Scott,
You are right. The data out on the GI7B is hard to come by. The Pd max
of the GI7b is 7w. But I've not been about to find a set of curves that
reflects the common set of op conditions which makes it hard to model
the Ig max.
However, from experiement, 90 ma per tube is about the max before
strange things begin happening.
With 2500V on the plate loaded, this level of drive will give me over
1KW out. Lower plate voltages will require higher drive levels and
given the low grid dis of this tube, I opted for a higher plate voltage
so that I essnetially operate at a lower drive level for a given PO level.
If you drive more than this approx 90 ma per tube, you will start to
notice a strange thing with the grid current. It will zoom up, and then
over the 1-2 seconds, slide back. There is no hard evidence as to what
is happening but a reasonable case can be made that as the grid heats
up, it's dimensions change slightly. PO does not drop under this case,
however.
It's not know if this is bad for the tube or not. The late (and great)
Tony W4ZT told me once the tube could take up to 250ma, for example. I
suppose a guy could setup a test and hammer the grids wtih a
progressivly higher current (pausing at each step) - untill the tube
dies, and then chop the tube up to confirm the grid damage.
On the plate current, I use a 1A scale for a pair. At higher plate
voltages, the typical Ip is in the 600-700ma range for the set -
limiting factor is running up to the plate dis limit (assuming a 60%-ish
overall efficiency).
Good luck.
73/jeff/ac0c
KD7QAE wrote:
> From the curves, it looks like Igmax is about 0.5A under normal
> operation and biasing so a .75A meter face would work well. Max grid
> power dissipation is 26W on this tube. The curves are on
> http://amp.w4zt.com/gs35b/index.html.
>
>
> Tomm
>
> KB0NLY wrote:
>
>> Working on scaling my meters today using that Meter program from Tonne
>> Software. For those that don't know i'm using the GM3SEK Triode Board and
>> it has outputs for Grid and Anode metering onboard, so i'm working on
>> getting those meters ready today.
>>
>> I can only find that the GI7B has a max Plate/Anode current of .600mA, so
>> figure a 1a scale will be plenty on the Plate Current meter.
>>
>> What about the Grid Current meter? I can't find any info showing what the
>> max current is for the Grid on these tubes. I want to make the scales nice
>> and neat with colored bands showing the normal operating range, a quick
>> glance to see if i got a problem, etc..
>>
>> Someone on here must know! None of the english or russian spec sheets that
>> i can find mention grid current.
>>
>> Thanks and 73,
>>
>> Scott KBØNLY
>>
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