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811 bias for Mod




 
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w9jsw
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« Reply #50 on: January 02, 2019, 06:36:30 AM »

Tom,

Deal. Phil and I have an agreement. I will be getting the 2750VDC PS as well. Guess I need to start on assembling the rest of the BOM and get started on the driver.

Gonna need a bigger rack!

I won't get the hardware until late January as Phil has a trip planned then which will allow me to get the iron without having to pay shipping. A real nice deal as well.

John

Will be selling some now surplus to my needs components. A NOS S-49 UTC Transformer, some tubes, sockets, ART-13 Mod Transformer, etc. PM me if anyone is interested.
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« Reply #51 on: January 02, 2019, 11:01:42 AM »

THIS is ham radio.

Good on you Tom.

Take it from a guy whose been there and done that.  If Tom says you should go a certain way, you probably should. 

Or, you'll end up like Brett, and have a LOT of beautiful rigs and not enough time to talk on all of them.  Such a horrible situation!

--Shane
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« Reply #52 on: January 02, 2019, 12:31:35 PM »

John,

Good!  Then we can get started....

You should probably plan on a vacuum variable cap for C1 and turns counter - for plate tuning.  500 pF @ 10KV is common.  You can get away with a 4 section 365 pF variable for loading, C2 as long as it is of goood quality and has good plate spacing. Some are junk and will arc over. The more strapping ones will do 500 watts AM carrier, maybe arc with a weird load occassionally.  Ask around. You can also use a vac cap for C2 - 2000 pF @ 3000 - 5000V.   You may luck out and find a vacuum variable pair for C1/C2 with turns counters. You're having great parts luck lately!

For the GFZ driver printed circuit MOSFET driver board, I would contact Rich, W7SOE and see what he says. I think moving just a couple of PCB tracks for the +- voltage will suffice and give you a working PCB. He has the software already set up so could make it real easy for you to build it.


The 2750 VDC HV from Phil... is that a complete power supply or just the HV transformer?   Figure with a C.T., choke input power supply, expect to get about 0.9 X the CT AC voltage UNDER LOAD.   So 5,500 VAC  center tapped = 2,475 VDC under load.        If you can end up with 2500- 3KV, you will be FB.

Plate choke.... The common 7"? tall National chokes wound on white ceramic will work FB.   You can also wind your own using heavier wire. (recommended) Decide which way you wish to go and we can help you. I wind all my own single layer plate chokes using heavier wire.

Get some decent Russian 500 pF coupling and plate bypass caps. Do not use the cheap 500 pF/30KV TV doorknobs. You should use 500 pF for plate coupling and 500 pF for choke bypass so that the audio will not be shunted at the extreme highs.  

BTW, all of this will work down to 160M except maybe for the C2 365 pF loading cap needing a padder on 160M - have to see.


For a plate tank coil, unless you have something strapping made from copper band or whatever, wind your own using copper tubing. 1/8" is OK on 160M and 75M - 1/4" and larger on 40M and above.  I have also used a very strapping rotary coil, but it has to be heavy duty with heavy rollers.

You will need two 10A/ 10V CT filament transformers.  These are available on eBay, etc. or maybe here from the guys

There's more, but you have most of it covered already. Make a list of what you need and either the guys here will fill you in or try some ham boards with "wanted ads".


Shane, yes, helping to mentor others is a great thrill. If they have the spark to build a rig, then we must help them.  The help John is getting here reminds me of the Amish. When someone needs a barn built, the whole community comes in for a day and knocks it out - painlessly.

John, I may have some more critical parts you need.  Just to be clear, the 813 sockets and plate caps I have for you are brand new.  I have about (10) 813s, some are NOS and others are near new, all mixed together, all major USA manufacturer labels.  Amazing tubes.  Bottom line is I will pick out the four best ones for you. I don't expect to build another 813 rig here since I have the 4-1000A plate modulated rig now.

T
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« Reply #53 on: January 02, 2019, 01:15:23 PM »

Oh, before I forget, John...

The plate bandswitch needs to be really heavy duty.  Something from a T-368 or BC-610 is the caliber needed.

The problem is that when you short the tank coil to change bands, the switch contacts carry very high RF voltages and will jump the gaps.  The test is to picture the RF path on the switch and see where it can jump and bridge switch contacts, etc.

A 4" diameter ceramic bandswitch for 813s with 3KV is not over doing it.

Take a look at the bandswitch I used in my 4-1000A RF deck. It's about  8" diameter and uses TWO sections in parallel for lower inductance and higher current capability.  It has never arced or failed.


Also, notice the technique I used to hang my vacuum variables on the front panel and the connections to the turns counters.  There are many ways to do it.

T


* 4-1000A Plate Modulated Rig.JPG (324.25 KB, 960x1280 - viewed 35 times.)
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« Reply #54 on: January 02, 2019, 01:19:44 PM »

Ok on the caps

The ps matches the other parts 3500-0-3500 at 1.5a ccs, plus a matching swinging choke. It also has a 8uf 3kv cap. I have 2 10uf 3kv caps I can use. They also have a 2uf 3kv cap for the mod coupling. Is that a high enough rating?

On the board, i am fluent in board layout having built a 1/2 dozen various boards for other projects. I will contact him and see if I can pick it up. I usually have my boards made at Elecrow.

I have 1 fil trans already. I also have one new 813 ceramic socket.

Thanks much,
John

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« Reply #55 on: January 02, 2019, 05:55:00 PM »

Ok on the caps

The ps matches the other parts 3500-0-3500  at 1.5a ccs, plus a matching swinging choke. It also has a 8uf 3kv cap. I have 2 10uf 3kv caps I can use. They also have a 2uf 3kv cap for the mod coupling. Is that a high enough rating?

Thanks much,
John


Hi John,

OK on the PCB and your experience there.

The 2 uF Heising blocking cap needs to be at least X2 the plate voltage
 
Anyway, you are using 240VAC primary, yes?  

The HV filter caps need to be at least 1.5 times the HV DC voltage.  I like X2 or more myself. Another issue is that the HV will soar upwards without a load, depending on how well your swinging choke works and how heavily you bleed the HV with power resistors. One way to keep the soaring voltage at bay is to use a step-start. Put a 5-10 ohm 200 watt power resistor in the 240 AC primary and key on the 240... then 1/2 second later have a set of contacts short the 5 ohm resistor. The HV will stay well below VDC MAX during key-up and un-key.  Plus, the soft start will be so much easier on ALL your power supply components.

The reason I mention this is because your filter caps are rated at only 3KV. Is there two separate HV terminals for plus and negative on these filter caps? If so, you can put your two 10 uF caps in series for a 6KV rating but only 5 uF.   That is pretty low filter capacitance even with a good choke like you have.  

My power supply uses a pair of 70 uF @ 10KV caps in parallel.  (140uF @ 10KV)  with a large 30H choke. Step start.  Rock solid and clean.  That is extreme, but WTF, I had the parts... :-)  So, you can use what you have for now, but look around for better caps.  There are "photo flash" caps out there about the size of a loaf of bread at 51 uF @ 5 KV. I see them all the time at flea mkts. I realize some say they cannot handle continuous service, but I have used them for 40 years and have never had a failure. I remember Peter Dahl used to sell them as filter caps.

The next logical step may be to pick up a heavy duty  Variac. It will be invaluable for initial testing at 1500 volts and later creeping the voltage up and up as you get more confident in the rig. You can actually use a 30A 120 VAC Variac across one side of the line. IE, you will always start at 1575V and turn it up to 3150 KV.   A  240VAC Variac @ 30A is good for 7,200 watts.  Once the rig is tested, you can turn some Variacs all the way up to the "stop" and it will be out of circuit.  You will always get SOME loss from a Variac, from voltage drop = less regulation, so the ability to take it out of the system is a good option.   The bigger the Variac, the less HV voltage drop under load at the HV end.

You will need a string of bias diodes in the modulator cathodes once you get above say, 1800 VDC or so. That's why a rotary switch is a good feature to add or short out diodes when needed.

That should do it for now, OM.

T

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« Reply #56 on: January 02, 2019, 06:18:13 PM »

Here are the specs for the components as describe by AC0OB (edited out shipping details)

Power Supply Group from a BC-1T

Used with 833A’s in Push-Pull Class B service modulating a pair of paralleled 833A’s with 2600 Volts on the plates.

This Power Supply combo produces 2700V @ 1.5A CCS.

This item is known to be functional and was removed from a Gates BC-1T Broadcast Transmitter.

Dimensions Power Transformer: H = 12.75,” D = 6.5,” W = 8.5”
Pri: 230V, Secondary: 3800V CT@1.5A CCS;
Dimensions Swinging Choke: H = 10,” D = 7.0,” W = 7.5”
Dimensions 8 uF 3000V Capacitor: H = 7.5,” D = 3.75,” W = 4.5”

1kW Modulation Transformer

This item is known to be functional and was removed from a Gates BC-1T Broadcast Transmitter.
Dimensions: H = 9.75,” W = 7.75,” D = 5.75.”
Frequency Response: 40-15000 cps (40-15k Hz).
It is marked “AM-30469 C” and was made by Electro Engineering Works for Gates.

0.75 kW Modulation Reactor

Used with 833A’s in Push-Pull Class B service modulating a pair of paralleled 833A’s with 2600 Volts on the plates.

This item is known to be functional and was removed from a Gates BC-1T Broadcast Transmitter.

Dimensions: H = 9.75,” W = 7.25,” D = 6.5.”
It is marked “AC-10458E” and manufacturer is currently unknown.
He also has included the C4 2 uF 3000V Coupling Capacitor from the transmitter

That is all I know. Phil stated that since these came from Gates, they should be good to go. (Phil, feel free to opine if you are monitoring the thread)

John
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« Reply #57 on: January 02, 2019, 06:46:30 PM »

Gates....very good info to have....  I didn't realize you had a complete power supply design -  just assorted parts from mixed sources. Excellent!

2700 VDC will be perfect for the 813s. (Higher using solid state diodes.)  Looks like a lot of the work has been done for us.

What puzzles me is they're using only 3KV rated filter caps with a 2700 VDC HV.  Must have great swinging choke action. I'll bet the caps are "Gates" 3 KV rated and really good for 5KV... :-)   And the Heising coupling cap is only 3 KV - maybe they placed it in the negative lead..... hmmm.

It is good the constant carrier of AM helps regulation for the modulator variation vs: a linear amplifier.

It's hard to argue with success.  Go with it.  Use my power supply suggestions if you need to modify things later on.


T
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« Reply #58 on: January 03, 2019, 06:42:28 AM »

http://www.wd8das.net/Gates/GatesBC-1Tmanual.pdf

Page 61 has HV supply.

Where can I find some good Diode blocks? These are all I seem to be able to find...not sure of quality. I have a pile of 1N5408 so I can make strings if I have to.

https://www.amazon.com/PRHVP2A-20-Voltage-Rectifier-Leakage-Current/dp/B07BPW8HJX

John
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« Reply #59 on: January 03, 2019, 08:44:28 AM »

Easy as pie step start.....

Wire one side of a 120v contactor to neutral.

Wire the hot side of the contactor to the transformer side of the step start resistor.

As the cap charges, the current draw lowers, causing the loaded line side voltage to rise.  At some point, it will close the contactor.

You only have to size the resistor properly this way.  No RC circuits, no external timers, etc.


KISS



As to diodes?  Since k2aw passed, good luck........  And I never really liked those.  A string of 6A10 or 10A10 will never fail, 400A surge capability, etc.


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« Reply #60 on: January 03, 2019, 09:37:11 AM »

Easy as pie step start.....

Wire one side of a 120v contactor to neutral.

Wire the hot side of the contactor to the transformer side of the step start resistor.

As the cap charges, the current draw lowers, causing the loaded line side voltage to rise.  At some point, it will close the contactor.

You only have to size the resistor properly this way.  No RC circuits, no external timers, etc.


Important safety note here:  Imagine a significant issue with the PSU. Choke shorted to case/ground for example.  Current will never decrease so contactor will not pull in. Be sure the combination of the resistor, overloaded power supply, and main breaker are sized so that the breaker can/will blow when the resistor is in line or you can have a runaway situation where the resistor limits current just enough to prevent the breaker (or fuse) from blowing while the power supply burns....

Ed/KB8TWH
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« Reply #61 on: January 03, 2019, 12:10:20 PM »


Where can I find some good Diode blocks?
John


John,

I have always used these 6A, 1KV diodes. Inexpensive.  Mount the diodes on a piece of drilled Plexiglas. (tiny holes for leads)  Mount the board on standoffs.  They are bulletproof and will take lots of abuse. They get much better air cooling than the blocks. I have been using the same stack of 100 (25 per leg in a bridge) for 25 years now.

https://www.parts-express.com/power-supply-rectifier-diode-6a-1000v--6a-1kv

For your situation, 15-20 diodes in each leg (15-20 KV, two legs for a full wave) should be way beyond safe headroom ratings - for both voltage and current. No equalizing resistors or bypass capacitors needed.

These SS diodes will bring your HV up somewhat (compared to the original Gates tube rectifier design) and the full current load will pull it back down. I will be interested to see what your key down fully-loaded HV is in the end, but should be FB for 813s.


T
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« Reply #62 on: January 03, 2019, 12:30:39 PM »

Easy as pie step start.....

Wire one side of a 120v contactor to neutral.

Wire the hot side of the contactor to the transformer side of the step start resistor.

As the cap charges, the current draw lowers, causing the loaded line side voltage to rise.  At some point, it will close the contactor.

You only have to size the resistor properly this way.  No RC circuits, no external timers, etc.


Important safety note here:  Imagine a significant issue with the PSU. Choke shorted to case/ground for example.  Current will never decrease so contactor will not pull in. Be sure the combination of the resistor, overloaded power supply, and main breaker are sized so that the breaker can/will blow when the resistor is in line or you can have a runaway situation where the resistor limits current just enough to prevent the breaker (or fuse) from blowing while the power supply burns....

Ed/KB8TWH

Always size parts for the job at hand.  And, if you really worry about this failure mode (it can be a problem.....  I've repaired a couple Ameritron amps with broken step start), you can put a fuse inline w the step start resistor.

Or, spend the money and use a breaker along with a solid state zero crossing relay.  Just don't depend in the ssr to have the chassis at zero volts.

In my step starts, I use the ubiquitous Dale (chicom clones) and size it with a 10 to 25 Watt R.  Use heat sink compound and mount to a wall, etc. These I've found have NO problem sacrificing themselves 😁🤔.

Many ways to skin this cat......  Also, I DO use timers in the step start for a tube filament.

--Shane
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« Reply #63 on: January 03, 2019, 05:39:26 PM »



...What puzzles me is they're using only 3KV rated filter caps with a 2700 VDC HV.  Must have great swinging choke action. I'll bet the caps are "Gates" 3 KV rated and really good for 5KV... :-)   And the Heising coupling cap is only 3 KV - maybe they placed it in the negative lead..... hmmm.

T

They did place the Mod. reactor cap in the negative lead to ground. All caps are oil filled and have at least a 20% surge capacity.

Yep, Phil Corleone made John an offer he couldn't refuse.  Grin
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« Reply #64 on: January 03, 2019, 06:15:46 PM »

He had me at “modulation transformer”. Was love at first sight.
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« Reply #65 on: January 05, 2019, 08:09:35 AM »

Took the generic circuit and transcribed it for my implementation. I like to show the exact circuit layout so that I can remember what I did a few years down the line.

I perused the Gates schematics and believe I am true to their design for the HV and modulator. Pls comment.

In reading an old thread from Slab Bacon SK? - what a great ham - glad his knowledge is still helping others. He warns about using the chokes on the center tap as perhaps being counter to the transformer mfg intent. I chose to follow that advice. Gates did not wire it that way, and the screen bias transformer that I have is circa 1960's so I thought it best to not do it there as well.

Added demarcation points on the interconnects to start thinking about how I will partition the design into separate units.

The PS on a wood platform near the floor, of course. A panel plate to cover the front of the PS with input voltage control breakers/fuses/switches. Next up will be the modulator, which I think will be a larger wood platform sliding on rails, with a smaller AL chassis to mount the tubes and a front panel to cover it up. That should give me short interconnect between the plates and the mod trans. Next will be a plate with a row of panel meters (I think). Lastly, on top will be the RF Deck on a standard large chassis with front plate also on sliders.

I am going to use a quality RG-8 with a poly dielectric for the HV direct connect. No Millen connectors. Please advise how to connect the shields to avoid excessive ground loops if that matters. Also suggest how to ground all of the chassis together. Was thinking of some copper strap.

I am attaching the schematic and a BOM. If anyone can help out on vacuum caps, doorknobs and bandswitches that would help. I will pay a fair price.

John W9JSW

Edit - looks like I need to add a string of diodes in the Mod cathode path. And add Bandswitches to the BOM. Just reread those suggestions...


* 813 Transmitter.pdf (569.67 KB - downloaded 14 times.)
* BOM_813 Transmitter.pdf (189.54 KB - downloaded 8 times.)
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« Reply #66 on: January 05, 2019, 09:19:45 AM »

Wow, looks NICE  John. I wish I could get the parts here in Costa Rica to do the same.
I have sufficient vacuum caps, but it will not be possible to get the HV parts here at all. Transport and import cost is completely prohibitive to import heavy stuff. I am planning to make a small switching power supply to generate 2 - 4 kV at 0,5 Amps for such projects. If that works out well, than I may follow your design.
Just a few points.
5kV for the output cap at the PI filter C19 seems quite overdone to me and 1000 pF too low a value. It will be completely meshed. Putting caps in parallel will give false resonances if the connection between these caps and the variable cap isn't VERY low inductance. I have been there. two caps of 1000 pF in parallel using short wires may result in parallel resonances well within the amatuer bands. So be carfull there. When there is 500 V RF at that cap, you already have 5 kWatts at 50 Ohms. In order to avoid arcing at modulation peaks, 1.5 - 2 kV seems quite sufficient to me.
I advice to put an RF decoupling cap between the RF choke for the G2 L3 to avoid RF flowing into the LF choke L4
The cap C20 for the bias is reverse.
I should use RG58 for the HV instead of RG8. The mechanical stress at the connectors of RG8 when moving chassis may result in bad contacts and losing up the shield connection. RG 58 is much more flexible and the HV connectors for RG58 are readily available and low cost and due to the fexibility results in a safer system. With RG58 and those HV BNC connectors you can safely transport 5 kV at 4 Amps
Also for the interconnection between the chassis, NO copper strip, something flexible so there is no stress at the wingnuts to connect the safety grounds when moving the chassis.
I am very interested to follow your progress. Thanks for posting
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« Reply #67 on: January 05, 2019, 09:43:44 AM »

Thanks for your comments. I am a very lucky person to have been offered the BC Iron. And doubly so to be offered the tubes/etc. Otherwise I would be building a lesser rig. Still would have been ok, but this is much better.

I have a S-49 trans. How much to send 31 lbs to Costa Rica? It will do 1800VDC at 300ma or so.

Agree on C19. I have a 1150pf BC 4-gang variable now, but looking for one higher with slightly wider plate gaps. 1150 won't get me to 160M, I worry. Or a vacuum variable if found at reasonable cost. I want the deck to be able to cover 160,75,40 and hopefully be stable at 20M. I think 20M will be largely how well I lay it out and the care in assembly.

On L3/L4 is C7 and C2 not enough decoupling to preclude RF feeding back to L4 or are you suggesting another cap between L3 and L4.

I should also add caps across the meters, I think. Forgot those.

C20 is correct, I think. It is a -75V bias.

I recall a thread suggesting some good HV connectors. RP-BNC.

John
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« Reply #68 on: January 05, 2019, 10:16:39 AM »

The problem isn't sending it, the problem is it not arriving.  Nico said in other threads customs can be very liberating......  So to speak.

Might need some cartel mules in reverse (tongue in cheek).....

As to the HV switcher, I believe Manfred (ludens.cl) has built one....  He runs a shack off a river in Chile, so his station is pretty efficient as well.  Last I heard he was doing a class e or similar amp, a red pitaya for sdr and was wrapping it around predistortion.....  Have to have super high efficiency on a water wheel stream powered shack!



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« Reply #69 on: January 05, 2019, 11:51:50 AM »

Need a spec on the 3A Variac. Can I use a rheostat?

Is 2W ok for the 50K Cathode drop resistors in the PTT circuit?

John
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« Reply #70 on: January 05, 2019, 01:13:53 PM »

Need a spec on the 3A Variac. Can I use a rheostat?
Is 2W ok for the 50K Cathode drop resistors in the PTT circuit?
John


Good job, John!  You are making progress.

I did a quick once-over and see a few things to comment on.  Once we address them we can look for more:


Yes, 2W is OK for the 50K cathode keying resistor.

All meters need .001 bypasses.

Use a Variac for the screen transformer AC primary. A rheostat will burn up power for no reason since there is constant current flow during keyup. (and screen power supply bleeders)

You have the C20 electrolytic  cap polarity backwards.  That is a negative voltage at the diode anodes, thus a negative cap polarity.

A .001 on left side of  L3 to ground should be added. Don't be afraid to sprinkle .001 disc caps around in the DC grid and DC screen circuits.. can't hurt.

OK on the transformer center tap precautions... that's fine - do it as you described.

Your 75V VR tube in the grid DC is a good idea -  to keep the RF from charging those filter caps and fixed bias drifting all over the place.  Check it during initial testing for stability.

The plate tank vacuum cap can be 500 pF at 5KV, though 8-10KV is a common rating.  Use what you can find with at least 5KV min.

The tank loading 4-section air variable should be 1KV if possible -   2000 pF will cover 160M barely.    A vac cap is better and can be 2000 pF at 3KV (common rating found) if you can find one. They are more rare.   Remember that these voltage ratings are min and larger is always FB.  The common 365 pF multi section air variables for loading will barely handle 500 watts carrier and might arc over during heavy modulation with funky antenna loads...   For 160M, I usually end up with a 500 pF or .001 padding loading cap that gets switched in with a relay or heavy duty switch. This cap needs to be physically large to handle the 160M RF current in amps. (like a golf ball size or bigger) The "G1, G2"?  versions of Santimago? caps from commercial BC rigs are good for this. I use them in my 4X1 rig for plate bypass and load padding.  They are best used on 160-20M. They may exhibit some inductance on the higher bands I have been told.

Good on wood insulation for certain HV iron mountings. You are thinking ahead.

Use decent relays for the antenna T/R switching keying. Open frame relays the size of a golf ball or larger, rated for the proper current and voltages involved are needed. No micro tiny crap.  An antenna relay that arcs across its poles can easily feed TX RF into your receiver. It happened to me and was a disaster. Trace it out and see what I mean.  On my biggest rigs, I use a vacuum antenna T/R relay in this position for safety.  The cathode CT keying relay can be smaller and handles less abuse.

This rig is being built using high quality, robust parts. Just like a drag racing car... if everything is rated for 2000 HP and you cheap out and install a 400 HP rated torque converter, the weak link will always blow first.  Try to use over-rated parts in every position -   and the longevity and trouble-shooting process will be GREATLY improved.

Nothing worse than spending your time blowing up and replacing parts, redrilling and messing up your work... all because of using parts below reasonable ratings.  That goes for the plate choke too. I always wind my own and cannot remember having blown one in the last 20 years. It is rare.  Winding a plate choke and having it be resonant in a ham band is HARD to do.  Like winning on a 36:1 roulette wheel.

The best outcome is to fire up the rig and most everything works - just requires basic testing and optimization.  It can happen - you blow just 1-2 parts and then it runs forever... :-)

I can sense you are doing things right. Now let's spend some more time fine-combing this schematic...

T
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« Reply #71 on: January 05, 2019, 03:09:23 PM »

John,

Just to give you something to look forward to - we all need a carrot:   Wink

I looked back at some operating notes for my pair of 813s X pair of 813s. I usually keep a cheat sheet on settings from band to band for quick access later on.

My rig, similar to yours, uses BC iron and a  2.5KV, 3KV and 4KV switchable master HV supply with the GFZ MOSFET audio driver. Tank circuit: all vac caps and heavy tank components.  Audio NFB around the modulator and driver board.  I have glass lantern chimneys blowing a slight breeze thru all four 813s.  I believe they are now rated at 200W plate diss with the air, rather than 125W.     Regular uncooled 813s are REALLY 160W tubes in my opinion - bad ass tube.

Under full strap conditions, 3KV, 75M into a dummy load:

Output 1KW carrier with 120% positive peak modulation.  Monitoring on the SDR and scope. (Negative peak limiter to protect mod xfmr during tests)   100 Hz Triangle wave looks near perfect.  Finals dark gray, modulators JUST starting to show color. (carbon plates)  Grid biasing well into class C with larger grid leak resistor, approaching class D with heavy RF drive.  Final efficiency near 83%.  

I usually abuse the rig during the testing period and once it is sorted out, (blown parts)  I drop the power down to a reasonable level and it usually runs forever without failures.  Slam it and then baby it.

My next step is to keep the voltage up in the 3KV level and play around with loading. Lets say the carrier is 1KW with heavy C2 loading  (C2 unmeshed) ... what if we load it lighter (C2 more meshed) and drop the carrier down to 600 watts? The audio headroom increases and we see 150%+ clean audio.  We have the choice of keeping the voltage up at 3KV or dropping it back to 2500V.  Add more grid drive (a little past manufacturer grid current recs) and see how the audio peaks increase and clean up. A little more or less screen voltage (Variac) and see what that does.

After experimenting and all parts are stressed out and hold together, we will find a sweet spot where power, audio, efficiency and abuse all come together for optimization.

Using heavy duty parts lets us forget about "babying" the rig but rather shooting for best results.

T
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“Remember, remember, this is now, and now, and now. Live it, feel it, cling to it. I want to become acutely aware of all I’ve taken for granted.”  -  Sylvia Plath

Favorite Song - Trololo thru the years:  
https://www.youtube.com/watch?v=IVqUecYGnoM
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« Reply #72 on: January 05, 2019, 04:53:44 PM »

All suggested updates incorporated.

I want to make some inductors. How much Cu to buy. A $1 a foot locally. How many feet do I need? How many turns on how big of form. Going to also make a K1JJ Tuna... Should I just buy a 50ft roll?
 
How to build the plate cap?

How to build the input inductor?

Antenna Relays - RFParts has quite a few clean pullouts in the 50-75 buck range. Are these robust enough? Too many to choose from. Which ones are right?

Thx for the help, Tom!

John

* 813 Transmitter.pdf (576.25 KB - downloaded 5 times.)
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« Reply #73 on: January 05, 2019, 07:52:28 PM »

All suggested updates incorporated.
I want to make some inductors. How much Cu to buy. A $1 a foot locally. How many feet do I need? How many turns on how big of form. Going to also make a K1JJ Tuna... Should I just buy a 50ft roll?
How to build the plate cap?
How to build the input inductor?
Thx for the help, Tom!
John


Hi John,

Below are some pics of tank circuits. I especially like the first one by Chuck / K1KW.

The easiest way to ruin a great rig is to install a shoddy tank coil circuit. The easiest way to make it look and perform super is to silver plate it, good coil placement and short strap leads with a robust bandswitch.  The tank and plate circuit is a piece of art and should be treated this way...  Cheesy   There is nothing more stunning than a lot of silver plated shiny "chrome" that shines brilliantly from the filament light. It gives the rig a soul and depth.

You can use heavy duty Mini-ductor stock for 160M effectively like Chuck's rig below. Silver plating for the other coils using 1/8", 3/16" or 1/4" copper tubing is not expensive.  Notice the incredibly short silver plated strap leads from the switch to the coil as well as other tight parts placement.

Check around your area for silver platers.  They also have kits on the web where you can apply the plating yourself - not quite like the tanks but still very FB..  

Calculate each coil for Q=12 and install. Then in the testing stage, you will probably find you can do better by experimentally moving the bandswitch taps around a turn or two in either direction.

Ccalculate the coil lengths and buy the copper tubing by the foot in the various diameters you need.  Just keep the interconnecting paths short and make good use of copper strap that also gets silver plated.  Make a large rectangular panel window so you can see the tube plates and the silver plated coils.


The 50 ohm input RF link coil is simply 4-6 turns of high voltage wire wound on top of the center of the grid coil. You will have to see what works best on all the bands, 4, 5 or 6 turns.
That grid coil resonates with the grid variable cap and the whole assembly is floating at grid voltage above ground, so use an insulated tuning rod.

What is a plate cap? (I am sending you four plate caps.)  Did you mean plate choke?


There are a few good threads on AMFone for the "JJ" tuner.  Forty turns of 3/16" or 1/4" copper tubing, 5" diameter, will easily cover 160M (and higher bands). Make the tuner so it will config both parallel and series feed as shown in the thread... to cover ANY impedance match known to man...   Let me know if you have questions after reading the threads. Be sure to use #10 Home Depot black insulated stranded wire or equivalent for the dipole feeder and flat top. Good quality spacers are important, or just space the line 16" apart, pull tight and use NO spacers at all - for best OWL possible.

Do search on AMFone:  "K1JJ Tuner"

T


* K1KW Rig.jpg (124.93 KB, 800x600 - viewed 22 times.)

* wv7u Rig.jpg (83.69 KB, 774x591 - viewed 25 times.)
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“Remember, remember, this is now, and now, and now. Live it, feel it, cling to it. I want to become acutely aware of all I’ve taken for granted.”  -  Sylvia Plath

Favorite Song - Trololo thru the years:  
https://www.youtube.com/watch?v=IVqUecYGnoM
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« Reply #74 on: January 05, 2019, 08:42:18 PM »

Antenna Relays - RFParts has quite a few clean pullouts in the 50-75 buck range. Are these robust enough? Too many to choose from. Which ones are right?

Thx for the help, Tom!

John


You will need one DPDT relay or can use two SPDT relays for antenna T/R.

The ultimate is the Jennings vacuum DPDT relay below.  Cost is $147.


Or you can get two SPDT  vac relays for cheaper to do the same job.

Or, you can get an open frame Potter and Brumfield  24V DPDT relay for $27.  It will "probably" never arc over at your power level.  I used them for years until I went to all vac ant relays for safety of my receiver in case of flashovers as I mentioned.

My opinion? I would use the Jennings sample below. Look around for a similar Jennings DPDT vacuum or equivalent relay. That way you are sure.

Consider using 24 VDC as your shack keying voltage. This will match many, many different BIGGER relay coils.  I have both, 12V and 24VDC here.

BTW, do you have the circuit for antenna switching? IE, the ant connects to the receiver during standby. During key up the antenna connects to the 813 power output while the 813 input connects to the RF driver.  Can you visualize how an RF arc can travel from the 813 output contacts to the receiver input contacts by bridging the relay?

Also, see the DPDT (or two SPDT relays) antenna relay and exciter switching below.  R3A / R3B   using  J1 RF in  and  J2 RF 0ut SO-239s.  


T

 



* Jennings Vac relay.jpg (26.29 KB, 438x438 - viewed 8 times.)

* Potter and Brumfield.jpg (42.24 KB, 438x438 - viewed 8 times.)

* Ant-driver relay.jpg (50.95 KB, 800x600 - viewed 3 times.)
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“Remember, remember, this is now, and now, and now. Live it, feel it, cling to it. I want to become acutely aware of all I’ve taken for granted.”  -  Sylvia Plath

Favorite Song - Trololo thru the years:  
https://www.youtube.com/watch?v=IVqUecYGnoM
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