Re: [AMRadio] Lake Erie BoatAnchors Group - Winter Meet
Mark, Good luck with your get-together. Do you plan to mount any operating activities during the event? Dennis DuVall, W7QHO Glendale, CA Chairman, Military Radio Collectors Group (MRCG) 2004 meeting: Apr. 30 - May 1. --- StripMime Report -- processed MIME parts --- multipart/alternative text/plain (text body -- kept) text/html The reason this message is shown is because the post was in HTML or had an attachment. Attachments are not allowed. To learn how to post in Plain-Text go to: http://www.expita.com/nomime.html ---
[AMRadio] Mike Cable Capacitance
John Coleman, WA5BXO, posted: (Regarding 50-ohm coax attenuating the high audio frequencies when used as a microphone cable). I feel there must be some other thing that is overlooked about the connector or cable. 15 ft of cable would not normally cause any noticeable effect on audio unless the terminating Z was greater that a few mega ohms as it would be for some of the older equipment made for Xtal mike input but I can't imagine a modern day line input being greater than 100K ohms The impedance to be concerned with in this case is not the terminating impedance, but rather the source impedance of the microphone itself. In the case of the D-104, although the impedance of the microphone is specified at a nominal 10K-ohms, its actual source impedance is much higher. It is a well-known fact that the element must be terminated in a resistive impedance of at least 10-Megohms to obtain adequate low-frequency response - indicating a source impedance of at least that amount. Additionally, since there is no DC path through a crystal acoustic transducer, one would be suspicious that whatever the actual source impedance is, it would contain a capacitive reactance as a series component. The best solution to the problem is that advocated by several other posters here - incorporate a preamplifier very close to the microphone element (inches, not feet, away) having an imput impedance in the tens of megohms and capable of driving a 500-ohm termination at unity gain. Jim Bromley, K7JEB Glendale, AZ James E. BromleyTel: 623-848-8711 5128 N. 69th Ave. E-Mail: [EMAIL PROTECTED] Glendale, Arizona 85303
RE: [AMRadio] Mike Cable Capacitance
I replaced a 10 or 15 foot piece of rg8m with a 20 foot radio shack regular audio cable. This went between the berringer on the desk, to the nikko power amp in the rack (now empty and out of the way). The rack will hold the homebrew pair of 4d32 rig in the future. The level was the same except for the extreme highs, which jumped from 20% modulation to close to 100% with the radio shack cable. This was from making loud s sounds into the mike. Doing more checking, I found I had put bypass caps in the audio power amp, both on the input, .047 uf, and the 8 ohm output .01 uf. These were likely to large, and along with the coax, reducing the highs. There was a large change between the coax and the regular audio cable when I tried that first, but its very likely it interacted with the bypass caps and pushed the roll off frequency down to 3000 to 4000 hz??? I changed the caps to .003 in that amp, and also bought 2 new amps, a one rack mount space 20 watt per channel symetrix amp, that seems to need no RF bypassing at all, and a samson 60 watt per channel amp, also one rack mount space (nice and small). It was mail order, and has not got here yet. The 20 watt symetrix (pawn shop special) works fine on the 811a mod deck, and the 4x150a mod deck (ab1), but does not have enough power to drive the push pull parallel 100th mod deck, it gets up to about 90% mod at the symetrix clipping (20 watts). I likely need to change taps on the driver trans to get more voltage, 4 100th tubes should take less than 20 watts drive... My ears are no good, but I think it sounds much better than it used to, much less high boost for the same sound (in my ears). I guess the 120 watt per channel nikko amp will be a ham fest special, its worked great for 20 years of abuse, has nice analog meters on it, but its quite large and heavy for the shack. I like having all the audio stuff close together on the desk, the berringer mike amp/compressor/eq/etc, the power amp, the tape deck, and the receiver audio amp (marantz). With a one rack space berringer, and a one rack space audio amp or two, you can drive a bunch of modulator grids in a very small space. High quality audio in about 4 inches of total rack space! I paid $90.00 for the symetrix, $180.00 for the (new) samson 60 watt per channel amp. And yes, I still have the good tube audio in the 32v3 transmitters, so I am not a total sell out. I hope to build up a nice tube mike and line preamp/mixer/eq/ compressor/power amp to drive the various homebrew rigs. A tube compressor that works well might be a bit tough though. I have bunch of nice balanced 600 ohm to grid hi fi type transformers that need to go in something. A pair of KT90 tubes will do 160 watts in AB1, very low distortion. Tone control circuits are in the back of the RCA receiving tube manual, along with the mike preamp and mixer circuits. That and the homebrew RF vfo/exciter/driver are all that is left to have a completely home brew station from mike jack to antenna. (can you home brew a mike?) I heard the first part of the article on the second homebrew receiver is in Electric Radio this month, but have not got my copy yet. I have no idea what pictures they used, I sent in a whole mess of photos of various things in the shack. Brett N2DTS
[AMRadio] A Reminder - ALL PLEASE READ
For those who use more than one email account, must use the one you entered when you signed up to this list when sending a post to this list. If you belong to more than one QSL.NET mailing list, and have different email accounts setup on each, then it is likely you will not be able to CC the other ones as well. I am getting a hoard of rejections from the list manager (software) that I have to sift through every day, simply because many posts are sent using the wrong (the one not subscribed to the AM List) account. PLEASE be more careful when you post to this (and other) list in regard to what account you are sending from. This is an open list, in other words, anyone can join, but you can only use the email account you setup. I do this so that we do not have SPAMMERs trying to either post to the list, or farm email addresses from the members. So far we have been blessed from that intrusion for the past several years. If anyone would like to suggest we make the list totally open to anyone without membership, please, let's discuss it openly on the list for all to see. Thanks, Brian Sherrod W5AMI PS: I normally let the list flow without my intervention, and think that is a good policy. However, I must insist that we decide on what to do if so many folks want to post from different (those not subscribed) email accounts.
RE: [AMRadio] Mike Cable Capacitance
I use an outboard audio amp for my 75A-4 receiver with a system of adaptors that requires no modification to the receiver itself. I pull audio directly from the grid pin of the 12AT7 1st audio stage (with the tube removed). This is a high impedance point, 470k if I recall correctly. To avoid high frequency loss in the 5 ft. or so of shielded cable between the tube socket and amplifier, I built up a cathode follower stage to replace the 12AT7. It is a plug-in module that plugs right into the 12AT7 socket, and gets its B+ from the screen grid pin of the 6AQ5, which was also removed to conserve drain on the power supply and reduce unneeded heat in the receiver. I can remove the plug-in units and replace them with the original tubes, and the receiver will be completely stock once again. -k4kyv _ Learn how to choose, serve, and enjoy wine at Wine @ MSN. http://wine.msn.com/
RE: [AMRadio] A Reminder - ALL PLEASE READ
If anyone would like to suggest we make the list totally open to anyone without membership, please, let's discuss it openly on the list for all to see. Let's leave it like it is. Recall what recently happened to the AM Window open-without-membership BB. -k4kyv _ Get a FREE online virus check for your PC here, from McAfee. http://clinic.mcafee.com/clinic/ibuy/campaign.asp?cid=3963
Re: [AMRadio] A Reminder - ALL PLEASE READ
Don't open the list to all. The crazies and spammers will take it over if you do. 73 Damon Raphael, W7MD Tucson, AZ - Original Message - From: B. Morgan Sherrod [EMAIL PROTECTED] To: AMRadio amradio@mailman.qth.net Sent: Thursday, January 15, 2004 1:28 PM Subject: [AMRadio] A Reminder - ALL PLEASE READ For those who use more than one email account, must use the one you entered when you signed up to this list when sending a post to this list. If you belong to more than one QSL.NET mailing list, and have different email accounts setup on each, then it is likely you will not be able to CC the other ones as well. I am getting a hoard of rejections from the list manager (software) that I have to sift through every day, simply because many posts are sent using the wrong (the one not subscribed to the AM List) account. PLEASE be more careful when you post to this (and other) list in regard to what account you are sending from. This is an open list, in other words, anyone can join, but you can only use the email account you setup. I do this so that we do not have SPAMMERs trying to either post to the list, or farm email addresses from the members. So far we have been blessed from that intrusion for the past several years. If anyone would like to suggest we make the list totally open to anyone without membership, please, let's discuss it openly on the list for all to see. Thanks, Brian Sherrod W5AMI PS: I normally let the list flow without my intervention, and think that is a good policy. However, I must insist that we decide on what to do if so many folks want to post from different (those not subscribed) email accounts. ___ AMRadio mailing list AMRadio@mailman.qth.net http://mailman.qth.net/mailman/listinfo/amradio
