Starting to look for the HP6268B power supply, no hurry. Could be a fixer upper as long as cosmetics are decent. Anyone got one they want to sell? Shipping to Miami FL.
Yes I have looked at ebay, and there are a couple, most are between overpriced (to me) or just to plain ugly looking (broken, bashed, badly scratched, etc) for what they are asking.
Hoping to get a better deal here and from a trustworthy source.

Also, anyone can tell me of known issues to look out for, or parts that are no longer available, in case I run into a potential "for parts only" opportunity.
Sellers seem to mention very often the loud humming under load, not sure how loud it really is, but seems like a "normal".
One seller says the humming at 60% load gets louder than the internal fan running.
Also I see quite a bit of bashed in broken meters, not sure how fixable those are, if only the side mounting ears break off and can be reattached.

Thank you.

"Humming" is an artifact of transformer core magnetostriction, caused by the AC line pre-regulator.? It is normal for these supplies.

Dave

On Mon, Oct 25, 2021 at 05:30 AM, Alex wrote:

Starting to look for the HP6268B power supply,

My question/curiosity... would be why?
I mean it's okay if you fancy one... say, just to hold the basement floor down.
But assuming you want one to do something... why one of those?

On Mon, Oct 25, 2021 at 05:57 AM, Dave Hills wrote:

Humming" is an artifact of transformer core magnetostriction

Yes, humming, due to magnostriction, used to be a common problem in transformer designs; but, better steel and lamination design has made transformers quieter.
I know, it's a design issue in large power distribution transformers. (They used to hum annoyingly loud... but, are now smaller and quieter too.)
The hum can be a symptom of transformer core de-lamination.
It could also be an indication that the transformer is being run past its current(s) rating(s)... for whatever is causing that. (partly shorted filter cap?)

On Mon, Oct 25, 2021 at 05:36 PM, Roy Thistle wrote:

My question/curiosity... would be why?
I mean it's okay if you fancy one... say, just to hold the basement floor
down.
But assuming you want one to do something... why one of those?

I will need to test 12V and 24V equipment up to 20Amps, so the 40V 30Amp model seemed to fit the bill.
And HP being HP, why not. Do you have another suggestion? Thanks.

Thanks for the confirmation of the humming described by some sellers being normal.
Sounded strange that HP would use regular transformers that would start to hum over time.
Now its clear its more like a feature.

Bonjour à tous

We manufactured transformers since 1970s, and did not suffer magnetosstriction noise, as the lamination was secured tightly and usually vacuum varnish impregnated.

I have fixed loud hum in other HP linear power supplies, like 6114A and 6115a.

the "transformer hum" was caused by yellow Mylar 0.47 uf AC capacitors across the windings ( probably at primary side) used perhaps to reduce electrical noise.

I replaced them with new caps at a higher voltage rating. In the process I tightened the mounting screws in each lamination stack. My HP supplies are now quiet. The caps had loostened over the decades and became electrostatic speakers!

I am not familiar with the HP 6268B, but from the same era. I would check for such caps before blaming magnetostrepiction!

Bon courage


Jon

The 6268B (and similar models) holds up well in adverse conditions, and many pallets full of them have been sent to our military in Irag and Afghanistan for those "wars". I still see requests for them on want lists.

I have a few of them here. The problem is, they weigh a ton and are a royal PITA to pack and ship.

Where are you located? I may have one but I'm near Denver and won't ship it. If you are close enough I'll check on it.
Leonard

Alex:

I bought and rebuilt a 6268B,I was told it was working,which it was not.
All of the black diodes were rendered to grey dust but easily replaced. How this happened, I don't have a clue.The only "unique"? part I replaced was a little transformer that I had to find a substitute for .
I think it was a "pulse" transformer. About the size of a DIP relay. It is not a snap to align this thing but I did it, so it cannot be that hard. All transformers "Hum" they are musical. I cannot hear the hum over the fan noise, which is not inconsequential. Run mine at 28 Volts for a GRC 106 military radio mostly.
I bought the PS because I was sick and tired of dealing with birdies on SMPS PS. This thing has no birdies. (Maybe the humming scares them?)
A really nice PS.

Wally KC9INK

On Wed, Oct 27, 2021 at 02:59 PM, Wallace Gasiewicz wrote:

I bought the PS because I was sick and tired of dealing with birdies on SMPS
PS. This thing has no birdies. (Maybe the humming scares them?)
A really nice PS.

Wally KC9INK

There you go, just another -very- good reason to stay with a good old linear PS. I have enough birdies already just dealing with the Ethernet cables and routers, don't need any more :-)

On Wed, Oct 27, 2021 at 12:36 PM, kc0wox Leeper wrote:

Where are you located? I may have one but I'm near Denver and won't ship it.
If you are close enough I'll check on it.
Leonard

Would have to ship to Miami FL.
I know these can be a bear to pack and ship.
Thank you.

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Dear Wally,

Alwyn

I use my 6271B all the time with My GRC 106 Military transceiver. Puts out maybe 350 W with two 350Z tubes.
But the GRC is so loud (fan) that I would not notice any PS noise.

Wally

I have four of the 20V 20A versions.? The Humming/Buzzing I think is mainly due to the Thyristor Pre Regulator in these PSUs.? This maintains the input to the Linear Regulator to just a bit more than the drop out so little heat is generated in the Pass Transistors.?

Denis

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