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465, HV fixed byt still no trace


Bill Meara
 

With a spare HV multiplier sent from the UK by a fellow radio amateur, I managed to get the HV supply in my 465 working.  (Has anyone told you guys that working on these things is NOT easy?)
 
The HV probe shows more than -3000 volts from the supply. But still no trace.  I took a look at the base end of the tube and see no light (in any part of the tunnel).  Could it be that when the tube went bad it took the HV multiplier down with it?  What fate away its 465s with dead tubes?  How can I tell if mine is really dead?
 
Bill (N2CQR)


Artek Manuals <manuals@...>
 

Start by ohming out the filament pins, pull the socket off the CRT(make sure the HV is full discharged)  and look for very low ohms across pins 1 and 14

Filament open = really cool lampbase/CRT

Dave

 On 10/20/2013 5:37 PM, Bill Meara wrote:
 
With a spare HV multiplier sent from the UK by a fellow radio amateur, I managed to get the HV supply in my 465 working.  (Has anyone told you guys that working on these things is NOT easy?)
 
The HV probe shows more than -3000 volts from the supply. But still no trace.  I took a look at the base end of the tube and see no light (in any part of the tunnel).  Could it be that when the tube went bad it took the HV multiplier down with it?  What fate away its 465s with dead tubes?  How can I tell if mine is really dead?
 
Bill (N2CQR)


-- 
Dave
Manuals@...
www.ArtekManuals.com


danishcah@...
 

If the filament reads OK (ohms ) but won't light up, leave it on for a minute,then turn it off and see if the CRT neck is warm/hot .. if so the tube has air in it ( it's cracked, etc ), which conducts the filament heat away so it never reaches incandescence ..but the neck will get unusually hot in a very short time. Have seen this in ordinary tubes as well as at least one broken (UPS) CRT .. Dana



---In TekScopes@..., <tekscopes@...> wrote:

With a spare HV multiplier sent from the UK by a fellow radio amateur, I managed to get the HV supply in my 465 working.  (Has anyone told you guys that working on these things is NOT easy?)
 
The HV probe shows more than -3000 volts from the supply. But still no trace.  I took a look at the base end of the tube and see no light (in any part of the tunnel).  Could it be that when the tube went bad it took the HV multiplier down with it?  What fate away its 465s with dead tubes?  How can I tell if mine is really dead?
 
Bill (N2CQR)


wb5tka <dan@...>
 

Bill, I agree with Dana on checking the filament leads. Pins 1 and 14 and the reading should be at or close to zero ohms. To be sure you will need to unplug the socket from the base of the CRT otherwise you will be reading across the transformer winding which powers the filament. By the way, it's not a bad idea to check that too just in case the transformer winding is open or there is an otherwise break in the path.

You said you are reading more than -3000. The voltage should be -2450 or about that amount. Ideally you should be able to adjust it down to that amount with the HV adjust pot on the board.

In addition to making the test Dana suggested, check to make sure that one or more of the deflection plate leads has not come off. Those are connected to pins on the sides of the neck of the CRT. One set is accessible through a round opening in the centre of the main board on the scope bottom. The other set are accessible from the metal neck housing visible from the bottom of the scope under the metal frame where the amplifier board is located.

One more thing make sure that the output high voltage from the multiplier is actually making it to the CRT. I don't know what the multiplier you installed is like but assuming that you used the same original connector from it to the lead running to the CRT top, you should be able to read a much higher voltage there at the connector.

--- In TekScopes@yahoogroups.com, <danishcah@...> wrote:

If the filament reads OK (ohms ) but won't light up, leave it on for a minute,then turn it off and see if the CRT neck is warm/hot .. if so the tube has air in it ( it's cracked, etc ), which conducts the filament heat away so it never reaches incandescence ..but the neck will get unusually hot in a very short time. Have seen this in ordinary tubes as well as at least one broken (UPS) CRT .. Dana



---In TekScopes@yahoogroups.com, <tekscopes@yahoogroups.com> wrote:

With a spare HV multiplier sent from the UK by a fellow radio amateur, I managed to get the HV supply in my 465 working. (Has anyone told you guys that working on these things is NOT easy?)

The HV probe shows more than -3000 volts from the supply. But still no trace. I took a look at the base end of the tube and see no light (in any part of the tunnel). Could it be that when the tube went bad it took the HV multiplier down with it? What fate away its 465s with dead tubes? How can I tell if mine is really dead?

Bill (N2CQR)


Albert Otten
 

A HV over 20% too high means the CRT filament voltage is also too high. Now 20% might not be a problem for a healthy filament, but if the filament was already weak for some reason... who knows.

Albert


> The HV probe shows more than -3000 volts from the supply. But still no trace. I took a look at the base end of the tube and see no light (in any part of the tunnel). Could it be that when the tube went bad it took the HV multiplier down with it? What fate away its 465s with dead tubes? How can I tell if mine is really dead?
>
> Bill (N2CQR)
>


Dave W1BVV
 

Just a thought, pull the socket off the end of the tube and check all the pins. When I reassembled mine, one pin evidently got bent and was not making contact. There was no sign of a beam. Carefully straightening the pin and gently replacing the socket brought it to life.

On my 465, when the HV multiplier died, it loaded down the -2460V supply enough to zero out the beam. You can disable the multiplier by lifting a link to ground on the pad where the black ground wire from the multiplier connects to the interface board. Its under the HV shield on the exterior side of the interface board.

Dave W1BVV