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Author Topic: Got a "technician special" SB-101 on the way -- what to expect?  (Read 8061 times)
KX4QP
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Posts: 404




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« Reply #75 on: April 12, 2019, 03:37:55 PM »

Perhaps you have seen this article (one of many):
https://www.qsl.net/k5lxp/projects/SaltLoad/SaltLoad.html

Yep, I'm pretty sure I have that one bookmarked.  I don't have anything to measure SWR (at least until I get my SB-102 running, or buy a meter to set up an antenna for something else), but I've got a digital multi-meter.  Get 50 ohms, with 50 ohm cable from radio to load, it should give SWR pretty close to 1:1 (unless you have a transmitter with a high impedance output -- unlikely to exceed 75 ohms if it was made after 1960, I think).

AS for "not being a proper ham" due to limited funds...it is a myth!

If you have a FCC license and make contacts, YOU'RE A HAM RADIO OPERATOR !

BTW I like your "can do " spirit to forge ahead with creative low cost solutions.

Yep.  I was joking.  I do make a few QSOs every week during my afternoon commute, with my 8W HT (upgraded to 1/4 wave Nagoya 771 antenna), inside my car.  I can still get full quiet on the repeaters that are high enough out to 15-20 miles, and key the repeater from as much as forty miles, if terrain cooperates.  Not bad for having about $125 invested, including more spare batteries than I'm ever likely to actually need (bought extended capacity, didn't realize it was a two-pack -- now I've got more than a week of battery life if I take all three).  Next week is payday, planning to get the power supply and cable, plus some antenna connectors (need a BNC for the Cricket 80a, got to look in the back to see what the Heathkit wants, and then something to connect both to an outdoor antenna, as well as make that available to my Hallicrafters S-120).

Future months will bring more toys.

I've played this game before; I also shoot and reload, put together a stable of nice, OLD film cameras on a tighter budget than this one, built and flew radio control and started using home computers (in the 1980s!) when I was working as a cab driver in Seattle -- just can't have everything at once, that's all.
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W9IQ
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« Reply #76 on: April 13, 2019, 05:08:58 AM »

Perhaps you have seen this article (one of many):
https://www.qsl.net/k5lxp/projects/SaltLoad/SaltLoad.html

Yep, I'm pretty sure I have that one bookmarked.  I don't have anything to measure SWR (at least until I get my SB-102 running, or buy a meter to set up an antenna for something else), but I've got a digital multi-meter.  Get 50 ohms, with 50 ohm cable from radio to load, it should give SWR pretty close to 1:1 (unless you have a transmitter with a high impedance output -- unlikely to exceed 75 ohms if it was made after 1960, I think).

If you do experiment with salt water dummy loads, make certain that there is a proper air vent so that as the vapor pressure increases, the container doesn't uncontrollably vent hot water or steam or worse yet, explode.

If using plastic containers, make certain you know the softening/melting temperature of the material - this is well below boiling temperatures for many plastics.

While the dummy load may measure 50 ohms with an ohm meter, the construction of the probes may add reactance at RF frequencies. This is undesirable for a dummy load. Check it with an SWR meter or antenna analyzer to be sure it is nearly purely resistive.

If you wish to minimize the RF leakage of the dummy load, a properly vented metal container should be used.

Many of the claims regarding the power handling characteristic of salt water dummy loads are not well founded. I showed the thermal analysis math on other threads if you are interested.

- Glenn W9IQ
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- Glenn W9IQ

I never make a mistake. I thought I did once but I was wrong.
W5RKL
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Posts: 1113




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« Reply #77 on: April 13, 2019, 05:52:47 AM »



An inexpensive 50 ohm dry dummy load is the MFJ-260C 300 watt unit.
They can be purchased for $50 free shipping on eBay or less on other
websites.

I use the MFJ-260C with my Kenwood TS-520S, Heathkit and other
100 watt transceivers. The max power and constant carrier time period plus the
cool down period must be adhered to. The manual can be obtained at
the following link

https://www.mfjenterprises.com/Downloads/index.php?productid=MFJ-260C&filename=MFJ-260C.pdf&company=mfj

73
Mike W5RKL
www.w5rkl.com
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KX4QP
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Posts: 404




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« Reply #78 on: April 13, 2019, 10:02:41 AM »

I don't have anything to measure SWR (at least until I get my SB-102 running, or buy a meter to set up an antenna for something else), but I've got a digital multi-meter.

Check it with an SWR meter or antenna analyzer to be sure it is nearly purely resistive.

Once again, the only instrument I have at present is a DMM.

An inexpensive 50 ohm dry dummy load is the MFJ-260C 300 watt unit.
They can be purchased for $50 free shipping on eBay or less on other
websites.

Thanks for the pointer -- that might be within reach before I have a transmitter big enough to need that sort for rating.  I can build one easily enough for QRP. Need to get a BNC connector to plug into the Cricket 80a, and some 1/2W or larger resistors.
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KC1BMD
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Posts: 959




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« Reply #79 on: April 13, 2019, 04:30:39 PM »

...that might be within reach before I have a transmitter big enough to need that sort for rating.

Don't misunderstand the 300W rating. My 1500W Palstar DL1500 can only withstand 1500W for 10-sec and 100W for several minutes before it needs a cool-down. Be sure to read the specs (e.g. power vs time curve)

Once again, the only instrument I have at present is a DMM.

Are there any local radio clubs? Any hams nearby? I'm sure someone would be happy to lend you one or come over to help.
« Last Edit: April 13, 2019, 04:37:31 PM by KC1BMD » Logged
KX4QP
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Posts: 404




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« Reply #80 on: April 13, 2019, 07:01:36 PM »

I understand duty cycles.  I've got a cheap welder (20% cycle at full power -- weld one minute, cool for four, or it shuts off and the manual warns that the shutoff won't dependably prevent damage).  I also don't have any expectation of exceeding 100W output in the foreseeable future, so a 300W dummy load should have useful duration.

And yes, my club has a member who's turned his "carriage house" into a club shack, and I'm sure he or one of the other members has a SWR meter or antenna analyzer I could use at the shack.  Generally, I'd expect little capacitance for a salt water load (just that of the cable), and inductance should be confined to just the "loop" formed by the cable splitting to the electrodes and the water between them -- but it never hurts to check.

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KC1BMD
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« Reply #81 on: April 14, 2019, 05:03:28 PM »

Sounds like you've got a plan. Let us know how it works out.
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KX4QP
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Posts: 404




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« Reply #82 on: May 16, 2019, 03:24:46 PM »

Well, latest update: payday today, so I ordered the power cable kit.  All brand new parts and includes a repro of the Heathkit manual covering assembly of the cable.  Not that it's difficult to solder to socket contacts and plug pins, just have to keep the pinout straight.
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W3RU
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« Reply #83 on: May 16, 2019, 05:40:29 PM »

We are glad your project is alive and well.  Please keep us informed on your progress.

Jack  W3RU
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KX4QP
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Posts: 404




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« Reply #84 on: July 05, 2019, 06:05:56 PM »

The cable kit has been here for a couple weeks, and my variac came on Wednesday (a pleasant surprise; I hadn't expected it until next week).  Today I had time (partner's out of town getting a new puppy to train for a service dog) and got the power cable assembled, connected everything except the power cable, and brought the power supply up on the variac.  No voltage on any of the outputs.

Took me three passes at various variac output voltages to realize that two of the wires I'd soldered in the power cable were for the powered unit to control the AC; unless I jumper pins 9 and 10 together, I won't get any output from the PS.  Okay, plugged in both ends of the cable and set the variac to about 50V output.  Dial lights in the SB-102 glowed faintly when I moved "function" to CAL.  HV read about 200V.  No smells other than the never-absent faint hot rosin odor of electronics.  I brought the variac up to 100V in a couple stages, still no smoke.  Brought it the rest of the way up to 120V -- and the HP-23-A popped its internal breaker.

A little more fiddling with it and I found that the plate current was non-zero in Cal, and creeping upward, presumably until it drew enough to pop off the PS breaker.

I just realized, however, that I had the Mode switch set to Tune, which might have been powering the finals into a bare antenna terminal  I just brought it back up, and with HV reading close to around 750V, plate current in CW mode is a happy zero, nice and steady, and the PS isn't popping it's breaker.  Got nothing in my ear buds (yes, wrong impedance, but if the audio stage is putting out, I should hear something).

I've got the manual in PDF; I guess it's time to read the operating parts and find out important stuff like where to attach the receive antenna, whether I really must have an antenna relay (I didn't wire in the output from the power plug for it, but in theory I can get the shell back off and install the necessary wire -- not obvious why it'd be a coax, however).  If I can find the receive antenna terminal (or verify it's the same as the one marked "RF OUT") I'll hook up the FM broadcast folded dipole I have in my shack so I can check receive with actual signal.
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AC2EU
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« Reply #85 on: July 06, 2019, 09:44:50 AM »

The cable kit has been here for a couple weeks, and my variac came on Wednesday (a pleasant surprise; I hadn't expected it until next week).  Today I had time (partner's out of town getting a new puppy to train for a service dog) and got the power cable assembled, connected everything except the power cable, and brought the power supply up on the variac.  No voltage on any of the outputs.

Took me three passes at various variac output voltages to realize that two of the wires I'd soldered in the power cable were for the powered unit to control the AC; unless I jumper pins 9 and 10 together, I won't get any output from the PS.  Okay, plugged in both ends of the cable and set the variac to about 50V output.  Dial lights in the SB-102 glowed faintly when I moved "function" to CAL.  HV read about 200V.  No smells other than the never-absent faint hot rosin odor of electronics.  I brought the variac up to 100V in a couple stages, still no smoke.  Brought it the rest of the way up to 120V -- and the HP-23-A popped its internal breaker.

A little more fiddling with it and I found that the plate current was non-zero in Cal, and creeping upward, presumably until it drew enough to pop off the PS breaker.

I just realized, however, that I had the Mode switch set to Tune, which might have been powering the finals into a bare antenna terminal  I just brought it back up, and with HV reading close to around 750V, plate current in CW mode is a happy zero, nice and steady, and the PS isn't popping it's breaker.  Got nothing in my ear buds (yes, wrong impedance, but if the audio stage is putting out, I should hear something).

I've got the manual in PDF; I guess it's time to read the operating parts and find out important stuff like where to attach the receive antenna, whether I really must have an antenna relay (I didn't wire in the output from the power plug for it, but in theory I can get the shell back off and install the necessary wire -- not obvious why it'd be a coax, however).  If I can find the receive antenna terminal (or verify it's the same as the one marked "RF OUT") I'll hook up the FM broadcast folded dipole I have in my shack so I can check receive with actual signal.


Reading this makes me concerned for your safety. I hope you don't electrocute yourself or do serious damage to the rig. Please be careful.
It's like the amateur radio analog to the show "Naked and Afraid".  Shocked Grin
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KX4QP
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Posts: 404




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« Reply #86 on: July 06, 2019, 04:08:19 PM »

@AC2EU Thanks for your concern.  I'm not all that worried about the electrical exposure -- I have considerable respect for electricity (I repair power tools for a living, which often requires running a partially disassembled tool to observe brush arcing or isolate a vibration), but I'm not irrationally afraid of it.  I'm well aware of the hazards of large capacitors and high voltage (by high voltage standards, 800V isn't all that big a deal, but I got bit by a photoflash capacitor at about 350V when I was 14, and have no desire to repeat the experience with twice the voltage).  At no point in this process have I poked around anything with power on (other than pushing meter probes into the socket on the PS), and I watch the HV meter down to zero before lifting the top of the case.

I'm much more concerned about damaging the finals, but I doubt I've done so; Tune mode should be producing next to no power to the antenna terminal.  There was no change in aroma, no visible smoke, and plate voltage still reads up to 800V depending on the variac setting.  I haven't tested on transmit yet, as I don't have an adapter to connect my one HF antenna to the RCA terminal at RF Out (ordered a couple of those adapters today).

I did connect a speaker to the antenna terminal (it had the correct connector, and several feet of wire going to the speaker enclosure) and was able to faintly receive a signal on 40m SSB that was clearly people talking, though not really intelligible -- but that verified that the tuner is dead on frequency, as I found the same signal on a web SDR at the exact frequency I read off the dial and was able to hear that one of the stations was in Delaware, working stations all over the eastern half of the US (though I couldn't always hear the other stations in his QSOs on the DVR, which is located in kentucky).  Given this was in daylight, and the poor antenna, I think it's reasonable to think the receiver, at least, is in good shape.  I found the problem with the phone jack on the front -- a bad 1/4" to 3.5mm adapter; a different adapter gave me reasonable sound in the ear buds.  A cheap speaker ($6 for a pair from Goodwill) had the right connector for the 8 ohm RCA connector on the back, and gives useful sound.  RF gain, AF gain, preselector, calibration oscillator, SSB filter work, as far as I can tell with the antenna available.

Not sure if the CW filter works, or is even present (it was an optional part for this model, at least according to the manual I downloaded -- though that's an early manual and the rig I have appears to be a later version; for instance, the manual shows 180-35-1 for the audio stage circuit board, while the one in the rig is silk screened 180-35-3).  The S meter appears to work correctly in all settings I can test (Grid and Plate current, ALC, and HV; Rel Power I can't test yet).

What I've read suggests that if the diode in the Molex connector in the back were bad or not making contact, I'd have zero plate voltage to the finals (plus, it tests good on the diode setting of my DMM)..  Everything else seems to work, so I probably can't usefully test any further until I have means to test the drivers and finals.  I'll check cost for a light socket at the local hardware store, and if reasonable, get one for a dummy load; otherwise I'll order an actual dummy load from GigaParts next payday (300W rating is about the same as I paid for my variac).
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AC2EU
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« Reply #87 on: July 06, 2019, 05:49:34 PM »

you can get away with a light bulb but a dummy load is obviously a better choice.
Don't assume that there is little power i tune mode! Many old rigs can produce full power. It's basically CW mode but you don't  need a key!
S.O.P when testing this stuff is to be sure that drive is set to zero and MOX is not engaged BEFORE you flip the switch.
In SSB mode you could put it in TX and check Ip to see if the final tubes are at 60ma. There should be no carrier with no mike attached and drive at 0.
You don't really  need to test the tubes . You can usually tell by the way the rig acts. Ie; if the rig biases ay 60 ma without having to crank it up beyond 50% of travel, then the finals will probably be good. If the drive never seems to be sufficient ( after best tuning solution) , they you may have a soft PA .

I'm no expert on this model, but many vintage rigs that offered an external VFO required a jumper somewhere if this option was not used. You did get some reception , so maybe it's there already , otherwise the internal VFO would be disabled.
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KX4QP
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« Reply #88 on: July 07, 2019, 04:11:16 AM »

S.O.P when testing this stuff is to be sure that drive is set to zero and MOX is not engaged BEFORE you flip the switch.
In SSB mode you could put it in TX and check Ip to see if the final tubes are at 60ma. There should be no carrier with no mike attached and drive at 0.
You don't really  need to test the tubes . You can usually tell by the way the rig acts. Ie; if the rig biases ay 60 ma without having to crank it up beyond 50% of travel, then the finals will probably be good. If the drive never seems to be sufficient ( after best tuning solution) , they you may have a soft PA .

Thanks.  How would I key transmit in SSB without a mic?  Obviously, I'd need to emulate the PTT action -- does that connect one of the two conductors to the shell (= chassis ground)?  That would be a preferred early test, before keying CW, because it's much less likely to radiate significantly even from an improvised dummy load.
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AC2EU
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« Reply #89 on: July 07, 2019, 07:25:15 AM »

S.O.P when testing this stuff is to be sure that drive is set to zero and MOX is not engaged BEFORE you flip the switch.
In SSB mode you could put it in TX and check Ip to see if the final tubes are at 60ma. There should be no carrier with no mike attached and drive at 0.
You don't really  need to test the tubes . You can usually tell by the way the rig acts. Ie; if the rig biases ay 60 ma without having to crank it up beyond 50% of travel, then the finals will probably be good. If the drive never seems to be sufficient ( after best tuning solution) , they you may have a soft PA .

Thanks.  How would I key transmit in SSB without a mic?  Obviously, I'd need to emulate the PTT action -- does that connect one of the two conductors to the shell (= chassis ground)?  That would be a preferred early test, before keying CW, because it's much less likely to radiate significantly even from an improvised dummy load.

No Mox switch on the SB101 , so just take the ptt pin to ground or have the carrier and mike level to 0. That should leave you with nothing but the tube bias current in SSB mode.
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