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Author Topic: WA1HLR "LITE audio mods" for the Ranger, 2022  (Read 9907 times)
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« on: September 04, 2022, 11:16:01 AM »

Below are the 2022 LITE AUDIO MODS sent to me by Tim, WA1HLR. They differ somewhat from his previous Ranger mods, being designed to retain all the stock tubes and transformers with a minimum of circuit changes. I have performed them on a stock Ranger and can attest they give good results.

******************BEGIN WA1HLR RANGER “LITE” AUDIO MODS*********************
For many people the following mods may be considered acceptable. After a long hard look at the existing schematic, the goal is to do a minimum amount of changes that will result in a marked improvement. No major drilling and blasting is required. All of the stock tube types are used. All stock iron is retained. BEGIN AT THE BEGINNING. DO THE FOLLOWING, DO NOT OMIT ANY STEPS! Being that the low frequency audio performance drops like a rock below 50Hz there is no point in very large coupling capacitors that would guarantee low end to 10 Hz. This could cause other issues to crop up. This is based on the use of a D 10-4 or other piezo-electric microphonium.

*Change R17 (1meg grid resistor ) to a 10-22 meg ¼ -1/2 watt resistor.

*Change C 58 ( grid rf bypass) to 68-100 PF cap.

*Change C50 A &C 50 B (cathode bypass caps first and second stage audio) to 50-100 MFD 10 volt min rating caps.

*Change C 51 .1MFD (first stage audio decoupling) to 10-20 MFD @450V cap.

*Change C52 (500Pf audio coupling cap ) to .003-.005 MFD 600V cap.

*Change R27 (150K Grid resistor V8-12AU7) to 330K-470K resistor. Connect from grids of V8 Pins 2&7, to ground. Do not connect to negative feedback winding. Introduction of negative feedback discussed later.

*Capacitor C55 (.1 MFD second stage decoupling) need not be replaced. It is an unnecessary component and may be removed with no change in performance.

*Change C59 A (cathode bypass) from 15MFD to 50-100 MFD @ 25V cap min voltage.

*Change C59 B (Bias stabilizing/bypass) from 15 MFD to 100-200 MFD@ 50 volts cap min.

*Change R 28 (cathode resistor V8) 820 ohms to 680-820 ohms @2watt resistor.

*Coupling Cap C 57 (.02 MFD) remains in place. Check for leakage. Replace if necessary  A value as low as .005 may be used if the grid resistor is at least 500K.

*Replace capacitor C 60 (.005 MFD) with a 10K 1W resistor to provide a constant swamping load on the secondary of T3 the driver transformer.

****Negative feedback details****
It has been found that the method of the introduction of negative feedback in the Ranger modulator has issues. I found it difficult to obtain good low frequency response even at low power mode. A simple change of introducing negative feedback is as follows:

*The cathode bypass capacitor C50-B has its' ground lead lifted from ground. A 330 ohm resistor is inserted in series with the capacitors negative lead and ground.

*An 18K ½ watt resistor is connected from the junction of the 330 ohm resistor and the capacitor The other end of the 18 K resistor is connected to the tertiary negative feedback winding that at one time was connected to R 27. This is nothing more than a voltage divider circuit. Feedback levels may be adjusted by either increasing or decreasing the value of the 18K resistor or the same with the 330 ohm resistor. It is dependent on the values of resistors readily available.
****Parts to be removed or changed****
The following components are detrimental to the high frequency audio response:
*C53 200 PF across Gain Pot.  
*C56 470 PF from plate of second audio to ground.
*C69 across secondary of modulation transformer.

The following are all .002 MFD 1500 volt disc ceramic capacitors, and should be removed: C 66, C67,C68, C83,C84.

The following need to be changed in value:  
*C47 & C48, the .002 1500V bypasses at bottom of pa plate RF choke. Replace with 500Pf 3Kv caps. 1000 PF @3Kv may be used as well. Removal and change of the last two should markedly improve the high frequency audio response.

****Parts to be added: minor schematic changes****
*Add a 1 MFD 100 volt non electrolytic capacitor in parallel with the tertiary negative feedback winding. This mod from Chuck, K1KW, helps to eliminate the ultrasonic oscillation problem.

Between the 1MFD cap across the feedback winding, and the resistor across the secondary of the driver transformer, the modulator should be unconditionally stable. If there is an ultrasonic parasitic oscillation, increase the value of the 1 MFD cap across the negative feedback winding. Try adding a .5MFD 100V cap across the 1MFD cap. Also try increasing the value of the negative feedback resistor from 18K to 22K, hopefully there will be no issues here.

****Adding Line Level Input****
Much greater utility of the Ranger transmitter may be had by adding line level input. Many operators have an audio chain of some sort consisting of equalizers, compressors, limiters and other forms of semi pro, and  AM broadcast grade audio processing equipment. All pieces are line level output. Using an attenuator  to bring the level down is not the best engineering practice. You leave yourself open to ground loop hums,RF susceptibility  and possibility of front end overload of the input stage. Simply carefully mount a ¼ inch phone jack or RCA connector to the rear of the chassis where the microphonium and key jacks are. Run a piece of shielded audio cable from the newly installed jack to the audio gain pot (R21) The center conductor is tied to the top on the pot. The braid to ground. This will handle a wide range of input signal level. The existence of the first section of the speech amp (V7-A) and cap C 52 will have no effect on the much lower source impedance presented by the usual solid state audio equipment used. With ALL audio and other modifications performed you are ready to enjoy the fruits of your labors.

******************/END WA1HLR RANGER “LITE” AUDIO MODS*********************

*NOTE* Tim strongly advises that ALL his previously published power supply, bias supply, T/R modifications, etc. be performed for safety, reliability and efficiency reasons. The above represents ONLY his “LITE” AUDIO MODS to a stock Ranger.

And I'll mention something here that is not strictly an audio mod, however I've found that it's really worthwhile in the long run. Depending on the age and condition of your Ranger, I advise removing ALL the AC line-to-ground capacitors as well as the crowded mess of TVI inductor-capacitor filters at the 9-pin accessory socket (ceramic disk caps C61A, C61B, C62A, C62B, C63A, C63B, C66, C67, C68, C74, C75. Firecracker style or enameled wire inductors L25A, L25B, L26A, L26B, L27A, L27B, L23, L24, L20, L21, L22). Leave the socket in place, but bypass all the connections into and out of it. For the vast majority of Ranger owners, there is no need to have accessory socket connections to the modulated HV and center tap of the mod transformer outside the rig. In my case, the decades-old spaghetti insulation on the connections in the accessory socket shield would *intermittently* short circuit to ground as the chassis expanded and contracted during heating and cooling cycles. And the old ceramic disc capacitors themselves had a habit of failing and arcing over. Best to get rid of all of this junk and use appropriate gauge hookup wire to make any necessary point to point connections formerly made by the inductors.

- de W1GFH

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« Reply #1 on: September 04, 2022, 12:00:19 PM »

I will echo your sentiments about the spaghetti on the accessory socket of the Ranger. That stuff dried out and kept blowing the fuse. It wasn't until me and Duane, KK4AM went through it and systematically removed each leg from the LVPS. After that we went and used the insulation from some THHN wire I had in the shack. I like the idea of removing all the TVI coils/caps. I think it was just recently on Facebook where a Ranger owner showed that one of those disk ceramics had the AC line voltage arc over to ground! That being said, if you haven't already done so I advocate replacing the ELMENCO dual fuse plug to a polarized plug with a stand-alone fuse.

Invisible airwaves crackle with life, bright antenna bristle with the energy. Emotional feedback, on timeless wavelength, bearing a gift beyond lights, almost free.... Spirit of Radio/Rush

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« Reply #2 on: May 24, 2023, 09:28:59 AM »

Unofficial UPDATE from WA1HLR.

Tim recently spent a month "doing up a Ranger" for Pedro AJ4OO and has made a few minor refinements to his "lite" mods. The most significant refinement is substituting a 12AV7 for the 12AX7 speech amp tube. Tim found that the lower gain 12AV7 improved headroom and reduced the possibility of self oscillation in the modulator.

I tried it and can report markedly better performance. If you look at Tim's design, he had moved the feedback injection point from the 12AU7 driver to the second stage of the 12AX7. As a result, the 12AX7 simply had way too much gain, and often produced distortion on peaks unless the audio gain was throttled back to between "1" and "2". The 12AV7 cures all of that, and lets the audio gain control operate within a more reasonable range.
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