From owner-qrp-l@Lehigh.EDU Mon Oct 6 20:37:59 1997 Received: from fidoii.CC.lehigh.EDU (fidoii.CC.lehigh.EDU [128.180.1.4]) by oucsace.cs.ohiou.edu (8.8.5/8.8.5) with ESMTP id UAA29886 for ; Mon, 6 Oct 1997 20:37:57 -0400 (EDT) Received: from Lehigh.EDU ([127.0.0.1]) by fidoii.cc.Lehigh.EDU with SMTP id <34848-35114>; Mon, 6 Oct 1997 20:33:54 -0400 Received: from nss2.CC.Lehigh.EDU ([128.180.1.26]) by fidoii.cc.Lehigh.EDU with ESMTP id <35052-35114>; Mon, 6 Oct 1997 20:23:54 -0400 Received: from m7.boston.juno.com (m7.boston.juno.com [205.231.100.196]) by nss2.CC.Lehigh.EDU (8.8.5/8.8.5) with ESMTP id UAA73102 for ; Mon, 6 Oct 1997 20:21:59 -0400 Received: (from gsurrency@juno.com) by m7.boston.juno.com (queuemail) id U]L01180; Mon, 06 Oct 1997 20:20:05 EDT Message-Id: <19971006.171710.6566.4.gsurrency@juno.com> Date: Mon, 6 Oct 1997 17:16:24 -0700 Reply-To: gsurrency@juno.com Sender: owner-qrp-l@Lehigh.EDU Precedence: bulk From: gsurrency@juno.com (Gary L L Surrency) To: "Low Power Amateur Radio Discussion" Subject: HW-9: The (nearly) complete guide to the mods Part 3 of 3 X-Mailer: Juno 1.38 X-Juno-Line-Breaks: 0-5,11-12,19-20,27-28,37-40,50-51,58-59,68-69,81-82, 87-88,94-95,100-101,109-111,122-125,132-133,145-148,159-160,166-173 X-Listprocessor-Version: 8.1 beta -- ListProcessor(tm) by CREN Status: RO ******************************************************************* HIT DELETE NOW IF NOT INTERESTED IN HW-9 MODS ******************************************************************** IMPROVING THE PSA-9 MATCHING POWER SUPPLY Heath really did a bad job on the power supply for this great little rig. The original design has three series-connected 1N4149 diodes in the ground lead of a LM78L12 three-terminal 100 ma regulator. This is to compensate for the approx. 0.7 volt drop in the current-boosting transistor that is added to increase the output current capacity to 1 amp, and to also boost the output voltage to 12.6 volts or so. This is bad practice for good voltage regulation, since the added diodes and series current-boost transistor are all outside of the LM78L12 regulator's error amplifier, which in itself is a pretty good device. It's just plain bad design, and whoever at Heath designed this should have known better. Heck, an ordinary LM7812 would be simpler and much better regulated, but I wanted to have the ability to adjust the output voltage and still have good regulation. Enter the LM317T three-teminal adjustable regulator, (R/S pn.276-1778, $1.99) I stripped all of the parts off of the smaller terminal strip in the original design, and saved the diodes in the bridge rectifier. I decided to use a 4700 uf 35v filter cap instead of the 2500 uf 50v cap Heath provided. The Heath cap is probably adequate, but I had the Radio Shack electrolytic (R/S pn. 272-1022, $3.95) and felt the added filtering couldn't hurt. Since I like a narrow range of voltage adjustment, I employed a 100 ohm trimpot for the fine voltage adjustment, and used fixed resistors to set the limits of voltage ranget. A 150 ohm 1/4 resistor is used from the output pin of the LM317T to the adjustment pin, and after doing some calculations and a few trial and error tests, I used a parallel combination of a 2.2K and 3.9K resistor between the adjustment pin and the 100 ohm trimpot that connects to ground. The resulting range of adjustment is about 13.1 to 14.1 volts, with 13.6 volts near the trimpot's center setting. MAKING THE MODS TO THE PSA-9 Mount the 4700 uf 25 v (or re-mount the original 2500 uf 50v cap) electrolytic on top of the larger terminal strip to provide room to work on the new regulator circuit that is built on the small terminal strip. Remove Q1, and the small terminal strip from the power supply. Remove the pilot lamp assembly and save it for later re-installation. Strip all of the parts from the small terminal strip, and save the 100 uf cap for later re-use. The 1N4149 diodes, the 1 ohm 2w resistor, and the 1500 ohm 1/4 resistor can all be discarded or tossed into the junk box. Clean all of the solder, flux, and crud from the small terminal strip using a Solder Sucker or Soder Wick and acetone and prepare it as follows: Cut the terminal strip so that it has only 7 lugs, with 4 on one side of the ground lug and two on the other side of the ground lug. Mount it with the 4 lug side towards the left edge of the power supply chassis as viewed from the front panel. This is flipped from the way it was originally mounted. You may want to pre-mount most of the following parts to the terminal strip temporarily mounted on the outside bottom of the chassis for convenient access to the lugs. If you have another value for the trimpot, you'll need to experiment with the fixed resistors between it and the adjustment pin to get the 13.6 volts or so I think is ideal for the HW-9. Use another pot of 3K to 5K in place of the fixed resistor for a coarse control and use the small value trim pot you'll keep for the fine adjustment. Set the range with the 3K or 5K pot with the 100 ohm to 500 ohm fine adjust pot in its center setting. Then, measure the value of the 3K to 5K pot with an ohm meter and select a fixed resistor or combination of fixed resistors to match the measured pot value. I soldered some 16 gauge wires to the LM317T 3-terminal regulator and covered the connections with insulating tubing. It is mounted in the same hole as Q1, (Heath pn 417-852, TIP31) the pass transistor was bolted, using the same insulating mica washer and nylon shoulder washer. I soldered the input pin of the LM317T to the positive terminal of the 4700uf 35v (or 2500uf 50v cap if you keep the Heath part), and connected the adjustment and output leads of the LM317T to the first and second lugs of the small terminal strip, as viewed from the front of the power supply, left-to-right. The 150 ohm resistor is connected from lug 1 to lug 2, and one end of each of the parallel combination of the 2.2k / 3.9K resistors are also soldered to lug 1, with the other ends soldered to lug 4. The 100 ohm trimpot (a CTS blue knob miniature trimpot, like the ones Heath uses in the HW-9) is soldered facing up across lugs 4 and 6, with the center (wiper) lead in the bottom hole of lug 5. Bend the outer terminals of the pot so they are flat against the terminal lugs, and at a right angle. I re-used the 100 uf electrolytic cap C2 from the old circuit for transient load suppression. The negative lead connects from lug 7 to lugs 6 and 5 (ground). The positive lead goes to lug 2 and 3 (output). Also run a wire from the bottom hole of lug 2, which is the output, to the fuse mounted on the back of the case. The pilot lamp is retained and connected to lugs 2 (output) and 7 (ground). I heavily painted the terminals of the AC power slide switch with some red fingernail polish, so I would be less likely to touch 110v when adjusting the trimpot to the desired output voltage. You could also use some insulating sleeving if you re-dress the wires on the switch lugs slightly. I noticed some voltage drop across the original 1 1/2 amp output fuse that reduces the loaded voltage regulation. I replaced it with a 2 amp fuse that had less series resistance and caused less voltage drop under load. A better solution would be to move the fuse to the unregulated side of the LM317T chip, between the filter cap and the input terminal. This would eliminate all fuse-induced voltage drop, and still provide the desired protection from short circuits across the output, and would also protect the LM317T and rectifiers better. The new regulated supply is adjustable from about 13.1 volts to 14.1 volts, with 13.6 volts near the center of adjustment. Output current is more than 1 amp, typically 1.5 amps, and the ripple is below 1mv on my DVM under a load of 1.5 amps using a 8 ohm load resistor. The output voltage as measured between the power supply chassis and the input to the fuse does not measurably change from no load to 1.5 amperes. The only measureable voltage drop is in the wiring and connections to the HW-9, and this is only approx. 0.2 volt during transmit. The HW-9 now has a very stable power supply that is ripple-free and well regulated, further reducing the chance of any frequency shift of the BFO, or HFO, since they are supplied from the 12 volt (13.6 volt actual) PSA-9 DC supply. REMOVING THE VFO CAP AND RESTORING THE POTS I find it easier to remove the screws securing the back panel and middle shield to the sides of the chassis to permit room to remove the VFO capacitor. Leave the middle back panel screws alone, and spread the sides slightly to allow both the T/R and Oscillator boards along with the middle shield to slip back an inch or so. Then the VFO cap will come out easily if you have removed the tuning shaft extension and the four 4-40 nuts from inside the VFO shield. If the pots for some or all of the front panel controls have gotten dirty or feel poor, you can unsolder the wiring and remove them to be cleaned. By prying up the tabs that hold the back of the pots together, the resistance element and shaft can be removed. Clean the wiping contacts and the resistance elements with Q-tips or a toothbrush and Soft-Scrub (tm). Rinse everything well under water and dry. I use silicon grease on the shaft and shaft bushing to get that nice "feel" when rotating the pot. The RIT pot needs to have a little grease on its back cover to allow the center detent to act properly. Replace the pot cover and gently squeeze the tabs back in place with some large needle-nose pliers. This may save you some money on new pots, and will generally restore the pot's function to new condition. SUMMARY If you try some or all of these mods, please let me know how well they did or didn't work for you. I welcome your comments or observations. Note that Heath made several errors on the schematic, and that all of the active audio filter ceramic disc caps should be identified as 1000 pf (.001 uf), even though C339 and C341 are shown as 100 pf. Also, R354 is shown as 15 megohms, when it is really 1.5 megohms as R359 is. I am still trying to find out what device Q403 is, as the manual fails to mention it in the Semiconductor Identification Chart. It is only identified as a Heath part number 417-865, for which I have no information. There are surely more errors and omissions in the manual and schematic if you look for them. Thanks for the interest in improving the HW-9, and try these ideas if you get a chance. I think you will like the results. For more info on improving the crystal IF filter, see the ARRL's Hints and Kinks for the Radio Amateur, 13th edition, pages 1-4 and 1-5. I have the Kenwood IF filters to do this mod, but I think I'll use the radio as-is for a while before getting out the soldering iron again. ;-) 72 and good luck with your HW-9! AB7MY Gary Surrency Chandler, AZ (Near Phoenix), QRP-L #571, AZ ScQRPions, ARRL VE