HP 6114A, 6115A PRECISION POWER

[jonpaul]

Bonjour a tous,

Had the 6114A for a decade, a classic HP design and built like a tank!

I only recently had occasion to use, checking  a 5 1/2 digit DVM, and I  realized what a great device it is, then reading the previous notes on this forum.

It was in mint condition from an old silent key friend estate. SN 2314A....

The 10 turn OPT current adj had a bad Helipot dial and was a plastic low grade potentiometer, so I replaced it with a Beckman 1K and new dial, works fine.


I have made a deal on a "parts only" 6115A  $90,  single turn screwdriver current pot,  seems in great physical cond,

A  thumbwheel switch (left most, upper) actuator button is missing.

In my old stock, a Beckman 1 K Helipot and dial ready for upgrading the unit.

Questions:

1/ Is $90 a good deal?

2/ Ideas on finding and replacing the thumbwheel switch actuator button?

3/ Any  common failure modes and  things to check, besides  lytics, thumbswitches?

4/ Any comments on accuracy you have seen, beyond  the HP specs 0.025% accuracy?

Mille Mercis,

Jon

[guenthert]

1/ Is $90 a good deal?

     If you had $90 you didn't need otherwise and the device serves a need, then yes.  But you know that better than any of us.

4/ Any comments on accuracy you have seen, beyond  the HP specs 0.025% accuracy?

     The accuracy clearly depends on how well you're able to calibrate it.  They seem to be very stable with good resolution and low noise, so they can be calibrated well.  Mine matches (matched last I looked at it, it's unfortunately out of my hands in storage now) my HP3478A.  I've seen them given the nickname 'adjustable reference'.

[jonpaul]

Bonjour, guenthert many thanks,

 I checked the 6114A, set   10.0000, using  Fluke 8842A, perfect!

Asking advise on the missing thumbwheel switch button replacement in photos.

Must entire switch be disassembled or can a new button be inserted from the front?

Many thanks again,

Jon

[guenthert]

    I opened mine only briefly to have a peek, but as it seems to work well, left it at that.  I suspect you've seen https://www.eevblog.com/forum/testgear/hp-6114a-precision-power-supply-restoration/msg261499/#msg261499
    Might be worth pinging robrenz as he probably knows more about it than most of us.

[Tomorokoshi]

    I opened mine only briefly to have a peek, but as it seems to work well, left it at that.  I suspect you've seen https://www.eevblog.com/forum/testgear/hp-6114a-precision-power-supply-restoration/msg261499/#msg261499
    Might be worth pinging robrenz as he probably knows more about it than most of us.

Yes those pictures show clearly what's involved with repairing the switches.

I took all 4 pushbutton units apart in my two 6114A supplies because the grease used on the gold-plated contact disks make them operate inconsistently. I cleaned the grease off with alcohol and 3M Novec. Once they were reassembled they have been accurate and stable ever since.

However, that isn't your problem. Was the button broken off? It looks like possibilities would be:
- Somehow attach something to what remains of the button
- Find a spare assembly and substitute it in
- Make a model of the button and 3D print it

[jonpaul]

Hello all,  guenthert and Tomorokoshi many thanks, for your notes.

The machine just arrived yesterday, was carefully packed and basically works to spec,

 Inside very dirty and dusty, no rework or noticeably bad parts, all capacitors seem fine.

 Current control is normal pot, will replace with Beckman Helipot 1K
 Meter bezel slightly cracked
Vernier voltage dial on right was scratchy, used  IPA 99%  and contact cleaner.
I will use high pressure air to blow out dust and wash the PCB with IPA 90%

____________________________________

The 10s thumbwheel dial on left has the + button broken off about 1/2 way inside. If I use a small tool, I can poke the dial to increment up.
All other thumbwheels are Ok and voltage is accurate.
The thumbwheel seems hard to source an exact replacement, i believe its IDEC and custom made for HP.

Insted of 3D, I propose:
use black polycarbonate or delrin rod stock, machine to the 0.100 x 0.300 button dimension. Cut to legnth and drill small hole in end.
Take a needle, heat in flame and push into broken button end,  and into the new machined button.

Another source of the button can be a plastic glasses frame sidepiece with center metal rod.

__________________________________________

I have the manuals and HP Tech Notes article, testing the AC noise, load reg, and accuracy, I can only marvel at theis great analog design.



Open to your comments,

Kind Regards,

Jon

[Stray Electron]

    The owner of two HP 6114s and a 6111 here. In the US I would say that $90 is a fair to good deal for a working one. It's probably a great deal in France considering that everything seems to be more expensive there.     I have three of those type power supplies and they all work great but as the previous poster said, the accuracy depends on the vernier adjustment. It probably shouldn't even be called accuracy IMO but probably stability instead. The only problem that I've encountered on mine are dirty controls and dried grease but I've cleaned mine  with spray tuner cleaner with out having to take the switches apart.   The ones with the optional 10 turn pot are very nice! I have that in one of mine and I may convert the others to the same feature.  I found the last one of mine a few months ago in the storage room of a local surplus store and bought it for $10 :-)

   The ten turn pot was a option on many of the old HP/Harrison power supplies and it's well worth getting IMO.

   The US is flooded with old HP, Harrison, Lambda and other GOOD power supplies. I don't know why people bother buying the cheap Chinese power supplies.  I have several very old HP supplies, one that I know what made in 1966, and they all work fine and I've never had to recap them or do anything other than clean the switches and pots and they still work great. The fact that there are complete service manuals available for them and that most of the component parts are stock off the shelf items and not custom made hybrids is a real plus IMO.

[jonpaul]

Stray Electron your comments  appreciated,

This one came off epay USA and cost me ~ $110 with shipping. My earlier 6114A was from a silent key estate,  ~ $15.

Using a Fluke 8842A, both are in CAL, the 6114A is mint. I need to do a full CAL on the 6115A, but the REF and PSU voltages all are in spec.

  I shall add the Bourns 10T current pot and   fix the broken + button on the left thumbwheel.

These are built like tanks, highest quality gold plated PCB and all USA components.

The article in HP tech notes by the designers is very good.

 my sentiments exactly re old HP/Lambda/TEK quality vs current junk from China.


Enjoy,

Jon

[jonpaul]

Hello again: All fixed and works fine except for the broken button.

Now seeking the 7" ling front and rear feet to complete the job, these are unique to these style of HP chassis, the HP parts are

Foot assembly front  and  rear both are HP # 5060-0728 

Finally the meter surround bezel is broken, trim, meter 5020-8061

I am sure other instruments of same case size use these feet.

Any sources or spares are appreciated, also may have HP parts to swap.

Kind Regards,

Jon

[Gribo]

Omron, C&K and TE have thumbwheel switches available, you might want to look into those. https://www.digikey.com/en/products/filter/thumbwheel-switches/214?s=N4IgjCBcoLQdIDGUBmBDANgZwKYBoQB7KAbRADYB2AThALAAYAOOihhgZgFYHWAWHqw60AugQAOAFyggQAXwIwATFFDJIkgE4BXfEVIguIMSCkz5CkCshkAKgAttAWwBGAd3s4cGAARY3AJaSiPbGBEYI4lBgElGQPHJyQA

[Stray Electron]

   I just noticed that Walter Sphere in Canada has a bunch of the HP 6114 type power supplies for sale at a reasonable price.  This would be a great deal for any of you that are in Canada since there wouldn't be any exchange rate of import tax to add to the costs.

   Walter's webapge is here https://www.sphere.bc.ca/test/power.html but I don't have the specific page that the power supplies were on so you'll have to hunt.  It was some kind of a "Specials" page.

   PS    I think it was this page but they don't seem to be there any more, perhaps they sold already. But you can contact them and ask https://www.sphere.bc.ca/test/new.html

[jonpaul]

Hello to Girbo and Stray Electron!

Mille mercis pour votre gentil aide:

1/ I have researched the switches, the original were IDEC or German Hartmann. I believe the same model is still made and called "push wheel switches"

similar but wrong dimensions: https://www.mouser.com/datasheet/2/26/DPS9_PUSHWHEEL-5271.pdf


2/ I am in both USA and Paris, not Canada. Walter at Sphere is fine but the internationals shipping costs and paperwork are the issues.

3/ I have restored everything!

Cleaned it inside with comp air and iPA, lubed the internal trim pots, added the Beckmann 10T 1K current helipot, and calibrated using a Yokogawa 2554 CAL.

Final touch: The buzzing was not a loose transformer lamination,  but the 1 mF 250 VAC (yellow plastic) cap across the transformer winding

I replaced with a modern dipped film 250 VAC X cap, and its now almost silent.

So my want list is only:

Black long HP feet
Meter bezel black trim ring
replacement for thumbwheel switch or button

I can send photos of the missing and broken parts.

4/ The problem on most used 6114A and 6115A is the weight makes them easy to damage in the lab or in shipping, so very hard to get one that does not have physivcal damages.

End result: My CAL lab has both 6114A and 6115A, very fine additions!

Bon Journee!

Jon

[Tech RAH]

I have a 6115A with the smaller thumbwheel for the thousandths unit place (0-9 mV) and based on the photos I've seen in this forum, I find the ones on the 6114A look much nicer, more "solid." I'm just wondering if those have fared better over the years than the 6115A's. I did some resistance measurements and realized that I can't actually go all the way down to zero or all the way up to the maximum value of 20 ohms. According to the service manual, both models have a 20 ohm, ±5% pot. Anyway, here are my readings:

0: 1.26 (should be zero) 
1: 2.23
2: 4.17
3: 5.89
4: 7.86
5: 9.87
6: 11.85
7: 13.90 (only value within the 5% tolerance)
8: 15.56
9: 17.38
10: 19.27 (should be 20) 

If anyone else has done measurements, I'd be interested to know if they were any better... or worse 

I should have taken pictures when I last removed the front panel resistance board. The potentiometer is separate from the thumbwheel so I'm wondering if it can be removed and replaced. I fear that trying to find the right size (and value) replacement might prove to be fruitless. I'd even be willing to replace the whole thumbwheel + potentiometer assembly if I could find it.

[TizianoHV]

I bought mine for 55+9€ in 2021. It wasn't in great shape but it was my first PS and it has been really good.



The meter needed a rebuild, some caps were dead. I added an on/off switch to set the output to zero without need to reset all buttons, a 10 turns current pot, front sense posts and a low voltage mode (400mV full scale).



Regarding accuracy, before calibrating, you should check its temperature coefficient. You can set the output to 10V and measure the warmup drift from cold. Mine measured +200ppm drift (+16ppm/°C when warm), not so good. After some searching, I found out that the reference zener had high tempco (+9ppm/°C, hould be 5ppm/°C spec). By increasing the value of R9 (1% resistor, nothing special) I tweaked the tempco down to -2ppm/°C (negative so that it nulls out with the other drifts, in my case). Now the warmup drift is just +25ppm (+4ppm/°C when warm).



Regarding the 20ohm pot I get similar values. It's not easy to find a 20ohm potentiometer.

[jonpaul]

Hello the controls both thumbwheel and fine adj pots become scratchy and oxidized.

Need clean with Iso Alcohol and then contact lube/control lube.

Switches and wheel pot can be disassembled but  easy to loose parts or break old plastic.

See previous posts here and on Groups.io HP.

Jon