HP 5334A Field Upgrade Option 010 Ovenized Oscillator

[ekoloski]

I recently stumbled across a rather old post inquiring if it is possible to retro-fit option 010 (Ovenized oscillator) into a HP5334A. I posted there as well but it's a little late to help the OP out. Regardless, I thought this may be helpful for someone else out there, and wanted to post with additional details. The components required for the adapter board are all jellybean through hole stuff, the most difficult component will probably be the 12 pin 'card edge' socket.

For some background, my daily driver counter is an HP5334. It's rock solid but was unfortunately not endowed with the 010 option. Many years ago I decided that the high stability would be beneficial. Finding the required adapter board (05334-60003) proved impossible at the time, unless I was willing to purchase an entire  broken counter. I enjoy repairs as much as the next guy, but I did not need two counters, which is what would happen if went down that path. Fortunately the oscillator itself (10811-60111) was readily available through various online auction sites for a fair price. I decided to spin a quick board to fill the gap. The kicad project files and gerbers for which are attached for anyone who may find them helpful.

Before installing the board and oscillator a coupling capacitor C8 must be removed and placed in the empty position C100. This will reroute the input of the timebase circuit from the standard oscillator to the ovenized oscillator. No additional changes are needed on the board assembly.

There are two (arguably optional) modifications to the chassis that follow. The first is to install a panel mounted 10-turn potentiometer for tuning the oscillator output via EFC. It looks like the original HP board had this part pcb mounted, leaving the adjustment buried deep inside the chassis yet still available through an access hole. I opted to use the same access hole but simply mount the potentiometer at that point. The second modification is to install a small LED to indicate the oven status. It does require drilling a hole. I placed mine on the top right of the front panel. The LED indicates that oven is not at operating temp, and the stability of the oscillator should not be trusted.