[drakelist] Re: VA7TO 2-B: Drake 2-B Project Part 1
Garey Barrell <[EMAIL PROTECTED]> made an utterance to the drakelist gang -- Darrell - Nah, it won't hurt anything, the tube is effectively out of circuit with the diodes in there. You might want to consider getting a black DPDT slide switch, bending up the tabs on the back, and swapping the red part for the black part. It depends on the particular switch parts, but I believe the Drake switches are Switchcraft, and I have done this with them. Running AC up to the front panel in this area, and locating an AC relay somewhere could be problematic from a hum standpoint. I believe I would try a "compromise" resistor selection first to see what sort of problems it "might" cause, or not. 73, Garey - K4OAH Glen Allen, VA Darrell Bellerive wrote: Garey, Thanks so much for all of your assistance! I never thought about removing the tube. I guess that was what was confusing me. I've been running the receiver with both the tube and the diodes since I acquired it. Hope that didn't damage anything. I will remove the mod and put it back the way that Drake designed it. I like the advantages of the lower noise due to lower B+ voltages, and the delay in B+ reaching full voltage. I would expect the delay and lower B+ voltages to have a positive effect on the life of the tubes. Also been thinking about the double pole slide switch for the AVC. If I can't find a replacement switch, a small DPDT relay might be the answer. Use the existing switch to control the relay and let the relay do the switching. A relay with a low current 6.3 VAC coil would be ideal as it could be powered from the filament supply. 73, Darrell On Thursday 24 July 2008 19:28, Garey Barrell wrote: Darrell - The "mod" has replaced the 6X4 rectifier tube with solid state diodes. The tube is serving no purpose and can be left out. Most likely the modifier left the tube out, and the "seller" inserted the tube to keep from answering the question "why is this tube socket empty". There are at least two schools of thought here. One is that the solid state diodes are more efficient (less voltage drop), don't consume filament power (and produce attendant heat), and eliminate the need for a tube! The 100 ohm resistor is just to limit the current when those "zero drop" diodes with 60 A surge current capabilities see those discharged filter caps that look like a short circuit! On the negative side, the resultant B+ is higher than the design was intended to have (resulting in additional heat dissipated throughout the receiver). One of the reasons the 2-B (and Collins 75S-x receivers are so quiet is the low B+ (reduced thermal noise from the tubes). Also, the rest of the tubes in the receiver are subjected to full B+ before the tubes have any chance to warm up and generate the space charge (electron cloud) around the cathode to protect it from back bombardment. There is some evidence that this causes the cathode to be damaged, and shortens the life of the tube. Drake and most manufacturers went to solid state rectifiers en masse, starting with the R-4, albeit with a lower voltage transformer to compensate. The two diodes were considerably cheaper than a tube and socket and filament winding and associated assembly costs, tubes were almost all around a dollar, and so nobody cared. Personally, as long as 6X4 tubes are plentiful and available for a buck or two, I'll stick with the tube. 73, Garey - K4OAH Glen Allen, VA Drake 2-B, 4-B, C-Line & TR-4/C Service Supplement CDs Darrell Bellerive wrote: I have found two mods that have previously done on my 2-B: 1) A second headphone jack has been added to the back panel. It is wired in parallel with the headphone jack at the front. It is wired for connection of an external speaker as it will not break the connection to the normal speaker output. I will simply remove it. 2) A 100 ohm resistor and two solid state diodes have been added in the high voltage section. R55 (470 ohms) was lifted from pin 7 of V10 (6X4 power rectifier) and a 100 ohm resistor inserted in between. Two diodes (1N2071A) are attached from the junction of the new 100 ohm resistor and R55 and connect to each of the two plates in V10. The anodes of each of the solid state diodes are attached to the anodes of V10. Attached is a picture showing the high voltage mod. The diagram on the left is the factory schematic, and the diagram on the right show the mod in red. What would have been the purpose of such a mod and should it be reversed? 73, Darrell VA7TO -- Submissions:drakelist@zerobeat.net Unsubscribe:[EMAIL PROTECTED] - unsubscribe drakelist in body Hopelessly Lost:[EMAIL PROTECTED] - help in body of message Zerobeat Web Page: www.zerobeat.net - sponsored by www.tlchost.net --
[drakelist] Re: VA7TO 2-B: Drake 2-B Project Part 1
Darrell Bellerive <[EMAIL PROTECTED]> made an utterance to the drakelist gang -- Garey, Thanks so much for all of your assistance! I never thought about removing the tube. I guess that was what was confusing me. I've been running the receiver with both the tube and the diodes since I acquired it. Hope that didn't damage anything. I will remove the mod and put it back the way that Drake designed it. I like the advantages of the lower noise due to lower B+ voltages, and the delay in B+ reaching full voltage. I would expect the delay and lower B+ voltages to have a positive effect on the life of the tubes. Also been thinking about the double pole slide switch for the AVC. If I can't find a replacement switch, a small DPDT relay might be the answer. Use the existing switch to control the relay and let the relay do the switching. A relay with a low current 6.3 VAC coil would be ideal as it could be powered from the filament supply. 73, Darrell On Thursday 24 July 2008 19:28, Garey Barrell wrote: > Darrell - > > The "mod" has replaced the 6X4 rectifier tube with solid state diodes. > The tube is serving no purpose and can be left out. Most likely the > modifier left the tube out, and the "seller" inserted the tube to keep > from answering the question "why is this tube socket empty". > > There are at least two schools of thought here. One is that the solid > state diodes are more efficient (less voltage drop), don't consume > filament power (and produce attendant heat), and eliminate the need for > a tube! The 100 ohm resistor is just to limit the current when those > "zero drop" diodes with 60 A surge current capabilities see those > discharged filter caps that look like a short circuit! On the negative > side, the resultant B+ is higher than the design was intended to have > (resulting in additional heat dissipated throughout the receiver). One > of the reasons the 2-B (and Collins 75S-x receivers are so quiet is the > low B+ (reduced thermal noise from the tubes). Also, the rest of the > tubes in the receiver are subjected to full B+ before the tubes have any > chance to warm up and generate the space charge (electron cloud) around > the cathode to protect it from back bombardment. There is some evidence > that this causes the cathode to be damaged, and shortens the life of the > tube. > > Drake and most manufacturers went to solid state rectifiers en masse, > starting with the R-4, albeit with a lower voltage transformer to > compensate. The two diodes were considerably cheaper than a tube and > socket and filament winding and associated assembly costs, tubes were > almost all around a dollar, and so nobody cared. Personally, as long as > 6X4 tubes are plentiful and available for a buck or two, I'll stick with > the tube. > > 73, Garey - K4OAH > Glen Allen, VA > > Drake 2-B, 4-B, C-Line & TR-4/C Service Supplement CDs > > > Darrell Bellerive wrote: > > I have found two mods that have previously done on my 2-B: > > > > 1) A second headphone jack has been added to the back panel. It is wired > > in parallel with the headphone jack at the front. It is wired for > > connection of an external speaker as it will not break the connection to > > the normal speaker output. I will simply remove it. > > > > 2) A 100 ohm resistor and two solid state diodes have been added in the > > high voltage section. R55 (470 ohms) was lifted from pin 7 of V10 (6X4 > > power rectifier) and a 100 ohm resistor inserted in between. Two diodes > > (1N2071A) are attached from the junction of the new 100 ohm resistor and > > R55 and connect to each of the two plates in V10. The anodes of each of > > the solid state diodes are attached to the anodes of V10. > > > > Attached is a picture showing the high voltage mod. The diagram on the > > left is the factory schematic, and the diagram on the right show the mod > > in red. > > > > What would have been the purpose of such a mod and should it be reversed? > > > > 73, Darrell VA7TO -- Darrell Bellerive Amateur Radio Stations VA7TO and VE7CLA Grand Forks, British Columbia, Canada -- Submissions:drakelist@zerobeat.net Unsubscribe:[EMAIL PROTECTED] - unsubscribe drakelist in body Hopelessly Lost:[EMAIL PROTECTED] - help in body of message Zerobeat Web Page: www.zerobeat.net - sponsored by www.tlchost.net --
[drakelist] Re: VA7TO 2-B: Drake 2-B Project Part 1
Garey Barrell <[EMAIL PROTECTED]> made an utterance to the drakelist gang -- Darrell - The "mod" has replaced the 6X4 rectifier tube with solid state diodes. The tube is serving no purpose and can be left out. Most likely the modifier left the tube out, and the "seller" inserted the tube to keep from answering the question "why is this tube socket empty". There are at least two schools of thought here. One is that the solid state diodes are more efficient (less voltage drop), don't consume filament power (and produce attendant heat), and eliminate the need for a tube! The 100 ohm resistor is just to limit the current when those "zero drop" diodes with 60 A surge current capabilities see those discharged filter caps that look like a short circuit! On the negative side, the resultant B+ is higher than the design was intended to have (resulting in additional heat dissipated throughout the receiver). One of the reasons the 2-B (and Collins 75S-x receivers are so quiet is the low B+ (reduced thermal noise from the tubes). Also, the rest of the tubes in the receiver are subjected to full B+ before the tubes have any chance to warm up and generate the space charge (electron cloud) around the cathode to protect it from back bombardment. There is some evidence that this causes the cathode to be damaged, and shortens the life of the tube. Drake and most manufacturers went to solid state rectifiers en masse, starting with the R-4, albeit with a lower voltage transformer to compensate. The two diodes were considerably cheaper than a tube and socket and filament winding and associated assembly costs, tubes were almost all around a dollar, and so nobody cared. Personally, as long as 6X4 tubes are plentiful and available for a buck or two, I'll stick with the tube. 73, Garey - K4OAH Glen Allen, VA Drake 2-B, 4-B, C-Line & TR-4/C Service Supplement CDs Darrell Bellerive wrote: I have found two mods that have previously done on my 2-B: 1) A second headphone jack has been added to the back panel. It is wired in parallel with the headphone jack at the front. It is wired for connection of an external speaker as it will not break the connection to the normal speaker output. I will simply remove it. 2) A 100 ohm resistor and two solid state diodes have been added in the high voltage section. R55 (470 ohms) was lifted from pin 7 of V10 (6X4 power rectifier) and a 100 ohm resistor inserted in between. Two diodes (1N2071A) are attached from the junction of the new 100 ohm resistor and R55 and connect to each of the two plates in V10. The anodes of each of the solid state diodes are attached to the anodes of V10. Attached is a picture showing the high voltage mod. The diagram on the left is the factory schematic, and the diagram on the right show the mod in red. What would have been the purpose of such a mod and should it be reversed? 73, Darrell VA7TO -- Submissions:drakelist@zerobeat.net Unsubscribe:[EMAIL PROTECTED] - unsubscribe drakelist in body Hopelessly Lost:[EMAIL PROTECTED] - help in body of message Zerobeat Web Page: www.zerobeat.net - sponsored by www.tlchost.net --
