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Ampdog

R.I.P. 23 June 2022
Joined
Aug 27, 2006
Messages
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Location
Pretoria, South Africa
A different angle on this amplifier which graced my bench recently.

In one of the references given, the problem with most Chinese amplifiers is highlighted: They offer no primary voltage adjustment; only 220 or 110VAC. The writer claims with some justification that such amplifiers should not be imported. Here in RSA, using a 220V primary at 235 - 240VAC line, means that tube heaters will often be operated at about 6,9V. This can lead to premature emission failure of the power tubes. I had to replace another KT88 here because of cathode coating shedding - typical bits of white flake inside the glass when shaken. (These could form G1-C shorts, with obvious results.)

The cure is not very practical. Either use a fairly bulky 240-220 autotransformer, or put in resistors, at least in the heater chains. I do not have to illustrate. This is a caveat when buying commercial tube amplifiers.

Others' experience in this regard?
 
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