The AM Forum

Hola,

I received an email from an AMer using an 813 AM rig. He heard some guys on the air talking about possibly using 813 chimneys but didn't know who sold them.

The Dietz lantern chimney called "FLG" will do the job.

Here's the website and actual info.  Take a look at the pics on these old threads to get an idea how to drill the 3/8" holes around the 813 sockets for air to pass. It also helps to sub-mount the socket 1/2" to allow even more air to pass. Make the main tube hole somewhat larger so there is a good air gap around the metal band at the bottom. Use a Variac on the blower to keep it quiet, but still pass some wind... :-)

Pics:
http://amfone.net/Amforum/index.php?topic=18192.20


Dimensions:
Monarch,Blizzard & Dietz #70 #FLG #FLGR
A              B        C
3 3/8" X   2¾" X  6¾"

 
The actual chimneys can be bought here and are called, "FLG"  at only $4.95 each - what a deal for high temp glass.

http://www.lehmans.com/shopping/product/detailmain.jsp?itemID=284&itemType=PRODUCT&iProductID=284

(Click on "more info" for more detailed dimensions)


BTW, these Coleman lantern chimneys may work for 4-400's and 3-500Z's  or other finals - check out the dimensions first.
http://www.rei.com/search?cat=11753602

73,

Tom, K1JJ

Tom...I'm going to order some of those for the "BAD DOG" transmitter....A highly modified RCA BTA1S that now uses 813 modulators...in place of the original 4-400's..The original 4-400 glass doesn't have a large enough opening at the top for the air to get out when placed over the taller 813...The chassis is already blown and I am running close to 3 kv on the 813's (triode connected of course)  They get a little red in the face even after I put -8 volts bias on them..... I have been running it like this on 160 but I think the chimneys will help...

Yeaah, baby - YEEEAAAH!

Nice looking layout there Steve.  The chimneys WILL help. The 813's will look pretty with the chimneys and stay cooler for sure, esp with 3KV on them.

Yep, with 3KV on the 813's they will sing nicely. I run that voltage on my SINGLE 813 X 813's and get out 500-600W if pressed. Though, 350 out is a nice cool number with big audio.  I run the WA3KLR MosFET cathode driven audio driver - 5 watts total.

Be sure the tube hole diameter will be covered by the chimney bottom. Worse case, you could always glue a smaller ring under the chimney to close the gap.  Check the dimensions on the website.

BTW, I see the Fred Flintstone rig in the second pic. That's the one where VW said it looked like the tubes smashed thru the wall like a Flintsone cartoon... :-)  I see you have a love affair with 813's there too.

Later -

T

I love it.

replacement globes available....see models then search for pix and dimensions

http://lanternnet.com/globes.htm

Hi Dave,

Thanks for the extra info. 

The "FLG" chimneys are not a perfect fit for the 813's, but are acceptable. I'd rather have them hug the tube a bit more at the center - and have another 1/2" diameter at the bottom.

But maybe someone will take the time to search thru that data and find something even better.

I doubt they made lanterns big enuff for 4X1's but that wud be a good find too... :-)

T

813 modulators rock!  They don't seem to be real particular as to mod iron ratio...and you can whip them hard and they come back for more

the audiofreakz are gonna get a hold of em all soon.  :'(

The 813 is a great tube, hard to kill.

OK guys -- now you've got me scared.  Where is a GOOD seller for 813's?

Al VTP

Well, this company is a good seller... look at their warranty for their $55.00 US made 813...   klc



All tube sales: We offer a NON DOA warranty on most tube sales. Most tubes
are tested on our local tester and if they are less than 90% we will not offer them.
 
We DO guarantee them to power up. Although tested tubes should be fine, because we  do not have a factory to fall back on for warranty.  And can not control where  they  may be used. We can not guarantee them
to work on your tester or work to your satisfaction on any circuit you may wish to use it/them in.  All other guarantees are otherwise AS-IS. After receiving your tube/s if there is a problem  please feel free to email us as
we do not want  to be unreasonable regarding our  NON DOA  warranty. ... THANK YOU

All of the 813's I have are ham fest purchases.....most are JAN and quite a few are marked with the Navy anchor symbol...I haven't had many purchases turn out to be duds...I think there are still a lot of mil surplus (navy especially) 813's available on the west coast because of all the bases out here.....I   have made some major mistakes with 813's and had the plates go from bright red and actually start to turn yellow and the tube still works...The plates might sag a little but they keep on tickin...I am speaking of graphite plate tubes....I have 2 NIB metal plate 813s that I have never used...They just look so weak.......

Does anyone know (from actual experience) how much drive power it takes for one or two 813's in grounded grid linear service to make full output? Hopefully you were using a tuned cathode input and at least 3KV.  How much drive and how much output, maximum dead carrier? (or pep)

By full output I mean just touching saturation.

I know a few guys here run them, like Bob/W1RKW once ran a pair in linear.

I've been toying with building an 813  "barefoot linear."  What's a barefoot linear? One that runs totally silent so no one knows... :-)


Steve, I've NEVER come across a bad 813 yet... :-) I have maybe 7-8 of them and all were bought blindly at flea mkts over the years for about $5 each - and all tested good. The ones in the rigs have been abused for years and can't tell the difference. I have always run chimney air on them, though.

BTW, looking at your first shot of the 813's - I like the idea of having a LARGE main hole for the tubes instead of smaller the holes like I did. You have bigger air flow - if the chimney covers the hole. How are the sockets mounted underneath to support themselves without bringing  brackets across the hole?

T

Tom....The tube sockets are mounted on  ceramic spacers off the bottom plate of the chassis...You will notice that the chassis is only about an inch deep....The blower is mounted on the back side ...Genuine RCA stuff....The 4-400 sockets were removed and the 813 sockets were put in their place...

OK, I see... the whole tube assembly drops down with the bottom plate and the chassis above has no fasteners to it at all. Interesting arrangement. I'll have to consider that when I build my new 813 amp.

I'm still trying to figure out what the db gain is for GG 813's.  If I can get at least 16db, I'd be all set with the SS driver I have.

T

Tom..great idea!!...There are several GG 813 amps in use in the Pacific NW....I believe there are 2 tube 3 tube and even a 5 tube model out there.   most of the ones I have heard on the air were built by Jerry K7LFE.   W7JHS has one(2 tube) and uses a Harvey Wells tbs-50 to drive it ..Check out his web site..there may be more info....Another 2 tube is used by W7JHU driven by a ranger...I believe JHU uses an attenuator to cut down the power on his ranger..

hi Tom and others ... I have used/built several 813 gg amps for ssb  ... at 2.5kV load to 450 mA with about 750 W out to 20 mtrs for a pair .... zero bias ...... requires about 30W drive per tube ... will make more but in power compression (going non - linear)

knew a fellow ham who called himself 'poverty radio' ... used a pair of 813 in gg with 4kV on 75 mtr with -9V bias ... claimed he could get 1500W out ( driven with a Swan 350) for about a year but the the failure was spectacular !

It takes all kinds ....   73 ...John

Hi John,

Thanks for the info.

Hmmm...   325 watts out per tube with 30w drive is barely 10 db gain.   Maybe that's what to expect with a pentode in "triode" configuration. 

I was doing some calculating and see that twelve in parallel would give about 168 pf plate to fil,  plus stray capacitance. All you'd need on 75M would be a tiny 3-30pf  vacuum variable for plate tuning (tweaking) ... :-) 

I have twelve sockets and plate caps. 

Twelve in parallel would equal 12 X 125W = 1500 watts dissipation. That's like a standard  8877, but without the noisy air.
I can see it now - a plexiglass front panel and a mirror behind the tubes.

Does anyone here have used 813's for sale?  I can use another seven  more tubes for the project.


Tom, K1JJ

Question:  I have a 7.5V at 75A CT fil transformer = 562W.  The twelve 813's requite 10V at 60A = 600W.

Will the 7.5V transformer using a 33% primary boost (=10V) handle the extra voltage?  I think the wattage (KVA) core size is OK, but worry about stepping up the voltage that much.

I plan to put the fil transformer on a PTT key step up where it goes to 50% voltage when in standby.

T

What company?

Al

Tom,
You will saturate a 7.5 volt transformer trying to push it to 10 volts. I was barely able to get 9.1 out of a 7.5 for the 4CX3000A linear.
I knew a guy who ran a pair at around 2500 volts and needed a fair amount of drive with a 100 watt exciter. 50 watt heater I bet they would do close to 500 watts PEP with 4 kv. The problem becomes output C with many in parallel. I suspect you would need an inductor ahead of the pi network.
Wind a transformer with a variac core to get 10 volts.
I bought an 813 last year marked bad. I showed the friend I got it form and noticed the pins very dirty. I cleaned it up and gave it to Bob RKW who said it worked ok. I'd like to stuff one in a Viking 2 and jack the plate voltage..

Yeah, that's a good idea about winding a fil transformer on a Variac core. I've done that a few times and always worked out FB.

Another idea wud be to find an old 12V batt charger transformer and Variac it down. But I like the core winding idea better.


Well, the P-F stray is about 14pf per tube, or 168pf for twelve.  Wouldn't that be a reasonable C1?  I have a tiny 3-30pf vac cap that I can use for fine tuning.

Oughta be a fun project.

T

Yes, Mr. Vu is right, I built an 813 GG linear 7 or 8 years ago using a pair of  813s.  If I remember correctly the plates had 2.2kV on them and it cruised easily at 600w or so. Drive power was around 60w to get the power level.  There was no input tuning.  Eventually it was cannibalized for the  new 813 rig.

Did the tube output C as the pi net 'tune' cap on a grid-driven, grounded-screen, 6-meter 4CX1500. Used a variable L in the pi net which functioned like a 'tune' cap...since there was no actual tuning cap in the circuit. Worked out well.

Your probably going to have a fair amount of stray C with a big dozen toob layout. Could add a small roller inductor in series with your main coil for some added 'tweakability'.   

http://stores.ebay.com/LYNNTRONIX-Surplus-Electronics

OK Bob - 60W to 600W is 10db gain. Guess that's all I can expect with GG 813's.


Jay:  Yes, I think the P-F capacitance and stray might even put the whole plate structure up to 190pf without adding external tuning.  It will be a monoband 75M amp, so once set it will require minor tweaking. C1 will want to be high anyway due to the low plate impedance.

I'm looking around for a big Variac core for the fil xfmr. Collecting parts.... :-)

T

Plate Z will be pretty low. A series inductor will raise the Z ahead of the pi network. A simple Pi network would have a small inductos since the Plate Z may be under 500 ohms. Layout will be critical. I wonder if it would be better to configure it as a traveling wave amplifier.

I'm open to design ideas, Frank.

I was initially planning to  put four tubes across and three deep in a big rectangle. Then run some wide brass or copper stock down the lines to bolt off the grids and screens directly to ground/chassis.   

For the bifilar choke I wud use a long string of ferrite cores with the two #4 wires run through. That worked well in my other linears.

I know your 4cx-250 1kw test amp is a traveling wave. Tell me the advantages and basic physical layout for it to work.

I think the traveling wave is a broadband amp maintaining 50 ohms along it's path?  How broad is "broad" when centered on 3.8 mhz?

Are we talking a class A1, grid driven config now?  If so, that would solve the gain problem, but make it more complex and harder to tame.


T

I've used Coleman glass in practice on a single 4CX5000 as well as a 4-1000.

--Shane

Tom,
I don't know of any NB application for a TWA but each tube is isolated from each other by a series inductor setting up a delay line with the tube C.
Just don't know you might surf and see what you find. They also make solid state TWA amps. Not very efficient in BB class A. I think we run about 6 to 7 KW to get 1 out.

That's what I thought - poor efficiency with little to gain in ham service.  I'll stick with the GG config and go from there.

T

hi Tom ... 12 - 813 in parallel would be a visual marvel but VERY difficult to get each tube to equally share the load ... at the very least you would need to use some resistance in the grids to ground ( or individual bias adjustments) to equalize the individual tube gains ... unfortunately this would tend to lower the gain even more ... i'm not sure what b+ you were planing to run ... getting the parasites under control could be a huge challenge ... maybe using 2 / 4 to drive 8 / 10 as a 2 stage amp with a different gg topology (the control grid tied back to filament or some impedance between cathode  and ground - see Bill Orr WCHB 14th or so for a 4-400 gg discussion) .... I think gg may be too difficult to do in one stage and if one stage is what you want, then consider grid driven (especially a variant of G2DAF) ... most interesting ...73...John

Some good points there, John.

Yes, I wondered myself about the difficulty of setting all the tubes to similar idle AND pull current equally under load. In GG for idle, that wud be tough cuz they are all fed with a common CT fil xfmr with diode biasing. To add individual diode bias wud mean separate fil xfmrs  or diodes in the fil leads which wud then upset the fil volatge... sigh.  New tubes would help the balance compared to random used ones, so that's why I'm looking at the Russian tubes.

Individual bias pots wud be the way to go in grid driven service. They wud be easier to drive with higher gain too.  I never really considered anything but GG to this point.


I didn't want to go grid driven cuz of the good chance of taking off - and it wud be a cleaner amp running in GG.  They could be neutralized, grid driven - wouldn't that be something.

I want to run 4KV to get the plate impedance up as high as possible and of course give it some kick.

I dunno. To see them under Plexiglas with a mirror behind them wud be cool. I also like the heat and quietness for Winter. But the technical problems make me wonder if it will be a waste of time.

I've always advocated one of two tubes max in a linear.  This wud be breaking all the rules... :-)

T

yup, this agrees with my experiences .... most folks ignore the G2DAF topology since the importance of the screen voltage filter time constant is poorly understood ... a lot of drive power is converted to screen voltage ... typical drive power of an G2DAF 813 is also about 30W / tube  with about 25 or so of those W as converted screen V ...The inportant thing is that the Varney circuit also has a 6 db or so distortion improvement over straight grid driven and approaches gg distortion performance ... the screen voltage could be generated by another method ... if you are interested, I will gladly share ...73 ...John