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465B dead: ? HV transformer.

aakmoe
 

Hi

I turned my 465B on and it is dead.
I mean power and trigger lights are on.

Checked the 5 15 55 110 and they are OK.
F4508 the +15 unregulated line fuse is blown.
no dead short to ground either .
H out Q4009 seems Ok on simple ohm check.At least it is not dead.

the HV primary resistance is very low, about 0.26 ohms.Pretty low.

Does anyone know the primary resistance.

I don't have the replacement fuse yet and I dare not jumper the fuse
incase it will blow the transister.

I put my 25 w iron in series and the current measures about 9 miliamps.
considering the fact that +15 unregulated is about 21-22 volts SO
almost all is dropping across the resistance.

I assume the transformer is gone.Turn short or almost dead short ?

HOW easy it is to get another one?

Should I try with a new fuse and cross my fingers and pray ?


I am only a hobbyist , sorry for the long post.

May it is time to get another scope.

If it is in other stages I will be stuck.

Any help appreciated.

moe
Denis Cobley
 

Hi Moe
I would expect it's the High Voltage Multiplier.
It will load the output of the transformer and cause the fuse to blow.
They are not easy to find and the transformer and HV multi are not easy to get at as you need to remove the side board and the metal cover under it to access the transformer and Multi.
I have seen many HV multi's bad but no transformers.
You can disconnect the HV multi and try again - this should restore the HV supply (-2400VDC) but without the Multi you will not get a trace on screen.
Good luck finding a good one.
Regards
Denis

----- Original Message -----
From: "aakmoe" <aakmoe@...>
To: <TekScopes@...>
Sent: Wednesday, October 06, 2004 9:22 AM
Subject: [TekScopes] 465B dead: ? HV transformer.




Hi

I turned my 465B on and it is dead.
I mean power and trigger lights are on.

Checked the 5 15 55 110 and they are OK.
F4508 the +15 unregulated line fuse is blown.
no dead short to ground either .
H out Q4009 seems Ok on simple ohm check.At least it is not dead.

the HV primary resistance is very low, about 0.26 ohms.Pretty low.

Does anyone know the primary resistance.

I don't have the replacement fuse yet and I dare not jumper the fuse
incase it will blow the transister.

I put my 25 w iron in series and the current measures about 9 miliamps.
considering the fact that +15 unregulated is about 21-22 volts SO
almost all is dropping across the resistance.

I assume the transformer is gone.Turn short or almost dead short ?

HOW easy it is to get another one?

Should I try with a new fuse and cross my fingers and pray ?


I am only a hobbyist , sorry for the long post.

May it is time to get another scope.

If it is in other stages I will be stuck.

Any help appreciated.

moe










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Jimmy
 

Hi
I have a similar situation. The Transformer is OK -Checks out. But am now thinking it might be the EHT pump rectifier.
However do you know where I can find out how to build the HV Tripler. Just in case?. I saw a blog some months ago where someone did build one
annoyingly I cannot find the thread . - any Ideas? tks.
 

I have built a couple of these for 465/475. If memory serves me correctly you will need 6 - 20kV diodes and 6 - 1000pF 20kV ceramic caps and a 470k 1/2W resistor. I bought the caps and diodes from a popular auction site. I have a 3D printed STL file for an enclosure that mimics the original one. Fits into the original location.

--
Michael Lynch
Dardanelle, AR
 

Remember, the diodes need to be fast-recovery types since the wave being rectified is ultrasonic.

Dave Wise

From: [email protected] <[email protected]> On Behalf Of Michael W. Lynch via groups.io
Sent: Monday, December 13, 2021 8:03 AM
To: [email protected]
Subject: Re: [TekScopes] 465B dead: ? HV transformer.

I have built a couple of these for 465/475. If memory serves me correctly you will need 6 - 20kV diodes and 6 - 1000pF 20kV ceramic caps and a 470k 1/2W resistor. I bought the caps and diodes from a popular auction site. I have a 3D printed STL file for an enclosure that mimics the original one. Fits into the original location.

--
Michael Lynch
Dardanelle, AR
 

Dave,

Thanks for filling in the important gap in my comment.

--
Michael Lynch
Dardanelle, AR
 

In my experience with a number of 465B (and 468's which are identical in this area) a shorted multiplier will cause the HV to go down to a few hundred volts, but will not blow the fuse. Check for a shorted C4006. The low resistance of the primary is normal. As mentioned by another poster, the HV multiplier can be disconnected by unsoldering a ground jumper. Then the HV will go back to -2450. Replacement of the multiplier or transformer requires removal of the vertical preamp and mode switch boards.

The vintageTEK Museum has used, tested multipliers and transformers. Contact the Museum directly to inquire.

--
Bob Haas

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