|[AMRadio] Viking II no output|
jpl15 at panix.com
Fri Feb 9 22:51:31 EST 2007
On Fri, 9 Feb 2007, Geoff/W5OMR wrote:
> ante up.
Not till you finish trouble-shooting!
> Let me make this perfectly clear...
> There -is- full plate voltage on the plates of the 6146's. I've been saying
> 'around' 600 and 600'ish...
I'm not sure trhere should be that much - if the tubes are conducting.
> doesn't measure more than 600vDC. It tries to read, goes up - I see a two
> sets, quite possibly a few sets of numbers, as the voltage is rising, before
> the reading on the LCD screen read "OF" (out of range).
Ummm - eBay - better meter? To maintain your BA stuff? Decent test gear
is a must - and cheap if you scrounge the swapmeets, eBay, etc. Even a
1KVDC panel meter with well-insulated test leads... c'mon.
B+, as measure on
> the plate caps of the 6146's is 600VDC+
Sounds like too much at the caps. Perhaps I'm wrong - the Valiant is
roughly the same circuit, but with three of 'em. Under load it's different
- but you must use a meter that decouples the RF, if the stage os working,
or it 'swamps' the typical el-cheapo DMM...
> At No time does the plate current rise about 20mA. Moving the Roller
> inductor around -does- dip the plate. it dips to around 10mA and power
> output is around'ish 10w, thereabouts. (between 7 and 12)
I got this already.
> Measuring at the tube base, there are:
> 280v of Screen
> -57V of bias
Dude: What Is The Voltage On The CATHODES????
> I can draw as high as 15mA of grid current. There just isn't any plate
I got this the first couple of times you wrote it.
But you still haven't checked the voltage at each step in the Final Amp
B+ chain - from the place in the circuit that B+ comes in (The 'bottom' of
the Plate Choke) to the place where it meets ground - somewhere right
after the cathodes of the 6146s.
If you find that there is a complete path to ground for the usual DC
PLate current - THEN you can be reasonably assured that the tubes are
operating properly - and that the trouble is elsewhere. And yes, those
old Johnson doorknobs do fail - I replaced all of them in my Valiant and
both Rangers - one had split in half, yet the rig still loaded up and
'talked'... the fact that the tubes will only pass 10-20 mA, yet they are
under proper bias - is very suspicious and 'telling'..
That's why I tried to offer a logical 'checklist' - to trace out the DC
Plate Current path *completely*. I still would like to know what the
voltage is on the 6146s from pins 1, 4, and/or 6 w/respect to ground. If
they all go to the same wire, and that wire has come off it's lug - the
symptoms you describe will most likely be evident.
But at least you will have logically eliminated a bunch of Things that
could be causing your trouble - and it will only take a few minutes to
check the various places with your DMM...
Also - please be careful - especially with cheap meter leads and HV...
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