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K1JJ's 813 Maul Questions (was 807 instead of 6146)




 
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Author Topic: K1JJ's 813 Maul Questions (was 807 instead of 6146)  (Read 15172 times)
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David, K3TUE
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« on: November 28, 2006, 11:18:13 PM »

Despite a lot of encouragement from K1JJ, I have to shy away from building his 2x813 x 2x813 maul (http://www.amwindow.org/tech/htm/813/813.htm) because of size/weight/voltage concerns.  I knwo the tubes themselves are not much bigger than what I am proposing below, but I suspect the necessity of the supporting cast for them adds up to 50% more in size and weight.

The nice thing is, it seems like a straightforward and adaptable circuit.  I was wondering how easy such a circuit would be to adapt to 2x807's x 2x807's (or is this ill conceived).  I have read about plenty of rigs using 807's and variants to modulate 2x6146's (dx-100 comes to mind).  I suspect that 2x807's in this configuration would not measure up to the power output of 2x6146's (viking 2 comes to mind as well).  As best I can understand from the 807 data sheets it would only be good for about 90W input, which would be fine.  I guess I just like the 807's better than the 6146, probably because of it's kinship with the the 6L6 and perhaps even aesthetics (not an uncommon consideration in homebreq rigs).

Any advice?
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« Reply #1 on: November 29, 2006, 12:07:08 AM »

Probably this thread should be in the tech section... but:

The DX-100, as you may already know is 2 x 807 modulating 2 x 6146...
Whereas the Apache is 2 x 6CA7 modulating the same 2 x 6146...

Otoh you can still get 4D32s which are used in the Collins 32V, iirc, and one is about the same as a pair of 6146.

The 6146 is akin to an "RF" version of a 6550, whereas the 807 is akin to a 6L6, but both of the RF tubes will take more B+ than the audio tubes will...

If ur only building for 75m, then you can pick a tube that is not normally thought of as an "RF" tube as well... (in most cases)...

I think I'd pick a single 813 and run it at llower voltage, if you like, and then figure out what to modulate it with!  Grin  (there are also some Ruskie tubes, I think...)

If you make a two section rig - RF deck/PS and a Mod deck/PS (or maybe a single PS... whatever) you have the option of later upping the voltage on the 813 and building up a different modulator... a pair of 811a would be nice for the modulator - again you do not need to run it at full B+.

But quite frankly the 750vdc is pretty much high voltage[/b] just like the 1500vdc or more that you'd normally hit the 813 with...

But that's my pick 813 modulated by 811s or similar... inexpensive, sexy and capable of some reasonable power anyhow...

      Grin

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Steve - WB3HUZ
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« Reply #2 on: November 29, 2006, 09:24:37 AM »

At HF, the 807 and 6146 are virtually interchangable. You may be able to get a little more power from the 6146Bs, but no enough to matter. A pair modulated by a pair would be a cool combo, but I tend to agree with Bear - go 813 route. It's not likely any more effort, and with the right selection of iron, not much heavier.
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« Reply #3 on: November 29, 2006, 12:27:54 PM »

807s make TVI much better than 6146s
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John K5PRO
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« Reply #4 on: November 29, 2006, 03:54:42 PM »

I don't understand the physical mechanism which would make an 807 produce more tvi than a 6146? An amplifying tube may have saturation characteristics, which differ from another, and linearity differences, but for this to translate into more tvi is a stretch, isn't it? I would think that the big difference may be in the vintage construction which was used for 807 style transmitters versus later box-within-a-box 6146 style transmitters? For instance, compare a DX100 layout to an Apache TX-1. The difference (in RF proofness) is big. A lot was improved as hams learned, ARRL and Orr published, and TVs got less susceptable to TVI (another factor which changed over time).
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John K5PRO
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« Reply #5 on: November 29, 2006, 04:04:09 PM »

The DX100's weakness is the 1625 modulators. These tubes are rare to find, in matched strong pairs, anymore. In 1958 they were plentiful due to JAN parts in surplus everywhere. 807s would be an improvement but required a new filament tranny and socket, so conversion to 6CA7/EL34 in the Apache was a natural. I have my 100 running with 6CA7s now, and two things are apparent. Modulation can be higher % without causing one tube to glow bright spot on the anode,and distortion is slightly better. A lot of that can be attributed to fixing the blasted power supply,so that the screen doesn't run off the tap of the bleeder, instead regulating it at 300 VDC or so.

I tried 6146 modulators also, the difference was slight, I need to write up an article in ER someday, no time to write it seems. 
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« Reply #6 on: November 29, 2006, 04:18:08 PM »

807s have longer leads than the 6146. My Dad stopped stamping on the floor when I was transmitting as soon as I changed over to 6146s.
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flintstone mop
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« Reply #7 on: November 29, 2006, 05:48:15 PM »

Good thread guys
I think some of the TVI problems for the earlier TV's was the I.F. frequency. The tuners were/have to be wide as a barn. So easily overloaded from neaby RF. Be careful with newer TV's. 75 meters can shut down the preotection circuits in the HV (25,000VDC) and cause it to go haywire.
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Fred KC4MOP
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« Reply #8 on: November 29, 2006, 11:06:07 PM »

Quote
07s have longer leads than the 6146. My Dad stopped stamping on the floor when I was transmitting as soon as I changed over to 6146s.

Not sure how this is relevant in a properly designed, filtered, and shielded transmitter. If it was all about lead length there would be a whole lot of tubes worse than the 807.
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David, K3TUE
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« Reply #9 on: November 29, 2006, 11:33:58 PM »

I'm back to actually considering K1JJ's 813 Maul (http://www.amwindow.org/tech/htm/813/813.htm).  I was looking at the specs for an 813 and see you can run it plate modulated all the way down to 1250 volts, which should help me keep a lid on power consumption.  I have to run it all on 110, since I don't have a 220 line to anything upstairs in the house.

I think I'm gonna start by collecting the transformers and chokes first, as I believe they will be the hardest to come by.  As I collect these I will start by making the power supplies from low voltage to high.

o  Any suggestions on a reliable source for transformers and chokes for this project?
o  Or should I just start watching eBay as I will be doing for the variac?  And how about tube sockets?
o  And what hsould I use for interstage hi-V power connections?  I see those 4mm safety test lead connections are good for more current than I need, but only seem to be rated to 1000V.  I'd rath avoid open connections like barrier strips or ceramic standoffs for hi-V DC if can.
o  Should I be using something special like teflon wire for hi-V wires, since I suspect that average wire simply rated for the current capacity of the circuit will not be rated for the 600V or 1kV-2kV circuits in this project?
o  Should I step start the primary?
o  Should I devise a safety-interlock for the power supplies?
o  Why use fuses on all the power supplies and a breaker on the plate power supply?

I have more questions, but I'm still thinking right now.
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David, K3TUE
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« Reply #10 on: November 30, 2006, 07:37:53 AM »

Dave,

I'm building an 813 rig similar to Tom's Maul.  Below are responses to your questions.

o  Any suggestions on a reliable source for transformers and chokes for this project? Ebay, internet newsgroups, buy/sell websites, hamfests.  Most of my transformers I've collected came from hamfests.  I did purchase a couple from people off of some of the newsgroups years ago.

o  Or should I just start watching eBay as I will be doing for the variac?  And how about tube sockets?
I prefer hamfests only because I can handle the item before purchasing.  On Ebay one should be cautious. Some good deals can be had on Ebay too. Again, be cautious, contact and do research on the seller though I think the odds are in your favor for not getting burned

Antique Electronic Supply had 813 sockets when I purchased my set.


o  And what should I use for interstage hi-V power connections?  I see those 4mm safety test lead connections are good for more current than I need, but only seem to be rated to 1000V.  I'd rath avoid open connections like barrier strips or ceramic standoffs for hi-V DC if can.

Think Safety. Definitely minimize use of open connections.    I'm using the Millen type shown here: http://www.surplussales.com/Wire-Cable/HVWire-2.html
You don't need to buy them for this place.  RF Parts sells them for a little less, I think and probably a better place to deal with as well.


o  Should I be using something special like teflon wire for hi-V wires, since I suspect that average wire simply rated for the current capacity of the circuit will not be rated for the 600V or 1kV-2kV circuits in this project?
Several options here.  Silicone type wire like that used on the anode lead of a picture tube. Sparkplug wire like Packard wire.  RF Parts has various types of HV wire.  Don, W2DL helped me out with some HV wire recently. He has a ton of 10kv wire.

o  Should I step start the primary? 
Probably not a bad idea.

o  Should I devise a safety-interlock for the power supplies?
Good idea.

o  Why use fuses on all the power supplies and a breaker on the plate power supply?
Not sure myself.  It may have something to do with surge current

I have more questions, but I'm still thinking right now.

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Bob
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« Reply #11 on: November 30, 2006, 10:37:23 AM »

Dave,

You can run the 813 at any voltage (pretty much) you want - the 1250vdc is just a suggested value. No reason you can't run the tube on 750 or 800 or 1000 if you wanted to. It will just make less max power... but you can still draw gobs of current compared to a typical tube like a 6146 will at say 750vdc B+.

Idea:

So, in terms of building, you can build based on the idea that your first pass might be relatively "low" B+ like the typical 100watt class rigs 750vdc B+, but install or leave space for and/or higher voltage rated parts! Then down the line you can put in a higher/larger B+ tranny and increase the size/voltage rating of some parts and go for more power... even leave room for a second 813!

 Grin

This way you can put it together faster, since you don't have to worry about the size/voltage rating of all the parts, and that makes them easier to acquire...

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« Reply #12 on: November 30, 2006, 11:47:23 AM »

I've wanted to try an 813 in my PDM viking two for years. I have a bridge on the power supply to make 1550 volts. At carrier level there is about 600 volts across the final. I also have a switch that cuts the voltage in half. I wonder it a 6AQ5 would drive the 813 to 100 watts out with 600 on the plate. I've fried a couple sets of finals since '83 but the pair of 6DQ5s PDM modulators are as good as the day I installed them in '83. I replaced them last year as a test and no change in operation. I've driven the 6146 plates yellow. 
I've never seen curves with the screen voltage at say 150 volts.
 
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« Reply #13 on: November 30, 2006, 12:27:40 PM »

David,
         6146 ia a much better tube for rf service than an 807. the 6146 was designed to be an rf amplifier tube where an 807 is simply a 6L6 with a plate cap.

The 6146 has shorter more direct base leads and lowered interelectrode capacitances. it is cleaner and easier to neutralize than an 807. A lot of 807's were used in pre war equipment because 6146's hadn't been invented yet!

If you are really planning to build a H.B. rig build as big of a rig as you can. the influence for my 4-1000 transmitter came from the Derb! We were talking at the howard county hamfest some years back, and I was mentioning building a hb tx.
i was talking about using some unusual tube lash up when he gave me these words of wisdom: "If you are going to go through all of the trouble to build a home brew transmitter, think CB and build the biggest maul that you can". 10 minutes later I found a good deal on a 4-1000 socket on a hamfest table, and the rest is as they say history.

If you are going to build a rig, dont paint yourself into a corner, build one that is big enough or design it to be easily upgradable. We dont live that far apart, if you want contact me when you are ready and I will be happy to help you with layout and design.
                                            The Slab Bacon

 
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K1JJ
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« Reply #14 on: November 30, 2006, 12:33:04 PM »

Hi David,

I think you've got the right idea, now.  Even a single 813 in the final is a good way to go. That's what I've just built here... a single 813 modulated by a pair using that exact design. You will hear it on soon.

Audio driver - Use the 8 ohm audio transformer/ solid state amp for now, but the new KLR audio cathode driver looks promising. I've built two and have them in testing now. Transformerless and simple design. Plan on it later.

For HV connections, I use a ceramic 1" standoff insulator mounted on the chassis with a screw connection on the top. (The cone style stand offs you see everywhere). They are easy to connect/disconnect and are strong and never arc over. I usually have a line of them for HV, screen and grid input. Mount them near the back of the rig, but plan to have them covered and out of reach of cats, etc... Wink

Go to NAPA auto parts and pick up a 100' roll of spark plug WIRE for $35?  Look it up on the web... Belden wire I think.  I use that stuff exclusively. Any Napa store can have it the same day from their warehouse.

Yes, start with lower HV until you have the confidence and the bugs worked out. You can always ramp it up since the supply is outboard of the RF deck. This design is limited in LOW voltage by the idle current of the 813 modulators. You can run it at maybe 1200v and still get the modulators to idle, but I'm not sure if any lower. The 813's are running triode connected, so they need the HV to set the idle point. If they go to cut-off and below, you will have crossover distorsion, like running class C. There is no flywheel effect from a tank coil, like class C, with audio service and mod transformers.  But the good thing is you can go all the way up to 3KV (add a few series diodes in the mod fil CT for extra bias). There is a BIG HV range available to you since you have the final screens on a variac and can control the modulators with diode cathode bias.

You can buy EVERYTHING on ebay if you keep looking. I know many that have done this during the winter when there were no flea markets. Look hard and then afterwards post a list of items you need. The guys here will always help out. Post some pics of the rig in progress and you wil get lots of additional help and interest.

There's nothing wrong with using the smaller 6146's, BUT only if you intend it to be a little rig in the end. If your heart's desire is for something legal limit, then you are wasting your time not starting with the 813's . We ALWAYs grow into something bigger after we get confidence. Later, you will see that it was the correct decision to use 813's from the start.

For step start... I usually leave the HV on all the time and key the fil CT as shown in the schematic. Use very light bleeders for safety only and remember that the class C final will pull a constant load to insure a stable supply for modulator HV regulation.

For fuses/breakers...  Use a main breaker for the HV supply primary. For the smaller grid/screen, use the standard 1/2A, etc fuses in the little fuse holders. The HV breaker is all you need for the HV. In addition, I sometimes use a single strand of RG8 braid across two standoff insulators in series with the HV lead before the plate choke. This will be a fail-safe method to protect the diode stack. It's saved me many times in the big rigs.

The interlocks are a good idea, though I never use them here. The idea is that there is NEVER a technical reason you need to work on a hot rig with HV.  Even neutralization can be done with the rig off.  For arcing, put a mirror behind the rig and stand back and let her rip. Also use a shorting bar on the supplies before going in - and leave it on there until finished. You will probably forget it's there and blow out your little single strand wire HV fuse - I've done it many times.. Grin

I think that answers all your questions for now. Keep axing and thinking and looking for parts!

73,
T


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Frank / WA1GFZ says when he's working near high voltage, as a warning he sings this song by Jay and the Americans: "Come a little bit closer, you're my kind of man, so big and so strong, come a little bit closer, I'm all alone and the night is so long."
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« Reply #15 on: November 30, 2006, 12:38:40 PM »

I agree with Frank but I need a driver myself and the poor 6146s beg for mercey in QRO mode.
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K1KFI
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« Reply #16 on: November 30, 2006, 01:16:42 PM »

Dave,

High voltage wire is used in neon light wiring and radar systems as well. If you have people who build those sort of things in your area, inquire about where they get their wire. They may even give you some. Minumum should be  3kv or more for 813's run at 1500v. Oh, and they run very nice at that voltage! Coaxial cable is also an option. The idea is that the shielding of the wire not have a chance to become abraided or melt causing arcing or even a dead short to ground. Keep your eye out for ceramic insulators or use thick plexi to bring the wire into the chasis. Keep the run as simple and isolated as possible.       Smiley

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K1JJ
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« Reply #17 on: November 30, 2006, 01:59:05 PM »

Dave,
 Keep the run as simple and isolated as possible.       Smiley

Cliff
K1kfi

Yes, good point. I usually slide 1" flexible plastic water pipe over all HV wires that connect between rigs, if it is outside the rack.  The coax idea is good too as long as you don't use that cheap foam type. I've had RG-58 foam arc over at 4kv.  The polyethene dielectric clear/hard plastic coax works very well for HV, like RG-213 type for example.

T
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Frank / WA1GFZ says when he's working near high voltage, as a warning he sings this song by Jay and the Americans: "Come a little bit closer, you're my kind of man, so big and so strong, come a little bit closer, I'm all alone and the night is so long."
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« Reply #18 on: November 30, 2006, 02:14:28 PM »

This is a common  in weapon systems so you always fail safe. Short to ground
The wire gets crushed it always gets grounded never connects to another voltage or load.
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« Reply #19 on: December 02, 2006, 03:53:03 PM »

Tom,

I'm presuming your're talking about running the 813 modulators in "0 bias" class B?
And you think they'll be cut off if the B+ drops too low, especially strapped for triode?

I don't know the answer, but I'd add some bias, if that was needed...  Roll Eyes

Which, in part is why I suggested a pair of 811 in the modulator driving a single 813 running
at 1000-1250vdc as a target to start with... that'd even work down at 750vdc, I think...

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« Reply #20 on: December 02, 2006, 04:18:41 PM »

Quote
And you think they'll be cut off if the B+ drops too low, especially strapped for triode?


It's likely. 813s are good for zero bias upward of 2000-2500 volts. Even 811s idle a little low at 750 volts but would be OK. 809s would be a nice choice but are more rare.
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K1JJ
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« Reply #21 on: December 02, 2006, 05:18:27 PM »

Tom,

I'm presuming your're talking about running the 813 modulators in "0 bias" class B?
And you think they'll be cut off if the B+ drops too low, especially strapped for triode?

I don't know the answer, but I'd add some bias, if that was needed...  Roll Eyes

Which, in part is why I suggested a pair of 811 in the modulator driving a single 813 running
at 1000-1250vdc as a target to start with... that'd even work down at 750vdc, I think...
         _-_-bear


Hi Bear,

Yes, correct on all.  A triode designed for audio service would be a better choice. Running the triode connected 813's at lower than 1250v? (guess) would put them into cutoff.  I find a good voltage for them is between 1800-2200V. I've run them at 3KV, but they needed diodes in the CT to idle down.

How would you add a positive bias to the 813's if needed? Just curious.

The reason for the 813's is they are strapping and plentiful and cheap. A pair in the final modulated by a pair triode connected will put out 800W carrier and modulate at 130%.  Using a pair of 811's modulators will not come anywhere near that. But again, if the avaialble voltage is lower than 1250v or so, then the 811A's are a better choice.

I believe the 813 is an anomoly, like the 4X1, in that they are very clean in triode connected service. Though, I would expect an 811A to be slightly cleaner in comparison.

73,
T
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Frank / WA1GFZ says when he's working near high voltage, as a warning he sings this song by Jay and the Americans: "Come a little bit closer, you're my kind of man, so big and so strong, come a little bit closer, I'm all alone and the night is so long."
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« Reply #22 on: December 03, 2006, 12:02:45 AM »

The coax idea is good too as long as you don't use that cheap foam type. I've had RG-58 foam arc over at 4kv.  The polyethene dielectric clear/hard plastic coax works very well for HV, like RG-213 type for example.

I really like the failsafe nature of using coax.  I was looking at specs for LMR coax (I just like it better) and see that
o  LMR-240 (PE dielectrric) is rated for up to 1500V DC (which does not provide any safety factor voltage-wise even at the 1250-1500V I was planning on starting at),
o  LMR-400 for 2500V DC (which would seem to give me good safety factor up to 1500V), and
o  LMR-600 for 4000V DC (which would seem to give me enough safety factor for even the 2-3kV potential upgrade in the future).

But if I use what HV connectors would I use.  Millens seem out.  Would I just use SO-239/PL-259's?  And while LMR-400 is RG-8 size and can fit in this connector, what does one use with LMR-600 which is, I believe, almost 5/8" in diameter?
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« Reply #23 on: December 03, 2006, 12:28:08 AM »

The coax idea is good too as long as you don't use that cheap foam type. I've had RG-58 foam arc over at 4kv.  The polyethene dielectric clear/hard plastic coax works very well for HV, like RG-213 type for example.

I really like the failsafe nature of using coax.  I was looking at specs for LMR coax (I just like it better) and see that
o  LMR-240 (PE dielectrric) [...]

Man, I just realized, LMR coax is FPE, not PE.  I was thinking of using it (for RF) because of it's low loss for it's smaller diameter, but it looks like that comes at the cost of a lower breakdown voltage.

AFAICT though, this HV use asside, even at 5kW into 50ohms will only generate 500V, which is only 1/3 the rated breakdown of the dielectric.  but it does make it ill advised from use at a HV DC carrier.

I do, howver, see that RG-213 is good for up to 5000V, which should make it the smart choice.

So I guess the only question still would be, what connectors to use with it.
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« Reply #24 on: December 03, 2006, 12:50:52 AM »

I see this schematic (http://www.amwindow.org/tech/htm/813/813print.htm) that there are current meters for the screen and the bias power input.  If I wanted to round it out and add a plate current meter, where should I put it in this circuit?
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