The AM Forum

My head was locked on needing to do a second adjustment for CW/AM. Of course SSB bias is on the same pot hahah I went to the voltage chart and checked things out that way and finished the other adjustments now it all comes together with 250  (I like 240 as a precaution who can tell the difference) with 4-5 ma grid current and tested the clamp tube works very well.

This may be a second response so I won't elaborate. Does a posting take some time to "Post"? 73 and thanks one million times. I will read the posts to see if I can help or I can learn.

Who is "Mike" above the microphone connector?   hihihihi Must ber a 60's thing.

73 am'ers BCNU.


Tony

Horrible manual scans out there; you should get a real manual  :D

All testing and adjustments start on page 91.
Follow the instructions carefully.
Make sure all the linkage is working properly.
Keep grid current to 6 ma
Actual audio gain control is behind the key jack. Have to insert screwdriver through key jack. Front panel "audio gain" control is the clipper.

Great transmitter. I built mine in 1960 and still use it today.

Open the case and remove chassis and check the circuitry against the manual's schematic. Very important first step.

I assume you're going to be AMing with this rig so here is my abbreviated procedure:

After circuit check-out, power up and make sure all filaments are lit and fan is turning.

In Phone Mode:

With a DMM check Pin 5,6 of 6CA7 for a negative voltage (bias) of about -35V. We need bias before we ever think about Keydown.

With a DMM check Pin 5 of 6146 for a negative voltage (bias) of about -50V.

Check right side of L24 (LV PS choke) for 350V.

Set VFO to 40 meters at about 7.2 MHz and RF drive pot to zero.

With dummy load and RF Wattmeter, Keydown and slowly increase RF drive while keeping grid current below 6 ma and do multiple plate dip and loads up to about 50 Watts output. Keep an eye on Grid current.

Using an insulated screwdriver for all adjustments, place a DMM probe at Final's screen, Pin 3, and at Keydown adjusting the Clamp tube pot for an initial 160 volts.

Increase drive for 90 Watts output while keeping grid current at or below 6 ma. Do multiple plate dip and loads as necessary.

Readjust Clamp Tube for Final screen voltage (Pin 3) of about 175 volts. Multiple plate dip and loads may be necessary.

BTW, I still have my TX-1/RX-1 twins.

i strongly advise that after checkout, a new, low profile 110V muffin fan of at least 35 cfm be installed atop the RF cage to suck out hot air.

Phil - AC0OB

Tony,

Congrats on getting an Apache. I've been using mine on AM since about 2013.

Phil & Pete,

Is your fan drawing out air through the factory perforations in the RF cage cover? I have a new lower profile fan on order after breaking the plastic flange on the stock fan again.

Also, the CW signal is jumping frequency a few hundred Hertz up and down keying the VFO. The problem is in the VFO stage, not the buffer/multiplier, and the crystal oscillator is stable. I've tightened every screw I can reach, reheated all soldered connections inside the VFO enclosure, swapped tubes, and cleaned the band switch contacts. Maybe some crud on the variable cap wiper I missed?  Have you experienced this sort of thing?

Brad K4RT

I removed the top cage cover and mounted a suck out fan in the opening with a couple of brackets. The fan now is a 24 v dc fan operating at roughly 18 volts. I also rigged the same type of suck out fan over the modulator section with some brackets. Keeps the entire area cool.


Over the years I've had two occasions of jumping frequency. The first time was a bad NE-2 in the time sequence keying. The second time, a few years later, it seemed to be originating in the VFO compartment. Rather then trying to determine the actual culprit, I removed the VFO, opened it up, and replaced all the resistors and capacitors. Problem went away.

Pete,

Thanks. Once the new fan is delivered I'll take a closer look at where to mount it.

I forgot to mention that I replaced the NE-2 and reheated the solder connections in the vicinity. I may have to replace the caps and resistor as you did.

Brad

I mounted the fan atop the RF cage to suck out air and placed aluminized Ducting tape on the cage top and upper sides so air gets sucked only into the bottom and out the top.

Make sure the 0A2 is functioning and pin 6 of the Osc. socket has about 115V on it.

Replace the 6AU6 with a 6AH6 in the VFO Osc. stage.

Phil

Thanks to all that replied. For some reason I got lost in the adjustment section. It seemed a bit scattered to me but with your clarifications I'm ready to go. The adjustments I thought were necessary as it's been sitting for about ten years. The lockdown brought it back up! The procedures had me going between the Notes, steps and locations and spun my head around a bit.

The muffin fan is at the top of my list. It doesn't seem to move much air but the final cage doesn't get too warm. We live in a coastal climate and it never gets too warm either! New filter caps are in the making but the old ones seem to be holding their own.

Thanks for providing this resource and help. After the adjustments and cleanup I'll come back and let you know how it went.

73 for now and have a happy holiday weekend.

Cheers Tony WA6LZH

I looked at my notes and the fan is a 65cfm fan.

After Modifications here was the Measured Data:

Power Out at Keydown* in AM Mode (120VAC input) 120W
Final Vp* = 730V
Final Ip* = 250 mA
Final Icg* = 3.8 mA
Final Grid Bias* = -78V (Measured at junction of R20, L15)
Final Screen Voltage* = 175V (Measured on Blue-Green Screen Voltage wire going into RF cage)
Modulator Screen Voltage Vmsg* = 355V
Modulator Grid Bias* = -35 volts
 
Tube Complement:  Finals – WestingHouse 6146B
Modulator – Svetlana EL34
Speech Amplifier – 12AX7A
Audio Driver – 12BY7A
VFO - 6AH6
Osc/buffer - 6CL6
Buffer/Multiplier – 5763
Clamp Tube – 6AQ5  
LV Rectifier – 5V4 (Solid Stated)
HV Rectifier – 5R4WGB
 
 
Phil

Grid current should to be set to no more then 6 ma for two parallel 6146's.

Yes, you have mentioned that twice.

If you are referring to my post in reply #8 above that was the actual  grid current with 120 Watts carrier for the dual 6146's.


Phil

Actually it good to mention it several times since I think it's important to proper operation of the finals. Less obvious is the actual gird shunt resistor which is 5.55 ohms at +/-1%. Of course the +/-1% was when manufactured back in the middle to late 50's if still original. Aging and use, after 60 years, could have moved the actual resistance beyond tolerance causing the actual grid current meter reading to be something different then what it shows.
It's not good to fry your grids and it's equally not good to starve them. ;D

For more pain, bring on those Apache singing cats:

(https://i.pinimg.com/originals/be/6b/fe/be6bfe74c318cafbfa9d15aab1a02ab3.jpg)

Phil,

Not to be a nit but I went through everything in the manual concerning adjustment and I could not find anything regarding the AM/CW bias adjustment. Can I assume this should be at zero ma with the operate switch thrown or should I just measure the grid and set for -50v or should the transmitter be loaded up to full input while setting the bias? SSB, MOD went fine. Seems to me I should know what the resting plate current should be for the proper bias with no excitation? If my memory serves me a class C amp should be zero current at rest with no excitation.

Thanks,

Tony

Tony,

You may have seen this already, but in case not or for others searching this thread for information, on pg. 94 of the manual, the second sub-paragraph covers bias control adjustment and the third sub-paragraph covers clamp adjustment.  Pete already mentioned that the mic gain adjustment is behind the key jack.

Brad

I will only add to what Brad has already stated about Page 94 of the manual.

My original tune-up procedure was to make sure you at first measured Final control grid and modulator bias before beginning any tuneup in order to not stress those tubes.

The best place to measure actual control grid bias voltage is at the junction of C43, R20, point "B."

With B+ on the final's, a certain amount of protective bias, and RF excitation, plate current is going to flow so we cannot assume zero plate current at Keydown.

From page 94 the idling current will be about 50 mA with no modulation and this is assuming proper plate dip and tune and your control grid current is less than or equal to 6 mA.

Tweaking of R5 is only necessary if excessive Downward Modulation is seen.

Page 100 is a good reference for checking "ballpark" voltages.

BTW, later on you will want to rid this unit of the clipper circuits. The clipper circuit does not do what is was designed to do and just adds harmonics and distortion.


Phil

Phil,

Thanks for posting the pic of your Apache fan configuration. I received the fan I ordered, which is similar to your fan. I might order a second one for the back of the DX-100B.

Tony, stock, my Apache had clean audio with the mic gain and clipper adjusted correctly.  However, I removed the clipper circuit and essentially converted the speech amp to that of the DX-100 with changes to the inter-stage cap values. Conservative changes that sound good with a standard D-104 mic. I also moved the mic gain to the front panel GAIN position and I think I put the bias pot behind the  key jack.

Brad

Phil,

My thick skull finally saw what I was doing. In my defense I think it is very, very odd that they explain the ssb bias adjustment but not the AM bias adjustment. I realized it had already been done as there is only one adjust at all. I used the tube socket voltage chart and all bias voltages were correct for all the modes. I'll attach the tuner/power meter tomorrow but tuneup readings are lookin good. 240 ma with about 5ma of grid current and modulation kicks up nice and easy as well as tested clamp action by turning the driver off with the drive control goes to zero. Looks good on the scope even with the low impedance mike I was using. I have a hi impedance dynamic and it looks good too but I just turn the gain down. I monitored on another receiver with a small wire attached and audio sound pretty good but some years age I installed increased capacitance on the "Three bad boy" caps in the mic amp don't recall the values but on the air test showed up well.

One anomaly I'm sure you know about: The microphone jack is labeled "Mike"! hihi Maybe that was the thing in the 60's.

Thanks again all the help was invaluable. I'll probably do an on the air test in a few days but
I have to pair it up with my R-388 which I love as an am an cw receiver.

73   Tony

Tony,

Good to see you got your Apache adjusted.  Yes, the "Mike" label, it's the same on my DX-100B.  Maybe Mike worked in Heath's screen printing shop. :)

73,
Brad K4RT

"MIKE" not really uncommon label back in the "good old days"

Typical Boatanchor Examples:

Hallicrafters HT-32, Gonset GSB-100, Lafayette KT-390

Both of my Allied Knight's simply had "MIC."

Phil

More "Mike"

Elmac:

(http://kd4e.com/kd4e-images/elmac/af67mod-face2-sm1.jpg)

(https://forums.qrz.com/index.php?attachments/a54hfacesample-jpg.151844/)

Thanks again Phil. I pulled the 6al5 "Clipper" a long time ago. I think I'll jumper that audio band pass filter as well. After I resolve the hum issue. Scope says the ac ripple is extremely low less that 1%
I'm still looking for a 120  volt fan in my junk box. I have a hum issue but after pulling all the audio tubes it's still there. I think I have a ground loop or two as I have about a dozen plugged into the same circuit and antenna panel. I'll check it with a battery portable tomorrow.


Tony

Years ago I moved the audio level control (pot behind the key jack) to the position held by the Clipper pot. I then added a Tone control to the position behind the key jack with a phenolic rod extension through the key jack along with some tacked "tone" circuitry. I did it for fun and giggles but it worked so well I just left it in place. Of course, now I can't plug a key into the key jack.

I used a long-barreled Amphenol mic jack to cure that problem.

If you're into modifying the Apache's circuitry for improved audio here are my latest mods:


Phil

I don't get the connection between my running a phoenolic rod through the key jack ( so I can turn my tone control pot) and a long barreled Amphenol mic jack.

A mic jack in line, but behind, the key jack ?

The mic plug doubles as a deadly weapon ?

If it doesn't apply to your situation then be not concerned.

For the modification described on schematic 2 I had to use a long-barrel jack.

Phil

I already put it out of my mind.  ;D
In 60 years of owning and using this Apache and 59 years of owning the matching SB-10, my modifications have been minimal. I always liked the way the Apache operated even in its overall stock form although I did solid-state the power supplies back in the 70's. The tone control stuff wasn't meant to be permanent, but since it worked and didn't require much room or effort, I left it in.

I generally don't modify stuff unless I feel it's important to me or to the integrity of the equipment. If you Google "Heathkit Apache modifications, you'll get over 500K hits. That's funny!

I too like the way the Apache operates, its tuning, etc.,  which seems to be more straightforward than the Ef Johnson's  which is why I have my EF Johnson Viking II-CDC up for sale.

However, the Apache's audio was in need of major improvement, such as removing the 470k loading resistor on the mic input which was ok for slopbucket audio but not good for D-104 AM audio. The ridiculous 510 pF coupling caps were also problematic for low end audio, again ok for slopbucket use but not for AM.

If you know how to use the mic gain properly and use a scope to monitor your AM output envelope, the Clipper circuitry is not needed and your audio will sound much better if it is removed. Again, this junk circuit is ok for slopbucket audio but not for AM.

Anyway, the other mods are contained in the schematics if anyone is so interested in improving their Apache.

Have a great Memorial Day. Gotta go check the grill.


Phil

It's nice to hear good comments on the TX-1 Apache, Do you also like the RX-1 Mohawk? I see you have the matching set,
I've never owned a RX-1, I'd be interested in your opinion of the RX-1? They make such a cool matching set.
Nice pictures.
AG5UM

Since I never really cared for the D-104, I don't use it on the Apache. So D-104 AM audio (whatever that is) is unimportant. I use an EV 664. Also, since I don't really have an interest in sounding like Hi-Fi audio, and since 75 or 40 meter conditions can really chew up audio anyway, wideband AM audio is unimportant to me. I also generally keep the receiver bandpass to 6 KHz or less depending on band conditions.
Sometimes I'll play during a SSB contest weekend with the Apache and SB-10 and use a D-104 with the SB-10. Making the contact is what's important and not the audio during these sessions.

I also have an RX-1 Mohawk receiver. Took me plus 30 years after building the Apache to find one in great shape. It came from the original builder who became a silent key. The receiver is not bad on non crowded band conditions. I don't find the selectivity great and seem to spend a lot of time diddling with the IF Gain control on CW and SSB. It's not my primary boatanchor receiver. That's reserved for either the general coverage National HRO-500 or the amateur band coverage Squires Sanders SS-1R.

I bought two SB-10 units in nice condition for my DX-100, but I have'nt checked them out yet,
any comments from your experience with the SB-10??
I need to get mine up and going.Thanks for the comments on the RX-1.
Donnie
AG5UM

SB-10 is a phase shifting SSB exciter. After 60 years I would suspect many of the components in the audio and RF phase shifting areas need to be checked for value and condition. There was a great CQ article on updating the SB-10 back in the 70's. CQ Magazine, May 1970, page 22. Both Null pots should be replaced to a minimum 5 turn type pot. I use 10 turn pots. If you don't, you'll spend a good portion of your operating diddling with the original pots trying to keep the sideband carrier suppression near zero.

Did you modify your DX-100 yet for the use of the SB-10?

Hi Donnie,

I like it very much. I did do some minor circuit modifications. I have it on a Beverage antenna and when the conditions are crummy on my vertical I use the Mohawk.

My other two vintage receivers are the Hallicrafters S-108 and the Knight R-100.


Phil

Thanks for the CQ article info. I'll try to look that up. Sounds good on the 10-turn pots,
sounds like the voice of experience, thanks.
No, I have not modified the DX-100 yet, but I do have the Heathkit manuals for the DX-100 and the SB-10 also.
so I do have the instructions at least.
The beverage antenna is something I've been wanting to play with also, I've got the room...
Well, maybe this will inspire me to get the SB-10's out and see what I can do with them,
Thanks for the info..
Donnie
AG5UM

One of the common problems when using the DX-100 with the SB-10 on SSB, besides the inconvenience of connecting and disconnecting (mode switch is just for AM and CW), is the rather fragile and drifty VFO which requires almost constant diddling with the SB-10 controls. Many DX-100's also exhibit lower drive on 10 and 15 meters causing not enough SB-10 drive output. Personally, with two SB-10s, I would try to acquire an Apache and have all the necessary mods and switching already done for you.
It probably would be a lot less aggravation.

Yes, the Apache TX-1 with the SB-10 adapter would make a fun SSB station, I could then just use the DX-100 for
AM and code, what it was designed for. Thanks for the advice.
AG5UM