noob considering purchase of HP 6612C for bench power supply

[chewmanfoo]

I don't know much about it but it looks like it has a lot of resolution on amps and volts.

Anybody have any experience with this power supply?  I can get it on ebay for about $250.

[Berni]

Sure go for it. Most old HP power supplies are excellent units with great build quality.

If one has the room for them the rack mount ones can be a great bang for the buck too, just involves a bit of extra work to install banana terminals on the front.

[alm]

The 6612C is a good quality power supply. 20 V / 2A should be sufficient for many applications. It has a higher accuracy and readback resolution than most bench supplies (I believe they called it a precision power supply). One unusual feature is that it can sink current in addition to source (something that can be a blessing and a curse).

$250 is not particularly cheap, however, especially in the US. Now if this a guaranteed working model with some kind of warranty, that adds to the value. But I have seen similar power supplies go for half that. For example. the larger (both physical size and power) 6632A/B can sometimes be found for half that. The 66311B, which is basically an advanced version of the 6612C with more measurement features but 15V / 3A range. However, both are less convenient because they lack front binding posts. You either have to add these yourself, or make do with the connector on the back.

[wraper]

Unless you are going to modify a fan speed, I would suggest to stay away. They are very loud.

[Berni]

Ah yeah I forgot about the noise. A lot of these rack mount ones have powerful loud 120VAC Some actually have a 12V header ready that fits the headers on 12V computer fans, sometimes the header is unpopulated.

If I have to take it apart anyway to give it front panel terminals then irs a quick job to swap out the fan too. The big 4 channel HP one is now much quieter than my  Rigol DP832(Even after swapping the fans in it too). The reason is that this big boat anchor has huge heat sinks and a place to put the big 12cm fan. So even a very slow speed on the fan can easily cool it with all channels at max load

[wraper]

6612C has 12V fan and that fan is very fast. Considering heatsink size, and that it stays really cool as it's only 40W psu, it's a total overkill. However if lowering the speed, there is another issue. On the PCB there is a small heatsink, which runs quiet hot. If you remove the cover so there is no forced airflow around it, it heats up to 100+^oC. So this is huge limitation on how munch you can reduce the noise, making it silent guarantees that part will overheat. IIRC I changed R413 and R416 resistor values in the fan speed control circuit.

[julian1]

There is a possibility of disabling the fan, under noted conditions,

https://www.manualslib.com/manual/2871/Agilent-Technologies-6611c.html?page=36

But what the interaction is with the unit's other thermal protection is a bit of an unknown (risk of damage?).

Also the transformer is a big clunky E type, and may introduce winding hum noise independent of the fan. Modern supplies often use toroids.

[wraper]

Also the transformer is a big clunky E type, and may introduce winding hum noise independent of the fan. Modern supplies often use toroids.

Transformer itself is silent. However metal cover vibrates a lot under magnetic flux leakage from the transformer.