>Yo amps
>
>Interesting debate on the 4CX1600B tube. This is a real workhorse tube
>and it's too bad it has been dropped by the amp makers due supply
>problems.
>
>I never heard from anyone that had the tube "bang" and found it still
>good or bad unless I missed it from the postings.
>
>The history: QRO HF-3KDX 4CX1600B
>
>WW phone the amp had been on for 4 or 5 hours but mostly S/P, low
>duty cycle. While idle the amp "banged". Sharp report, like a firecracker.
>The fault light came on. I believe I saw a flash in the room but not certain
>anymore.
>
>The report was sharper then my normal 4-1000 "bangs". The 4-1000's
>seem to want to "bang" after sitting idle all summer, and usually happen
>only once. Those pops sound more muffled and occasionally open the HV
>glitch resistor.
** ... which indicates that a more capable R is in order. How many
Joules is available during an arc?
>
>A low voltage transformer feeds two power supplies. One is a 160 VDC
>that runs the TR switching relays. The other is -160VDC bias for the tube.
>On transmit the bias supply is routed through a DPDT relay to a stack of
>Zeners for -60 VDC.
>
>Both supplies are protected by fuses and both of these opened violently
>if the black vaporized coated glass is an indicator.
** it is. I've also seen fuses explode and send glass schrapnel about.
>Both diode stacks
>showed about .2 ohms short on the transformer side of the stack. The
>output side of the +160 supply for the relays was shorted to about 10
>ohms and the output side of the bias stack tested okay.
>
>Only the fuses, two diode stacks, and tube was replaced which returned
>the amp to service. Nothing else was damaged, that I could find anyway.
>
>So the question remains is the tube good or will it just blow those parts
>again?
** Good question. A high-potential test of the 4cx1600 would give a
pretty good clue. If the measured leakage is above 15uA @ +5000V and
-5000V, trouble seems quite likely. If you want, I will do these tests
sans-pay -- and I promise to keep my autopsy-saw at bay.
>
>Following the AMP reflector's discussion and in the name of science I will
>re-install the tube and jump back but only after the contest season. This
>amp has to be taken almost all apart to get to the LV/BIAS board including
>removing the front panel. All easy to do but putting it back together is a
>royal pain in the cathode.
>
>I will report back, thanks for the interest.
** Amplifier surprises tend to be interesting, Rich.
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