The AM Forum

I've been working on my 4-250 rig (finally) which has morphed into a real plate modulated transmitter.  I am going to use a pair of 811's modulating the class C
4-250 final.   I have a limited supply of meters (3)

So what currents would be most critical/benificial to monitor?  I can switch the meters but would rather keep it as SIMPLE/low parts count as possible.

IMO, screen current on the final, plate current on the final, modulator plate current, and bias voltages on both rf final and modulators.

meters are a dime a dozen. if you need some more, ask for some. somebody will help ye.  8) ( I have only 2, neither good for yer purposes. )

with only 3 meters, final plate current, screen current, mod plate current.

Derb's right, meters are cheap. If you have room on the panel, go for more. Or make a separate meter panel. But, if you are going to go with only three, you need grid current, plate current and modulator current.

Yep, agreed with you and Derb.  If you have the room, use as many as you can.

I have four homebrew plate modulated rigs and limit my meters. I use just FOUR meters per rig.  On each one, I use FINAL plate current,  final screen current,  final grid current, and modulator plate current.  One rig has two modulator current meters - one for each tube.  (I do see a small diffference between 833A modulator currents)

I've found that current is the most important parameter to know if you are limited to a minimum of meters. Once you initially measure screen or grid voltage with a VOM to know it's in the specification ball park, the currents are what really matter to set up the operating parameters.  Currents will change quite a bit based on RF drive, loading and plate tuning, whereas, DC voltages will stay pretty much stable. (except for grid leak, of course)


** I should mention that both my HV supplies have their own voltage meter and bright indicator light. I think this is important for monitoring as well as an added safety feature to having a visual when the HV is on.

T

I was of the 'less is more' mentality to keep the busy/cluttered look in check. Then I ran into an issue with the audio drivers on my transmitter, and discovered that adjusting the bias involved laying on the floor to install clip leads from the grids to a vom for adjusting. This involves either removing the whole chassis or reaching between the top of the plate tranny and lotsa pointy edges under the chassis. What a PITA! So I say meter the snot out of it, even if it means stashing one or some out of sight inside. It'll make troubleshooting a whole lot easier. In lieu of meters, maybe test point banana plug sockets?

If you need meters, lemme know. They are one of the things that managed to make the trip south.

Another way to handle metering of less used things, like voltages to the various stages or "minor" currents is to put a long row of mini bananna type sockets on the panel. Connect each pair to each circuit and label. Be sure to bypass them for RF and audio.

If everything is referenced to chassis ground, then you need only one socket per circuit.

This way you can access anything easily with your VOM or scope when needed. (troubleshooting)

Then there are those who install rotary "multimeter" switches and set up the resistive multipliers for a single meter like some mil gear does.

** I should mention that both my HV supplies have their own voltage meter and bright indicator light. I think this is important for monitoring as well as an added safety feature to having a visual when the HV is on.


T

Use big meters and watch the monkey Swing!!

klc

Used/surplus meters are still cheap (Shhhh!  maybe we shouldn't say that too loudly, lest this becomes another item for audiophools to discover). But try to buy a brand new analogue meter with a real D'Arsonval mechanical movement.

I like to use a separate plate meter for each modulator tube, and in my HF-300 rig I use a separate plate and a separate grid current meter for each of the two rf final tubes.  That transmitter has a total of 12 meters on the front panel.  Separate metering makes it easy to monitor how well the tubes in the stage are balanced.

the redder and bigger the better. :P

ummm..

dare I say it.
http://www.magnetosphere.net/

$2 each your choice, but you got to take 10 pcs or meet minimum. I'm trying to get rid of them. hundreds of them. I don't want to throw them out.
(this can't be considered a commerical ad. Not with these ham-cheap figures)

Lots of things to watch on meters:

RF plate current
RF screen current
RF grid current
mod plate current (individual)
mod grid current (or g-g audio voltage maybe)
high voltage
RF grid bias voltage
mod grid bias voltage
mod screen voltage
line voltage

not all of these are necessary, but they provide built-in first-level troubleshooting.