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Vintage Audio (record players, hi-fi etc) Amplifiers, speakers, gramophones and other audio equipment.

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Old 12th Jul 2019, 8:10 pm   #41
dekor8tor
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Default Re: Hacker GP42 and AL42 restoration help

Ok Frank i will change what Michael advises and do a re check
Many thanks
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Old 12th Jul 2019, 8:26 pm   #42
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Default Re: Hacker GP42 and AL42 restoration help

If you still have voltages that are a long way out after replacements are fitted. You could measure the cathode voltages of the pentodes, they are 1.4v and 4v at present. Swop the valves over, if the low voltages follow the valve then itís a sign that the valves are low emission.
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Old 12th Jul 2019, 9:20 pm   #43
dekor8tor
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Default Re: Hacker GP42 and AL42 restoration help

Hi Frank connected speaker and plug for stylus and checked voltages again this is what i got compared to last readings

HT1 C12 286V
HT2 C11 272V
HT3 C8 248V
V1A PIN9 164V
V2A PIN9 120V
V1B PIN6 265V
V2B PIN6 265V
V1A PIN2 0V
V2A PIN2 0V
V1B PIN 7 7.1V
V2B PIN7 7.2V
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Old 12th Jul 2019, 10:10 pm   #44
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Default Re: Hacker GP42 and AL42 restoration help

Voltages G3 = 257v on both
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Old 12th Jul 2019, 10:14 pm   #45
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Default Re: Hacker GP42 and AL42 restoration help

Those look more like they should do, have you changed any components but I would have expected pin 2 to have about 1v on them. The Pentode cathodes are about right so the emission is ok.
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Old 12th Jul 2019, 10:17 pm   #46
dekor8tor
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Default Re: Hacker GP42 and AL42 restoration help

No all i have done is connect the speaker
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Old 12th Jul 2019, 10:18 pm   #47
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Default Re: Hacker GP42 and AL42 restoration help

So the voltages you took before were without the speaker or dummy load?
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Old 12th Jul 2019, 10:19 pm   #48
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Default Re: Hacker GP42 and AL42 restoration help

Yes
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Old 12th Jul 2019, 10:21 pm   #49
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Default Re: Hacker GP42 and AL42 restoration help

Oh well you will know for the future, the amplifier was probably going unstable.

So back to the problem, check those components that Micheal suggested.
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Old 12th Jul 2019, 10:24 pm   #50
dekor8tor
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Default Re: Hacker GP42 and AL42 restoration help

Ok thanks will do
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Old 14th Jul 2019, 6:48 pm   #51
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Default Re: Hacker GP42 and AL42 restoration help

Incidentally a valve amplifier should never be run without either a loudspeker or eqivalent dummy load connected
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