[Heathkit] sb-303 problem

[John Page]

I also have an SB303 problem I hope someone can help with. tuning the lower end of any band the signal breaks into pure noise. Upper end is just fine. Even swapped the pto with another sb303. Same results. Opened up the pto and attempted to clean it out but no luck. Other than that it works fine. Even has great audio. Any thoughts? John

John Page K4KWM Hollow State since 1953 (ex W8PKU,N8BLB,NA8O)


 
> From: bluebirdtele at embarqmail.com
> To: heathkit at mailman.qth.net; yash at aol.com
> Date: Tue, 15 Dec 2009 22:29:46 -0500
> Subject: Re: [Heathkit] sb-303 problem
> 
> Looks like you missed something. The sensitivity should be very good. If 
> it isn't I would go look in the RF chain. The converter switch and the 
> attenuator can be jumpered out of the circuit to check it. Also, I would 
> take an oscilloscope to the output of the product detector to see if the 
> audio or rf boards (or both) need additional work.
> Mine is still plugging away here and is the most sensitive radio I have ever 
> owned. The only thing I can really whine about is having to rock the band 
> switch occasionally to get it on the band. There have been rumors of filter 
> blow by in this radio but no one has ever shown me this happening. Probably 
> one of Heathkit's very best kits. Right up there with the HP 23 supply.
> $5 says it's an electro-mechanical problem
> 73's
> Greg
> WA7LYO
> Kinston NC
> 
> ----- Original Message ----- 
> From: <yash at aol.com>
> To: <heathkit at mailman.qth.net>
> Sent: Tuesday, December 15, 2009 9:47 PM
> Subject: [Heathkit] sb-303 problem
> 
> 
> > Just finished with about 8 hours bench time with a sb-303. It worked 
> > poorly,but did basically work. Biggest problem, poor selectivity, poor 
> > sensitivity some hum and bad,tinny harsh audio.
> > Did the following
> > 1. Pulled apart and cleaned all pots,switch's,connectors and a good 
> > general board and chassis cleaning, looks great.
> > 2. replaced all the filter caps in the power supply and replaced all the 
> > electrolytic's and coupling caps in the audio section.
> > 3. Did a total alignment,per the 303 manual with a AC vtvm and sig. 
> > generator,every thing peaked up, as per the manual right on the numbers.
> > 4. did some spot checks of voltages ,everything is well within spec.
> > Put the 303 back in line, added the 47 ohm shorting plug for the LMO 
> > per the manual and turned it on
> > SAME problems I started with,maybe marginally better ,but just so ,all 
> > the original problems still exist, no more hum,same bad audio.and all the 
> > other problems.
> > I don't know where to go from here. This is not a complicated 
> > receiver,but I just can't seem to get a handle on the problem. I had a 303 
> > a few years back and it would stay right there with my drake r4b,so I know 
> > the 303 can perform very well.
> > Any suggestions at this point would be very welcome.
> > thanks
> > dale wt4t
> >
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