Low voltage in Philharmonic power supply - EH Scott Radio Enthusiasts2024-03-29T06:05:31Zhttps://ehscott.ning.com/forum/topics/low-voltage-in-philharmonic-power-supply?commentId=3925821%3AComment%3A93613&feed=yes&xn_auth=noI am thinking spot on voltage…tag:ehscott.ning.com,2021-03-12:3925821:Comment:1171162021-03-12T02:31:41.413ZDavid C. Polandhttps://ehscott.ning.com/profile/DavidCPoland
<p>I am thinking spot on voltage readings are not too critical, because the radio is designed to operate well over a range of of 100 to 130 volts AC, in conjunction with the hi-low switch, allowing a 15 volt range on the power transformer primary which translates into an allowable 50 volt or so variation of the 400 volt B+ ahead of either B+ choke. </p>
<p>I did have -C divider voltage problems on my BOL amp I built it from Scott Philly amp parts. My wiring of the interstage transformer on…</p>
<p>I am thinking spot on voltage readings are not too critical, because the radio is designed to operate well over a range of of 100 to 130 volts AC, in conjunction with the hi-low switch, allowing a 15 volt range on the power transformer primary which translates into an allowable 50 volt or so variation of the 400 volt B+ ahead of either B+ choke. </p>
<p>I did have -C divider voltage problems on my BOL amp I built it from Scott Philly amp parts. My wiring of the interstage transformer on the amp was the problem. Has a center tap primary for 3 wires of the set cable. And two separate secondaries feeding the signal to each pair of 6L6 grids. I had crossed connected the secondary wiring which created oscillation issues evidently consuming power and dropping all -C voltages - and the supply -C from the amp of -27 to about -20 volts. That one leg of each secondary connects to the earphone jack was what lead to my error. A simple fix which fixed the -C bias bring it in to proper ranges, and my -C candohm was actually good after all.</p>
<p>But if the amp's interstage transformer has issues, I can see it might affect the -C divider.</p> Troy, on the negative voltage…tag:ehscott.ning.com,2021-03-12:3925821:Comment:1171132021-03-12T01:54:14.354ZRobert Feenstrahttps://ehscott.ning.com/profile/RobertFeenstra
<p>Troy, on the negative voltage divider, I've had to play with the resistances to get the voltages close to spec. If the -27 volts is high ( as you indicated: -23.7), it will affect the bias on the output tubes causing them to conduct a bit more ( and the bias for the AVC system). Perhaps your voltage divider needs a bit of work. Once you get that right, you might find the rest of the voltages will fall into place.</p>
<p>The bias on my AM/FM outputs are -23 volts Grids to cathodes with 290…</p>
<p>Troy, on the negative voltage divider, I've had to play with the resistances to get the voltages close to spec. If the -27 volts is high ( as you indicated: -23.7), it will affect the bias on the output tubes causing them to conduct a bit more ( and the bias for the AVC system). Perhaps your voltage divider needs a bit of work. Once you get that right, you might find the rest of the voltages will fall into place.</p>
<p>The bias on my AM/FM outputs are -23 volts Grids to cathodes with 290 volts on the plates. This would indicate it is in the Class AB region of the push pull output - that is if I am reading the tube specs properly. someone please correct me if I am wrong.</p>
<p></p>
<p>Reducing the resistance of the cathode resistor would reduce the negative grid voltage, turning the tube on more. Increasing the cathode resistor would increase the negative voltage on the grid, reducing the plate current.</p>
<p></p> Hello-
As I continue to liste…tag:ehscott.ning.com,2021-03-11:3925821:Comment:1170242021-03-11T01:01:29.917ZTroy Taylorhttps://ehscott.ning.com/profile/TroyTaylor
<p>Hello-</p>
<p>As I continue to listen to this wonderful old set, I have a new question. How do verify that the output tubes in the amp are properly biased? And, if they are not, how do I correct the problem? I am presently using a matched set of 5932s; a ruggedized 6L6 built by Sylvania.</p>
<p>Listening to this set now as I type. Sounds great and I love it. Will be even better when I get the cabinet built.</p>
<p>Thank you!</p>
<p>Troy</p>
<p>Edmonds, WA</p>
<p></p>
<p>Hello-</p>
<p>As I continue to listen to this wonderful old set, I have a new question. How do verify that the output tubes in the amp are properly biased? And, if they are not, how do I correct the problem? I am presently using a matched set of 5932s; a ruggedized 6L6 built by Sylvania.</p>
<p>Listening to this set now as I type. Sounds great and I love it. Will be even better when I get the cabinet built.</p>
<p>Thank you!</p>
<p>Troy</p>
<p>Edmonds, WA</p>
<p></p> Hi Troy,
If there was a probl…tag:ehscott.ning.com,2021-02-08:3925821:Comment:968532021-02-08T07:49:58.640Zmike hadleyhttps://ehscott.ning.com/profile/mikehadley
<p>Hi Troy,</p>
<p>If there was a problem with the power transformer you would know about it by now, if there is a shorted turn it's usually followed by smoke, dont't forget that the 6L6 tubes are running in class A and will be pulling a fair bit of current, plus there's 53 watts of heater's and 30 watts for the rectifiers, then there is the dropper dissipating 12 watts, and that's without the radio itself pulling current.</p>
<p>After 3 hours your power transformer is ok, I would try a new set…</p>
<p>Hi Troy,</p>
<p>If there was a problem with the power transformer you would know about it by now, if there is a shorted turn it's usually followed by smoke, dont't forget that the 6L6 tubes are running in class A and will be pulling a fair bit of current, plus there's 53 watts of heater's and 30 watts for the rectifiers, then there is the dropper dissipating 12 watts, and that's without the radio itself pulling current.</p>
<p>After 3 hours your power transformer is ok, I would try a new set of 6L6's and go from there.</p>
<p></p> Troy - Would appreciate a vol…tag:ehscott.ning.com,2021-02-08:3925821:Comment:968012021-02-08T02:59:05.779ZDavid C. Polandhttps://ehscott.ning.com/profile/DavidCPoland
<p>Troy - Would appreciate a voltage reading on the 6J7 plate (pin 3) - front far left, 2nd back, Scratch Suppressor.</p>
<p>See if it is somewhere 160 volts? </p>
<p>Troy - Would appreciate a voltage reading on the 6J7 plate (pin 3) - front far left, 2nd back, Scratch Suppressor.</p>
<p>See if it is somewhere 160 volts? </p> I should also mention that th…tag:ehscott.ning.com,2021-02-08:3925821:Comment:966612021-02-08T02:18:55.335ZTroy Taylorhttps://ehscott.ning.com/profile/TroyTaylor
<p>I should also mention that the power transformer is running about 118F; noticeably warmer than either of the chokes, which are both lukewarm at best. Set has been operating continuously for over 3 hours now.</p>
<p>The 6L6 tubes test "OK", but are near the marginal line on my Jackson 648. They all test very nearly alike. I have not measured the resistances in the transformers yet.</p>
<p>-Troy</p>
<p>I should also mention that the power transformer is running about 118F; noticeably warmer than either of the chokes, which are both lukewarm at best. Set has been operating continuously for over 3 hours now.</p>
<p>The 6L6 tubes test "OK", but are near the marginal line on my Jackson 648. They all test very nearly alike. I have not measured the resistances in the transformers yet.</p>
<p>-Troy</p> Hello-
Thank you all for the…tag:ehscott.ning.com,2021-02-08:3925821:Comment:967422021-02-08T01:47:54.772ZTroy Taylorhttps://ehscott.ning.com/profile/TroyTaylor
<p>Hello-</p>
<p>Thank you all for the suggestions and advice. I went through the power supply/amp chassis again and checked everything. The biggest problem I discovered was the 10H and 30H chokes were miswired opposite of the schematic. So the 10H was supplying the receiver chassis, and the 30H was supplying the 6L6 output tubes. I do not know if I made this mistake, or if it was made by the last guy who worked on this chassis.</p>
<p>When I got it, the 30uF, 30uF, 40uF, and 60uF caps had…</p>
<p>Hello-</p>
<p>Thank you all for the suggestions and advice. I went through the power supply/amp chassis again and checked everything. The biggest problem I discovered was the 10H and 30H chokes were miswired opposite of the schematic. So the 10H was supplying the receiver chassis, and the 30H was supplying the 6L6 output tubes. I do not know if I made this mistake, or if it was made by the last guy who worked on this chassis.</p>
<p>When I got it, the 30uF, 30uF, 40uF, and 60uF caps had all been replaced with four 40uF caps. I replaced these with the correct values, but I do not know if I made the wiring mistake at this time, or if it was already there and I didn't catch it. Regardless, I corrected it, and now the chokes both operate at low enough temperatures that, even after several hours of operation, I can comfortably hold my thumb on both of them.</p>
<p>All the capacitors are new and I could not find any problems with any of them. All of the resistors measured within 10%, but I replaced all four of the 150 ohms anyway, since two were right at +10% and the other two were a -10%. I used 1% replacements, so now they are all very close together.</p>
<p>The voltages still measure low after these changes; minimal difference from what I posted earlier. Not sure where else to look for a potential problem, or if these lower voltages even _are_ a problem. The set is working great, playing Super Bowl LV right now.</p>
<p>Is anyone else listening to the game on a Scott?</p>
<p>Thank you all and best regards-</p>
<p>Troy Taylor</p>
<p>Edmonds, WA</p> Hi ,Troy,
I powered up my poi…tag:ehscott.ning.com,2021-01-18:3925821:Comment:936132021-01-18T01:34:32.200ZDavid C. Polandhttps://ehscott.ning.com/profile/DavidCPoland
<p>Hi ,Troy,</p>
<p>I powered up my pointer Philharmonic about 75 minutes ago. The power transformer is mildly warm to touch on top.</p>
<p>Both amp's chokes are mildly warm. Nowhere near hot, just warm, no problem leaving a finger on either 10 seconds or more.</p>
<p>After checking the suggestions above, and if you think you have a defective 10 Henry choke, let me know.</p>
<p>Hi ,Troy,</p>
<p>I powered up my pointer Philharmonic about 75 minutes ago. The power transformer is mildly warm to touch on top.</p>
<p>Both amp's chokes are mildly warm. Nowhere near hot, just warm, no problem leaving a finger on either 10 seconds or more.</p>
<p>After checking the suggestions above, and if you think you have a defective 10 Henry choke, let me know.</p> Thanks Mike, I had that info…tag:ehscott.ning.com,2021-01-17:3925821:Comment:936122021-01-17T15:09:24.678ZKarl Sherwinhttps://ehscott.ning.com/profile/KarlSherwin
<p>Thanks Mike, I had that info from this site, but didn't have the entire Riders Vol 14 info, now I do!</p>
<p>Thanks Mike, I had that info from this site, but didn't have the entire Riders Vol 14 info, now I do!</p> Karl
Look at the top of this…tag:ehscott.ning.com,2021-01-17:3925821:Comment:937332021-01-17T14:52:24.124Zmike hadleyhttps://ehscott.ning.com/profile/mikehadley
<p>Karl</p>
<p>Look at the top of this page, Scott info and archive, see Philharmonic folder, lots of information there</p>
<p>Karl</p>
<p>Look at the top of this page, Scott info and archive, see Philharmonic folder, lots of information there</p>