>> >is no good. I should have a known good one tomorrow to check it out.
>> >In the meantime I have seen several things that need to be done.
>> >glitch diodes, glitch resistor, new suppressor unit, etc. Live and
>> >learn (or re-learn??)
>
>99% of that stuff is just needless folklore originated by people who
>sell kits.
>
>Some people just can't face the fact that tubes fail, and so they
>"invent" odd reasons to explain a common event. For example, during
>some production runs nearly 20% of new Amperex tubes developed
>grid/filament shorts without ever applying high voltage!
>
>You should install the glitch diode mod if your amp does not already
>have one, but do it the way the factory did it.
** The factory never errs ?
>You must have a
>couple bypass capacitors from the electrolytics to ground, a small RF
>choke to the negative end of the electrolytics over to the diode,
** Why ?
>and the meter lead leaving from there. A diode with a threshold higher
>than .6 volts is necessary to prevent diode conduction on current
>peaks, which is aggravated by any tiny amounts of stray RF.
>
** 1N5400-series rectifiers begin conducting c. 0.5V @25ºC.
>> Take care about the glitch diode. In an SB-1000 (same animal) that
>> someone else had "pre-repaired", I had weird meter readings on 160m
>> until the glitch diode was replaced with a 1N5408. It turned out that
>> his no-name diode was rectifying at 1.8MHz!
>
>He might not have installed the RF choke or the bypass caps, or used
>a diode with a low threshold voltage.
>
** Putting glitch diodes in parallel with the meter movement protects
the meter. If the meter is RF-sensitive, there isn't enough bypass-C on
the anode supply. Bypassing both sides of the HV+ glitch resistor seems
to help.
> > ...
- R. L. Measures, a.k.a. Rich..., 805.386.3734,AG6K,
www.vcnet.com/measures.
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