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Author Topic: Got a "technician special" SB-101 on the way -- what to expect?  (Read 7966 times)
W3RU
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Posts: 56




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« Reply #15 on: March 27, 2019, 06:00:46 AM »

"There also could be other problems that contribute to loss of transmit RF output." (Mike's quote)

Mike has some good suggestions to check through.  I can add one more: check the mode switch for contact damage or being cracked/broken.  This switch is highly susceptible to physical damage when a previous owner has attempted to repair the SB and pulled too much on the loose front panel after disconnecting most of the controls, but not the mode switch since it is not used to hold the panel to the chassis.  This is a common shortcut when replacing the O-rings on the final loading and pre-selector shafts, which require additional space in front to gain access when the brass shaft bushings and knobs have not been completely loosened and removed.

The four black wires attached to the top of the modulator board from this switch (the wires which switch the carrier crystals) are short, and relatively heavy gauge wire compared to the numerous harness wires soldered to the rest of the terminals.  These can exert substantial force on the rear wafer which can cause wafer fracturing when pulled forward.  Depending upon what may be damaged, the transmit function can do all sorts of funny things intermittently, or not pass any mode signals at all, if any terminals are damaged or the wafer is cracked.  You will not get any RF output without a functioning carrier oscillator signal on any mode, unless your final stage is undergoing self-oscillation.

The most effective way to test your modulator board carrier oscillator operation is to probe the 3.39x MHz crystal frequency with a frequency counter for the tune, LSB and USB modes off the center wiper terminal of the carrier null pot as you switch through the modes.  The CW mode will read the USB crystal frequency in receive, and when the key jack is closed, you can read the actual CW crystal frequency.  This test may also reveal other common problems, namely, inoperative or off-frequency carrier crystals which directly affect optimal RF output power and receive audio quality differences between USB and LSB (another parts rig opportunity).

A dirty switch can also exhibit the same symptoms - deoxit and "rocking" it back and forth may help identify this condition, but the interior wafer surfaces are somewhat difficult to access - even with a Q-Tip.

Unfortunately, the only way to fix this condition to ensure reliability is to find a parts rig for a "donation" - assuming the  mode switch is undamaged, of course.  My previous attempts to fix cracked wafers using superglue have failed miserably, and this switch requires considerable time and effort to replace due to the number of wires involved and required total disassembly of the front panel.  Collateral damage to the VOX panel control wires usually results during the process.   Thoroughly clean and test any switch before installing it as a replacement while it is bare.

Mike's suggestion regarding the 50ma current check is valid - you will get the current reading regardless if the mode switch is working, or not.  

Jack  W3RU
« Last Edit: March 27, 2019, 06:21:02 AM by W3RU » Logged
AC2EU
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« Reply #16 on: March 27, 2019, 07:30:58 AM »

Until this radio arrives and gets hooked up to a power supply, all of this is moot speculation.
With a "technicians special" there is a good chance that it was:
miswired
mistuned
badly soldered or not soldered in places at all.
modified
used as a parts set

All of the above is much different than a single failure event that can be found with normal troubleshooting and logic.
It is likely that there are multiple issues which may be very frustrating to a person whom has not repaired anything since the 70's and has no equipment to do so.
Your first task is to verify that everything is there that is supposed to be there.
If repairing boat anchors is what you want to do, then I would suggest that you start collecting some bench staples such as a good scope ( 100 Mhz or more), frequency counter , DMM and signal generator.

You say that you have a tight budget. All of this can get quite expensive and time consuming . It's probably not worth it to fix one radio.
If you do intend to do more radios , then start saving your lunch money...
« Last Edit: March 27, 2019, 07:52:30 AM by AC2EU » Logged

KD0REQ
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« Reply #17 on: March 27, 2019, 07:43:12 AM »

in going through my HW-100, I found every 22K to B+ was way off, shotgun those things. also wildly off resistors in the vicinity of the driver tube. the parasitic choke resistors were pretty cooked, so I unsoldered and slipped the coils off and slid them onto new resistors. then life got in the way, and it's been under the bench for a little bit.

I formed a chassis after I found the correct transformer on eBay, got the rest of the parts, and built my own HW23A.  I'm also gunning those .02 bypasses that look a little cooked.  good luck with the project.
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KX4QP
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« Reply #18 on: March 27, 2019, 03:28:27 PM »

If repairing boat anchors is what you want to do, then I would suggest that you start collecting some bench staples such as a good scope ( 100 Mhz or more), frequency counter , DMM and signal generator.

You say that you have a tight budget. All of this can get quite expensive and time consuming . It's probably not worth it to fix one radio.
If you do intend to do more radios , then start saving your lunch money...

Repairing boat anchors is not the primary interest here.  I somehow thought I might be able to get one working without learning a new career.  The interest was and is to have a good radio with wide band coverage that I can afford, and stand some chance of repairing if it breaks down in service (odds are much better for that in the tube era, vs. anything modern, I think).

You make it sound like I'd be ahead to send the radio out to be fixed, or (barring a miracle -- wouldn't be the first I've had from eBay, though the others were in the old days when you could still buy good stuff cheap) keep looking for one that's been in recent service, i.e. needs only minor touch-up work, and keep this one for spares.

Someone asked up the thread a bit how my shop is equipped -- I got busy answering something else and forgot to answer.

At present, I have a heat controlled 60W soldering iron, a higher power soldering "gun" (momentary heat, and it's a cheap one, but it works well), some basic plier/cutter tools, including a small stripper/crimper and tweezers that came with the 60W soldering iron kit -- and a digital multimeter from Harbor Freight ($17, cheapest I could find there -- what happened to the tiny shirt pocket ones for under $10?).  I'm pretty good with solder (built an eBay frequency counter kit with the clunky old "gun", despite closely spaced plated-through pads) and I have experience with electricity (though not so much with high voltage or RF).  Once I get the plastic housing assembled, I'll have my freshly built frequency counter (5Hz-50KHz 4 digits), and I have a kit for a marker generator that shouldn't take more than a couple hours to put together (when I have time).

I don't have deep enough pockets or space to think about a well equipped electronic shop -- if I can pick up an old, working O-scope at a hamfest, I'll be happy, otherwise anything in that class will have to plug into a USB port or microphone jack and have software that runs in Ubuntu.
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AC2EU
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« Reply #19 on: March 27, 2019, 07:38:49 PM »

If repairing boat anchors is what you want to do, then I would suggest that you start collecting some bench staples such as a good scope ( 100 Mhz or more), frequency counter , DMM and signal generator.

You say that you have a tight budget. All of this can get quite expensive and time consuming . It's probably not worth it to fix one radio.
If you do intend to do more radios , then start saving your lunch money...

Repairing boat anchors is not the primary interest here.  I somehow thought I might be able to get one working without learning a new career.  The interest was and is to have a good radio with wide band coverage that I can afford, and stand some chance of repairing if it breaks down in service (odds are much better for that in the tube era, vs. anything modern, I think).

You make it sound like I'd be ahead to send the radio out to be fixed, or (barring a miracle -- wouldn't be the first I've had from eBay, though the others were in the old days when you could still buy good stuff cheap) keep looking for one that's been in recent service, i.e. needs only minor touch-up work, and keep this one for spares.

Someone asked up the thread a bit how my shop is equipped -- I got busy answering something else and forgot to answer.

At present, I have a heat controlled 60W soldering iron, a higher power soldering "gun" (momentary heat, and it's a cheap one, but it works well), some basic plier/cutter tools, including a small stripper/crimper and tweezers that came with the 60W soldering iron kit -- and a digital multimeter from Harbor Freight ($17, cheapest I could find there -- what happened to the tiny shirt pocket ones for under $10?).  I'm pretty good with solder (built an eBay frequency counter kit with the clunky old "gun", despite closely spaced plated-through pads) and I have experience with electricity (though not so much with high voltage or RF).  Once I get the plastic housing assembled, I'll have my freshly built frequency counter (5Hz-50KHz 4 digits), and I have a kit for a marker generator that shouldn't take more than a couple hours to put together (when I have time).

I don't have deep enough pockets or space to think about a well equipped electronic shop -- if I can pick up an old, working O-scope at a hamfest, I'll be happy, otherwise anything in that class will have to plug into a USB port or microphone jack and have software that runs in Ubuntu.

The reason that the shop question was asked is because it takes test equipment to troubleshoot, align and test radios.
I just had two radios last week which were 'Ebay specials". No section or subsection in those radios were operational, either due to normal failure or weakness due to age or due to 'intervention". I have seen some serious messes and I am concerned that your SB-101 radio may be one of those multiple problem radios which has to be brought back to life a piece at a time. The fact that it was kit built is a concern in of itself.

How will you know if the IF section is working or where the fault resides without a signal generator and scope? The frequency counter may not play well with the LO, so you will have to deal with loading issues.
If you bought a working radio and it failed. At least you know that it DID work before something happened. You might be able to do a quick fix that way.  With non-working stuff there is no baseline which is much more difficult because someone may have exacerbated the problems by trying to fix it.
Did you ask the guy what he knew about it's condition other than "it powers up"? Does receive work? does transmit work? Is it intermittent, etc?
The more you know before you start , the better.
Good luck, I hope my concerns are unfounded...
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KX4QP
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Posts: 404




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« Reply #20 on: March 28, 2019, 02:18:16 AM »

Good luck, I hope my concerns are unfounded...

So do I.

My experience with eBay is that there are two kinds of sellers -- the ones who know nothing about what they're selling (brokers, yard sale resellers, and so forth) and those who know exactly what they have and claim to know little or nothing.  I've seen a number of listings recently (for SB- and HW- family Heathkits, specifically) in which the seller listed them as "parts/not working" specifically in order to defend against costly returns caused by buyer misconceptions of what to expect.  For cameras, I used to be able to tell everything I needed to know from the photos (and what wasn't presented in photos, to hide a visible defect).  I never bought one that was worse than I thought it was, and I bought a bunch in the $10 to $50 range that I fixed up just a little bit and became good shooters.  As a result, I never really established a habit of asking a lot of questions, because they often didn't get useful answers in time to make a bidding decision.  However, it's easy to forget that my heyday of getting screaming deals on cameras (like $15 for a mislisted but clean, working, collectible model of plate camera with three plate holders) was also the relative infancy of eBay.

With radio equipment, I can't tell as much by looking (in part because I have much less experience in knowing what to look for).  The radio I bought came from a seemingly knowledgeable seller, likely a ham  himself, possibly a restorer.  I'll know more (at least from opening the case and looking inside for things like burnt components etc. -- don't have a power supply yet) in a few days, when the transceiver arrives.

If I had (room and money for) a well equipped electronics shop, I'd have been a licensed ham 30-40 years ago.
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VK6HP
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« Reply #21 on: March 28, 2019, 02:54:30 AM »

My self-imposed boat anchor rules*only permit me to buy items in excellent original condition (no obvious modifications), with a-grade cosmetics and well cared for interior.  I figure there's nothing else I can't fix.  With those conditions applied, it means that when the hours of repair and restoration have been put in, the outcome should be first class.  Still, I must admit that despite the SB-102 I described previously meeting the main criteria, the LMO warble fix and a replacement rear panel power connector taxed my patience.  But it made victory all the sweeter.

The Heathkits are pretty easy to troubleshoot.  You can get the receiver working using the crystal calibrator as a signal and that will also take care of many of the shared stages.  The manual is very good and includes dc quiescent voltages corresponding to e.g. correct oscillator levels.  If it's any comfort, in working on the SB-102 I only reached for the scope twice: once because I was tempted to try and pull the 40 m heterodyne oscillator  crystal frequency and once to do accurate neutralisation using my preferred 'cold' method.  Neither were essentials in getting the radio on the air.

73, Peter.

*rules may vary based on whim because this is, after all, ham radio
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W5RKL
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« Reply #22 on: March 28, 2019, 02:56:40 AM »

If you have access to or can borrow a frequency counter, you can check the
CAR GENERATOR, LMO (VFO) and band switch select HET OSC crystal oscillators.
All 3 oscillators are common to both receive and transmit.

Connect the frequency counter to the CAR NULL pot's center tab.
USB -- 3396.4Khz (receive/transmit)
LSB -- 3393.6Khz (receive/transmit)
CW -- 3396.4Khz (see note below)

Note:
CW -- 3395.4Khz is only active in TUNE and CW transmit modes.
CW receive uses the "USB" crystal oscillator as the "BFO".


Connect the frequency counter to pin 7 of V11 first receive mixer to check each
band's HET OSC crystal frequency. You do not have to key the transmitter to perform
these measurements.

80 meters -- 12.395Mhz (3.5)
40 meters -- 15.895Mhz (7.0)
20 meters -- 22.895Mhz (14.0)
15 meters -- 29.895Mhz (21.0)
10 meters -- 36.895Mhz (28)
10 meters -- 37.395Mhz (25.5)
10 meters -- 37.895Mhz (29.0)
10 meters -- 38.395Mhz (29.5)

Connect the counter to pin 7 of V12 second receive mixer to display the LMO
(VFO) tuning frequency range frequencies which are 5.5Mhz at the bottom of
all bands to 4.9Mhz at the top of all bands. The LMO (VFO) tuning
range from 5.5Mhz to 4.9Mhz is the same regardless of the band switch setting.
You do not have to key the transmitter to perform this measurement.

Added note:
Crystals age so the frequencies you see may vary from the above listed crystal
frequencies.


73
Mike W5RKL
www.w5rkl.com
RMC(SW) USN RET

« Last Edit: March 28, 2019, 03:02:42 AM by W5RKL » Logged
KX4QP
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Posts: 404




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« Reply #23 on: March 28, 2019, 03:35:42 PM »

Thanks again for all the information.  The UPS folks dropped off the radio today -- big ol' box, inside was a thick layer of bubble wrap and a smaller box.  Inside that was another layer of bubble wrap protecting the radio.  I can say with confidence that nothing bad happened to it between Colorado and here.

However, I can't say the same for my memory.  I looked at the closed eBay listing at least ten times in the interim (including when the seller sent me a payment reminder -- too used to Buy It Now, and thought I'd paid when the auction closed) -- and still kept thinking it was an SB-101.  In fact, it's the slightly younger brother, an SB-102.

I presume most of what's been said here applies, though I'll obviously need to download the correct assembly/operation manual.

And the first thing I thought when I got the radio out of the bubble wrap was, "This has just about enough knobs on the front."  All the knobs and switches look fine, the pins on the power connector are undamaged.  I see a plastic connector in the back, looks like about a 9-pin Molex type, with a single component (looks like a 1/2W resistor, but I didn't notice the value) connected between two pins.  Other than that, given lack of power supply and (on a weeknight) time, I just put the radio up on a shelf to await future detailed examination.  Band selector has 3.5, 7, 14, 21, and four positions to cover the 10m band!
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VE7DQ
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« Reply #24 on: March 28, 2019, 10:51:27 PM »

That 9-pin Molex connector is for the external VFO option.  The power connector is the 11-pin B11A circular female connector on the chassis.
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W3RU
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Posts: 56




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« Reply #25 on: March 29, 2019, 06:37:25 AM »

I think the molex connector on the SB-102 as built is used to interface power requirements for the SB-500 2 meter transverter if ever used with the SB-102.  The discreet component in the jumper plug is actually a diode in the screen circuit if I am not mistaken (I don't have the schematic handy just now, but I'll check later).  Careful - there is 800 vdc available on this plug for the 6146 final plate circuit in the transverter.  I also don't have the SB-500 schematic available, but I recall that the screen and final voltages are switched in and out at the SB-500 transverter, when connected.

The SB-102 was the only model that had this connector as part of the original construction.  The plug and bracket had to be mounted and installed as a modification for the rest of the HW/SB series - there is a rectangular access knockout on the later cabinets, which was not present on the first SB-100 models.

There is also space on the molex bracket for a second 9-pin molex connector which must be modified in to the SB-102 for the outboard SB-640 LMO to be used.  Easy conversion - if you have the SB-640 manual!

Jack  W3RU
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W3RU
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« Reply #26 on: March 29, 2019, 07:02:16 AM »

"However, I can't say the same for my memory.  I looked at the closed eBay listing at least ten times in the interim (including when the seller sent me a payment reminder -- too used to Buy It Now, and thought I'd paid when the auction closed) -- and still kept thinking it was an SB-101.  In fact, it's the slightly younger brother, an SB-102."

The main differences with the '102 are the SS LMO, an added LV power supply to power the SS LMO, pilot light differences, the previously mentioned molex plug, a few minor component value changes, inclusion of the Miller Effect modification, and replacement of the 6AU6 RF tube with the 6HS6 for supposedly increased RF sensitivity.  This tube has become nearly unobtanium and very expensive - unless you are really lucky.  The 6HS6 tube is now in the price class with 12AX7 and 6GW8 tubes used by the audiophools who don't seem to care what anything related to vintage HiFi equipment and the 6C10 compactron tubes used in geetar amplifiers costs to keep them going.

Fortunately, your 6GW8 audio tube is fairly rugged, and will most likely be serviceable going forward.  The 6HS6 may be weak, although still serviceable, but you can substitute a 6AU6 in it's place if it is bad - a NOS $2-$3 (very common and readily available everywhere) tube at most.

If and when you get really bitten by the Heathkit SB-bug, and decide to add an SB-610 monitor scope to your collection, heaven help if your 6C10 horizontal driver tube is bad - I am afraid to even guess what that one may cost to replace.

Best of luck when you get going!

Jack  W3RU
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KE4OH
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Posts: 234




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« Reply #27 on: March 29, 2019, 07:17:50 AM »

Not to worry - The SB-102 is a great radio. Some of the SS LMOs don't let the dial track as accurately as the tube LMOs, but it's not a big deal. Other than the different LMO, everything else is practically identical to the SB-101.
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73 de Steve KE4OH
KC1BMD
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Posts: 959




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« Reply #28 on: March 31, 2019, 11:22:35 AM »

From my limited experience with a SB-102 refurb (similar to the SB-101):

1. There may be several versions of the Heathkit manual, some of which might not match exactly what you have (e.g. resistor values, grounding, etc). That was certainly the case with the SB-102.

2. I found nearly all 100K Ohm carbon comp resistors drifted quite high (some as much as 30-40% or greater).

3. Check resistor values "in-circuit" first. If it reads higher than nominal, it is certainly high. If it reads lower than nominal, then you need to lift one end to check it.

Have fun!
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W5RKL
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« Reply #29 on: March 31, 2019, 01:38:05 PM »

If the SB-102 will not be used with the remote VFO then a diode
between the 8 pin Molex connector, pins 8 and 3, is required. A
1N4007 will work.

The diode's Anode connects to pin 3 and the diode's Cathode to
pin 8. This can be seen on the main SB-102 schematic.

Without the diode and the plug there will be no final tube screen
voltage resulting in no 50ma idling current and no RF output. The
SB-101 does not have this diode but the HW-101 does. You might'
be able to get by with just a jumper wire but a 1N4007 is cheap
so I would use the diode and the Molex plug.

73
Mike W5RKL
www.w5rkl.com
RMC(SW) USN RET
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