The AM Forum

I tore apart my dual 3-500 amp because it was constructed in such a way that the HV could be accessed if a person were determined to. Too dangerous for little children to be around.

I'm looking at building another tube amp though, this one with a much better enclosure. I don't want to stick to the conventional 3-500 pair though either. How about the 3CX1500 (8877)? The price is acceptable. I'm wondering about the tube's availability in the future. Are there any rumors of it becoming obsolete?

How about other tube options?

Jon
KA1TDQ

Many years ago, I built an amplifier using a 4X500.  Knowing that I might get bored and want a new toy sometime down the road, I cut a large square hole and mounted a 6 inch square aluminum plate over it with plenty of screws.  The tube socket sat on that.  The idea was that when I wanted a tube transplant, all I had to do was unbolt the socket plate and bolt in another to utilize some new tube socket.  I left room around the filament transformer to hold something different that might be larger.
I ended up dismantling the whole thing much later and using parts in other places but, with a little forethought, you can build a reconfigurable amplifier that would potentially hold an 8877, GS35B, 3-500Z or many other bottles. 

Just a couple of comments: doesn't the 3CX1500 have a relatively low grid dissipation power spec?  Also on the GS-35 is the socket for this excellent tube hard to come by?

The idea of a linear that has a sub-chassis that will accommodate different tubes is an excellent one - one that Ameritron successfully employs.  One only then needs to pressurize the sub chassis.

Al

3 washers and bolts with nuts make an excellent socket, if grounded grid is OK.   Works on the 35b as well as other tubes.

--Shane
KD6VXI

I had an RF deck that started out as four 813's in grounded grid, then went to four 4x150's, then went to four 4-125's.

My 813 rig has the tube sockets mounted on a plate with holes in it, almost like a screen, air flows up past the tubes, but any socket or sockets could be put on the plate.

I think its a very bad idea to try and make anything that runs any power or voltage small in size.

And for protection, I just put all the high power stuff in 6 foot tall cabinets with doors that lock.
In addition, you can kill the ckt breaker feeding the shack and even lock it out.

I had many nice cabinets at work I tried to get rid of here, they all went to the scrap people.

Serious concerns about preventing the gear from being turned on by children or the occasional snooping person could be helped by a simple key switch in series with the coil of a "main" contactor that controls all of the juice beyond the point where the power cable enters the cabinet. 

Alternately, a toggle switch up high in the top panel of a 6 FT cabinet out of reach of children could help. One of those military-type switch guards would be a nice touch and require a deliberate effort.

Get tricky and mount a reed switch behind an aluminum panel and have a little V shaped iron bracket on the front of the panel. A small round magnet salvaged from a miniature speaker, placed on the bracket with a pole against the panel, would stick in place there on the bracket and also close the reed switch on the other side of the panel. When not in use the magnet could be stuck to the side of the cabinet or anywhere else. No one would know and no key to fret over.

The contactor and line input fuses etc could even be enclosed in an internal small metal box into which the power cable goes after passing through the cabinet strain relief, so that if the cabinet door is opened there is no live 120 or 240V to be touched, maybe only 24VAC or low control voltage, fused.

Nothing is foolproof though.

That's true... nothing is foolproof.  But, I think this time I'll build it into a communications cabinet that locks.  I already have the 220 mains box that I can lock out. 

After giving more thought to the tube selection, I'm again leaning toward another dual 3-500 design.  It's cheaper and this'll be the third one that I've built.  I could incorporate again what I did with the first one for cooling.  I used chimneys and pumped air directly to each tube socket using PVC piping and a super quiet bathroom fan. 

I had considered buying a solid state Ameritron amp, but I just can't settle for 125 watts-ish carrier. 

Jon

Where have I seen this before?

Al...W1VTP
One tube socket for the GS35B is made by Raco, VA3YP.  I bought mine from him on Ebay for around $100, plus or minus.  Raco is a real craftsman, the thing is chock full of nice finger stock, and it even looks pretty.  He doesn't always have one listed, but they are available, as well as sockets for some of the other Russian tubes.  I run into him in the 80m DX window occasionally.
Norm W1ITT

Here is a box with most of the work already done for you, all really needed is a cheap way to get it from 3000 miles away.

http://www.ebay.com/itm/C120906-Henry-Electronics-3000D-RF-Generator-w-Eimac-3CX3000A7-Power-Triode-/391319393387?hash=item5b1c74146b:g:SugAAOSw~bFWMVJp

Yeah that's nice! A little far away though.

There's a ham here locally that I sometimes buy stuff from. He can probably source a good cabinet for me. It's amazing. The hamfests here aren't as big as the ones in the NE, but I've managed to accumulate two BC-610 plate transformers, and a Henry 2k filter choke.

Jon

 Gilroy is less than an hour from here.

 Having been to the Fall NEARFEST 3 times now I will say it is bigger than anything here in California but we have more swaps.

 Enjoy your posts, you build some interesting things.

Unless there are objections, why not add a third 3-500Z? So many amps have two, and then it's a little marginal for high power high duty cycle use.

Now there's an idea!  My components will definitely handle the extra load.  I'll just use vacuum variables this time around. 

I have an LDG autotuner for the input, so that's easy.  My only question would be about the output pi inductor.  What value do I use?  A pair of 3-500's has an output impedance of 2500 ohms, and using 3 would be less.  I'm using a BC-610 plate transformer, so Eplate is about 3100 volts. 

I laid awake last night thinking about how to construct this, and it's definitely doable.  Just put the plate choke in the center of the three tubes. 

Jon

maybe consider putting plate tune vac cap in middle ....

Amforum/index.php?topic=40736.msg297329#msg297329

The plate load resistance is a function of Plate E and I at your planned operating power.   There are lots of PI net calculators around.

Adding a third 500Z will impact the output capacitance & therefore the value for C1.  Figure the total output C of the tubes, then subtract from the calculated C1 value... with three 500Zs it will likely go negative on the higher frequencies.

Corrected the following:

The trick for this is to add a small inductance between the plate choke and plate blocking cap. This will have minimal effect on the lower frequencies but will offset the tube(s) output C on the higher freqs.

Have fun!    Bill  N2BC

 

On the topic of safety:  My 2 x 813 hb transmitter had micro switches on all doors.  These were wired in series with a contactor that had a hold-in circuit.  To bring up the transmitter a "start" button was pressed which engaged the contactor. After that the hold-in circuit kept the contactor engaged.  If at any time a door was opened, the line going into the whole transmitter mains was broken.  One had to close any door that had been opened, hit the "start" button and power was restored.

This had an additional benefit where if we had a brown out,, the contactor would disengage and therefore any main voltage swings were not imposed on the transmitter.

Jon

If you want to go with another tube. Just contact me.. I have quite a selection you might want to build with.. Glass or finned ceramic. Have both..

Hi Jon,

After watching you put the last 3-500Z amplifier together with 2X4s I figured it would only be a matter of time until you tore it down and started over...  ;D   I've done the same thing in many different ways.  

Check out the YC-156 tube. It's similar to a 3CX-5000A7 but slightly different fil requirements.  Both amplification factor of 200.  No socket required and uses 225 watts to light the fil and is probably the cleanest tube on the market. They used it for precision MRI work.  

With 3.5 KV on it, you can run it VERY conservatively at 2500 W out and achieve a 3rd IMD approaching -45 dB or higher, depending on how good your driver is.  CLEAN!   It's like an 8877 on steroids.  It would just laugh at AM KW service.

I know of someone who may part with a good pull since he never built an amp with it yet.

T

I thought the YC156 was the same as a 3CX15000B7 but had a 5000w cooler not a 3CX5000... ;)

I just went to a hamfest this morning and picked up a couple extra 3-500 sockets. Sometimes the parts you get dictate the project, so I'm going to go with (3) 3-500's. It would be nice to go with higher power, but my antenna system wouldn't handle it anyway. 350 watts-ish carrier is plenty for me.

I also got a nice ceramic form to build a nice plate choke on.

Jon

Yep, this is true. They are the same construction inside.  Amazing.  

The 3CX-15000B7 is very hard to find and costs too much new.

The 3CX-5000A7 is similar except  the fil is slightly lower at 175 watts.

A 3CX-5000A7 or YC-156 / YC-179  are great choices.  All clean, low fil and amazing performance.   The good thing is that the fil requirements, being an indirectly heated cathode, is efficient.  So if we run the amp at low power, no big fil waste like with a directly heated cathode.  The drawback is it needs a good 6 minutes of warm-up time before use..

T

The 3-500Z is also a very clean tube and three in parallel will do nicely.  Be sure to use air chimneys this time with a pressurized chassis or sub-chassis.

T

I have a plan to do just that. A friend back east told me that Coleman oil lanterns can work as chimneys. I'll have to Google the dimensions. If not, I'll just get the regular chimneys.

Jon

I once used lantern chimneys for a pair of 813s and it worked FB.

However, the key is be sure to find a set of lantern chims that will taper in at the top of the tube so that the air gets pushed into the plate cap structure. Otherwise the air will run straight past the glass without cooling the plate cap and seals.  This requires a precise height to the glass. I would just spend the money on real 3-500Z chimneys.  

The correct Eimac 3-500Z chimney is slightly shorter than a 4-400A chimney to compensate for the tube height difference - by about 3/4", so get the 3-500Z type to get the right air flow.

http://amfone.net/Amforum/index.php?topic=20186.0;wap2



ebay:

http://www.ebay.com/sch/i.html?_from=R40&_trksid=p2050601.m570.l1313.TR0.TRC0.H0.X3-500Z+chimney.TRS0&_nkw=3-500Z+chimney&_sacat=0

T

Ah, good stuff... and cheaper too!  God bless the Chinese.

Jon

I doubt you will need much cooling running three at 350 watts carrier.
I have three 4-400's in a rig I screen modulate and it does 400 watts carrier with almost no color showing on the plates and very little air flow.

A good rule of thumb is 1/3 of the plate dissipation for power output, which in your case would be 500 watts.
Under that, gentle air flow should be fine I would think.

Mayanoisse,  pickle and other jars can work as well.

A piece of string,  lighter fluid,  match and sink can cut to height.

With the added benefit of having a taper at the top.

With your having a complete two tube box adding a third was the best way to go.

With the added dissipation,  make sure you run the carrier up,  or at least the bias,  from time to time,  to blush the plates and getter your tubes.

PVC makes GREAT air director material.   No corrugated means max airflow through it at minimal noise.



--Shane
KD6VXI

I have a quiet bathroom squirrel cage fan with a 4 inch duct that I will use to pressurize a box below the tube sockets.  I'll just go ahead and do it right.  I'll make it so that I can put a filter on the intake to minimize dust buildup.  I'll also minimize components inside the box so that they don't collect dust.  I also have to make the box serviceable so that I can get into it once a year to remove dust.

The RF deck will be built on a steel 19" shelf and I'll cut a square hole to accommodate the 3 tubes, plus a little extra.  I'll then mount the box to the bottom of the shelf.  This would make things convenient in the future should I decide to use different tubes.  Just remove the box.  

That's a good idea about making sure the plates blush.  Either increase the bias on the cathode or run more carrier.  There would be a limit though for bias before you run into linearity problems.  Maybe 10 volts maximum.  My transmitter puts out 24 watts carrier, but I could adjust that if needed.  

These Chinese sockets/jars are cheap enough that I'll just go with them.

I've run a 500Z to 50 mils of resting current,  sometimes even lower,  for am operation.   The trick is to make sure you have enough carrier to make sure the tube self biases up to at least class B.

At 3.3kv, about 20 volts is good for the 500z.

There is a good thread about this,  started by Tom K1JJ iirc,  about this operation.

Honestly,  though,  having 3 tubes means you won't really need to worry about efficiency from a Pdiss standpoint.

I've seen 10 and 12 tubes on ten meters.   Three will be easy peasy from mf to 40.... 

--Shane
KD6VXI

I run 11V bias and 3600V in my Henry 2K-4.

Here is the PS Schematic in case you might be interested:

Phil - AC0OB

Here is a picture of the HV power supply under construction.  I wanted to build the power supply separately from the RF deck to make things simpler the next time I want to build something different.  Also, these will be just small enough to be rolled in/out of the walk in closet adjacent to my radio room.  This adds a little extra security by being able to be locked behind a door.  Obviously though, the closet door will need to be open for air circulation during operation. 

The blue lights on top are visual aids.  One indicates when blower/filaments are on and the other when HV is energized.

The RF deck will be a welded steel frame structure with metal on all sides, except for a plexiglass front. 

Jon

Massive. I guess you'll enclose with mesh or perforated sheet metal.

Say, who're the good looking pair with sun glasses in upper left of Pix?

Plywood. I'll leave a small air gap in the back. The front will have padlocks on the switches as well as a 240 service box with a padlock. The RF deck will use massive amounts of steel.

The good looking person in the photo is my wife. I was just along for the ride that day. She likes me because I'm a Ham radio operator. Hams are studs.

Jon

A small fart fan,  very low sonne,  in the top of your closet would probably be capable of exhausting your hot air.....

At least that created by the amp.   The hot air the amp amplifies,  that's the antennas job :-)

--Shane
KD6VXI

I knew someone would post a tube with HANDLES

Fred

That's a nice sturdy looking cabinet. The power transformer - a serious 2KVA one? very nice.  There's one like it here, a beast.
Will you use the blue CFLs to light the inside of the amplifier cabinet?

I've posted another picture of further progress.  What's left to go on front is switch lock covers for the switches and a voltmeter on top. 

Yes, the transformer is 2kva. 

It's tempting to put CFLs in the RF deck as well.  But from my last amp, the glow of the tubes is just the right touch.  Especially now since I'm going to use 3 tubes rather than 2.  But, I guess you could put a couple in not connected to power.  That way, when you transmit, the room glows even more!  But, as G.W. Bush used to say... "Na - ga - doit."

Jon

Looks like a fire hazard...

True.  Steel framing would've been safer, but it's a manageable risk.  It's always good to have a fire extinguisher in the shack.

Jon

I like it.  Just keep that fire extinguisher handy   ;D

Over the years, building many homebrew rigs and shaking them down in testing, I've had plenty of fires.  Resistors flame, capacitors blow, wires arc over and flame, transformers overheat, wire fuses arc and catch the surrounding stuff on fire, spark gaps get unruly, etc.  It does happen to all active home brewers at one time or another.

Using a metal cabinet is the best method. A second alternative is to line the critical areas inside with some aluminum sheet.

In your case Jon, at least put a smoke detector in the cabinet.  I use a couple in my shack above the rigs just as a precaution.

(I even got rid of all the Plexiglas and went to all steel / aluminum cabinets)

T

(http://www.amwindow.org/pix/jpg/w8ahb.jpg)

That's a good idea! It'll give you a head's-up if something starts to smolder.

Jon

The rf might set it off.

The power supply is 95% done.  I've attached a picture.

I was on the air yesterday and someone from Tucson heard me talking about the new amp.  He has a 17 x 17 x 7 unmolested aluminum chassis that would work perfect.  I'm heading down next weekend to pick it up.  It should fit 3 tubes nicely.  I still need to weld together the steel structure it will sit on.  It's perfect for the RF deck, but I still need to pressurize the bottom of the tubes and enclose the bottom "stuff". 

So, yeah... people can still hear you with 20 watts carrier!  :-)

Jon

No stain on the wood?
A nice harvest color with clear coat would look nice...

It looks good. Yes some finish and it would look like furniture.

Okie-dokie...

There you go, now maybe add some brass hardware, or at least paint the electrical boxes gold hammertone...

Now you're just being a silly-willy  ;D

On to the RF deck!

Jon

I just ordered the last parts for the RF deck (minus the toobs... $600 for three 3-500s, ouch!). 

Actually, I just wanted to post a picture of this thing with the lights on.  I like it.

Jon

I'm trial fitting everything.  The ceramic insulator on the right will be a homebrew plate choke.  I didn't have enough room in the chassis for a massive loading capacitor, so I'm using a smaller value one in combination with a doorknob capacitor.  The Ruskie vacuum capacitor was new in the original sealed plastic bag with the manufacturing stats. 

I'm using a Home Depot PVC box to pressurize beneath the tube sockets. The whole thing is on a 4-foot high welded steel frame.  The 12" x 12" PVC box will hold (3) 3-500's nicely in a triangle pattern.

Jon

I got the holes drilled and I'm just waiting on my sockets/chimneys to arrive from China.  I'm hoping that they didn't get lost in the mail... it's been like over 3 weeks now!

I did order three high performance plate caps from www.73cnc.com.  He has a YouTube video comparing his custom plate cap to an ordinary plate cap, and the difference is remarkable.  He takes temperature crayon dust that melts at 225 degrees F and places it on top of both plate caps.  Then he cranks up the power.  The dust on top of the ordinary plate cap melts very quickly and the other doesn't melt until about 1.25KW. 

Three 3-500's draw 45 amps of filament current, so I'm going to use two MFJ 30 amp filament chokes in parallel (Also waiting on those for delivery).

Jon

Hi Jon,

Shipments from China have been disrupted for a few weeks. It is Chinese New Year time again.

73,

Jack WA9NQW

Will that "half" the inductance of the chokes since they are in parallel?

That's true, I didn't think about that.  MFJ lists the frequency for a single filament down to 160 meters.  My guess is that two in parallel would still be fine for just 40 meters. 

I've attached a picture of the homebrew filament choke I used with my last linear (using just a pair of 3-500's).  The ferrite rod is 6-3/4" long and 5/8" in diameter.  The wire is tightly wound solid #12.  I think it'll handle the 45 amps fine enough, I'm just worried about the voltage drop.

Jon

I've said it before, and I'll say it again... God bless the Chinese.  My tube sockets and chimneys just arrived.  They are absolute masters of packaging efficiently.  I had to destroy the packing boxes because they shipped everything in tight boxes with expandable foam.  But, it made it from China a-okay!

Jon

I didn't have enough room in the chassis for a massive loading capacitor, so I'm using a smaller value one in combination with a doorknob capacitor.

Hi Jon
Take care with this set-up, The caps have relatively high capacitances so the interconnection wires should VERY short and better be copper tape to reduce the inductance. I had several problems with parallel resonance at higher frequencies this way that gave a high load impedance, high harmonics or incorrect loading.

So I had to remove the fixed caps and went back to a high value loading cap.

I'm definitely going to use copper strapping on the output network.  And the way things worked out on the layout, the lengths aren't going to be too long.  The loading capacitor lead lengths in particular are going to be very short.  Also, I have a little bit of fluff-forgiveness factor built in since this will only be used on 40 meters and not the higher bands.

I've got most of the major components mounted now.  I'm using two Hammond transformers in phase for the filament power.  Heck, if I used them out-of-phase it'd be a quick show.  And the bias will be around 9 volts with 12 1kv/3amp diodes in series.

I'm waiting on one more part to arrive and then I'll whip out the soldering iron.

Jon 

I'm about 90% done except for buying the tubes.  I need those to measure the placement for the parasitic chokes.  I have another day of wiring underneath the chassis and that'll be all done. 

I would've made the plate choke longer, but I ran out of #20 wire.  I ended up with 6" long and 1" diameter.  At 31 tpi, that works out to be about 135uH, or about 6200 ohms on 40 meters.  It's good enough, so I'll just go with it.

Jon

Very pretty, Jon!  See how good your building skills are becoming?   A few rigs and you're an expert.


Questions:  

1)  Did you leave room for a turns counter for the vac variable?  A turns counter is fast - counting revolutions is slow.  


2)  Is that air variable the loading cap in the back? About 600 pF?    You have 3 tubes which makes the impedance even lower - if so, you may need up to 2000 pF for 160M. 1200 pf for 75M at times.  Maybe you plan to pad it.

( I see a couple of fixed caps back there)


Use a heavy duty rotary switch to add in incremental stages of padding, if that's the way you go.  Don't use TV door knob caps. Try to get as much of the air variable meshed as possible when in use.  (compared to the % of padding)   The air variable is much more efficient for circulating current and heat than most fixed caps.  That is a resonant circulating circuit where Total RF current  = Q * I.

T

Jon
From where did you get that mount for the vacuum variable capacitor ?  I have a few nice ones without mounts and, as simple as they look, it's not always easy to fabricate something that pretty.
Norm
W1ITT

Thanks Tom! 

To answer your questions, this will be used on one frequency on 40 meters so I don't need to count turns on the vacuum variable.  Just tune it and park it. 

That is a 150 pf loading capacitor in the back that I have paralleled with a 680pf (I think) Ruskie doorknob cap.  Again, once I find the right value, it'll be parked. I went this way because I ran out of room in the chassis for a larger sized air variable. 

Norm:  I was on eBay at the right time.  I found those vacuum variable mounts from a Ukrainian seller.  He got them as a pull from old military equipment over there.  I overpaid for them (I think $65 shipped), but they're perfect for the job. 

Jon

In case it has not been mentioned and the cathode circuit not completed, three 3-500Z in grounded grid have an impedance of 38.33 Ohms according to the attachment.

That's true.  A pair of 3-500s has a nice 50 ohm impedance match, but three don't.  I'm going to use an LDG auto tuner in line before the amp. 

Jon

All done except for buying the tubes.  Here's how it'll look in the closet.  The chassis does have a top that I'll put on once I insert the tubes.

Jon

I am in awe of this build, it truly is a thing of beauty and not many things impress me except when something is designed very and look nice when it is finished.  Do you have an estimate what the amp would cost for someone that has an empty junk box. For now, I will continue to use my  Drake L4B and dream of a home built amp at night in my dreams.

73 and Good Luck with the amp,
Kevin - KG0MN

Thanks Kevin!

Well, it still wasn't cheap.  I bought everything for the project except the parts for the HV power supply (I already had the plate choke, filter and caps).  After I buy the tubes, I'll be in it for over 2 grand I'm sure.  I'm too scared to add it up. 

It's still somewhat of a bargain though.  The Ameritron dual 3-500 amp goes for over $3000.  And you get all band, compact size and a factory warranty.  I only operate 40 meters though and I wanted the extra tube.  Plus, it's a little more rugged than Ameritron, which is good for AM service.

OR...

You could go a lot cheaper for the same power with class E.  My building ability just isn't there yet.  I'm still stuck in the building furnaces stage.   :)

Jon

Let's see:

 $2,000 ... Parts
-$1,000 ... Fun Factor discount
--------------
 $1,000 ... Total cost

Sounds like a bargain to me!  Enjoy Jon  Maybe we'll hook up on 40 some time

Al

Ha! True. 

I talked with Steve one time using my old 2-holer, so I'm sure I'll be able to make the trip with 3.

Jon

The difference between 2 tubes and 3 tubes is about 1.5 dB.... :-)

You'd have to go to 8 tubes to see a meaningful 6dB increase. (1 S-unit)

You'll be fine with 3 tubes.  Once you get above  1 KW, it gets harder and harder to get meaningful increases.  Just like adding horsepower to a drag car. Diminishing returns.

T

   Question: Doesn't the gain stay the same whether it is 1, 2, or 3 tubes? I've never used a 3-500Z, but I'd presume something around 10-13 db gain depending on circuit conditions. If the driver can only drive one tube to full output, then adding 1 or 2 more won't do much. A tuned input will help increase the gain. Perhaps the LDG tuner if close enough to the tube cathodes will act as a tuned input.

Jim
Wd5JKO

Yes  that's right - if the high voltage, idle current per tube, Q and general circuit parameters are the same, then the amplifier stage gain remains the same when the number of tubes is increased.

I wasn't referring to stage gain. I meant that by increasing the number of tubes the amplifier would have more power output capability before flat topping -  AND of course, it would take more proportional drive to do it.  IE, twice the tubes would require twice the drive to double the output. (3dB more power out, with the same stage gain of 13 dB or whatever -   and 1/2 the plate load impedance)


BTW, Jon, I have run an outboard tuner into GG amps like you plan and it has worked FB. Be sure to use as short a coax cable as possible, like less than 2'.  Even mount the tuner inside the amp near the sockets if possible.  A 'T' or 'Pi'  tuner circuit works well for 50 ohms into  30-100 ohm type loads.   A  Q=3 or so is all that's needed.

T

In regards to an external tuna. 

Your efficiency on the upper bands will be helped even more by putting 100 or so pf at the tube socket (or,  appropriately sized caps divided up to equal about 100 pf).

This moves the return pulse path to the cathode pin  rather than down your tuned input coax.

This being a 40 meter mono bander it won't help much,  but maybe some 2 to 350 puffers  (or,  75 pf per fil pin on this 3 holer)  may help.

--Shane
KD6VXI

That closet is going to be warm in the winter and a great place for drying fruits and making jerky in the summer. How will the waste heat be dealt with?

I had to use an RF attenuator in line between my transmitter and my old dual 3-500 linear.  My transmitter puts out about 22 watts carrier, and I had to do that in order to give me some headroom.  Now with the three tubes, I should just be able to drive it directly and not have to worry about headroom. 

I'll mount the LDG tuner directly at the input to the amp. 

Heat in the closet could be a problem.  I'm definitely going to keep the door open during operation.  I chose the closet to keep my radio room neat and to keep my little ones locked away from high voltage.  The closet is a good size, but if keeping the door open isn't enough I'll put a fan on the shelf to blow the heat out.  The intake for amp blower is on the bottom of the floor. 

Jon

I just ordered the tubes and I bought the RF Parts brand 3-500.  They come with the 3 year warranty rather than the 2. 

I have one last concern though:

My plate caps were machined to fit directly on the plate pin.  Is the plate piece you see in the picture removable on the RF Parts brand tube?  It looks like there's a set screw in some pictures.  It would really suck if my plate caps wouldn't fit. 

Jon

I forgot  size,  Jon,  but yes.   A teensie weensie (I believe that's the military term)  hex wrench will expose the anode pin.

I've never checked the Chinese tubes for pin size though.   

Show off your seckzi anode caps!

--Shane
KD6VXI

How's this for sexy?  I'll install them when the tubes arrive.  I want to mount them as best I can to eliminate mechanical stress on the tube, so I'm patiently waiting.

The tubes should be here Wednesday or Thursday, and then I need the assistance of my lovely wife for tuning up.  Transmit switch in one room... amp in the other. 

Jon

my plate caps would not go on, very close to fit but just would not go all the way on. I clamped the in a vise, one at the time and drilled the out one size up. Just make the hole a c hair bigger and fit perfect.

Jon, what a neat looking project!!!!!!  Way Cool! 

The Chinese sockets/chimney's and Ruskie vacuum variable w/mounts are pretty dawggoned sweet!!!!

Can't wait to hear it strappin down into Tucson on 7293 in the mornings!

Best 73's
Geo W8VG
Oro Valley, AZ

Hey George! Yeah, I'm hoping to put out some serious power soon. Tubes arrive tomorrow, and then whenever I can fit in time for testing. Work gets in the way...

Jon

...and power!  I'm getting about 365 watts carrier.  Had great audio and signal reports from Tucson, Los Angeles and Las Vegas.

https://www.youtube.com/watch?v=Ns7FshDPrSs (https://www.youtube.com/watch?v=Ns7FshDPrSs)

Jon

NICE! Triple threat.

Maybe I'll hear ya now Jon....   Lol.

--Shane
KD6VXI

Ha!  Yeah.  I've heard you on 40 a couple times, but did't try to talk because you probably wouldn't have heard my little 22 watt transmitter. 

Here's a little YouTube video that my wife shot while I was transmitting.  You can see the linear in all it's glory.

https://www.youtube.com/watch?v=e85oJAjfVkU (https://www.youtube.com/watch?v=e85oJAjfVkU)

Jon

The correct term for that modification is an "RCH"...  ;D

   

  Very nice amp !! What 40 meter net?? Wonder if you would hear the Bay Area??

This neck of the woods,  we prefer them blonde lol

Or,  nonexistent!

--Shane
KD6VXI

With that amp, maybe we could hear you in TX on the Sunday 7160 AM round table, vaguely from 11AM to 1PM Central.

I'm going to Vegas next Sunday, so I'll listen out the following week.  "Viva Las Vegas, baby." (In my best Elvis voice).

Jon

Wow. I'd never figure girls like that  are on 6m AM!

klc

They are all standing in front of a giant 3CX3000.

This is remarkable!  Great build and great thread.  I enjoyed the ride.

This is grounded grid, but it think I'll throw in that trying that with a low drive high power class C stage can make the meters go as crazy as an outhouse rat until it stops. If it stops.