Scope CRT current
 

I'm having another look at my Sun engine analyser. It has a scope for displaying various ignition wave-forms. The mains transformer supplying all the voltages has long since died and scrapped.I have one that will provide the -1.2kV and the heater allowing the heater to float. The other potentials , focus and astig are catered for with another transformer. The final anode runs at 2kV This has been a problem! I now possibly have a solution. I have rescued from work a PSU that was originally used to supply an ion pump. It has an EHT PSU as a single block device, 12v in and 4kV out. The data sheet shows the o/p to be directly proportional to the input voltage so to get the 2kV needed I supply it with 6v. All good. The EHT block is rated at 0.75mA at 4kV. nowhere can I find any indication of what a small tube will need as eht current. can anyone suggest a ball park figure for tube current?
The tube is a RCA 4490 and the EHT block is an EMCO E40

Malcolm

Re: Scope CRT current
 

In my head I have a few 10's of micro amps for a black and white telly, and that lights the whole screen. Should be much less than that.

Re: Scope CRT current
 

.75mA will be more than plenty assuming we are talking monochrome. I think 100uA is roughly were a mono telly CRT would be.

TTFN,
Jon

Re: Scope CRT current
 

Excellent. Thanks all. I thought it was in that area but it’s good to have it confirmed. I’ll press on and get something together

Re: Scope CRT current
 

Hi Typical VCR97 scope etc run at 2KV took about 0.5ma (4Meg) on the bleeder chain, actual tube current would be quite a bit less than that.

Ed