[Drakelist] Drake L-7 FS/Trade
Hi All, I have a very nice condition L-7 that I am not using. This amp has performed flawlessly for me but I recently bought a new solid state amp and it is not being used. The ALC has not worked for me but all else is in great condition. I would use it on AM but it is too big to fit my available space. I'm asking $1,200 for the amp and we would need to discuss how to ship it. I live in the Seattle metro area and would, of course, prefer pick up or a meet somewhere within reason. I would also consider a partial trade including cash and a small, medium power desktop unit I can fit in the small space I have for use with my C line on AM. Models of possible interest in this category might be the AEA LA-30, Amp Supply LA-1000, Dentron DTR-1200, Heath Kit SB-200 or something similar. Of course, a Drake L-75 would be great if it would fit in my space. I can't remember the dimensions on it though. Can anyone help with that? Thanks much for reading and very 73. Kevin :) Amateur Radio: K7RX ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
[Drakelist] R-4B Mods (Epilogue)
Earlier today , I finished the last set of R-4B mods. Those of you following my progress, this marks the ten week point of incremental changes. The last (and final, I swear!) set of modifications: 1) Added the Sherwood PD-4 active product detector; and 2) Replaced the Sherwood AMP-4 audio amp with something truly special: a modified form of the SM0VPO Class AB design. This amp is rated at 4W into 4-ohms, so it can accommodate both headphones and an MS-4 speaker. The circuit board was made by FAR Circuits, based on the artwork available on the SM0VPO website. IMHO, this is the Holy Grail of "single supply" audio amps. Adding the PD-4 was easy enough now that the Sherwood PS-4 board is delivering regulated and decoupled +12V throughout the R-4B. Findings? Not a whole lot. AGC attack is much smoother but I notice no other changes. An ancillary benefit of the active design is that In/Out isolation is better than that of the diode product detector and as such, there's probably less opportunity for audio to feed back into the AGC circuits. I was not expecting much change between the Sherwood AMP-4 and the discrete SM0VPO design. However, the new amp board elevates the R-4B audio to a new level of audio performance. I searched for low-noise transistors for use in the high gain stage and kept the TIP-41 types in the output stage as a truly low-Z drive source for the headphones and MS-4 speaker. The output coupling cap is a low ESR type with a whopping 2700 uF of output C. The only way this amp can be improved is to utilize a bipolar supply to attain DC coupling between stages. I cannot justify that level of extra effort just for DC-coupling "bragging rights." Just adding the Sherwood PS-4 to the Drake R-4B was complicated enough (see prior message threads for details). http://72.52.250.47/images/AMP-1.jpg The discrete audio amp has zero residual noise, no hiss, no hum, no buzz. Unlike the monolithic LM3xx series, it's totally silent. I raised the amp's ground buss potential above the R-4B's chassis and used a large conductor size between the new amp board's ground buss and a common ground point on the Sherwood PS-4. Likewise, the audio input shield ties back to the same ground point. I did this to avoid buzz-inducing currents on the chassis from the AC tube filaments and the CT high-voltage secondary of the power transformer. The common point is in the corner tip of the R-4B chassis -- a point where AC currents are minimum. http://72.52.250.47/images/AMP-2.jpg I had one issue develop: As I unplugged the headphones, I noticed intermittent instability. For clues, I went to the National Semiconductor datasheets for the familiar LM383, LM380,and LM386 output amps. Each uses a small resistor in series with a cap (e.g., 2.7 ohm in series with 0.1 uF) at the output to better stabilize the amp under changing loads (e.g., un/plugging headphones). That worked very well with the discrete design and completely cured the instability without affecting performance. When I have time in the next couple weeks, I will measure the THD and IMD of the new amp. I have a Tektronix TM series test set with ultra-low-distortion oscillators and automated distortion analyzer. According to SM0VPO, typical THD at 2W is under 0.01%. So, perhaps now is a good time to summarize all my R-4B mods: 1) Eliminated all power-hungry voltage dividers and substituted with a Sherwood PS-4 board; 2) Replaced power transformer with an R-4C NOS unit thanks to the generosity of a list member. This R-4B runs super cool to the touch; 3) Replaced the multi-section power supply cap with a multi-section type from Tom at hayseedhamfest.com; 4) Removed the entire R-4B audio section and replaced with a modified SM0VPO Class AB audio amp board; 5) Changed H/P jack to TRS so newer stereo phones can be used without hunting for an adapter; 6) Replaced all 12.6V tubes to their 6.3V equivalents (e.g., 12AX7 is now 6AX7). This, because the R-4C transformer only uses a 6.3V filament secondary since the R-4C uses all 6.3V tubes. From the factory, the R-4B has a mix of 12.6V and 6.3V tubes -- and a CT 12V filament secondary; 7) Using an outboard inrush surge limiter on the AC line cord: Two CL-90 thermistors in series. In addition to inrush limiting to the filaments, the filaments now see 6.3V instead of 6.8V from my high AC mains line voltage (runs about 125VAC); 8) Replaced all paper caps with "yellow-jacket" metalized Polypropylene types; 9) Replaced the diode product detector with the Sherwood PD-4; 10) Replaced both dial lamps with blue LEDs from N9OO. Love the new look against the orange neon dial indicator; 11) Was going to replace a tired NE-2 bulb. For whatever reason, reversing the neon lamp leads has given it new life; 12) Changed AC line cord to 3-wire for safety; 13) Changed AGC "Slow" time constant; 14) Changed several audio coupling and bypass caps to extend the
Re: [Drakelist] TR-7A SHUTDOWN
This is getting confusing. Is it the RADIO or the POWER SUPPLY that is closing down? Nobody has said. On 13-Apr-11 22:17, Gary Poland wrote: Check the PIN diodes 73, Gary ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist -- Nigel A. Gunn, 1865 El Camino Drive, Xenia, OH 45385-1115, USA. tel +1 937 825 5032 Amateur Radio G8IFF W8IFF (was KC8NHF 9H3GN), e-mail ni...@ngunn.net www http://www.ngunn.net Member of ARRL, GQRP #11396, QRPARCI #11644, SOC #548, Flying Pigs QRP Club International #385, Dayton ARA #2128, AMSAT-NA LM-1691, AMSAT-UK 0182, MKARS, ALC, GCARES, XWARN, EAA382. ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] TR-7A SHUTDOWN
Check the PIN diodes 73, Gary___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] TR-7A Shutting Down At High Power
Lee is very correct about the PS7 and a little bit of stray RF. If you have any accessories on the 12 volt line (RCA jack) of the PS7, make sure that there is a .01uf cap across that line inside the PS7. I believe that was a factory upgrade/mod fairly early in the PS7 history. Usually this show most often on 40 meters becasue it is the peak gain of the original final RF brick. If you fix it there, you then usually have a stable PS7. BTW if you are not currently using a switched AC power socket, I would recommend that you look into one (computer switch deck is a good solution). The TR7 power switch/pot combo is put under quite a bit of stress with on/off cycles. I have not tried to locate a duel pot, duel switch combo, but my guess is that it is non-existent. 73, Ron WD8SBB --- On Wed, 4/13/11, leecra...@aol.com wrote: From: leecra...@aol.com Subject: Re: [Drakelist] TR-7A Shutting Down At High Power To: rfch...@verizon.net, drakelist@zerobeat.net Date: Wednesday, April 13, 2011, 4:16 PM Also have your friend check his grounding. Stray RF getting into the PS-7 will also shut it down. 73 Lee WB6SSW -Inline Attachment Follows- ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] TR-7A Shutting Down At High Power
Also have your friend check his grounding. Stray RF getting into the PS-7 will also shut it down. 73 Lee WB6SSW ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] TR-7A Shutting Down At High Power
As a side note, "full power" means different things to different people. If the final brick is adjusted for max output, then yes more current will be drawn but so also the instability might rear its ugly head. Best to keep things at a "manageable" level... -Original Message- From: rfch...@verizon.net To: drakelist@zerobeat.net Sent: Wed, Apr 13, 2011 2:24 pm Subject: [Drakelist] TR-7A Shutting Down At High Power I have a friend who remarked that his TR-7A shuts down when he tries to run full rf output. Otherwise the rig runs fine. Is this problem related to the current adjust pot in the PS-7 power supply? Any suggestions would be appreciated Tnx & 73EdK2ZE ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
[Drakelist] TR-7A SHUTDOWN
Hi Ed, I am no expert in this but the PS adjustment could be the problem. Also, I have found that low input line voltage can cause the same problem. This I discovered on field day when I was at the end of a long power cable. All was fine until I started tuning up with the antenna tuner. As I approached max power, the rig would shut down and I had to turn it off and then back on to "re-boot" . After I discovered that the line voltage was dropping to 105V under maximum load and ran a separate, heavier and dedicated power cable from the generator, the problem was totally eliminated. I'm sure you will hear from Garey shortly who is the consummate expert in Drake gear. 73, John, W4AWM ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] TR-7A Shutting Down At High Power
Ed, >From my limited experience, that is indeed the problem, the PS-7 is current >limiting due to a need to adjust it. I think that instructions for adjustment >are in the PS-7 manual. One friend's rig had a bad pass transistor and >exhibited this same symptom, however. I would still try the adjustment first. 73, Don, WB5HAK___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
[Drakelist] TR-7A Shutting Down At High Power
I have a friend who remarked that his TR-7A shuts down when he tries to run full rf output. Otherwise the rig runs fine. Is this problem related to the current adjust pot in the PS-7 power supply? Any suggestions would be appreciated Tnx & 73 Ed K2ZE ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] TR-3 S Meter
Tom - What happens if you turn the RF GAIN full CCW?? 73, Garey - K4OAH Glen Allen, VA Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line and TR-4/C Service Supplement CDs pony...@aol.com wrote: Hi Gang, I have a nice TR-3 that looks, and works well with one caveat. I can't get the S Meter to deflect past S2. So far I have swapped all the tubes involved??? Removed the meter, and it tests OK, so far, I haven't found any resistors out of spec. Tried changing the value of the shunt resistor, which is connected to the zeroing pot. Not much help there. I don't see much change in the voltage at either the receive IF, or the transmit IF. I understand that the TR-4 has a meter sensitivity pot, whereas the TR-3 has only the zero pot. Does anyone have any other ideas? Thanks for reading this Tom, WD8JPP ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] TR-3 S Meter
Hi Gang, I have a nice TR-3 that looks, and works well with one caveat. I can't get the S Meter to deflect past S2. So far I have swapped all the tubes involved??? Removed the meter, and it tests OK, so far, I haven't found any resistors out of spec. Tried changing the value of the shunt resistor, which is connected to the zeroing pot. Not much help there. I don't see much change in the voltage at either the receive IF, or the transmit IF. I understand that the TR-4 has a meter sensitivity pot, whereas the TR-3 has only the zero pot. Does anyone have any other ideas? Thanks for reading this Tom, WD8JPP ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
[Drakelist] 2C & 2CQ
The 2NT has been sold. The 2C & 2CQ are still available. Photos on request. 2C excellent condition $175 w/manual 2CQ excellent condition $225 w/instructions Postage from eastern Ontario is about $30, probably less for 2CQ. John, VE3PMA___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
[Drakelist] WANTED 4 NB
Hi all... Looking for a 4 NB board with cable. Or possibly a R 4 C with an NB board installed. Thanks, Bud, W7CWY <>___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
