All,The replacement MRF-247 arrived today and I installed it in the amplifier. Wow, these transistors are old, the date code was 9842, it appears to have been manufactured on 42nd week of 1998.
The amp appears to be working fine. I can only drive it with about 5 watts CW on 2 meters (that's all the 2M power I have here in the home shack), but it is putting out ~125W and no oscillations. Tomorrow afternoon, I will realign the input ciruit, because I tweaked with it during troubleshooting. The preamp is working fine and provides ~18dB of gain.
I may be able to reinstall it in the SARC radio room this week, but I am busy through next Monday. We need to really think about hard keying this amp and get away from the RF sense keying. I have a sequencer built and ready. I just need it interface it with the radio and amp, when I get some time of course.
73 John N6VMO----- Original Message ----- From: "Bill McMillan" <12647@xxxxxxxxxxx>
To: <sarcmembers@xxxxxxxxxxxxx> Sent: Monday, January 18, 2010 18:58 PM Subject: [sarcmembers] Re: IC-736 and the TE Systems amplifier...
I will donate the money for one Transistor ($50.00) Bill McMillan KI6LXV -----Original Message----- From: sarcmembers-bounce@xxxxxxxxxxxxx [mailto:sarcmembers-bounce@xxxxxxxxxxxxx] On Behalf Of John Maetta Sent: Monday, January 18, 2010 5:59 PM To: sarcmembers@xxxxxxxxxxxxx Subject: [sarcmembers] Re: IC-736 and the TE Systems amplifier... So, how am I to proceed? Do I purchase the component or will the club? John N6VMO----- Original Message ----- From: "Avery Wright KD4GBA" <kd4gba@xxxxxxx>To: <sarcmembers@xxxxxxxxxxxxx> Sent: Sunday, January 17, 2010 16:34 PM Subject: [sarcmembers] Re: IC-736 and the TE Systems amplifier...UPDATE: American MicroSemi has the MRF-247 in stock and on sale for $49.94 each. You can find it here:http://store.americanmicrosemiconductor.com/mrf247.html?gclid=CM_h-7_XrJ8CFRD7agod1Bfl0w Avery -----Original Message----- From: sarcmembers-bounce@xxxxxxxxxxxxx [mailto:sarcmembers-bounce@xxxxxxxxxxxxx] On Behalf Of Eric Lemmon Sent: Sunday, January 17, 2010 4:29 PM To: sarcmembers@xxxxxxxxxxxxx Subject: [sarcmembers] Re: IC-736 and the TE Systems amplifier... John, I checked with several suppliers, including RF Parts, and could not find one that stocks the MRF-247. Since I assume(?) that the amplifier has four75-watt transistors in parallel, it seems prudent to use a genuine MRF-247transistor for replacement, if one can be found. If a substitute transistor is used, such as the 2SC2782 or NTE478, it might be advisable to replace all four transistors to avoid mismatching issues. Since the 2SC2782 costs about $32 each, this is a significant expense. I hope we can find an MRF-247 rather than risking further damage with a mismatched component. Is TE Systems still in business? 73, Eric Lemmon WB6FLY -----Original Message----- From: sarcmembers-bounce@xxxxxxxxxxxxx [mailto:sarcmembers-bounce@xxxxxxxxxxxxx] On Behalf Of John Maetta Sent: Sunday, January 17, 2010 3:24 PM To: sarcmembers@xxxxxxxxxxxxx Subject: [sarcmembers] Re: IC-736 and the TE Systems amplifier... Today is a great day to keep dry, listen to the 40 meter swap net on 7.240MHz and work on radio gear.I opened the TE Systems amp and discovered the T/R and RF Sense relays andcircuits are working, but the amp continues to draw 15amps after PTT is removed. The o'scope then revealed that the amp starts to oscillate whenPTT is asserted and will not stop oscillating until power is removed. Theamp has turned itself into a 100W noise generator. The noise emitted by the oscillations drowns out the swap net. :) Troubleshooting detected that one of the four MRF-247 final transistors, Q3, is the culprit. With Q3 disabled, the amp keys, draws 2 amps bias currentand then current drops to ~0 when PTT is removed, just like it is supposedto. If any of you have one in your junk box, please let me know. Or we can order one. Here is what we need to repair the amp: http://www.datasheetcatalog.org/datasheet/motorola/MRF247.pdf I also need some wide solder wick (1/4" or wider) to help remove the transistor from the amp. All I have is the narrow wick. The other option is to leave Q3 disabled and run the amp at reduced power out. 73 John N6VMO----- Original Message ----- From: John Maetta <mailto:j.maetta@xxxxxxxxxxx>To: sarcmembers@xxxxxxxxxxxxx Sent: Sunday, January 17, 2010 12:05 PM Subject: [sarcmembers] IC-736 and the TE Systems amplifier... Hello, Last week a member asked me to have a look at the IC-736 and TE System 2 meter amplifier. It was reported that the antenna(s) were exhibiting a high SWR and the TE Systems amp would constantly draw 15amps from the Astron power supply after the PTT was released. This morning I noted the following: A quick check of the setup found the IC-736 and amplifier are currently connected to the 2 meter AZ/EL antenna 'A' via the MFJ-864 SWR/Watt Meter. Using the IC-736 only and running 25 watts output, I noted antenna 'A' is also displaying >3:1 SWR on the MFJ-864 SWR/Wattmeter. A more thorough inspection found antenna 'A' was incorrectly installed on the HF output port of the swr/watt meter, instead of the UHF output port. After correcting this, the SWR of antenna 'A' was 1.1:1. Power up of the TE Systems amp was normal and the preamp appeared to be working too. Keying the amp and applying 20W of CW drive, the output power went to ~300 as normal. But, after releasing the key the IC-736 returned to receive mode as expected, but the S-Meter displayed >S-10+ noise. The amplifier power output dropped to 0 as normal, but the amp continued to draw 15amps of current. Only after powering off the Astron power supply would the amp stop drawing current and IC-736 S-Meter return to normal levels of noise (S-1 or so). It appears the amplifier is working as far as power output and preamp, but the TX/RX relay and/or RF sense circuitry may be holding the amp's bias voltage on and not releasing the amp to RX mode. Operating the system into the high SWR due to incorrect placement of the antenna on the swr/watt meter may have caused the amplifier to fail. I have removed the TE Systems amp and Astron power supply from service and they are on my workbench at home. The IC-736 is currently available to operate 'barefoot' by SARC members. This seems to be a easy problem to fix and I will keep members notified of my findings. 73 John N6VMO _______________________________________________ You have received this because you are subscribed to the Satellite Amateur Radio Club Members Mailing List To post on the mailing list, simply send email to sarcmembers@xxxxxxxxxxxxxx This mailing list will only accept email from subscribed members so SPAMMERS will not get your email address To unsubscribe, send an email to sarcmembers-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field OR by logging into the Web interface at: //www.freelists.org/cgi-bin/lsg2.cgi _______________________________________________ You have received this because you are subscribed to the Satellite Amateur Radio Club Members Mailing List To post on the mailing list, simply send email to sarcmembers@xxxxxxxxxxxxxx This mailing list will only accept email from subscribed members so SPAMMERS will not get your email address To unsubscribe, send an email to sarcmembers-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field OR by logging into the Web interface at: //www.freelists.org/cgi-bin/lsg2.cgi_______________________________________________ You have received this because you are subscribed to the Satellite Amateur Radio Club Members Mailing ListTo post on the mailing list, simply send email to sarcmembers@xxxxxxxxxxxxxxThis mailing list will only accept email from subscribed members so SPAMMERS will not get your email address To unsubscribe, send an email to sarcmembers-request@xxxxxxxxxxxxx with'unsubscribe' in the Subject field OR by logging into the Web interface at://www.freelists.org/cgi-bin/lsg2.cgi _______________________________________________ You have received this because you are subscribed to the Satellite Amateur Radio Club Members Mailing ListTo post on the mailing list, simply send email to sarcmembers@xxxxxxxxxxxxxx This mailing list willonly accept email from subscribed members so SPAMMERS will not get your email addressTo unsubscribe, send an email to sarcmembers-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field OR by logging into the Web interface at: //www.freelists.org/cgi-bin/lsg2.cgi
_______________________________________________ You have received this because you are subscribed to the Satellite Amateur Radio Club Members Mailing List To post on the mailing list, simply send email to sarcmembers@xxxxxxxxxxxxxx This mailing list will only accept email from subscribed members so SPAMMERS will not get your email address To unsubscribe, send an email to sarcmembers-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field OR by logging into the Web interface at: //www.freelists.org/cgi-bin/lsg2.cgi