Can someone shed some light on my 800B FM front end? - EH Scott Radio Enthusiasts2024-03-28T23:17:19Zhttps://ehscott.ning.com/forum/topics/can-someone-shed-some-light-on-my-800b-fm-front-end?commentId=3925821%3AComment%3A36432&feed=yes&xn_auth=noThe 800B is working pretty we…tag:ehscott.ning.com,2013-04-09:3925821:Comment:363482013-04-09T20:17:01.136ZTom Jardinehttps://ehscott.ning.com/profile/TomJardine
<p>The 800B is working pretty well now overall. I added the tone control mod. The sound is a overly bright on mid-range highs, even with the treble set for mid-range. Any suggestions for taming that? I checked and re-checked my work for errors. The drawing asks for a 220 pf cap on the CCW end of the treble control. I only had a 300pf, but I shouldn't think that would make much of a difference. <br></br> <br></br> <cite>Norman S Braithwaite said:…</cite></p>
<p>The 800B is working pretty well now overall. I added the tone control mod. The sound is a overly bright on mid-range highs, even with the treble set for mid-range. Any suggestions for taming that? I checked and re-checked my work for errors. The drawing asks for a 220 pf cap on the CCW end of the treble control. I only had a 300pf, but I shouldn't think that would make much of a difference. <br/> <br/> <cite>Norman S Braithwaite said:</cite></p>
<blockquote cite="http://ehscott.ning.com/forum/topics/can-someone-shed-some-light-on-my-800b-fm-front-end?xg_source=activity#3925821Comment36639"><div><div class="xg_user_generated"><p>If the problem persists after replacing leaky capacitors and out of tolerance resistors on the tuner chassis, consider replacing the 100pf capacitors at the input and output FM IF transmission line matching networks. An acquaintance has recently found a bad one (tan Sangamo). The symptom was erratic FM signal strength. All other components known to be problematic had already been replaced.</p>
<p>Norman</p>
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</blockquote> Thanks, Norman. I've found lo…tag:ehscott.ning.com,2013-04-06:3925821:Comment:364322013-04-06T23:43:35.292ZTom Jardinehttps://ehscott.ning.com/profile/TomJardine
<p>Thanks, Norman. I've found lots of OOT resistors on both chassis and have replaced some leaky caps. I found the discriminator is a very tough one to align, but finally got it. I now have very good sensitivity on FM and AM. I miraculously solved the erratic FM tuning problem. I sprayed some Cramolin on the movable shaft of the tuning capacitor and the erratic tuning completely disappeared. Apparently I was getting intermittent grounding of the non-stationary tuning capacitor stator. I do want…</p>
<p>Thanks, Norman. I've found lots of OOT resistors on both chassis and have replaced some leaky caps. I found the discriminator is a very tough one to align, but finally got it. I now have very good sensitivity on FM and AM. I miraculously solved the erratic FM tuning problem. I sprayed some Cramolin on the movable shaft of the tuning capacitor and the erratic tuning completely disappeared. Apparently I was getting intermittent grounding of the non-stationary tuning capacitor stator. I do want to try your tone control mod. Does it make that much of a difference? My 800B is the later (S/N3187) version, has a Thorens changer and the H H Scott dynamic scratch suppressor. It has the Magnavox coaxial speaker without the bell covering the field coils.<br/> <br/> <cite>Norman S Braithwaite said:</cite></p>
<blockquote cite="http://ehscott.ning.com/forum/topics/can-someone-shed-some-light-on-my-800b-fm-front-end?commentId=3925821%3AComment%3A36639&xg_source=msg_com_forum#3925821Comment36639"><div><div class="xg_user_generated"><p>If the problem persists after replacing leaky capacitors and out of tolerance resistors on the tuner chassis, consider replacing the 100pf capacitors at the input and output FM IF transmission line matching networks. An acquaintance has recently found a bad one (tan Sangamo). The symptom was erratic FM signal strength. All other components known to be problematic had already been replaced.</p>
<p>Norman</p>
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</blockquote> If the problem persists after…tag:ehscott.ning.com,2013-04-06:3925821:Comment:366392013-04-06T22:11:42.881ZNorman S Braithwaitehttps://ehscott.ning.com/profile/NormanSBraithwaite
<p>If the problem persists after replacing leaky capacitors and out of tolerance resistors on the tuner chassis, consider replacing the 100pf capacitors at the input and output FM IF transmission line matching networks. An acquaintance has recently found a bad one (tan Sangamo). The symptom was erratic FM signal strength. All other components known to be problematic had already been replaced.</p>
<p>Norman</p>
<p>If the problem persists after replacing leaky capacitors and out of tolerance resistors on the tuner chassis, consider replacing the 100pf capacitors at the input and output FM IF transmission line matching networks. An acquaintance has recently found a bad one (tan Sangamo). The symptom was erratic FM signal strength. All other components known to be problematic had already been replaced.</p>
<p>Norman</p>