Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: bakerlite on January 26, 2012, 06:38:24 pm
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Got a bit of a weird one with an orange ad15
all voltages are down 10% everywhere like a really uniform volatge drop.
wouldnt really mind only the 5v line is only 4.2v and the 3.15v lines are 2.4v
Its almost like the mains power taps are wired wrong but they aren't? (wall is showing 230v and taps are wired for 230v)
Amp showing no other signs symptons of problems - was just giving a look over, apart from tired 150R 4W power resistors its like new.
Has anyone else come accross a similar thing before? I dont have a spare gz34 handy but seeing as the 5v and 6.3v are down in power I dont reckon its the cause.
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First thing you do is check the battery on your voltmeter. MANY of us have been concerned about "wrong" voltages only to find the battery in the voltmeter is not good.
Have you played thru the amp? How does it sound?
What are the voltages on the 5v and 6.3v with NO tubes in it?
With respect, Tubenit
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10 % seems normal for me. What is your voltmeter ? Good one or low cost ? And is precision on AC voltage ?
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when did you check the voltages ? at supper time, power line drops from 120 to 110 easily and will affect the PT voltages.
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all voltages are down 10% everywhere like a really uniform volatge drop.
wouldnt really mind only the 5v line is only 4.2v and the 3.15v lines are 2.4v
You mention 10% off, but 4.2v is 16% low on the 5v winding, and 2.4 is ~24% low on the 6.3v winding. How certain are your numbers? Are these low-voltage readings on a 200v setting (which might have some added range error)?
Regardless, if the amp seems to perform correctly, then it's not really an issue to worry about. Your wall voltage might be lower than the specified 230vac.
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Amp showing no other signs symptons of problems - was just giving a look over, apart from tired 150R 4W power resistors its like new.
Has anyone else come accross a similar thing before? I dont have a spare gz34 handy but seeing as the 5v and 6.3v are down in power I dont reckon its the cause.
If you have a heater voltage lower than 6 volts on preamp and power tubes there are a power transformer or wall outlet voltage problem or your voltmeter ??
On GZ34 , 4.2 volts is too low ( "short " ) , also this is the power transformer or wall outlet, probably not the GZ34.
It could also have a tube's heater with too low resistor ? Remove ALL TUBES and mesure youre 6.3 and 5 ac volts. If those voltages are good chance is too low power transformer or tube heater "short" . If voltage are low ; "bad" power transformer ( not enough powerfull ) or wall voltage too low.
Or you'r voltmeter wrong