustralia is offline
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Default Re: KEL84 rebuild low HT voltages

Hi John.

Yes, it was c3 across R38.

I also noticed a couple of joints on the diodes under the pcb looked a bit dirty so I sucked all the solder out and soldered them again with my Goot soldering iron.

The iron I used originally was very hot and I have the feeling that the solder may have started burning before the legs of the diodes were hot enough.

The Goot runs cooler so the solder melts at the same time as the component without burning... another lesson learned I think.

I am about to compare my KEL84 with the Output Transformerless 'Son of Beast' I just built. It used 8 EL509s valves and six 12ax7's and is rated at 15 watts. The sound is absolutely exquisite on quality recordings, but merciless on mediocrity. The bass is tight and awsome. It also generates much less heat than the KEL84.

It's interesting that some CD's that sounded magic on the KEL84 sounded muddy on the S.O.B and CD's that sounded boring on the KEL84 turned into lifelike performances on the S.O.B.

I have just turned 71 and have been obsessed trying to find that elusive valve sound I experienced when I was about 14. I have heard dozens of quality amplifiers at Hi Fi stores but nothing made me happy until I built my KEL84 and now my S.O.B. and matched them to a brilliant pair of Aussie speakers.

Thanks for everybody's help!

Cheers,
Rob
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Kel84 Amplifier
Transcendent Sound OTL 'Son of Beast' Amplifier
TD160 with Ortophon 2M Blue
Australian VAF DCX Gen IV 'time aligned' tower speakers
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  #16  
Old 9th August 2013, 11:38 AM
Richard Richard is offline
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Default Re: KEL84 rebuild low HT voltages

Sorry for late post, been away, well done Rob and all! Great to hear you're enjoying yourself
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