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Old 13th March 2003, 06:09 PM   #51
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Default An unusal amp...

Well,

I understand that the volume pot is still in it's original position, as it is too difficult to remove from the PCB - therefore hum pickup must be around V1.

Have you tried leaving that pot at maximum, and connecting another pot for controlling volume at the input to V1 - that would mean that the feedback was always at maximum and help indentify if the hum pick-up was occuring in the input leads/connectors.
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Old 14th March 2003, 07:51 PM   #52
Foes is offline Foes  Belgium
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Dear Jorge,

I have mesured voltage on different point of the circuit :
R3.R2=0.2V
V1(2)=1.7V
V1(7)=86V
V1(8)=89V
V2(2,8)=9.7V
V3,4(1,6)=289V
V3,4(8)=14.1V
V3,4(2,9)=290V
Bad luck, when mesuring V2(4)and V2(6), it seems i have burned something. Hopefuly, The amp is under waranty. I will try to make warranty work...
Anyway,
R14=5.6K
R3=200Ohms

Dear Bournville,
In fact i have tryed to put at the input but it is now bak at the original position. Even with input short circuited, i ear 50Hz when pot is @ the max...

Regards,

Gauthier
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Old 14th March 2003, 08:03 PM   #53
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Default Hi Gauthier!!

Quote:
Bad luck, when mesuring V2(4)and V2(6), it seems i have burned something
Why you say so???
It's not working any more??'
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Old 14th March 2003, 08:29 PM   #54
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Default The solution!!!!!

Quote:
R14=5.6K
Of course...it must be!!!

THE SOLUTION!:

Delect and put out of circuit R5-470k
Delect and put the the pot at the input(sorry...but it must be)
Delet C2
Conect the grid 3 of V2 directely to the cathode 3 of V1
and it will work properly...

Trust me!

Cheers

PS: any doubt???
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Old 14th March 2003, 08:34 PM   #55
Foes is offline Foes  Belgium
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Thumbs up Alive !

Hi, Jorge,

No i'am not joking,
Left channel is giving continuous 50Hz @ a quite high level in my speakers...
I have tryed to swap V1 and V2 between both chanel withour result.
Well, after reading your message, i have tried again. I think i have a bad contact on one soldering. ("Soudure sèche" in french).
I fix it soon. OK my amplifyer is still alive... Nice !
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Old 14th March 2003, 08:46 PM   #56
Foes is offline Foes  Belgium
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Default Doubts...

I don't understand...
You want to short V1(8) with V2(3) ??
Presentely V2(3)=0V and V1(8)=89V. V2(3) is a grid and i can probably force it to this level, but a dV of 89V between grid and cathode is quite high, isn't it ? (heuh, sorry, i'm maybe wrong, i am from the AOP generation...).
Anyway, what would be the improvement in yur proposition ? I don't realy understand, even if you are probabely right ...
Regards,

Gauthier
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Old 14th March 2003, 10:46 PM   #57
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Default Only the one that think has doubts....

Quote:
You want to short V1(8) with V2(3) ??
Yes they need to be conected directely with a wire...(conection directe)

If not the grid 3 of V2 will be at ground potencial and the current across R7 ...R8 ...R9 will be to low...

This is the problem with your amp...

Quote:
Presentely V2(3)=0V and V1(8)=89V. V2(3) is a grid and i can probably force it to this level, but a dV of 89V between grid and cathode is quite high, isn't it
When you conect directly V1(8) to V2(3) the cathode of V2 will folow the grid voltage ( 89 volts) and the resistor of the cathode becomes properly biased...and the current in each of the triodes of V2 will be aproxi. 3mA and at the anodes the voltage will became aprox.140 volts under the high tensionn voltage...
In this condition the phase spliter work fine...
Quote:
Anyway, what would be the improvement in yur proposition ? I don't realy understand, even if you are probabely right
The inprovement is that the cliping and the distortions will be gone...now the voltage across R8 R9 are to low...

Trust me...thats the problem!

Ps but to work propely you must:
Delect and put out of circuit R5-470k
Delect and put the the pot at the input(sorry...but it must be)
Delet C2
AND ONLY AFTER THAT....conect V1 (8) to V2 (3)...

Compris???
En avant vers la musique!!!
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Old 17th March 2003, 04:43 PM   #58
Foes is offline Foes  Belgium
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Default Afraid you'r right

Dear Jorge,

I 'm afraid you are right.
I still not have tested, after documenting myself, it's indeed to design this stuff like dat.

http://www.bonavolta.ch/hobby/fr/aud...0Tailed%20Pair

is interesting about this subject...
I will visit a frend to unsolder it cleanly and i say you the result...
Thanks,
G
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Old 18th March 2003, 12:51 AM   #59
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Default A happy end...

Quote:
I 'm afraid you are right.
Nice to know!!!

Do the mod and give some news!!

Á la notre santée!
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Old 29th March 2003, 10:29 AM   #60
Foes is offline Foes  Belgium
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Smile Not so bad...

Hi Jorge,

I have tried the modifications you have proposed. I mean : Pot at the input C2 Shorted and R5 supressed.
The result is clearly better. No saturation due to high input level anymore. The sound is sharper also, i thing.
Well done, you where right.
I still have a quite high 50Hz noise in the speaker, but dificult to determine the reason why. Probably, this is generated (amplified) by the first stage, and now that i have no attenuation before the second one... I can hear it...
Another question also is the quite low curent in the first stage (89v-86v)/1.5k=2mA this is low for such a tube is'n it ?
Anyway, it's better, and thank you.
Regards,

Gauthier
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