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Author Topic: ART-13 Mod Iron Tube Substitutuions  (Read 9491 times)
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W9ZSL
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« on: July 29, 2015, 08:57:19 PM »

I scored an NOS ART-13 Mod Iron for $19.  Couldn't resist.  The classic set-up would be a pair of 811As and an 813.  I got to thinking that I have a plate transformer which will give me 1150-1250 VDC under load easy and I can build a single-supply amp/modulator.  Question.  What tube could be substituted for the 813?  I'd like to hold onto that for a higher-powered rig.  Would a 4-65A work?  200 watts input built around that tube would be a natural.
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Patrick J. / KD5OEI
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« Reply #1 on: July 30, 2015, 12:41:18 AM »

The 4-65's can be run at lower voltages like 900-1000V but it wants higher voltages to make its best use.

The trouble will be the current rating of 150mA max. A tube for 200W input at 1000V has to have a rated current of 200mA. at least. It might work for intermittent duty but the life would be shorter by a lot.

The data for class C plate modulated use 1000V says 120mA max plate current and 120W input and 90W output at carrier.

For 200W input on the 4-65 without exceeding the ratings the voltage must be higher. Two in parallel would be more appropriate if you want that much input at low voltages.

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VE3AJM
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« Reply #2 on: July 30, 2015, 03:39:38 AM »

Buzzardly tubes like the 814, 828, 803 would work well at the 1150-1250 volt level to achieve 150 watts carrier out or use a pair of those tubes in parallel.  Same as 4X150s. 1950s 60s ARRL Handbooks in their transmitting tube spec section or online info would steer you in the right direction too.

A cool tube to try would be a single 7094 which is a lower plate voltage higher plate current tube, or just find another 813.

Depends on what tubes and sockets that you have on hand or can get a hold of at a reasonable cost.

Al VE3AJM



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N2DTS
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« Reply #3 on: August 02, 2015, 10:28:56 PM »

4x150/4cx250b work well with 811 modulators.
I had a pair at 1200 volts, 300 watts carrier output in a very small deck with only a fan to
move a little air through the tubes.
Low filament power, plate voltage can be anything from 1000 to 1800 volts, 1200 volts works well with 811's zero bias.
One 4x150 can do up to 200 ma in plate mod service so you can match the art13 mod iron well.

All the 4- tubes like high voltage.
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W9ZSL
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« Reply #4 on: August 06, 2015, 08:28:11 PM »

I just managed to score a 250 uuf at 7 KV plate tuning cap.  With my roller inductor and a substantial antenna tune cap, voltage to an 813 doesn't matter.  I can build an RF deck and start with 1250 VDC on both the 811A's and a single 813.  That would match the AR-13 mod iron just fine and since I have a 250 watt UTC mod iron, I can work my way up to 350-400 watts RF input by using 2 supplies; around 1350 for the modulator and 2 KV for the RF.

I'm going to allow enough room on the chassis to add a second 813 in parallel if I get real ambitious and don't die first!
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N2DTS
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« Reply #5 on: August 06, 2015, 08:47:35 PM »

Sounds like a plan.
I like 813's in plate modulated service, about 600 watts out at 2000 volts for a pair loafing along.

I do not really like roller inductors because the Q can be all over the place, but you can sometimes gang it with the plate tuning cap and keep a fixed Q.

A pair of 4x150's make a good modulator for a pair of 813's as they can run 1000 to 2000 volts in AB1 to match any mod iron to any power level.

What about grid and screen circuits?
Fixed and grid leak bias, screen voltage and over current protection?
Screen modulation method?
Step start power supplies?

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W9ZSL
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« Reply #6 on: August 07, 2015, 06:37:32 PM »

So far I'm just speculating on an amp for AM/CW starting with the ART-13 mod iron and one power supply.  The RF deck with a single 813 will be built with high-power components for future expansion.  The ART-13 iron is good for about 110 watts and with the separate winding for modulation of the screen (separate supply) with maybe 250 volts and adjustable to start.  I can eventually kick the power up to about 400 watts input with 1 x 813.  Modulator (811As) and RF can start with around 1250 volts off one supply.  Once I get the thing working, I can modify with a second supply good for 2KV on the 813 and replace the ART-13 iron with my UTC 250 watt xfmr.

My original intent with this post was to build a RF deck using something other than the 813, but it makes more sense to just build around the 813.  I'm not going to allow for parallel 813's because there has to be a limit.  The UTC "S" series mod iron is NOS and going any higher power RF would mean more iron to find.  I don't think more than 350-400 watts input to the 813 is necessary.

Besides, starting small and modifying as I up the power is funner.

As for the variable inductor, I have a big B&W coil stock that can be used.  Figuring out the right inductance for each band is in the future.  The mind is an easy thing to change.  Ask any politician!
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w7fox
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« Reply #7 on: August 10, 2015, 12:07:26 AM »

Hi, I am using the art13 mod transformer in a homebrew transmitter that has 807s in the final and modulator.  It modulates 100% and I get good reports.  This transformer was made for final and modulator tubes that use the same high voltage.  Probably just about any tubes will work, as long as they use the same HV.  Good luck.
Chris W7FOX
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W9ZSL
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« Reply #8 on: August 10, 2015, 03:30:42 PM »

That's what I was thinking Chris.  What's the voltage each side of center on your plate iron?  Are you running a choke input filter?  One or two chokes?

Mike
W9ZSL
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N2DTS
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« Reply #9 on: August 10, 2015, 08:26:39 PM »

A single 813 will do 300 watts out at 2000 volts and 200 ma.
A bit more if you push it.
At 1200 volts and 200 ma its going to be much less.

What is the impedance of the art13 mod iron?
Voltage and current ratings?

You could likely use a number of tube combos.
I have a 4D32 deck that has three 4D32's in it modulated by a pair of 811's off one supply at 1200 volts.
300 watts out, but you can run 4D32's down to 500 volts.
$35.00 a tube new they go for, they seem rugged, about the same as two 6146's in one bottle.
I was surprised they take 1200 volts with plate modulation without any problems, ran them for years that way.

They might be a good match for the art13 mod iron, you can vary the plate voltage and current quite a bit.
From 600 volts and 400 ma to 1200 volts and 250 ma.

Not sure if you can get a NEW US made 6146 for $35.00 these days, and a 4D32 is like 2 in one.

I like having a design and sticking with it.
Trying to supersize the transmitter often makes a mess and causes problems.

I would rather build a 2000 watt rig and run it at 1000 watts then build a 1000 watt rig and run it at 2000 watts...
Some people like fireworks tho...ring up the engine room for flank speed..warp 11.

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W9ZSL
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« Reply #10 on: August 10, 2015, 11:16:54 PM »

I'm actually juggling a number of options.  I have 3 NOS modulation transformers.  The ART-13 was $19 so I couldn't pass that up.  Running 1250 volts, which I can do with a single supply, it's designed to present a plate-to-plate load of 15,000 ohms to a pair of 811's when the secondary load impedance is 7300 ohms.  The value of the secondary load is presented by a class C amplifier operating at 1250 volts and 170 MA.  The input to the class C stage would be 212.5 watts.  Since the ART-13 was designed with an 813 final, I can easily go that route, though the ART-13 actually operated at 1150 volts as I recall. That is option #1.

Option #2 has a pair of 811A's also into a UTC S-22 mod iron rated at 250 watts.  Using the same supply as above, I can crank up the voltage to about 1350 under load for only the modulator.  Using the same 813 on the RF deck and building a second supply, I can put 2 KV on the plate.  I'd have no problem coming up with 400 watts input at 200 MA. I just scored a massive 250 pf @ 7 KV plate tuning variable by Cardwell with a Cardwell 1000 pf at 1 KV for antenna loading.  I can switch in 5 x 270 pf @ 1KV micas with a shorting ceramic rotary for 2350 pf @ 1 KV available for loading.  In other words, I can build an RF deck using all HV components and run it at lower voltage from the one supply to start, then kick up to a higher power once the kinks are out.  I can swap out the ART-13 mod iron for the S-22.

Option #3 would be building an entirely separate amp using the ART-13 mod iron with a pair of 5933's (807's) in the modulator and another pair for the final.

Then there is option #4 using another mod iron; a UTC S-20 mod iron rated at 55 watts and build something else.

I'm going to build the RF deck with over-rated parts and allow room to add a second 813.  Starting with 1 modulated by a pair of 811A's through the ART-13 and one 1250 volt supply sounds like a good place to start.

 
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w7fox
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« Reply #11 on: August 10, 2015, 11:54:42 PM »

Mike,  I'm running 600 volts on the final plates, the recommended max for 807s, and 700 volts on the 807 modulators because that's the transformer I had in the junk box.  I run the modulators in AB2 and have power to spare.  Both plate supplies are single section, choke input.  I use a tuned choke on the final plate supply to improve regulation on cw.
Specs for the art13 mod trans are 50 watts.  I am running it at about 60.
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KA2DZT
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« Reply #12 on: August 11, 2015, 01:29:12 AM »

The ART-13 mod xfmr can handle way more than 50 watts even though that's what it is rated for.
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W9ZSL
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« Reply #13 on: August 11, 2015, 11:50:27 AM »

The ART-13 mod iron is rated at 110 watts according to the 1949 West Coast Handbook.
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N2DTS
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« Reply #14 on: August 11, 2015, 08:32:39 PM »

A pair of 4D32's would do well then, right in the ball park.
813's like more voltage.
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W9ZSL
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« Reply #15 on: August 12, 2015, 12:35:13 PM »

I already have one power supply that should give me close to 600 volts under load and judging by the size of the iron, I'm looking at around 300 MA.  It uses a solid-state bridge and is QUIET.  Choke is inside but I have a swinger that can be mounted on the top open space.  The two sockets are for VR tubes for an oscillator.  As for the Pi net, I could build for just one band (75).  I wouldn't use the rotary inductor or the shorting switch in the antenna tune circuit.  It would be a good starter since I haven't built anything recently and it would be a fun rig.

I've collected enough parts to build this 807 amp.  I can substitute 5933's and modulate with another pair through the ART-13 iron.  Note the supply has a tapped bleeder for screen voltage.  A bias supply is included.  Has anyone ever tried this circuit from the '57 Handbook?  It's rated at 120 watts input on phone and would be a quick-build.  If necessary I have another xfmr on hand but would rather use just this one supply.


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