Help please, with the apache mods.

[KR4WI]

Hello: I have my apache out of the cabinet, was looking for faulty parts on audio portion of it. I have been getting reports of my audio sounding like it is not fully modulated, I checked the audio bias, it is suppose to hit 125 ma when I whisle into mic, So I adjusted the pot behind the key jack, now it hits 125 on the meter. And sounds much better, I hope that fixed it.  Also I want to do the audio mods listed on other pages here but I am not for sure where the couplin caps are.  Is the coupling caps everyone change on the 12ax7 tube socket, .005 to .01 or more??  I hope to have it on air by Friday night, its the only tx I have with a vfo, to work all you 1x1s. Matthew KR4WI

[ve6pg]

MATT...CHECK THAT STUPID POT UNDERNEATH THE RIG...IT IS VERY CHEAP, SO GIVE IT A SPRAY, AND SET THE MODULATOR RESTING CURRENT AT 50-75 MILS RESTING CURRENT...YOU HAVE TO PROP THE RIG UP TO DO THIS, AND BE CAREFUL OF THE HI VOLTAGE. PUT THE METER IN THE MOD POSITION, THROW THE TRANSMIT SWITCH, AND ADJUST THE POT UNDER THE RIG FOR, AS I SAID, 50-75MILS..THEN ADJUST THE OTHER CONTROLS...THE ONE BEHIND THE KEY JACK IS REALLY THE "GAIN" CONTROL...YOU HAVE TO GET A BALANCE BETWEEN THE ONE BEHIND THE JACK, AND ON THE FRONT PANEL....DO A GOOGLE FOR GLEN ZOOK..HE HAS SOME SIMPLE AUDIO MODS FER THE APACHE, AND GENERALLY THEY ARE DEALING WITH THE SMALL AUDIO BOARD UNDER THE RIG...YOU CAN INCREASE THE CAPACITANCE, AND MAKE IT SOUND BETTER..GOOD LUCK, ES LET US KNOW...TIM....SK..

[n3lrx]

While you're at it, take out the 6AL5 (Clipper) and flush it down the toilet.. (If you haven't already! Then remove the socket, and mount your pot in the hole with the assist of a few fender washers..  That way you don't have to screw with opening the case and or sticking a screwdriver near dangerous voltages..

(Note: Popping out the 6AL5 'Clipper' requires no additional mods. It is in parallel so removing it does not require any wiring changes. Although removing the socket you will need to make some minor changes.)

Fattening up the caps does help.. There are ton's of mods on the apache. I'm just too brain dead to remember them. TimTron also had written a few ass kickin' mods for the TX-1 Apache..

I Miss my Infamous YellRX Scratchy Apache! I regret that I sold it!

[ve6pg]

...I SHUDA MENTIONED THE 6AL5...REMOVED MINE..I MOUNTED A POT ON THE CHASSIS, SO I CAN OPEN THE LID AND ADJUST AS NEEDED...NEVER THOUGHT OF THE 6AL5 SOCKET...TIM...SK..

[Pete, WA2CWA]

If it's a stock Apache, the pot behind the key jack is the audio gain control, The front panel "gain" control actually should have be called a "clipper gain" control. Running stock Apache, the front panel control should only be turned up a few degrees above the zero point (for a small percentage of clipping). Then adjust the audio gain control (behind the key jack) for approx. 125 Ma peaks (meter switch in Mod. position) while talking into the microphone. If the clipper tube is removed, the front panel "gain" control becomes more difficult to manage. A slight turn up, from the initial setting mentioned above, can turn the modulator into a distortion mess. Some believed that turning the pot behind the key jack down was the answer to clearing up the distortion which it wasn't. The stock Apache can be made to sound "decent" with some minor coupling cap changes between various stages. One such mod has been documented in Electric Radio.

[WBear2GCR]

Somewhere on this site, I posted some analysis of the audio "filter" part of the Apache circuit, with optimized values - the clipper part being removed totally.

If you go and search under my login, you'll doubtless find the thread, and the link the the "hidden" pages on my website with detailed information, iirc... although at the moment I can't actually recall if it is only here posted or the details on the website... either way, a good read for the Apache audio...

Also check the "AM window" site, it has an Apache mod as well...

      _-_-WBear2GCr

[w5rkl]

There is a small phenolic board on the side of the chassis in the modulator section. There are 3 interstage disc caps mounted on this board,
two 510pf and one .01ufd. Changing these caps to .01ufd orange drop caps will improve the modulation.

The better mod is the W3SCC mods. The link below is the W3SCC Apache modulator schematic modification.


http://www.amwindow.org/tech/htm/w3sccmods.htm

The mod takes about 2 hours to perform and it eliminates the 12AU7, 6AL5 stages plus the small round black filter. If you perform this mod
to your Apache, the 6AL5 and 12AU7 tubes no longer need to be in their sockets as they are no longer in the circuit. The EL34 bias will
have to be readjusted for an idling current of 50ma. Also, the only gain control, after the mod has been done, is the front panel control.
I run my gain control no higher than 9 o'clock which produces plenty of audio and no splatter. Although the schematic does not indicate it,
I highly recommend using shielded cable between each stage and also from the microphone jack to the input of the 12AX7. I used the
stereo cables that are used between DVD, VCR etc. Simply pull them apart, cut the cable to the desired length and solder between the
stages. It works very well.

73's

Mike
W5RKL

[WU2D]

Matt,

You have got to do the mods. That schematic by W3SCC is a nice piece of work. I have one more suggestion. Try some global feedback around the transformers. There should be enough gain in the four stages to easily throw some away. You may be surprised on how it straightens out the audio response in this radio. If the iron has too much phase shift, you may not be able to employ much feedback, but it is always worth a try. I guarantee that it will no longer sound anything like an Apache.

Phasing - If it oscillates and howls, you have to reverse the phase on the driver transformer.

You also may get some ultrasonic oscillations with feedback. A trick to kill this is  putting some capacitance across the secondary of the driver transformer like 680 pf to 4700 pF.

Mike WU2D

[WBear2GCR]

I'm not a fan of loop feedback around transformers generally speaking, but...

If you do use it, one can consider using a small value cap across the "feedback pot". That will have the effect of bringing the gain of the modulator to unity at some high frequency where the reactance of the cap is sufficiently low so that it looks like a straight wire in the feedback loop (in effect). The other part of that is a rolloff point is now added into the HF response that will roll off at 6db/octave starting at some frequency depending on the value of the cap. You can set the cap value to be down 6db at say 10kHz. for example. It may also help to kill any ultrasonics, depending on the phase relationships in the modulator... it could create oscillation if the phase relationships are problematic (iron has freq dependent phase shift). But this additional cap is standard practice on many tube audio amps.

Other options for "killing" ultrasonic oscillations include putting a cap or RC combo from the plate of a tube to the grid. This makes for very high local feedback, which drops the gain, at higher frequencies outside the audio band.

 Also one could consider dropping a small cap to ground at pin 2 of V9 or again a RC combo.
The effect of this is to dump all the HF energy above some frequency so that the feedback loop does not have HF energy to "boost" while it tries to flatten the response, therefore nothing to excite ultrasonic instability. Similarly one could do the same thing on the grid of the previous tube, before the feedback loop. In that case a small cap (some pf) could go across the pot.

If one puts a this sort of HF reduction/control in a few points in the circuit, then the rolloff slopes which are all 6dB/oct add up and you can get a higher slope HF rolloff for the entire modulator - which may have some real benefits.

If it was done in three places, then the total slope would add up to 18db/octave. If the nominal 3dB down point was 10kHz. then the rolloff at 20kHz would be ~21dB. Whereas with no rolloffs the response at 20kHz and at 10kHz. would be "0"dB.

It seems to me that not exciting the mod iron flat out to 20kHz at all is a good idea...

Which was the basis for my analysis of the Apache's filter components that were formerly used in the clipper - I found that one could make a jim dandy eliptical filter out of the basic components.My design gives you a nominally flat response out to ~6kHz and then rolloff at a very very high rate. My idea is to make that circuit switchable in/out which is easy enough to do (bypass with a relay + resistor), so that one can pop it in or out depending on band conditions and adjacent QSOs... a 6kHz audio width still sounds very good, and gives you a 12kHz wide signal. Switch it out and ur full range again.

           _-_-WBear2GCR

[w5rkl]

If your Apache is working fine without any problems other than "Scratchy Apache" ( original modulator wiring) audio then
I would not change the driver transformer wiring. I've never changed the original driver transformer wiring on any Apache
I've modified with W3SCC's audio mod. You will have to reset the modulator's bias adjustment to 20ma with no modulation.
This is done with the pot in the modulator section under the chassis. The front panel gain control should not have to be
any higher than 9 o'clock and with the normal modulator plate current should be between 40 and 60 mils with normal
voice peaks. I'm sure this mod can be performed with Apaches that have had their EL-34's changed to 6146's. However,
I've never installed this mod on an Apache with the EL34's changed to 6146 modulator tubes.

73's
Mike
W5RKL

[Pete, WA2CWA]

You will have to reset the modulator's bias adjustment to 20ma with no modulation.
This is done with the pot in the modulator section under the chassis.

If you're referring to the idling current; why does it change from 50 ma to 20 ma? Idling current for the pair of EL-34's should be approx. 50 ma.

The front panel gain control should not have to be
any higher than 9 o'clock and with the normal modulator plate current should be between 40 and 60 mils with normal
voice peaks.

Do you really mean normal modulator plate current on voice peaks to be between 40 to 60 ma?

[w5rkl]

You're correct, 50ma is the correct modulator idling current setting.
I incorrectly stated the modulator idling current value. I must have
been thinking of something else.

73's
Mike
W5RKL

[The Slab Bacon]

I'll give you all the "hot Frank tip of the day". as I have redone 6 Apaches to date.
If you are bulldozing and completely redoing the audio section per the AM Window / W3SCC mods, you no longer need the audio gain pot that is behind the key jack. Relocate the modder biass pot into that location behind the key jack, and you will no longer have to pull the rig out of the cabinet to adjust for aging mod tubes!!

                                                 the Slab Bacon

[Pete, WA2CWA]

You're correct, 50ma is the correct modulator idling current setting.
I incorrectly stated the modulator idling current value. I must have
been thinking of something else.

73's
Mike
W5RKL

I would also assume that in your phrase:
"normal modulator plate current on voice peaks to be between 40 to 60 ma"
You meant to say 140 to 160 ma on voice peaks.

[Tim WA1HnyLR]

Comming soon  to this website :Henry Nyelare Apache mods. 125% positive peak capability .50-15,000 freq responce.Uses all the stock iron. Line level ins and outs for external processing gear if wanted. Only one tube type change. De Tim WA1HnyLR

[WBear2GCR]

Lemmeee guess!

1500v B+ and 811s for the modulators?? 

But that won't getcha bandwidth like that... so maybe you're going series modulated a la QIX style?

   Inquiring minds want to know!

             

                   _-_-bear

[Steve - WB3HUZ]

If it's the ones I'm thinking of, nope. Just a turbo connection of the mod tranny, changes in the early stages and feedback. I've heard several of these and they sounded excellent. But ya never know with the Tron. He's always coming up with new stuff.

[WBear2GCR]

Ya, the ol' Timtron Turbo connection!

I do recall a descript-sheee-on of it do-ring a Kew-so...

Some are schept-ick-kul, but ahspose it kin werk.

                _-_-WBear2GCR