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I have three 204B oscillators I'm restoring. One had a problem where C2 (the 3 section, 1% capacitor) had a shorted section. I replaced the shorted section with single 1%, .3uF. Close enough for the Government!

My problem is, I'm converting the battery units to AC. It has a transformer a bridge rectifier and some filtering but secondary of the transformer isn't center tapped and it's not referenced to ground. I used a 7812 and a 7915 regulator to provide the +/- 12volts but when I wired it to the transformer the plus side dropped to 5.6 volts and the minus side was 37.6 volts. The plus side was drawing more current than the minus side. To balance it out I used a 15v Zener diode on the minus side and the plus side increased to 25.75 volts.

It appeared to be working but when the frequency was set to 250to 1KHz, there was a small amount ripple on the + 12v. To reduce the ripple, I used a 1000uF electrolytic on the +12v side.

Has anyone done a similar modification? Is there a better way?

There was such a modification in June and July issues of AudioXpress (which, I am going to guess, you don't have!). Uses a pair of 1N4742 12V 1W zeners to split the supply.

There's an important utility to running the oscillator off batteries -- you're going to get a much lower noise floor and no pesky 60, 120, 180Hz power supply artifacts. You can rebuild the battery packs with Nicads, or button cells and use the existing charge circuit, or use one of the intelligent charger chips from, for instance Texas Instruments (Unitrode.)

I rebuilt the battery pack of my HP3581 wave analyzer -- and it was worth the investment.

--- In hp_agilent_equipment@..., "willcoele@..." <willcoele@...> wrote:

I have three 204B oscillators I'm restoring. One had a problem where C2 (the 3 section, 1% capacitor) had a shorted section. I replaced the shorted section with single 1%, .3uF. Close enough for the Government!

My problem is, I'm converting the battery units to AC. It has a transformer a bridge rectifier and some filtering but secondary of the transformer isn't center tapped and it's not referenced to ground. I used a 7812 and a 7915 regulator to provide the +/- 12volts but when I wired it to the transformer the plus side dropped to 5.6 volts and the minus side was 37.6 volts. The plus side was drawing more current than the minus side. To balance it out I used a 15v Zener diode on the minus side and the plus side increased to 25.75 volts.

It appeared to be working but when the frequency was set to 250to 1KHz, there was a small amount ripple on the + 12v. To reduce the ripple, I used a 1000uF electrolytic on the +12v side.

Has anyone done a similar modification? Is there a better way?

Jeanette,

I had heard that as well. Do you remember what year the audio express article was published?

George

On Aug 30, 2011, at 7:26 AM, "Jeanette" <jdwalton@...> wrote:

There was such a modification in June and July issues of AudioXpress (which, I am going to guess, you don't have!). Uses a pair of 1N4742 12V 1W zeners to split the supply.

There's an important utility to running the oscillator off batteries -- you're going to get a much lower noise floor and no pesky 60, 120, 180Hz power supply artifacts. You can rebuild the battery packs with Nicads, or button cells and use the existing charge circuit, or use one of the intelligent charger chips from, for instance Texas Instruments (Unitrode.)

I rebuilt the battery pack of my HP3581 wave analyzer -- and it was worth the investment.

--- In hp_agilent_equipment@..., "willcoele@" <willcoele@> wrote:

I have three 204B oscillators I'm restoring. One had a problem where C2 (the 3 section, 1% capacitor) had a shorted section. I replaced the shorted section with single 1%, .3uF. Close enough for the Government!

My problem is, I'm converting the battery units to AC. It has a transformer a bridge rectifier and some filtering but secondary of the transformer isn't center tapped and it's not referenced to ground. I used a 7812 and a 7915 regulator to provide the +/- 12volts but when I wired it to the transformer the plus side dropped to 5.6 volts and the minus side was 37.6 volts. The plus side was drawing more current than the minus side. To balance it out I used a 15v Zener diode on the minus side and the plus side increased to 25.75 volts.

It appeared to be working but when the frequency was set to 250to 1KHz, there was a small amount ripple on the + 12v. To reduce the ripple, I used a 1000uF electrolytic on the +12v side.

Has anyone done a similar modification? Is there a better way?