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Author Topic: SB 303 alignment  (Read 5868 times)
AA6DQ
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Posts: 7




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« on: February 01, 2016, 06:20:02 PM »

I am working on a Heathkit SB303 and need at least the alignment instructions.  I have a schematic no manual.

Tim AA6DQ
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W5RKL
Member

Posts: 1034




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« Reply #1 on: February 02, 2016, 06:02:01 AM »

I am working on a Heathkit SB303 and need at least the alignment instructions.  I have a schematic no manual.

Tim AA6DQ


I have the complete SB-303 assembly manual. I'm not in my shack at the moment but later on today I'll get the instructions.

73
Mike W5RKL


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W5RKL
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Posts: 1034




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« Reply #2 on: February 02, 2016, 09:03:29 AM »

I have a simple alignment process you can use. Click the following link to download the file.

http://w5rkl.com/wp-content/uploads/2015/02/SB303-simple-alignment.pdf

Read the statement at the end of the file FIRST then read the entire alignment process from start to finish before you attempt to perform the alignment.

You will need the non-conductive alignment tools which you can get on ebay at the eBay ad #151533699586 for $18.95 free shipping.

You will also need the LMO 50 ohm load plug inserted into the rear panel's "LMO" socket and a shorted MUTE RCA plug inserted into the rear panel's "MUTE" socket. The LMO load plug is a 50 ohm resistor connected between the center plug and ground of an RCA plug. The MUTE RCA plug is a shorted RCA plug, wire soldered between the center pin and ground. The MUTE plug is required to use the receiver's Calibrator setting on the FUNCTION switch. Without the MUTE shorting plug inserted into the rear panel MUTE socket, the receiver will MUTE when set to the 25Khz or 100Khz Calibrator FUNCTION switch setting.

If any slug in a coil form will not rotate, do NOT use excessive force to rotate the slug nor should you use a metal hex wrench. More than likely the slug is cracked/broken which is preventing the slug from rotating. Replacing the coil and non-cracked/broken slug is the best solution.

I have an SB-303 and it works great. Quite often the LMO tends to become unstable/jittery when tuning. This is caused by dirt/corrosion on the LMO variable capacitor's shaft to frame connections at both ends of the capacitor. It also is caused by dried bearing grease on the LMO variable capacitor's bearing end. I also installed a Kenwood TS-520S Noise Blanker board in my SB-303. I changed/modified the RF gain control PUSH/PULL switch to control the Noise Blanker. It works great on pulse type noise such as auto ignition and power line arcing noises. The Noise Blanker board is powered by the receiver's +15VDC supply. Very little current flows in the Noise Blanker so robbing +15VDC from the SB-303 supply is not a problem.

The HET OSC crystals do tend to change frequencies over time. Dial alignment is quite good on 80 to 15 meters, slightly off on 10 meter bands.

The LMO tuning can be made to feel like oil on glass if you perform the main dial disc to circular dial setting. The disc should rest on the inner portion of the round dial just enough to prevent slipping when tuning the LMO. Any additional "downward" force on the disc to circular dial setting will result in stiff tuning. My LMO tuning is very smooth with no slippage.

The alignment adjustments use the SB-303's built in calibrator. You do not need signal generators to align the SB-303. You will need a long 5/64" hex wrench to make the dial adjustments. Most hex wrench sets will work but a much longer 5/64's inch hex wrench is much better. Check your local hardware, Home Depot, Lowes or Harbor Freight stores for long 5/64" hex wrench.

73
Mike W5RKL
« Last Edit: February 02, 2016, 09:22:08 AM by W5RKL » Logged
AA6DQ
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Posts: 7




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« Reply #3 on: February 03, 2016, 01:48:13 PM »

Mike,

Thank you so much!  This really helps and thanks tips especially about the slugs.

This receiver has all 3 filters.  It looks to be in good shape but in need of cleaning and grease/lub replacement. 

Have you found a source for the power cords or just the connector?

73's
Tim AA6DQ

 
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AD4U
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Posts: 2445




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« Reply #4 on: February 04, 2016, 09:32:16 AM »

The SB 303 is a very sensitive receiver, but is subject to strong signal overload like many early all solid state receivers. It was Heath's first all solid state ham band only receiver.

I bought one several years in absolutely MINT condition with all 3 filters. The build quality and soldering were excellent.  It supposedly came from an "estate sale" in unknown working condition, which according to ebay descriptions, they most all do.

When it arrived it was in absolutely MINT condition with the manual. I carefully fired it up and the panel lights came on but that is all. The receiver was dead.

To make a long story short, I decided to go through the step-by-step building process in the manual before firing it up and check off every step as I went. I found two wiring errors which I corrected.

My guess is that whoever built the SB 303 could not get it working and just put it away and possibly quit ham radio or bought a factory built rig. When the original builder became a SK the SB 303 was sold still with the two wiring errors, having never been used.

Once I found and corrected the two wiring errors I firmly believe the 35 year old SB 303 came to life for the very first time.

Dick AD4U
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W5RKL
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Posts: 1034




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« Reply #5 on: February 04, 2016, 02:08:52 PM »

Mike,

Have you found a source for the power cords or just the connector?

73's
Tim AA6DQ

 

No I haven't Tim. I haven't been in need of a power cord and/or connector replacement so I have not spent any time looking for one.

I picked up my SB-303 on eBay about 4 years ago for $167. I didn't think I was going to win the auction but I did. It was in excellent physical and electrical condition. Worked the first time I powered it up. It has the factory side band and CW filters, no AM filter. Those AM filters are way too expensive and not worth the $85 to $100 sellers are asking for them. The band width of the Heathkit AM filter, approximate 3.7Khz, is slightly more than half of a typical 6Khz wide AM signal.

Yes, the receiver, if operated wide open, will overload on very strong signals. I tend to set the RF ATTN control at 12 o'clock and when necessary, I slightly detune the Preselector. This helps reduce overloading and still allows to hear most weak stations. I use my SB-303 with a variety of transmitters

Marauder HX-10
SB-400
SB-401
DX-40

73
Mike W5RKL



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AA6DQ
Member

Posts: 7




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« Reply #6 on: February 13, 2016, 05:29:47 PM »

Mike,

I finally got my SB-303 working.  After a complete alignment it still seemed deaf so I first measured the 10db S+N/N ratio at 30 u-volts and then ran the stage gain tests.  It passed the 2nd mixer test and failed the first mixer test.  The 8.85 mhz LC bandpass filter was bad.  I measured over 30 db insertion loss in the filter itself - most likely the coupling stage in the filter is open.  I have not figured out how to get it open without destroying it yet. 

Anyway, I found a replacement mixer board on ebay with a good filter.
The result is that now the calibrator is S9 or better on all bands including 10 meters and I run the attenuator at 9 o'clock on 40 meters, 12 o'clock on 20 meters, 3'oclock on 15 meters and fully cw on 10 meters.   

Tim AA6DQ

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W5RKL
Member

Posts: 1034




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« Reply #7 on: February 14, 2016, 11:53:51 AM »

Glad to hear your SB-303 is working properly now.

I've been lucky so far, my SB-303 has worked flawlessly ever since I bought it a few years ago even after installing a Kenwood TS-520 Noise Blanker in my SB-303.

73
Mike W5RKL
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KG9H
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Posts: 75


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« Reply #8 on: September 13, 2017, 05:17:44 AM »

If you guys are still looking at this...
I just picked up an SB-303!
Works well now to figure it out inside.
I am trying to figure out filters.  Is there a filter for AM?  Is there a filter for CW?
No manual here, hi hi,
De KG9H
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W5RKL
Member

Posts: 1034




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« Reply #9 on: September 14, 2017, 04:33:13 AM »

If you guys are still looking at this...
Is there a filter for AM?  Is there a filter for CW?
No manual here, hi hi,
De KG9H

If you plan on working on and keeping your Sb-303 then I recommend you purchase
the complete SB-303 manual from one of the many on-line manual website. One I use
is w7fg.com

http://www.vintagemanuals.com/search.php?find=sb-303

The same SSB, CW and AM filters used in the SB-300, SB-301, and SB-313 will fit and work in the
SB-303. The CW filter found in the HW-101, SB-101, and SB-102 will also fit and work in the SB-303.

I have an SB-303 and I added a Kenwood TS-520 Noise Blanker board (X54-1080-10). The board is
powered by the SB-303's +15VDC supply and I modified the front panel RF gain control's Push/Pull
speaker switch to control the Noise Blanker. I replaced the rear non-switched 1/4" mono headphone
socket with a switched 1/4" mono audio socket. A bit of rewiring and mounting the Noise Blanker board
on the inside left panel and the SB-303 has a "pulse" type noise blanker that works very well.

I made a simple video of my SB-303 showing how well the Noise Blanker board acts on arcing noise.

http://w5rkl.com/wp-content/uploads/2015/02/Kenwood-TS-520-Noise-Blanker-in-a-Heathkit-SB-303.avi

73
Mike W5RKL
www.w5rkl.com
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