Re: [drakelist] R4C hum
Paul I would recommend the Sherwood psu mod. It'llget rid of most of your other dubious electrolytics in one fell swoopand will also significantly reduce heat disipation around the pto area Thiswill lead to a significant improvement in frequency stability. It's a straight forward installation too. 73 Bob, 5B4AGN - Original Message - From: AD3G To: drakelist@www.zerobeat.net Sent: Sunday, August 14, 2005 4:18 AM Subject: [drakelist] R4C hum Hello list...I recently acquired a nice R4C,but it has some issues...I powered up slowly on a variac,but the filter caps were hopelessly shot. I replaced with a Sherwood filter cap kit.I have far less hum,but it's still there,just not as bad(I can hear reciever hiss now). Would a power supply mod be in order,(Sherwood)or should I just change out the caps on the p/s board? I'm new to Drake gear and wanted to see what the general consensus of the Drake gang would be. I plan on keeping the R4C for a while,so I want to do it right the first time. 73 Paul
Re: [drakelist] R4C IMD problem (was image problem)
Bob Henderson [EMAIL PROTECTED] made an utterance to the drakelist gang -- Many thanks to those who have written off reflector expressing interest and offering encouragement. The primary mystery is why the 6EJ7 1st mixer in this particular R-4C has such an abysmal IMD3 performance. The mixer circuit isn't complex and I've been through it a dozen times looking for faulty components but find none. Without any specific knowledge of what the injection levels to the 6EJ7 ought to be, I've had little choice but to follow my instincts and aim to increase the ratio of premix to wanted signals. Having found the 6BA6 RF amp guilty of producing IMD3 products only 60dB or so down and having found that increasing the screen voltage to 100V improved this to around 80dB, Steve, VK6VZ told me that Tom, W8JI recommends increasing the screen volts to 130V. This I have done and so far as I can determine, IMD3 products at the output of the RF amp are now 90dB down. That has to be good. However, the big problem is the 6EJ7 1st mixer and of course, the increased output from the RF amp, consequent upon the increase in screen volts, exacerbates that. So I've reduced the gain of the RF amp to around 12-15dB through the introduction of a 2k2 resistor and 50nF bypass cap into the cathode feed. This allows me to leave the AGC1 feed to the RF amp unmolested. Next, I set about increasing premix injection. Basically I want to double this from around 2V p.p to around 4V p.p. It wouldn't be any use messing about with the premix circuit itself, as I need the same injection from the T-4XC premix chain. It certainly doesn't make much sense to have to modify the T-4XC premix chain too. I decided use of a 2:1 UNUN was worth a try. I wound 7 trifilar turns on a T37-2 core (I think T37-7 would be better, but I don't have one) and connected them appropriately. I disconnected the premix injection from the 10pF ceramic cap on g1 of the 6EJ7. I then connected the premix to the input side of the 1:2 UNUN and attached the output to the 10pF cap. Maybe the UNUN provides an unwelcome bit of loading but the premix level still increased to a more desirable 3.5V p.p. My fears about the T37-2 core not being good enough for 10m where the premix injection is around 35 MHz appear unfounded. I still get a good 3.5V p.p. there. So where has all of this got me? Well, with two 30mV signals at the input to the RF amp I now get an output of around 380mV, which feeds into the 6EJ7. The premix injection is now 3.5V giving me an injection ratio of 9:1. That feels a lot better to me than the 2:1 I had before I made any changes. So what about IMD3 response? Well that has improved from around 45dB to around 70dB. Now 70dB is somewhat short of impressive but nonetheless, it's a sackload more than 45dB :-)) This 70dB figure holds good for 60 kHz spacing and for 2 kHz spacing. (Sherwood CF600/6 installed). Remaining concerns? Despite the significant change in injection ratio at the input to the 1st mixer, examination of the IMD3 products at its output confirm that this mixer is still the fundamental constraint on overall IMD3 performance. I'm still scratching my head over why this mixer in its standard config should be so bad. Though at least I can now listen usefully to 40m in the early evening while I do so:-) 73 Bob, 5B4AGN -- On Behalf of Bob Henderson [EMAIL PROTECTED] Submissions:drakelist@www.zerobeat.net Unsubscribe:[EMAIL PROTECTED] - unsubscribe drakelist in body Hopelessly Lost:[EMAIL PROTECTED] - help in body of message Zerobeat Web Page: http://www.zerobeat.net Brought to you courtesy of TLCHost.net http://www.tlchost.net/ --
Re: [drakelist] R4C hum
Paul, There is a mod to relocate the wiring that connects from the power supply board to the can filter capacitor outside of the main harnessand route themalong the outside edgeof the chassis with heavier gage wire. This helps reduce the hum. 73, Gary
[drakelist] radio from h**l (was 4-pin mosfet)
My thanks to the all the list for all the help! I now have the 8.050mhz bfo working! I can hear signals !!! (sort of) So far I have completely replaced the 2nd IF/audio board and now also with help here, have replaced the 3n204 on the pbt board. and rebuilt the s-meter. This radio has been so very well taken care of! some one took out all of those ugly little orange caps and replaced them all with nice, shiny green ones! it looks soo much better now. they eve added a few extra ones! but to keep the vintage look , all the electro caps were left stock. I think that if I had taken the covers off, turn the unit on, then pretended it was a fresh field of snow while I wrote my name on it, I could not of done a better job of wrecking it. But this is good. it is stretching and growing my trouble shooting skills in a great way, as I am not going to give up on my tr7 !! SO , back to attempting the alignment procedure, setting the +10v, no problem, plenty of range. but when attempting the s-meter alignment, I have very little agc adjustment, enough to make an audible difference, but not enough to get the 2 s unit rise on the meter as the manuel calls for. so I am back to the 2nd IF board, at least its completely original, I thiink I saw a mod somewhere that gives you more adjustment to it, and I'll double check voltage supplies on the board and such. Thanks again to all the help, it looks to me like the drake community demonstrates the whole ham radio concepts of helpful service and enjoyment of a great hobby Don Frasher KB5GNH who someday will actually talk on the air with a drake!! avast! Antivirus: Outbound message clean. Virus Database (VPS): 0532-6, 08/13/2005Tested on: 8/14/2005 9:32:54 AMavast! - copyright (c) 1988-2004 ALWIL Software.
Re: [drakelist] radio from h**l (was 4-pin mosfet)
Don, If you do decide to autograph the rig, be sure its unplugged. Good luck, George KB2Z At 11:32 AM 8/14/05, you wrote: My thanks to the all the list for all the help! I now have the 8.050mhz bfo working! I can hear signals !!! (sort of) So far I have completely replaced the 2nd IF/audio board and now also with help here, have replaced the 3n204 on the pbt board. and rebuilt the s-meter. This radio has been so very well taken care of! some one took out all of those ugly little orange caps and replaced them all with nice, shiny green ones! it looks soo much better now. they eve added a few extra ones! but to keep the vintage look , all the electro caps were left stock. I think that if I had taken the covers off, turn the unit on, then pretended it was a fresh field of snow while I wrote my name on it, I could not of done a better job of wrecking it. But this is good. it is stretching and growing my trouble shooting skills in a great way, as I am not going to give up on my tr7 !! SO , back to attempting the alignment procedure, setting the +10v, no problem, plenty of range. but when attempting the s-meter alignment, I have very little agc adjustment, enough to make an audible difference, but not enough to get the 2 s unit rise on the meter as the manuel calls for. so I am back to the 2nd IF board, at least its completely original, I thiink I saw a mod somewhere that gives you more adjustment to it, and I'll double check voltage supplies on the board and such. Thanks again to all the help, it looks to me like the drake community demonstrates the whole ham radio concepts of helpful service and enjoyment of a great hobby Don Frasher KB5GNH who someday will actually talk on the air with a drake!! avast! Antivirus: Outbound message clean. Virus Database (VPS): 0532-6, 08/13/2005 Tested on: 8/14/2005 9:32:54 AM avast! - copyright (c) 1988-2004 ALWIL Software.
[drakelist] Need please: TV-7 Settings for Drake Tube
Re the 6HS6 (actually two of them) in my R4-A, there are no test settings called out in the TV-7 data Book. Does anyone have these, perhaps developed by others over time. My recent visit to EB5AGV'sfine TV-7 site came up short. Thanks in advance. (73) Les ---===WB6ORZ===---
[drakelist] Need Conversion Kit for L4B Relay
Hello to all, Sometime ago I bought a small kit to change the 2 pin vox relay to a RCA jack for keying. I have lost the email and im wondering if you know of someone that makes these little modifications precut to install for the Drake L4B? Any help is much appreciated. Best to all, Gary WC4F No virus found in this outgoing message. Checked by AVG Anti-Virus. Version: 7.0.338 / Virus Database: 267.10.8/71 - Release Date: 8/12/2005
Re: [drakelist] Need Conversion Kit for L4B Relay
Gary, John Kriner has the kit available from time to time on Ebay. Contact him at [EMAIL PROTECTED]. 73, Gary
