Heathkit Apache

[VE9WGD Daniel]

I have an heathkit apache that was given to me by a friend. The driver audio transformer is missing and someone tried to apply a phase splitter but apparently failed and that person also modified the audio speech amp which is a mess. I would like to know if there is someone that can provide me a drawing and information on modifying the apache with a phase splitter using the original EL34 "6CA7" tubes. I would appreciate any kind of help. I really hate the idea to put the apache in the junk pile just because of a missing audio driver transformer. I'd really like to put that BoatAnchor back on the air. The radio still put out a good carrier and working like a charm except for the audio, and is still in very good shape physically.

[VE3AJM]

http://w1cki.net/A%20Speech%20Amplifier%20For%20Everyone.htm

W1CKI has a great circuit.

Al VE3AJM

[VE9WGD Daniel]

Thanks Al, but that circuit still use an audio driver transformer. What i'm looking for is a phase inverted without the use of a driver audio transformer because the audio driver transformer is missing in the apache. Thanks for the link anyway, i really appreciate your help.

[N2DTS]

Very easy to do, you want the modulators to run AB1 so no driving power is needed, then the typical phase inverter setup.
Look at any tube hifi amplifier, they all used it, you can pick from 7 and 9 pin tubes or octal tubes, some Bill Orr handbooks had good circuits and a HIFI audio section.
The back of the RCA tube manual has circuits but they tend to be complex and use odd tubes.
I have a bunch of circuits, its best to look at low end hifi amps for circuits that will be good up to the grids of the modulator tubes.

You can also buy a driver transformer, a better one then Heathkit used, or drive the grids with an 8 ohm amplifier into an 8 to 10k ct transformer, or convert it to screen modulation.
No need to scrap a rig because of a missing transformer, that is like sending your car to the crusher because its got a flat tire!
Rip out the entire audio section mess and make something good, its easy to come up with something better then Heathkit did.

The 8 ohm to grid setup can have the rig sound close to broadcast quality.
Hammond makes good transformers for that...

[VE9WGD Daniel]

Thanks Brett, you gave me many options that i can choose from. I will look into these options and see what i can do. I appreciate your help.

[N2DTS]

The easy way with minimal change and the best results is the 8 ohm to 5 or 10 K ohm transformer to the modulator grids, bias goes to center tap.
And 20 watt audio amp will drive it, line input so you can get a VX2000 or some such junk and sound very good.
In my early days, I used a radio shack PA amp, mic input and tone controls (bass and treble).

If you wanted the rig to sound REAL good, you could plug in some KT90 hifi tubes and regulate the screen voltage with VR tubes.
I have a 32V3 set up that exact way, it sounds great.

With modern stuff, you could even get an IC chip based audio amp that would drive the transformer and build it into the rig to run off filtered filament power (12 volts).

That is the fun of AM, you can try and do all sorts of things other then set the radio on a table and talk into it...

[Pete, WA2CWA]

Pick a circuit that suits your fancy:
https://www.google.com/search?q=amplifiers+with+EL-34&source=lnms&tbm=isch&sa=X&ei=CjzBVPLHBIa_ggS6-oLwDQ&ved=0CAkQ_AUoAg&biw=1248&bih=798#imgdii=_

[VE9WGD Daniel]

Brett you said a 20 watts amp to drive the grid of the EL34. Unless i'm wong but i thought the EL34 was driven by just a few watts from a 12by7 preceded by a 12ua7 and a 12ax7 speech amp in the Apache?...I do have a few HIFI amps here and also some left over audio hardware from my recording studio. Also have 24 bits digital/analog studio console. Do i really need a 20 watts amp, because i do have some.

Also thanks to WA2CWA Pete for the link. You guys are awesome, i never expected to get help so soon.

[N2DTS]

I just say 20 watts because its hard to find an amp that puts out less power.
Its also good to run things easy and in the very low distortion zone, plus there is always some loss and mismatch.
In home brew rigs, I like to run everything at half power, its clean and lasts forever.
It also tends to be huge.

There used to be a small TO220 5 pin package IC chip that put out 7 watts at 12 volts with only 4 or 5 parts.
Then just use a high output mic like a D104 with an amp in the base, or one of those compressor/preamp jobs that fit in the base.

[Pete, WA2CWA]

You can buy 8 watt Class D audio amps for $10 on ebay.

[VE9WGD Daniel]

If i understood correctly, all i need is a 10 or 15 watts and 8ohms to 10k ct transformer and feed a 7 or 8 watts audio amp into it's primary and the secondary feeds the grid of the EL34 right? The center tap will probably be the audio bias setting, and that tap will be on the secondary side of the transformer right? Guys which part of what i've said was wrong, cause i'd like to make sure of this before i attempt this mod.

As for the amp i can build a pretty good one with very low distortion with mosfet. I will feed the amp at line level with studio outboard equipment. Hopefully i will end up having a decent audio quality, instead of the scratchy audio that the apache has been doomed with.

[W3GMS]

I have an heathkit apache that was given to me by a friend. The driver audio transformer is missing and someone tried to apply a phase splitter but apparently failed and that person also modified the audio speech amp which is a mess. I would like to know if there is someone that can provide me a drawing and information on modifying the apache with a phase splitter using the original EL34 "6CA7" tubes. I would appreciate any kind of help. I really hate the idea to put the apache in the junk pile just because of a missing audio driver transformer. I'd really like to put that BoatAnchor back on the air. The radio still put out a good carrier and working like a charm except for the audio, and is still in very good shape physically.

Getting back to your original question here are a couple of working circuits to get you going in the right direction.   One is for the Johnson Valiant and the other is for the Ranger.  One uses a hot cathode phase inverter scheme and the other just drives two separate triodes as drivers where each is driven 180 degree's out of phase.  With a hot cathode phase inverter you get no voltage gain but you do get gain if you use the second scheme shown.  You will have to tweak things a bit but both circuits work well. Both of these circuits work well as long as your modulators are running in AB1 and draw no grid current.    

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

http://www.amwindow.org/tech/htm/valiant/audio.htm

73,
Joe W3GMS

[VE9WGD Daniel]

Thanks Joe, i will look into those as well, it seems like a good option too.

[W4RFM]

I have the audio driver transformer you can have for the shipping costs.
Bob
 bobmayben@usa.net

[Pete, WA2CWA]

Hopefully i will end up having a decent audio quality, instead of the scratchy audio that the apache has been doomed with.

Here's where you're wrong. The Apache was never doomed with scratchy audio. Many operators confused the front panel Gain control as the audio gain control. In fact, the front panel control was the clipping gain control. So, most of the time, it was operator error. A few simple mods, like increasing coupling cap values between stages or removing the clipping tube, can make the Apache sound great. Gutting of the entire audio section, less the modulator tubes, really is not necessary.

[W3GMS]

As with any mod's it depends on what outcome your looking for.  Yea, a stock Apache can offer good communication audio if that is your requirement. 

The driver transformer in the Apache is severely lacking if your looking for any kind of fidelity out of the transmitter.  That and the 510 pf capacitors has earned it a well deserved name of scratchy Apache!  Just get your signal generator out and do a response plot and you will see why it sounds the way it does! 

I have modified many Apache's with excellent results.  If you don't want to go the ultimate path of removing the driver transformer, then just put a better transformer in it.  I have had good results with one that Hammond offers.  The modulation transformer can sound very good so no changes there.  3 to 6 db of negative feedback is icing on the cake! 

So again, think about how you want it to sound and then pick the approach that matches your requirements. 
 

[K4RT]

Daniel - If putting your Apache "in the junk pile" means it's headed for the dump, considering giving the Apache to a local newcomer to AM instead.  Too many boatanchors have gone to the landfill!

I have an Apache and I agree with Pete.  In stock configuration, I found that with the mic gain & clipper adjusted correctly, it produced good communications audio.  Some experimenting with the correct combination of settings is required. I later removed the clipper circuit and modified the speech amp section to closely reflect that of the DX-100, and changed the value of the interstage caps and achieved clean, good sounding audio.  I don't know that it's broadcast quality audio, but I'm not really shooting for that, just good audio.  Down the road, I may restore the clipper, which, if adjusted correctly has its advantages when running 100W carrier in noisy conditions.

In any event, you now have a couple of options to return your Apache to stock or near stock if you want to, including W4RFM's offer of an audio driver transformer for the cost of postage. However, if you are intent on using a phase inverter go for it.

[W4RFM]

I applied line level audio from a compressor to the grid of the 12BY7 audio driver, and had short wave station fidelity.  I know because I played music through it into a dummy load. I also increased the cathode bypass cap.

[N2DTS]

Lots of ways to go, that is the fun part, pick a way and try it, then try something else, its a hobby!

Yes, you get an 8 ohm to 5000 or whatever audio output transformer and hook the 8 ohm side to the audio amp.
The other side has the center tap go to the bias supply, same as the driver trans used to go to, the other terminals go to the grid.
If its a fair transformer, you get 50 to 10,000 hz audio right to the grids, it works fine with tubes in AB1, AB2 or class B triodes.
You do not even have to mount the transformer if you do not want to.

In the original post, Daniel said the audio section was hosed up with past mods, NOT STOCK.

Do what turns you on, its great fun building a nice tube audio modulator and getting it to sound good with a D104.
Or you can do the full pro audio chain into a good amp into the transformer with power supply upgrades and low distortion modulator tubes.
In the old ays before the rigs were collectors items, we used to try one thing after another just for the fun of it.

There is no reason to do any of this other then for the fun of it.

[VE9WGD Daniel]

First i'd like to thank each and everyone of you for taking the time to get back at me. What i'm really trying to aim for is to get an audio response a little more than just communication quality. Of course it would be nice to have broadcast quality but it's not a priority for me, at least not at this time.As long as it can produce some reasonable low's, mid's and high's. I mean a better audio response than the stock apache was. You guys have given me many options to choose from and i think that's what make this hobby interesting. I will experiment with all ideas that were put here and will pick the one i like the best. I will let you guys know what came of it as soon as i have something working.

[wd8das]

Here's what I did with an Apache that I bought that already had the audio sections completely cleaned out:

http://www.wd8das.net/TX1MOD.jpg

I use a D-104 mic into the instrument input of a DBX compressor/limiter, fed to a little solid-state amp kit based on a TDA-something IC.  The amp is probably rated at 5 watts max into the 8 ohm input of the Apache, probably only needs a watt or two.

Steve WD8DAS

[flintstone mop]

I have an heathkit apache that was given to me by a friend. The driver audio transformer is missing and someone tried to apply a phase splitter but apparently failed and that person also modified the audio speech amp which is a mess. I would like to know if there is someone that can provide me a drawing and information on modifying the apache with a phase splitter using the original EL34 "6CA7" tubes. I would appreciate any kind of help. I really hate the idea to put the apache in the junk pile just because of a missing audio driver transformer. I'd really like to put that BoatAnchor back on the air. The radio still put out a good carrier and working like a charm except for the audio, and is still in very good shape physically.

Getting back to your original question here are a couple of working circuits to get you going in the right direction.   One is for the Johnson Valiant and the other is for the Ranger.  One uses a hot cathode phase inverter scheme and the other just drives two separate triodes as drivers where each is driven 180 degree's out of phase.  With a hot cathode phase inverter you get no voltage gain but you do get gain if you use the second scheme shown.  You will have to tweak things a bit but both circuits work well. Both of these circuits work well as long as your modulators are running in AB1 and draw no grid current.    

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

http://www.amwindow.org/tech/htm/valiant/audio.htm

73,
Joe W3GMS

Hi Daniel
What GMS linked is really the best. No transformers involved. A little bit of innovation and re-working the audio section. The 510PF caps are cutting any bass freqs out of the audio. There are some nice mods in the AM WINDOW section of this site.
Broadcast quality audio is not for a 100W table top transmitter.
Do have the schematic?

Fred

[N2DTS]

The thing is, if you have broadcast quality audio, you can do whatever you want with it, if you restrict it it will sound very clean and punchy, and you can choose to open it up if you want, or anything in between.
If its restricted and distorted you are stuck with that.