HV Power Supply - 7704A - Neon Bulbs


Mark Vincent
 

Barry,

That is what the neons are there for in the high voltage section, a voltage clamp. They will flash for an instant at turn-on. That is normal.

Mark


n4buq
 

BTW, I don't find these neons described in the Circuit Description section. Are they there just as over-voltage protection?

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "Mark Vincent" <orangeglowaudio@gmail.com>
To: "tekscopes" <TekScopes@groups.io>
Sent: Monday, October 4, 2021 9:02:51 PM
Subject: Re: [TekScopes] HV Power Supply - 7704A - Neon Bulbs
Barry,

A 5AB is a direct replacement for a NE23. Mouser has these in stock. Get several
to have spares on hand. Broken leads at the base of neons is common.

Mark



n4buq
 

Thanks, Mark. I searched for "8.2" instead of "8,2". I keep forgetting that. :-)

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "Mark Vincent" <orangeglowaudio@gmail.com>
To: "tekscopes" <TekScopes@groups.io>
Sent: Tuesday, October 5, 2021 9:52:18 AM
Subject: Re: [TekScopes] HV Power Supply - 7704A - Neon Bulbs
Barry,

This is what I said: Mouser currently has 10, 12 and 18mfd 250V ULD in stock to
replace the 8,2mfd. If you decide to use the 18mfd, the additional capacitance
will not hurt. Replacing the two 100mfd for the graticule lights can be done
also. The 100mfd 16V of the same series are in stock. Your decoupling on the
vertical and horizontal boards may also be going bad. Those can be raised to
47mfd 25V in the ULD series for the 5V and 15V supplies. At the age of the
originals and being general purpose 85C types that would also be seen in
consumer grade products, replacement would be a good idea. The life of the
originals would be 2000-3000 hours.

Mark



Mark Vincent
 

Barry,

This is what I said: Mouser currently has 10, 12 and 18mfd 250V ULD in stock to replace the 8,2mfd. If you decide to use the 18mfd, the additional capacitance will not hurt. Replacing the two 100mfd for the graticule lights can be done also. The 100mfd 16V of the same series are in stock. Your decoupling on the vertical and horizontal boards may also be going bad. Those can be raised to 47mfd 25V in the ULD series for the 5V and 15V supplies. At the age of the originals and being general purpose 85C types that would also be seen in consumer grade products, replacement would be a good idea. The life of the originals would be 2000-3000 hours.

Mark


n4buq
 

Mark,

On the subject of the HV supply, I seem to recall an email (which I can't find) where you mentioned a suitable replacement for C4201 (8.2uF, 200V). I presume anything around 15uF to 25uF and, maybe, a slight increase in the voltage rating would be okay but thought I'd ask before ordering.

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "Barry" <n4buq@knology.net>
To: "tekscopes" <TekScopes@groups.io>
Sent: Monday, October 4, 2021 9:07:58 PM
Subject: Re: [TekScopes] HV Power Supply - 7704A - Neon Bulbs
Hi Mark,

I was just about to post that the older manual shows a 5AB-T for those. I plan
to replace all four in that board (along with the caps). I have a box of A9A
leaded bulbs but, unfortunately, those are the wrong striking voltage for this
application. So close...

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "Mark Vincent" <orangeglowaudio@gmail.com>
To: "tekscopes" <TekScopes@groups.io>
Sent: Monday, October 4, 2021 9:02:51 PM
Subject: Re: [TekScopes] HV Power Supply - 7704A - Neon Bulbs
Barry,

A 5AB is a direct replacement for a NE23. Mouser has these in stock. Get several
to have spares on hand. Broken leads at the base of neons is common.

Mark



Mark Vincent
 

Barry,

The A9A is NE-2E. Hold on to those. They are ,7mA.

Mark


n4buq
 

Hi Mark,

I was just about to post that the older manual shows a 5AB-T for those. I plan to replace all four in that board (along with the caps). I have a box of A9A leaded bulbs but, unfortunately, those are the wrong striking voltage for this application. So close...

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "Mark Vincent" <orangeglowaudio@gmail.com>
To: "tekscopes" <TekScopes@groups.io>
Sent: Monday, October 4, 2021 9:02:51 PM
Subject: Re: [TekScopes] HV Power Supply - 7704A - Neon Bulbs
Barry,

A 5AB is a direct replacement for a NE23. Mouser has these in stock. Get several
to have spares on hand. Broken leads at the base of neons is common.

Mark



Mark Vincent
 

Barry,

A 5AB is a direct replacement for a NE23. Mouser has these in stock. Get several to have spares on hand. Broken leads at the base of neons is common.

Mark


n4buq
 

The lead on one of the NE23 neons in my 7704A broke very easily when I moved it just a bit (apparently brittle from heat and age). Is a 5AB a suitable replacement? If not, what are some good choices?

Thanks,
Barry - N4BUQ