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Another 813 Build




 
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Author Topic: Another 813 Build  (Read 19800 times)
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KL7OF
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« Reply #150 on: October 20, 2019, 08:24:49 PM »

What is your parts count so far?




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w9jsw
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« Reply #151 on: October 20, 2019, 08:49:23 PM »

Confidential
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« Reply #152 on: November 02, 2019, 03:31:52 PM »

Started working with the Mod deck. Doing initial layout. 10x17x3 chassis. Have to lay out 2 tubes, 1 10V/10A trans, Mosfet driver board and 2 100x100mm heatsink mounted regulators. Got it mostly set out, just going slow before I commit to making holes.

Tubes will mount under the chassis about 1-1.5in deep. Big black heatsink is the driver. Board on the back. The al heasinks are there for spacing. The ones that are on the way will mount the same except a 280V regulator board will be attached to the side and they mount vertically. Trans for that supply will be underneath (toroid trans).

Struggling with what to do about the filament choke. Leads on the 10V 10A transformer are short, around 4 in long. I could get a ferrite rod and bifilar wind some insulated #12 wire from some romex. Could maybe try Tom's ferrite tube idea if I had a better picture in my mind on how it is accomplished.

Wish I had some large punches. Will use my largest then the nibbler to get the tube holes cut. Priced 2.25 and 2.75 punches on the bay - way too much $$. Labor is free.

Meters - One 500ma for Mod current, one 10V for filament voltage. I have a variac if needed if fil voltage is not right.

Need some ideas on portals for the tubes. What shape of hole or holes and how to cover the holes. Maybe 2 racetrack oval shapes?

Decisions, decisions....

This deck will go quick, then on to the RF deck. I decided to wait on testing the HV. If I kill myself then all the later fun will be missed.  Roll Eyes  Decided to keep building then do the testing when relatively complete.

John


* IMG_0350.JPG (513.05 KB, 2448x1836 - viewed 75 times.)
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w8khk
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« Reply #153 on: November 02, 2019, 06:56:59 PM »


.....Struggling with what to do about the filament choke. Leads on the 10V 10A transformer are short, around 4 in long. I could get a ferrite rod and bifilar wind some insulated #12 wire from some romex. Could maybe try Tom's ferrite tube idea if I had a better picture in my mind on how it is accomplished.

Need some ideas on portals for the tubes. What shape of hole or holes and how to cover the holes. Maybe 2 racetrack oval shapes?

I am wondering why you need a filament choke on the modulator.  If it is common cathode, grid driven, just bypass the filament pins to ground at the sockets.

On the RF deck, I assume you are also using grounded cathode, grid driven configuration.  This also needs no filament choke.  Grounded grid needs a filament choke in the RF deck, but if you are plate modulating, you really do not want grounded grid. It will not be possible to obtain 100 percent modulation, due to feed-thru power, unless you also modulate the driver stage.  Keep it simple, grounded cathode and plate modulate the final.  You will also need to modulate the screen of the tetrode to obtain linear modulation.

For the peek-a-boo holes, I prefer the rectangular holes, relieved in the corners by a circular, rather than a square cutout.  This is very easy to achieve by drilling the four corner holes, then cutting a rectangle via a straight line on a tangent with the outer side of each hole.  Look at my 250-TH rig for an example.  This shape looks very nice with 813s as well.

I have found a hole saw works very well for the larger tube sockets. Exact size is not critical.  One way to stabilize the work is to mount a piece of wood to the bottom side of the chassis top after some of the other holes are made.  Then you can easily clamp the wood on a drill press table.  Cut slowly and you will get a very clean hole.

I am not sure that it is wise to sub-mount the 813 bases.  Not needed for shielding.  It may also restrict natural convection cooling of the base pins.  Fan should not be needed for 813s.  I prefer surface mounting.  Make sure your panel is high enough for proper plate connector clearance
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w9jsw
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« Reply #154 on: November 03, 2019, 07:54:11 AM »

Thanks for clearing that up Rick. Got confused on the filament choke usage. On with the build!
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KL7OF
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« Reply #155 on: November 03, 2019, 10:20:18 AM »

QUOTE w8khk.....
For the peek-a-boo holes, I prefer the rectangular holes, relieved in the corners by a circular, rather than a square cutout.  This is very easy to achieve by drilling the four corner holes, then cutting a rectangle via a straight line on a tangent with the outer side of each hole. 

..........Peek a boo holes in my PP 100th X 813's Rig.......


* 100th_rig_003.JPG (83.37 KB, 600x800 - viewed 124 times.)
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w8khk
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« Reply #156 on: November 03, 2019, 10:55:35 AM »

..........Peek a boo holes in my PP 100th X 813's Rig.......

Now that is some fancy artwork!  I like it!  Could you do that for my P-P 250-TH rig?   Hi Hi
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« Reply #157 on: November 23, 2019, 05:37:17 PM »

Pat Bunn N4LTA generously gave me a vfo board that he is using for his class D project. I thought it would be nice for this one. Gave me the chips as well. Got it built and tested.

Also, laying out the RF Deck.

John


* vfo built.JPG (1278.99 KB, 3264x2448 - viewed 58 times.)

* vfo 3.885.jpg (1492.68 KB, 3264x2448 - viewed 64 times.)
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W1NB
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« Reply #158 on: November 23, 2019, 06:55:28 PM »

What size punches do you need?
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w9jsw
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« Reply #159 on: November 24, 2019, 07:28:13 AM »

2-3/4 in for meter holes. I found a 2.25 one for $25 on the bay so I bought it. Will make the tube holes and peek-a-boo holes much easier.
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W1NB
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« Reply #160 on: November 24, 2019, 09:04:11 AM »

Unfortunately, my set only goes up to 2 7/16Ē so I canít help you.
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w9jsw
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« Reply #161 on: November 24, 2019, 09:06:28 AM »

I appreciate the offer, though..
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W3GMS
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« Reply #162 on: November 24, 2019, 09:25:10 AM »

QUOTE w8khk.....
For the peek-a-boo holes, I prefer the rectangular holes, relieved in the corners by a circular, rather than a square cutout.  This is very easy to achieve by drilling the four corner holes, then cutting a rectangle via a straight line on a tangent with the outer side of each hole. 

..........Peek a boo holes in my PP 100th X 813's Rig.......

Gorgeous rig!
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« Reply #163 on: November 25, 2019, 11:49:38 AM »

I think that I have a 2 3/4" Greenlee punch if you want to borrow it. It is big and heavy.

Pat
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w9jsw
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« Reply #164 on: November 25, 2019, 01:37:45 PM »

Email sent!
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w9jsw
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« Reply #165 on: November 27, 2019, 06:54:18 AM »

Have a 5 day break so hope to make considerable progress... Going to try to complete the Mod Deck and then play more with the layout on the RF deck. Trying to keep it nice and tight so that it is capable of going to 20M if I want to later.  

N4LTA has a punch on the way so all of the meters will get mounted shortly, as well. Thanks Pat!

A few items to discuss -

Parasitic Plate Resistors. The schematic shows 50 ohms at 5W. I can find ceramic 2W 50 ohm easy for a buck or so each. Having a devil of a time finding non-inductive 5W units. Will 2W be sufficient? If I use 220ma and 50 ohms, I get 2.42 watts so I am guessing not, but I don't know if estimating that the current at the parasitic frequency will be 220ma. It has a DC short across it. Won't the parasitic, if present be at a lower current than that? Confused.

I will have the tank assembled this weekend, hopefully. Got the band switch rebuilt and it now gives me consistent readings on my LC meter. Whoever had it prior had done some jumpering for 160M. I want to check it out at frequency to see if I need to remove some of the jumpers. I want to play with the MFJ-259 testing tank resonance. So I need to calculate the impedance of the plates - I estimate that it will be V / (I * 2). K is 2 for Class C. V will be 2-2.5kv. What to use for I? The tube spec shows 220ma per tube at an ICAS voltage of 2250. So do I use 440ma or something a bit larger. Is 500ma a good estimate? That would give me a value of  2500 ohms. Is that correct?

I have a UTC GC-124 filament trans for the RF deck. I cannot find a pinout diagram. Reading the specs it can be run at 105, 115, 210, 220 and 230. I have 248V or 124V. I am planning to use 124V because that is the variac I have. Using the VOM I see that 1-3 is independent of the rest, likewise with 4-6 and 7-9. 7-9 has lowest DC resistance, 1-3, 4-6 are identical. So I surmise it has 6 input pins (1-3, 4-6) and 3 output pins (7-9). So I am asserting that 1-3 is a 105-115 input and same with 4-6. For 115V I use 1,2. 1,2 has a higher resistance than 2,3 so I think the picture is correct. For 105V I need more primary so it would be 1-3, right?  If I feed 105-115V I would parallel the  primaries? For 105V use 1,4 and 3,6 right? For 115V would I parallel 1,2 and 4,5? And I will still have to use a variac to keep it at 10V under load. Hope I explained this well enough. See attached.

John


* GC-124 Pinout.JPG (117.33 KB, 2448x1642 - viewed 36 times.)

* GC-124 Bottom.JPG (489.66 KB, 1836x2019 - viewed 26 times.)
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K8DI
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« Reply #166 on: November 27, 2019, 08:07:45 AM »

Youíve got it backwards on the primaries.  Think about turns ratio and voltage ratio.  If you had say for easy math taps for 110 and 100 on the primary and a ten volt secondary, the turns ratios would be 11:1 and 10:1 respectively.  You need the more turns connection, the full winding, for the higher voltage connection. This is why the secondaries are in series for the 220/230/240 type connections, more turns=higher ratio, 20:1 vs 10:1.

Ed
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w9jsw
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« Reply #167 on: November 27, 2019, 09:19:02 AM »

Thanks, Ed! Wire it this way, then?

John


* GC-124-115V.JPG (761.82 KB, 3264x1815 - viewed 39 times.)
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K8DI
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« Reply #168 on: November 27, 2019, 10:03:26 AM »

Thanks, Ed! Wire it this way, then?

John
Yup. Exactly.

Ed
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w9jsw
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« Reply #169 on: November 27, 2019, 10:26:55 AM »

On the supressors, I can go with 2W x 2 at 100 ohms in parallel with Ohmite OX/OY series. Ceramic.

Or I found 51 ohm Metal Film at 5W. https://www.digikey.com/product-detail/en/ROX5SSJ51R/A142769CT-ND/10231883/?itemSeq=310514103

Ohmite WNE series (non-inductive wirewound) has 5W values but gaps from 15 ohms to 100 ohms, no 50 ohm value.

So, Ceramic or Metal Film?
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K1JJ
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« Reply #170 on: November 27, 2019, 02:57:06 PM »

On the supressors, I can go with 2W x 2 at 100 ohms in parallel with Ohmite OX/OY series. Ceramic.

Or I found 51 ohm Metal Film at 5W. https://www.digikey.com/product-detail/en/ROX5SSJ51R/A142769CT-ND/10231883/?itemSeq=310514103

Ohmite WNE series (non-inductive wirewound) has 5W values but gaps from 15 ohms to 100 ohms, no 50 ohm value.

So, Ceramic or Metal Film?


Hi John,

Look for the "Glo-Bar" style power resistors for plate parasitic use..  They are sold under various names. Used, they are about $5- $10 each for a 50 ohm, 10-30 watt if you can find them.

Those wire wound 'canceling" resistors are NG for RF. Whatever you use, put it across an MFJ analyzer and sweep it up to 28 MHZ and see how it does.  The metal film type are usually OK, but a Glo-bar is best.

They are expensive but are the best. I always buy them at flea mkts when I see them.

https://www.google.com/search?hl=en&biw=1106&bih=951&tbm=isch&sa=1&ei=cdPeXaKICaTl_QaBroK4AQ&q=glo-+bar+resistors&oq=glo-+bar+resistors&gs_l=img.12...21907.22412..25073...0.0..0.99.317.4......0....1..gws-wiz-img.SqW-c0Ul1WM&ved=0ahUKEwjihOXulIvmAhWkct8KHQGXABcQ4dUDCAY

T



* Glow-bar non-nonductive resistors.jpg (3.95 KB, 334x151 - viewed 30 times.)
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« Reply #171 on: November 28, 2019, 07:53:28 AM »

Some thoughts on those resistors...

From a dc or audio (modulated dc) perspective, theyíre not there. The coil around them is essentially a short circuit at those frequencies.

In the 80m range, ten turns 3/8 diameter, 3/4 long (typical 2w carbon resistor sized) is 10 ohms of reactance...so the coil is still dominant and the resistor is carrying much less current than the coil.

At 60 MHz (VHF, as in suppression) the coil is a hundred or so ohms reactance and now the resistor is in charge. Itís role is to decouple, to reduce system gain, until thereís not enough to support oscillation.

There are many amplifiers and transmitters that donít use resistors at all, they just have the plate lead coiled up, usually made from a piece of strap rather than wire.

Iím going to claim (Iím sure there are some here who will disagree) that the resistor is a coil form, and it should be seen that way. If itís a parasitic suppressor, itís only going to have significant current/power dissipation if the amp is oscillating at VHF, and if thatís so, youíve got other, much bigger problems, than if that resistor is 5w or 2w.

Lastly, a note about metal or other film resistors: when manufactured, their value is trimmed by laser cutting out part of the film.  In an axial, leaded resistor, this trim is usually a spiral slot in the conductive film. A spiral slot makes it a coil. Film resistors can have some inductance, greater than that of a bulk resistor (is carbon composition, etc.) which may or may not matter in a given application.

Ed

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« Reply #172 on: November 30, 2019, 03:24:58 PM »

Modulator progress. Big black heatsink and board is the Audio driver. The 2 smaller heatsinks and boards are 280V FET regulators. They are fed from a toroid transformer mounted underneath.

Think I will mount the filament transformer lower in the frame. No real good place to put it topside and I fear that it will induce hum if it is too close to the audio boards or supplies. Another octal relay will fill the big hole.

I will cut the peek-a-boo holes and the meter holes tomorrow. Then will do some final metal work and it will be ready for wiring.

Do you guys cover the peek-a-boos with any tempered glass or something?

John


* IMG_0397.JPG (895.74 KB, 3264x2448 - viewed 48 times.)

* IMG_0395.JPG (425.79 KB, 3264x2448 - viewed 52 times.)

* IMG_0396.JPG (381.09 KB, 3264x2448 - viewed 45 times.)
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KB2WIG
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« Reply #173 on: November 30, 2019, 08:52:01 PM »



J,

Lookin nice.


klc
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What? Me worry?
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« Reply #174 on: December 01, 2019, 10:44:45 AM »



John,

   I see the Borosil glass lamp chimney's. I looked them up,

http://www.borosil.com/products/lighting/

  Just wondering, as implemented, how do you move air through them?

Jim
Wd5JKO
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