Metcal: varying tip temperature between power supplies.

[jonsig]

Good day.
I own Metcal mx-500 and recently bought another power supply (STSS-02 115V) And replaced the 115V mains transformer to 230V. I replaced the old one 241-8-28 to DP-241-8-28 that fits perfectly in place where the old one was seated. Recap-ed the station with same value capacitors except the main bulk capacitor, 2200µF=>2700µF and gave it disgraceful new color 

I´m wondering why i´m getting 23°C temp difference on the same tip, with same wand on both stations. 
Mx-500 reading @ 350°C and the STSS-02 373°C. STTC-138 tip. While both in within max temp spec.
I have limited information on voltages i should measure on the StSS-02 according to the patent schematic. (US4626767)
Stss-02 power draw is around 63W from the mains and 71W before recap, but with 115V/230V step down transformer that would explain the difference.

Mabey both stations are fine. i´m not sure what causing the different curie temps. Both stations are of course 13.56MHz by spec.

[jonpaul]

Jonsig: Fine question!

You use Original genuine Metcal tips or Chinese knockoffs?

Temp is function of tip curie point. Check tip models for the temp rate.

The Signal transformers have dual primary and can be rewired for 120 or 240 V

Check and compare input power with tip in open air and fully loaded eg on a copper block.

Finally solder tip temp measurement requires a small gauge thermocouple (we use type K, welded #30 Ga)

A 10-20 deg error in tip temp is easy to miss.

Just the ramblings of an old retire EE


Enjoy,

Jon

(PS: I had designed SP-200 500 kHz Metcal 1990..1994)

[jonsig]

Thank you for the reply.

The metcal tip was ordered from mouser. I took tvo sets of measurements with possibly 1C° variation between.
I use one of those FG-100 hakko knock-offs with new thermocouple to mesure.

Both supplies perform quite nicely. But this behavior between them is strange.

The old transformer only had three primrary tabs.

I have not confirmed the output RF frequency.

Forgot to mention the wand i'm using is on its last legs..  the coax has been shortened by half in length. I'm waiting for replacement. But DHL in Iceland are quite bad performers.

Best regards

[Runco990]

I have several MX-500 stations and discovered the same thing.  For me, the cure was to use the same tip and hand-piece as a control and test the temp on a thermocouple tester.  THEN set the power level pot inside each base to match the stated tip temp specs.

Now all my stations perform within only a few degrees.  I'm not entirely sure why this is, as in theory the base sends all the power the tip itself requires, but it worked just fine.

[jonpaul]

....the coax has been shortened by half in length......

Very bad, as the length at 13.5 MHz is part of the RF design.

Suggest  a new handle with correct length coax.


Jon

[Monkeh]

....the coax has been shortened by half in length......

Very bad, as the length at 13.5 MHz is part of the RF design.

Suggest  a new handle with correct length coax.


Jon

So how did they account for the old switch unit, power meters, and so forth?

[jonsig]

Thank you for the reply again sir. I i appreciate the solid replies.

I initially thought there was a problem with the wand as the metcal WS1 sleeping-stand increases stated output power on the mx-500 power indicator ! When the tip sits idle on the bench top it reads ~10W but goes to 18W when seated in the sleep stand.
But the SSTS-02 max power draw is as expected, peak draw around 70W with power factor of ~= .7

I got the questionable wand included with mint condition mx-500(digital) + sleep stand for 280$ -exl.shipping. And i bought the ssts-02 in hope to inherit my 2yr old doughter which i'm hoping that will follow in father's footsteps (hope in not sounding too corny)

Bought 2x MX-H1-AV wands week ago, but like stated Icelandic DHL is a mess. 100$ is not enough for them to prioritize.
(Now IS/DHL will probably call me to lecture me if they google ("DHL mess").

Is the F-connector 50Ω (Z) and wand RG-316/RG-174 coaxial cable ? in case i fix the old wand to use with the RFG-30,
also could you please inform me roughly on the single pot - calibration procedure on the vintage rfg-30.

Best regards
 

[jonpaul]

Bonjour jonsig,

RE Icelandic DHL


DHL was part of Deutsches post. Used to be excellent.

Some time ago DHL was reorganized into a different firm per country.

Result is terrible service, impossible to contact and lack of customs clearance even in packages to Germany.

Our firm stopped ALL DHL shipment in/out and we use only Fed Ex and second choice UPS.



RE:  F-connector 50Ω   wand RG-316/RG-174 coaxial cable 


Tru F conn is 75 Ohm not 50. I am aware of MX-500 Zo but the connector may be special, and the coax certainly was custom mde.

The RG-316/RG-174 may work electrically but the solder wand application demands two special properties:  super flexible and solder proof (silicone) insulation.

Mogami in Japan fabs such special wire.

I would just get a new wand.

Kind Regards,

Jon

[jonsig]

Thank you once again

Yes, DHL will mabey deliver the metcal wand to me one day.
So i should not bother to adjust the L4960 switching regulator in case the potentiometer has drifted ? i always have to repair to disrepair.

I admit i could be much smarter in the RF field, but i wonder if simple bird RF meter with 13MHz element and 50-70ohm dummy load would give me approximate reading of the forward RF power and standing wave ?

[jonpaul]

Rebonjour Jonsig, fine to hear from Iceland.

 DHL will mabey deliver ....

Suggest to call local DHL and track/expidite the shipment. Normally it will be a lack of customs /VAT documentation by the shipping party.

RE: adjust ...regulator in case the potentiometer has drifted.....
Highly unlikely unless unit was water or physically damaged. I would leave it till the real issues is fond.

RE: Bird RF meter with 13MHz element and 50-70ohm dummy   forward RF power and standing wave 

Interesting exercise but hardly worth the effort. 
On second thought, at  13.5 MHz  wavelegnth will be  22.2m in free air and quarter wave in a cable ~ 5.5m / roe so the cable length may not be an issue anyway.
Conclude that shortened or unshortened wand will not affect unless the loss of the cable is significant at 13.5 M

Jon

[jonsig]

DHL arrived at last. The excuse was potential covid-19 infection of their staff members, and they were very polite, so i forgive them. Guess convid-19 counts for everything these days.

With the new wand, i did re-check of the temperature on the SSTS-02 with the same STTC-138 tip and the result was... 351°C on the FG-100 test gismo. Previously ~373°C.  Interestingly the peak power draw from mains increased from 71W to 73.4W. Thinking back i should have noted changes to the cos Φ.
Both tests were far from being controlled in both cases the station is tested without any warmup period. But in temperature controlled room.

Is it possible that Digital variant of the MX-500 has more advanced RF feedback to compensate more efficiently ?
Yes, and with the λ /4  ~5mtr.. this makes no sense to me I must have screwed something up initially.

Now i just need to test the MX-500 for temperature change.

[jonpaul]

jonsig hello again,

Temp tests: Very hard to get a better than 5 deg C accuracy. Ambient, warmup, drafts, contact to tip etc are all variables.

A 30...36 ga  TC in a drilled hole or welded to the DUT is one solution. Also a thermal compound gives better accuracy.

Coax length : Easy to make a faulty splice on either end of a coax, that is more likely the fault than the length.
But aside from the matching and wavelength at 13.5 MHz, all coax have losses, eg 15 db/100' at a particular freq.
Consult the excellent data and app notes from Belden wire and Steve LAMPEN for details.
My SMPTE 2017 digital audio transmission paper had data on 18 TP and coax cables.
If you can ID the exact coax Metcal uses, then the attenuation at 13.5 MHz with various lengths may explain the differences if a cable is shortened.

Control: I have no info on MX-500, modern units, the  13.5 MHz Metcal nor the control systems, my design was SP-200 in 1990..1993!

The original system forced a constant current thru the cable and induction loop at the tip, and the curie point material maintained a calibrated temp as the tip heated up.
Thus for a calibrated current and particular tip, neither cable length nor power supply/workstation affected tip temp, only the tip model and curie point.
I suspect the same patented principle applies to the modern units and the 13.5 MHz.

Bon journée,

Jon

[jonsig]

Yes the coax cable splicing was done at male F-connector of the wand, it really looks like made in a hurry.
I own few meters of rg316 and ultra soft anti-esd tubing of same size as the original, i could try to make ghetto version of the wand. Just need to order new F- male plug