Apache (Heathkit TX-1) Restoration

[N2LDE]

Hi Gang,

It's Tom the AM Newbie here!

I have 2 questions about getting my 1960 Apache up to speed:

1) I was advised to replace the HV electrolytic caps. According to the schematic, they are both 125 mfd. I can find 100 mfd caps, and 68 mfd caps (which I can wire in parallel for 136 mfd.) Which would be better? Or, if someone can point me to a source for 125 mfd 450V caps, I'd appreciate that as well!

2) I found almost all the tubes I need on-line, except fot the 12BY7 Audio Driver. Can anyone suggest an equivalent tube? Or an on-line source for the 12BY7???

Thanks in advance!

Tom
N2LDE

[w4eal]

Hi Tom welcome aboard. I just did a Googlie and epay. Tonsof 12by7's available. Epay has about 80 of them listed (check stores too).

Den
w4eal

[WB2G]

Radio Daze has12BV7/12BY7A'S for $10,also carry an assortment of electrolyics. radiodaze.com.Joe WB2FQD

[Dan N3SMF]

Welcome to AM.. Pay close attention to working voltages of the new caps and how you wire them series vs Parallel..Look ahead to any future mods you may be considering such as solid stating the pwr supplies which will of course raise the B+. I learned the hard way starting out new. When I threw the switch and blew the caps..it was a eye opener. The Apache is a fine transmitter and with a little overhaul and modification it makes a great starter rig. 

[N2LDE]

Thanks for the tips and advice!

I found and ordered the tubes, but I still can't find the HV electrolytics at exactly 125 mfd.

What kind of tolerances can be expected with the Apache circuitry?

Would the 100 mfd's that I found be "close enough" or would I cause damage??

Tom
N2LDE

[N3DRB The Derb]

close enough. you got plenty o capacity. make sure they are rated for 500 working volts dc. Also make sure you DO NOT ground the cases of teh caps. They are above ground.

[N2LDE]

Thanks Derb!

I did notice the insulating sleeves around the existing caps...

I also noticed a 20-20-20 electrolytic cap....I should probably replace that one too, but I am having a devil of a time trying to find this stuff on the int-uh-net....!!!

 

Tom
N2LDE

[ve6pg]

...tom...welcome to AM...you will find alot of guys on here have alot of parts, and it has been my experience, that many will send ya what u need...tim...sk..

[w3jn]

Electrolytics are generally 20% tolerance.  100 uF ought to work Fine Business so long as the working voltage is the same or higher.

You're gonna have trouble finding new multisection can capacitors.  There are two ways to go about replacing them:

1)  If you want original appearance under the chassis, yoink the can, circumcise it with a Dremel cutoff wheel, and pull out the guts.  Solder the new capacitors to the base, making sure everything's gonna fit in the can, insulate the caps so they don't short to the can, and glue the can back on with JB Weld or similar.  Re-install in the chassis.

2)  If you don't care about original appearance under the chassis, remove the wires going to the can, and solder a terminal strip to the case tab of the can.  Use the terminal strip to mount your new electrolytics, then connect the previously removed wires to the appropriate places on the terminal strip.

Just don't leave the old can connected to the circuit.  It'll eventually short, ruin your power transformer, make a cloud of smoke, piss off your wife, kill your dog, and generally ruin your day 

[w5omr]

Electrolytics are generally 20% tolerance.  100 uF ought to work Fine Business so long as the working voltage is the same or higher.

Were it me, I'd go for 150uF caps, allowing for the margin of error on the 'plus' side.  In B+ filter caps, too much is better than not enough.

[WBear2GCR]

Tom,

There are quite a number of posts on the Apache here, try a search? 

You'll need to remove the speech clipper circuit from the speech amp too... it ends up looking like the circuit from the DX-100. There's info on  that mod and others in the "Am Window" link area...

Also, there is no need to use a 12BY7, unless you want to keep it stock. Other tubes with similar power ratings will work fine - some folks advocate a 12AU7 run in parallel for example... of course you have to rewire the socket and change some parts values to bias up the toobe.

I have two 'pachies boots up on the bench right now.   

                 _-_-bear

[N2LDE]

Thanks, Bear!

I don't want to do any mods yet....I just want to make sure it runs as originally designed first.....Then I'll search for mods and slowly make adjustments as needed....

I have a complete set of tubes and new caps ordered and they should be here next week...

Once I get inside the guts I may have more questions and I promise to do a search here first!

Tom
N2LDE

[WBear2GCR]

Hee hee... that was my idea too, get it working stock first!!

Fat chance around here!!

Imho, no reason to swap out the caps yet, IF you have a variac to bring it up slowly... just form the caps and check that there is no excessive ripple.

First check the caps with an ohmeter (assuming there is no charge on them, so test with a voltmeter first) and make sure there are no shorts. Really bad caps look like a short or low resistance that never changes, a good cap will tend to change resistance forever or until it goes very high... then:

One of the best ways to do that is to remove all the toobes, take each individual supply separately (so you can address the PS sections individually), and pop in a pair of silicon diodes... then bring up the DC slowly. Take a minute or two to bring up each PS section and watch the scope, or if no scope watch the AC volts on the cap as the DC goes up... once you get it up to at or near spec'd voltage let it sit for 10 - 15 mins. Watch for signs of the can overheating, watch for cans that are NOT at ground. Watch for excessive ripple voltage (>1-2% of DC in general terms). Watch for smoke! 

If they hold, and they probably will, then all is good and run it that way for at least testing until you get the rig working on the bench.

At least that's my view of it. No need to do extra work right away.


              _-_-bear

[The Slab Bacon]

Pay particular attention to the 2  125uF cans for the HV B+. These are 500v caps wired in series with the tapped bleeder resistor for equalization. These mothers get hammered from 0v-800v instantly every time you flip the transmit switch. If any of the electrolytics are going to break down, its these. They will usually fail to a short and NOT open.

You should replace those caps without even considering it. 500v caps are getting kinda hard to find these days, but you can get them. I have used 450v caps in a pinch, but since the HV is so close to the voltage rating of the 2 in series, I dont recommend it unless you absolutely cant find 500s.

All of this becomes even more apparent if you solid state the HV rectifiers (5R4s) as this will raise the HV by another 40-50 volts.

                                              The Slab Bacon

[N3DRB The Derb]

everything slab said. 150 uf or 100 uf wont make a difference. The 500 wvdc will. Hell, the Viking 2 gets by on a single oil filled 8 uf cap, with some more scroteful chokes. Where you need more filtering is in the LV side branching out to the vfo, doubler, an speech amp.

make sure you use NEW insulated phenolic mounting tabs - don't reuse the old ones. Carbon trouble again. Order them with the caps with about 5 spares.

[AF9J]

Geez Derb,

The Vike does that too?  That is funky!  I though only WRL did that.  MY WRL Globe Scout 680 is the same way. Only a 7 mfd with chokes for the HV. When I first saw it, it threw me for a loop, after recapping the HP-23A power supply (that used 4, 500V 250mfd caps for the HV feed). 

Tom, while you're at it, something to keep an eye on - the HV resistors, and (to a lesser extent) the other resistors.  These things are of the old school carbon composition type. With time, heat (from operating the Apache) will change their values.  This is of greater concern in the HV section, but can happen in the other parts of the rig.  I'd say just check them out with an ohmmeter for now.  Remember that Heathkits used (IMO) cheapo 20% tolerance resistors for many of their rigs. If resistor values are within tolerance - fine. If not - get rid of them.  If you do have to replace them,  the newer metal film ones are pretty good.  Get resistors of the same power dissipation rating as the ones you're replacing.  Don't go higher (remember, these things also act as a sort of secondary fuse).  Don't be surprised like I was, to find out that the replacement resistors are downright puny compared to the old ones (I ended up calling Mouser, AND looking at a spec sheet online before I was convinced I had the right ones).  Materials technology for resistors has changed a lot since your Apache was made.

73 & Have Fun,
Ellen - AF9J
On Vacation today - yeah!

[Steve - WB3HUZ]

It works, if AC ripple reduction is the only goal. But if you want to run any low frequency audio through the system, the 8 uF is not enough. The HV will sag badly under modulation (poor dynamic regulation). Of course, course this also affects the screen voltage on the 807 modulators too (read distortion).

Read the articles below for more dynamic regulation.

http://www.amwindow.org/tech/pdf/geps1.pdf
http://www.amwindow.org/tech/pdf/geps2.pdf

[WBear2GCR]

Ellen,

Metal film resistors are generally only available in power ratings up to 1/2 watt. After that ur looking at Metal Oxide resistors. In non-RF circuits I'd use wirewound if I was buying new from a distributor, they're more robust in terms of over heating. But since they are inductive, they're not a good idea in things like oscillator circuits or in series with an RF signal, etc... excellent in speech amp circuits for example.

                 _-_- WBear2GCR

[AF9J]

Very True Bear,

And actually, come to think, the HP-23A HV resistors I bought from Mouser, may have been metal oxide ones, since they were offered in 1/4, 1/2 and 1 watt versions for the value I bought (100 k ohm).  I bought the 1 watt versions.

73,
Ellen - AF9J
Getting up the gumption to pull apart (again), another radio tonight