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Author Topic: Apache selenium rectifiers or 6AL5 rectifier  (Read 14259 times)
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k3pf
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« on: December 21, 2014, 08:33:41 PM »

My recently acquired Apache does not have the two selenium rectifiers for the -150V power supply.   It has instead, a 6AL5 dual vacuum tube rectifier.  My first thought was that somebody who owned the rig before me had modified the transmitter by eliminating the seleniums and replaced them with the 6AL5.  However, the installation looks like a factory installation and not a mod.  There are no unused holes in the chassis and the tube socket is identical to the one used in the 6AL5 clipper socket.  The hole for the tube socket looks perfect and looks exactly the same size as the clipper 6AL5.  I still suspect this a mod but the install is just absolutely perfect.  My question is, were there any early, or on the other hand, late model Apache transmitters that used a 6AL5 for the -150 supply?

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KC4VWU
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« Reply #1 on: December 21, 2014, 08:48:23 PM »

Maybe the very early runs did use the DX-100 scheme for bias supply?
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Pete, WA2CWA
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« Reply #2 on: December 22, 2014, 03:13:33 AM »

You can make perfect tube socket holes with a chassis punch. I've never seen or heard of a 6AL5 used in the bias supply. Are the screws holding the tube socket in place identical to the screws holding the other tube sockets?
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Pete, WA2CWA - "A Cluttered Desk is a Sign of Genius"
k3pf
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« Reply #3 on: December 22, 2014, 12:16:23 PM »

The screws are exactly the same as all the other tube socket screws.  The nuts on the screws are exactly the same, too.  The socket is exactly the same brand.  Everything looks perfect.  I have made holes with Greenlee chassis punches.  One side of the punch has a wide side that keeps the punch tight against the metal while the other side of the punch with the cutters pulls through the metal.  The wide side leaves a faint telltale mark in the metal where it was forced against the metal while pulling the cutter through the other side.  There is absolutely no telltale marks on the transmitter's chassis.  Possibly a different style punch could have made the hole.  The installation is absolutely pristine.   I don't want to make this a major issue.  I am simply curious about whether anybody else has an Apache that came from the factory with a 6AL5 instead of the two selenium diodes.  Or, is my installation, as I assume, an excellently done modification by a previous owner.
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WQ9E
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« Reply #4 on: December 22, 2014, 12:35:35 PM »

Radio and Television News reviewed the transmitter in April 1959 which was less than a year after it was introduced, the schematic in their review (which would have been early production) shows the selenium bias rectifiers.   Is there a serial number sticker on your chassis?   Maybe you have one of the early test build units that might have been different from the first production units.
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Rodger WQ9E
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« Reply #5 on: December 22, 2014, 12:57:17 PM »

If anything, the 6AL5 may have been a later production version since the tube would be an improvement over the selenium rectifiers.

Fred
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KC4VWU
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« Reply #6 on: December 22, 2014, 01:25:20 PM »

LV transformers are different between the DX-100 and the Apache. One reason being fil. voltage winding for the 6AL5's, yes? Is it an O.E. part with with Heath stock # for DX-100?  Also as Roger stated, what is the serial # if it has one. Why would someone backwards engineer the bias voltage P/S from then current simple, straightforward technology? I had acquired an Apache LV transformer to retrofit into a DX-100 that had a bad one, but wouldn't consider the inverse using tubes. Indeed, a valid question. I wouldn't say you're making a major deal of it, you've just ran across something interesting that may be beneficial info for someone later later on.

I seem to recall reading on one fellow's website that he used to work for Heath as a design engineer and the company allowed them to take pre-production models home for extensive testing and could keep the units afterwards if they wanted. I can't remember a name or call: it was quite a while back.  
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k3pf
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« Reply #7 on: December 22, 2014, 01:30:03 PM »

Another interesting thing about this topic that piqued my attention was an article written by Bob Eckweller, AF6C.  In his article, he listed all the tubes from V1 through V19 along with the function of each tube.  Every tube was used except V13 which he showed being not used; and he wondered if "Perhaps V13 was to be the rectifier tube for the -150 volt bias supply, and was replaced by selenium rectifiers prior to production."

See his article at this site   http://www.w6ze.org/Heathkit/Heathkit_017_TX1.pdf



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k3pf
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« Reply #8 on: December 22, 2014, 01:57:10 PM »

I don't know anything about the DX-100 transformers.  However, the power transformer in this Apache is stamped on one side with the numbers 54-65 which is the correct designation shown in the Apache assembly manual.  There is another set of numbers stamped on the transformer below 54-65.  They are 138826.  I have no idea what those numbers mean.

Where is the serial number located?  I can't find any serial number.
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KA2DZT
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« Reply #9 on: December 22, 2014, 02:20:30 PM »

The other six numbers are a manufacturer and date code.  The 138 means that Chicago xfmr Co made the xfmr.  I would have to re-check how the date code is figured.  These number codes were used in the 40s, 50s, 60s and into the 70s .  Somewhere, stamped into the case, near the bottom you should find the Chicago logo.

Fred

I did a quick check,  the 826 means it was made in the 26th week in probably 58 or 68.  No way to tell which decade except by knowing the age of the xmtr.
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K4RT
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« Reply #10 on: December 22, 2014, 03:37:15 PM »

According to Chuck Penson WA7ZZE, author of "Heathkit - A Guide to the Amateur Radio Products", Heath stopped making the TX-1 in 1964, so that transformer was likely manufactured in 1958 going by that date code scheme.  I have looked for but have not found a serial number on my Apache. I believe my TX-1 is an early production unit because it does not have chrome knobs.

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k3pf
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« Reply #11 on: December 22, 2014, 03:45:10 PM »

So, it appears I most likely have one from 1958 which makes it an early production unit.  That might explain why I have the 6AL5 instead of the seleniums.  Still, it would be interesting to know if anybody else has an Apache using the 6AL5 for the -150 volt bias supply.

My transmitter has the aluminum knobs, too.

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Pete, WA2CWA
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« Reply #12 on: December 22, 2014, 04:24:12 PM »

So, it appears I most likely have one from 1958 which makes it an early production unit.  That might explain why I have the 6AL5 instead of the seleniums.  Still, it would be interesting to know if anybody else has an Apache using the 6AL5 for the -150 volt bias supply.

My transmitter has the aluminum knobs, too.


Where on the chassis is the 6AL5 mounted? Looking back on your posts, I didn't see it. My Apache is from early 1959. I'm the original owner and have the original manual from which it was constructed. It's conceivable that early on, Heathkit engineers wanted to carry over some of the circuit designs of the DX-100/100B and included a tube for the bias supply and then decided that non-tube rectifiers were more economical for low voltage stuff, less heat, etc.
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Pete, WA2CWA - "A Cluttered Desk is a Sign of Genius"
K4RT
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« Reply #13 on: December 22, 2014, 05:30:48 PM »

Mine had the stock selenium, but I replaced them with new diodes.
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WQ9E
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« Reply #14 on: December 22, 2014, 06:23:19 PM »

Either SS or the 6AL5 is fine for a rig like this where the HV supply should (and normally is) switched off until everything is warmed up.  But silicon is preferred for the bias supply in transmitters that have constantly on HV since the big tube type plate rectifiers and power tubes themselves come up to temperature more quickly than indirectly heated tubes like a 6AL5 causing a surge of plate current until the bias rectifier warms up and provides normal bias.

With the TX-1 I would leave it as you got it.
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Rodger WQ9E
k3pf
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« Reply #15 on: December 22, 2014, 07:54:08 PM »

Reply to Pete, WA2CWA question.  Where is the 6AL5 located on the chassis?

The tube is located on top of the chassis just above the area where the selenium diodes would normally be mounted underneath the chassis.  So far, I have not been able to figure out how to post a picture on the site.  If I can ever get that down, I will post a picture.
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Pete, WA2CWA
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« Reply #16 on: December 22, 2014, 08:46:05 PM »

To attach picture, file, etc.:
Look below

Attach: In the box, click Browse                         (more attachments)
Allowed file types: txt, rtf, doc, mp3, wav, pdf, jpg, gif, mpg, png, xls
Maximum attachment size allowed: 5000 KB, per post: 3

It should point to some directory on your computer. Change directory to where the picture you want to attach is located. Double click the picture. Close the directory. The name of the picture should now be to the right of the box with word Browse in it

If the picture you want to show is an image somewhere on the Internet, use the "Image" icon above. Second row; second item. Click the icon and then paste the URL of the image between this bracket ] and this bracket [ . The default position of the cursor after you click the image icon is between these two brackets.

Unfortunately, Preview is not working, so the only way to see if you did it correctly is to click Post.


* dds.jpg (156.31 KB, 768x454 - viewed 433 times.)
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Pete, WA2CWA - "A Cluttered Desk is a Sign of Genius"
k3pf
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« Reply #17 on: December 22, 2014, 11:06:01 PM »

Thanks Pete for the how to attach info.

Picture of 6AL5  -150V bias tube chassis location on K3PF's Apache hopefully is attached.


* 6AL5 -150V Bias Tube Location.JPG (502.65 KB, 2000x1500 - viewed 497 times.)
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k3pf
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« Reply #18 on: December 22, 2014, 11:10:22 PM »

Guess I should have pointed out that the tube in question is the one adjacent to the 5V4 low voltage rectifier tube.  Notice the 6AL5 is in the same location as the selenium rectifiers except the 2 seleniums would be underneath the chassis.
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KA2DZT
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« Reply #19 on: December 23, 2014, 12:13:57 AM »

The 6AL5 looks to be original to the xmtr.  You must have an odd version of the xmtr as no one else seems to have seen the 6AL5 in place of the selenium rectifiers.

Fred
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k3pf
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« Reply #20 on: December 23, 2014, 11:16:58 PM »

I'm guessing now that this Apache might have been an engineering prototype because of two other issues I discovered.  The first is that almost all of the soldered wires are not wrapped around the terminals of anything.  They were simply pushed through a hole and tacked on.  The soldered joints look good but its not the common way to wire something up like that.  This method would have made it easier to make engineering changes.

The second thing I noticed occurred when I followed the assembly manual tune up procedure.  My downloaded assembly manual says the cooling fan will run when the power switch is first turned on.  This Xmitter's fan comes on "only" when in the transmit mode when the 6146 tubes are operating.

Is there any worthwhile benefit if I rewire the fan to come on with the power switch, or should I simply leave it alone?


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Pete, WA2CWA
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« Reply #21 on: December 24, 2014, 12:57:49 AM »

I'm guessing now that this Apache might have been an engineering prototype because of two other issues I discovered.  The first is that almost all of the soldered wires are not wrapped around the terminals of anything.  They were simply pushed through a hole and tacked on.  The soldered joints look good but its not the common way to wire something up like that.  This method would have made it easier to make engineering changes.

Or, the assembler was very naive on proper assembly/soldering practices.

Quote
The second thing I noticed occurred when I followed the assembly manual tune up procedure.  My downloaded assembly manual says the cooling fan will run when the power switch is first turned on.  This Xmitter's fan comes on "only" when in the transmit mode when the 6146 tubes are operating.

Is there any worthwhile benefit if I rewire the fan to come on with the power switch, or should I simply leave it alone?

The 6146's are in a fairly tight enclosure with not a lot of air flow. Three sides, front, rear, and left side have restricted air flow. The filaments are always drawing current so heat is still developed even when you're not transmitting. The transmitter is better off with the fan running all the time. Unfortunately, the fan sucks air into the enclosure along with air borne dust and other contaminants. With the restricted air flow, all it does is move the hot air all around the inside of the enclosure. I got rid of that old fan, and installed a muffin-type fan that sucks the hot air out of the top of the enclosure. I also installed a similar fan on a homebrew bracket over the modulator section.
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Pete, WA2CWA - "A Cluttered Desk is a Sign of Genius"
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« Reply #22 on: December 24, 2014, 06:06:26 AM »

I'm guessing now that this Apache might have been an engineering prototype because of two other issues I discovered.  The first is that almost all of the soldered wires are not wrapped around the terminals of anything.  They were simply pushed through a hole and tacked on.  The soldered joints look good but its not the common way to wire something up like that.  This method would have made it easier to make engineering changes.

There was a USAF white paper that was reprinted in Radio and Television News in the mid-1950s that called for using that method except with very heavy components (like large coils).  Their testing found that with modern solder there is no reason to make a joint mechanically secure before soldering and the old practice of twisting the leads made subsequent repair more difficult and increased the likelihood of damage.  I expect this paper was widely circulated so both those inside and outside of the USAF would have been aware of it by the time your Apache was built. 

I would change your fan over to continuously on to provide better cooling.  The Apache fan is quiet and if your fan is noisy it needs rebuilding or replacement.
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Rodger WQ9E
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« Reply #23 on: December 24, 2014, 10:00:27 AM »

The 6AL5 looks to be original to the xmtr.  You must have an odd version of the xmtr as no one else seems to have seen the 6AL5 in place of the selenium rectifiers.

Fred

Guess that 6al5 is the V13 that was reserved and not used in the selenium models  Smiley
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WD5JKO
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« Reply #24 on: December 24, 2014, 11:53:55 AM »


   In the Central Electronics 20A transmitter there is a 6AL5 bias rectifier. If the filament pops, or if the 50+ year old socket to pin contacts are not made for the filament pins, then the protective bias is absent. This leads to a possible Chernobyl effect where the power supply and the RF PA tubes have a tug of war. If the stock OEM sized fuse where to have been increased, the end result can be a disaster. An easy fix is to put a silicon diode(s) (such as 1N4007) plate to cathode on the bias rectifier tube. On the 20A they only use 1/2 the tube as a bias rectifier. Maybe the Apache uses both sides.
   
Jim
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