2x 813 amplifier?

[N2DTS]

Yes, but if you look in the 'care and feeding of power grid tubes' some of the tubes you listed are poor when it comes to imd.
The book I have is old, and does not list the modern types, or the 813, but the 4-xxx series are poor imd performers.

When talking IMD, does that show up as grunge around the signal, or would it be audible?
Say you take a low distortion AM signal and feed it into a poor IMD amp, does it SOUND poor, or just get wide?

Brett

[W2VW]

I have all the parts to build the 4x813 amp, except the filiment transformer, but dont know if its a good idea, as I read on the web that the 813 and other older tubes are not very clean in output when used in grounded grid, not like tubes designed for grounded grid service.
a pair of 3-500z tubes would likely be much better?

Or just stick up a liquor store and get a real amp?

Brett

One dunce on QRZ tried to imply that. Same dunce has never worked with said 813.

Another dunce on QRZ tried saying there was not much chance of finding good 813s.

Both of these guys seem to have an answer for EVERYTHING.

That's the biggest problem with that site. People like you (Brett) remember most of what you read and it sticks in the back of your mind. Take information with a grain of salt unless it is peer reviewed or from a trusted source.

There isn't anything wrong with 813s in grounded grid service. They have been used by a lot of us as class B modulators with good results. The grounded grid configuration will be cleaner than simple grid driven modulators without feedback.

I have an old 4 holer 813 here. It had been used previously by another hamateur for condomtesting on ssb where I calculated dissipation of each tube to be over 300 watts!

[W1RKW]

Brett,
As mentioned in a previous post, I did the 813 linear thing. At the time, I had available to me a spectrum analyzer. The amp was clean or within amateur practice. You should not have any problem operating a 2x813 or 4x813 GG rig. Granted it is not the best way to increase power level but it worked OK Fine. The 813 is a sturdy cheap ass tube.

[N2DTS]

I suppose I will order a filiment trans from fair radio and give it a try!

Brett

[ka3zlr]

My Three 813's worked fine GG so an I just copied the circuit off of a Dentron circuit i liked an used the same or close as I could find components...but I do have a 3 kw supply I can draw on for alot of things that helps...
it'sa kick butt supply..LOL...Pick a voltage you wanna operate at and build to that spec...build heavier the sky's the limit here and the right hands are here to help...so your good to go start building an quit worrying.

Get-R-Done..

73
Jack.

[N2DTS]

I have some massive components, on a 17X17 chassis, there is not much room left for the tubes the caps are so large....

The power supply is already built, I dont need any sort of TR relay since I use the station one, and plan on driving it with the flex, using a seperate receive antenna port. PTT is already done, so I just have to build the rf deck and hook it up.

It sounds like a tuned input is the way to go, which complicates things somewhat, unless I can get one circuit to cover 80 and 40 meters....or would the built in antenna tuner in the flex work?

I plan on making 2 big plug in tank coils out of copper tubing, one for 40, the other for 80 meters.

If I had more sockets, I could do 6 813's....

Brett

[KM1H]

Bill Orr reported the 813 as one of the cleaner tubes for GG with 3rd order in the -33 dB range at 2500V. Thats not too shabby for a 70 year old tube and a lot better than some of the Russian crap some idiots keep praising.

Plus its still GIGO and your average ricebox cant even get out of the high 20's

Carl
KM1H

[N2DTS]

Here is the layout so far, with the 40 meter coil in...

About the meters, what will be the plate current and grid current for 4 813's in grounded grid?

Brett

[K1JJ]

Nice looking amplifier, Brett!

With 4kv on it you cud get out an easy 2KW+ pep.  I've always liked 813's in most any config -  linear GG, class C or class B triode-connected modulator service.  Six 813's - why not?  I have the tubes and sockets to do twelve. Almost did it. Quiet amp with little blower noise. But I opted out for Quadzilla instead to get a good glass fix..


Carl, did you say the IMD on some of the Russian tubes was poor?  I have long wondered how that wud work out now that there are many in the field. The prices have soared compared to a few years ago.

So what are you hearing and seeing for IMD these days with the Russian tubes?

I've heard a few on that were truly bad news, but didn't know if the amp had a problem itself or it was the tube....


BTW, to answer a question from a previous post - If the 3rd order IMD is about -15 to -20db or better, you wud not hear the distorsion on freq, just up the band. IIRC, a -30db 3rd IMD is equal to .1% distorsion. That's literally impossible to hear on frequency, especially on a noisy band.

T

[KM1H]

Tom, Ive personally only used the Svetlana 4CX400A and 4CX800, the latter especially needing a load of idle current to get IMD out of the 20's.

Ive seen SA plots from several triodes, from people I know and respect, that are pure crap in the high teens. I dont have the types handy ( I can never get their Ruskie designations memorized) but they are ones commonly used in various conversions and HB, usually at way higher than spec voltages.

Remember, none of those tubes were designed for linear service. They are all for military radar, and Class C comm gear. Try and find curves on any of them.

IMD may not be that important to you basement dwellers but a crappy amp can ruin it for all on 10/15M and up where I tend to spend a lot of time. Up there I even bitch about 4CX250B's   On the busy low bands it all adds up until at some point it is just band noise (white noise) since it keeps mixing and remixing . Its similar to what CATV trunking amps have to deal with and there the IMD has to be in the 40's or better.

You coming up for the canoe events Friday/Sat?

Carl
KM1H

 

[Opcom]

A good control grid current limit is the class C oscillator spec if the concern is tube life. 10mA for the control grid and 40mA for the screen. Will you connect the supressor to the filament's RF for a little degenration or to GND? I think you got an experiment to do.

Carl has a good point. can you up the Q on the pi-net to help with the distortion?

BTW - just keep adding 813's and you won't need a plate tuning cap. It is tricky to get a pair to work efficiently on 10-12M but the lower bands should be fine.

In the 1962 handbook, the article on page 194, "One Band Kilowatt Amplifiers" showed a stack of parallel 813 amps with a common power supply. This was called the "ne plus ultra" by the decently educated author.
The 10M one had a tap in the pi coil for the tuning cap, so that it was plate-PI-coil-C-tuning-PI-coil-C-loading. This was said to help with the large plate capacitance of the 813 pair. These were not GG amps but control-grid-driven amps with bias and screen voltage. Maybe this will help with the plate circuit design.

The HT-44 "CB leenyar" of a friend that had two 813's in GG converted from the original unobtanium GG 7094's was never very efficient on 10M. It also tore up TV sets real good so attention to the plate Q is a possible help.

[K1JJ]

Nope, a "reasonable" Q will have little to no effect on IMD cuz IMD mainly affects the freqs within +- 10kc or so. Q would have to be VERY very high to come in that close in the tank bandwidth curve to have any effect on generated side products.

OK on the Russian tubes. Wouldn't ya know it. Well, I thought there were some decent ones that were designed for GG triode service. How about that GU-34B? or what is it that has the big copper anode good for 2500w that's a very loose version of the 8877? How are they doing for IMD?

Yes, I'll be heading up for the water balloon fights and snowman contest Thurs nite. The Huzman will be here tmw morning and we want to play with some toys during the day. He wants to get on the DX portions and have some fun at night.  I'm looking forward to seeing his impression of the 40M 2x2x2 on the air. He'll be on as HUZ in VA so it oughta be fun.  If he likes being king for a night, I'm hoping to get him to put up a 2el 75M wire Yagi and build up a new linear. There might be some parts at HossTraders, ya never know.

See ya there, OM.

T

 

[WA1GFZ]

rotate the plate tuning cap 180 degrees plates up so the connection to the stators is shorter.

[N2DTS]

I will have to see if the cap can be inverted.
The tubes will mount under the chassis, lowering their height, plus the caps need to be aligned so the shafts are at the same height on the front panel.

Brett

[KM1H]

The old timers advice of short and wide plate leads and longer grid leads still works especially with tall triodes. If you can keep them from becoming a TPTG oscillator you have half the battle licked.

Tom, I dont know one Ruskie designation from another. I'll dig some stuff out and we can yak about it while attaching chains on the vehicles.

For all pratical purposes IMD is a function of the tubes internal construction and applied voltages and currents. Dont confuse IMD with operator caused splatter, totally different animals.

Carl
KM1H

[WA1GFZ]

All it takes to invert the cap is a couple L brackets held by the screws coming through the end plates. Inverted will also reduce the minimum C required to get on 10M. Also an easy way to adjust the height.

[KC4VWU]

I have a pair of 813's built GG that I saved from certain doom. Pretty nicely built except for the stand alone P/S, which has a pretty anemic looking plate transformer and sloppy construction. I finally got some Millen connectors for it, so I may work on it this weekend. I'll take some pictures of it and post them on another thread.
Phil

[ka3zlr]

There was Pictures of mine on here somewhere But I can't find'em I know Da gone well I put'em on here...maybe i'll take sum more an post'em....

73
Jack.

[N2DTS]

What is everyone doing for the rf input?
From what I read, a tuned input cleans things up and provides more power output.

I have an MB40L thing, supposed to cover 80 to 10 meters with one knob, has a link input, and single terminal RF output. It was two circuits, one series coil and cap, one paralell coil and cap, hooked up together to cover 80 to 10 with one tuning knob and no switches.

I have also seen a circuit where a cap tunes a coil the filiment power runs through, and also a pie net type circuit.

Or would the antenna tuna in the flex do it all?

Since its supposed to rain a lot this weekend, I may start drilling and blasting....

Brett

[Opcom]

I suppose I have to study more about IMD.

I do know the MB-40, if that is like the MB-150?. The HF band is divided in two and folded back across the shaft rotation, with no tuning position harmonically related to the other band. So at any position, it will resonate to two unrelated frequencies. The range on the 150 is 3.45 to 8.5 and 12-30. I'd suggest an escutcheon!

I have an 150, but have never built it in because of the lack of 160M and the gap from 8 to 12 MHz. These things might be fixable with a relay and some caps though the L may be lacking on the low end. I put the mnaual up, I hope it might help. Did you have the manual on the MB-40? A comparison would be very interesting.

One possible way to use it comes to mind: use the low-Z (link) connection as the tuned circuit for the input, and leave the hi-z connections alone. This is what I did to grid-dip my MB-150 to play with it.

Could the Q of the MB-40 be be lowered as people wish with GG amps by loading the high side with a non-reactive load? It (MB-150 anyways) otherwise is rather sharp.

IIRC though it is a hi-Z to lo-Z device intended to go from feedline to plate, or driver to grids. Not really for driving a 50-ohm to a cathode. I don't know if it would do for a GG input coupler.

Here is a schemo on it witn 813's, but not GG.
http://www.wb4gwa.netfirms.com/final.htm

[W2VW]

You want a low Q Pi or L network for a tuned input to the cathodes.

That Milton Bradley thing is a nice toy for another project. I have one here and now know what it does. Thanks!

The Flex tuner can probably handle the task at the expense of ever so slightly more (unnoticeable) distortion because the match doesn't exist right inside the amplifier.

[KM1H]

I sell a 6 band PC board for GG inputs for $20 shipped in the USA. You provide the toroids, wire, mica compression trimmers, and 12VDC DIP relays.

Carl
KM1H

[W3RSW]

Brett,
Very nice looking deck but I have my doubts that you'll get sufficient capacity on 160 or maybe even 80 with the plate tune cap you've mounted for 4 each 813's in parallel.  Check with any online Pi net calculator.
Your cap seems to be a couple of 100pf in parallel.  You'll need more than that unless your run 5kv+. 

You could parallel the tune cap with some decent 200pf/10 to 15 kv door-knobs.  Maybe you've already planned to do that on 160 anyway. (the old last band switch position to a loading pad trick, trick #611-405A in a series.)

I'd try to find a good 500 pf, 7.5 to 10kv or better vac. variable. May have to pad 160M  anyway.  4 813's really suck down final load resistance.

[N2DTS]

Well, I got it done and tested, and at 2000 volts, I get 200 watts carrier out with about 900 watts pep.
That is four 813 tubes at 2000 volts in grounded grid.

I need to rack mount it and hook it up to everything, and make some power supply changes to get up to 2500 volts or more.
A nice boost for the flex from 25 to 200 watts carrier out.

The only thing I had to buy was the filament transformer....

Brett
 

[w1vtp]

Brett

Got a final pic with the 4 x 813 in its home?

Al