The AM Forum

Hello,

I had bought a home brew amp that uses two 813's.  The power supply is huge and is separate from the Deck itself.  Actually the supply is so heavy that it is on wheels.  This amp is in storage at the moment.  Maybe later I can go there and snap a "Pic" of it.

Anyway, it was designed for SSB for 1KW output.  The supply output is somewhere around 2500 volts.  I think it has 6 or 8 large caps that equal roughly 45 pf altogether, in Series of course.  I had tried to use it on "AM" and ended up blowing one of the caps!  A very loud whistle letting out all the steam!

Is it possible to covert this amp in a way that it can be used on "AM" without any crazy redesigning the whole thing?

Thank you,
Ken



 

Ken,
   I can't help you with your question but, as I am building a 2x813 amp now I sure would like to see some pictures of yours.

Rich

Hi Ken,

2500 VDC  should work just fine in linear service.

45 pF on what band, 40 M?  

It would be of great advantage to replace those fixed plate tuning caps with one big single variable type. Many of the doorknob types will explode, if that's what is in there now.

Any RF linear designed for ssb is already set to run AM linear (or any mode for that matter) as far as biasing and tuning are concerned. The only problem may be getting adequate cooling for AM, if run to full power. The tube plates should not show any color if they are graphite.  I have used lantern chimneys over 813s to provide good air flow using a modest fan.  Just a small breeze does wonders for power capability and seal longevity.

Post a few pictures and we'll go from there.

Tom, K1JJ



 

Instead of 45 pf I think he meant to say 45 microfarads, referring to a collection of electrolytics in the HV supply.  That would best explain the pop and whistling sound.  The characteristic bouquet was not mentioned.

 ;D  Yep, that makes more sense.

Ken,

Just to be clear, the filter caps would not blow just because the linear and power supply were running AM.  Though there is a chance that some RF was leaking into the power supply through the linear plate choke, however. But most likely the filter caps were old, dried out  and needed replacement anyway - and should work FB when refreshed new.

T

Hello Rich,
I would be glad to take some pics.  If I remember its pretty basic.  Remember the deck is separate from the supply.

I will try to get to the storage this weekend.

Hello Tom,

Thanks for the reply. 

The Caps are those big can types not the door knobs.  When I say 45 PF altogether in parallel, I mean I added all the values of the caps using a capacitor calculator program here on the net.  I think this amp was built for 10-80 without the WARC bands in mind?

I will see if I can post some pics this weekend.  Oh, the owner had said when I purchased it way back when, it doesn't have enough capacitance to work on "AM".  I really didn't know if he met in the circuit with the can capacitors or not?  As I mentioned I did use it on "AM" and that is when one of the "Caps" had blown it's top!  Also I am talking about the "Caps" in the Power Supply.

Again Thanks.

[/quote]

Yes that is correct!

I stand corrected!

Thank you.

Oh!  That sounds great!  I will have to look for some new "Caps".

Although the owner/builder said there would not be enough capacitance for "AM" ???

What could he be talking about there?

As always, Thank You.
 

Ken

Perhaps what the previous owner meant to say is that there would not be enough power supply "capacity" for AM.

That is, the average current drawn from the power supply (averaged over several minutes) will be much higher in AM operation than it will be in in SSB operation. As a result, the heating of the HV power supply transformer will be significantly greater in AM operation. The transformer will run at a significantly higher temperature during "old buzzard" transmissions... shortening its lifetime, at a minimum, and, perhaps causing it to fail very quickly.

AM operation is very tough on linear amplifiers... even if the carrier level power output is set to be lower than 25% of the peak power output specification of the amplifier.

In SSB operation (with normal voice characteristics), the average current (averaged over several minutes) drawn from the power supply will be just a little more than the bias current for the output tubes + the current drawn by the power supply bleeder resistor.

In AM operation, the average current drawn from the power supply will be around 1/2 the peak current. I.e. the output tubes will draw 1/2 the plate current, at carrier, that they will draw on 100% positive peaks.

Stu

Hello Stu,

I have always known "AM" is rough on amps due to the constant carrier but I never thought of it this way for this situation.

The supply transformer is huge and heavy.  Is there anyway of knowing if the supply can take the current if there were some changes for the purpose of "AM"?

Maybe some info on the transformer?  I don't know if there is any information on the transformer or not. (Stamped Plate)

I definitely need to go to storage and check this out.

Thank you Stu.

About 100 watts carrier output in amplifier service?

I made one with four 813's and it was good for about 200 watts carrier I think.
Lots of heat.

Over the years based on practical on-air experience and testing, I've found the following rule of thumb generally applies to plate dissipation vs: power output for AM linear operation:

Simply take the plate dissipation and divide it by 2 to arrive at the maximum AM carrier output to run the tube on AM.  This assumes adequate cooling for the tube and its seals.


Based on this rule:

A pair of 6146Bs in linear = 35W plate dissipation  X 2   / 2  = 35 watts carrier output.

Quad 811As are good for about  130 watts carrier output. (65 watts X 4 / 2)  Like in a Collins 30L-1

A pair of 813s:  125 W X 2 / 2 = 125 watts output carrier. (An 813 is actually good for more than 125W plate dissipation  with some air, like maybe 150-160 W diss)

A single 4-400A = 400W / 2 = 200w out.

A single 4-1000A =  1000 W / 2 = 500 carrier out.

Again, these are maximum, full strap parameters and it assumes the power supply can supply the peak power (X4 or X5 carrier).   I would normally not run the tubes this hard, and de-rate the above figures by 20% or so for better longevity. Lots of air is recommended for whatever is done in AM linear. In addition, a linear amplifier needs to be loaded very heavily for clean and high peak power, thus, the efficiency will be reduced even more  (more heat).

T

And that assumes good efficiency of the RF deck.
Higher voltage and less current often improves things for me.

Screen modulation is about the same.

    If the 813's are in grounded grid, then some of the driving power will feed through which will add to the power output. With forced air cooling and chimneys, perhaps 150-200 watts out are obtainable at the expense of reduced tube life.

    My Central Electronics 600L with a grid driven 813 will do 100 watts out on AM with one tube and still be able to modulate 100%. That said, the graphite anode 813 is blushing red. In that amplifier on AM, 70 watts AM out is without any blush, and a better place to be.

    A pair of 6146B's plate modulated should do 125 watts AM....but here the efficiency is twice that of a linear amplifier. Imagine what a pair of 813's running class C with plate modulation will do.... :o

    We look forward to seeing that 813 RF deck and power supply.

Jim
Wd5JKO

"Is it possible to covert this amp in a way that it can be used on "AM" without any crazy redesigning the whole thing?"

Why not change this ssb amp to a grid driven class C AM RF deck and build a real plate modulated transmitter with a high level modulator? I guess that's "crazy"? I've done it before with 4-250s and 813s Rf decks that had been in grounded grid configuration, if you can handle it? Grounded grid AM operation of a pair of 813s seems to be a huge waste of 813s for AM operation to me, same as screen modulation of such tubes, unless you have no other AM txs there, or don't have access to heavier rated parts or inclination to take that project on, etc. to do such a refit.

Its a free world of experimentation of course. Have lots of good spare tubes there. You may need them. Just my opinion.

Al VE3AJM

I was never fond of running a linear in AM service, a huge waste of power it seems.
Two 813's will do 100 watts carrier in linear service if you don't beat on them, but will do 600 to 700 watts carrier plate modulated with less heat generated in the RF deck. 2400 watts pep or more.

But you need a modulator, and the mod transformer introduces frequency response issues and lots of phase shift unless you get a very good one.
Good ones for that power level are not easy to find.

A flex or some such nice low power exciter into a big amp can be very clean and flat.
Screen modulation can also be very clean and flat with no transformers in line at all.

Linear and screen modulation operation also do not need the extreme voltage components in the RF deck, the plate voltage is the maximum voltage the deck gets to.

Run 813's at 2000 volts in plate modulated service and you could see 5000 or more volts on peaks.
Run them at 2500 volts with screen modulation or in linear service and the most the deck ever gets to is 2500 volts.

Not sure how clean 813's are in linear service, but they do not seem to screen modulate well.
They plate modulate very well.

It is very easy to tune a plate modulated final, linear amps and screen modulation are more involved.

All Good stuff here to consider and most definitely a good learning too!

Maybe I should had mentioned that I don't have any real experience with iron and such.

Actually the reason I like "AM", is for the leaning!  You Guys and a like on "AM" actually talk "Meat & Potatoes" when it comes to radio!  So I am all ears to listen and take advice. 

My collection of Iron is next to none, so before going out and searching for materials I need to understand how things work when they are put together.  I recently purchased a BC1G that hasn't be converted to the Ham Bands.  And so it sits until I learn more about it?

Anyway I am listening, trying to take all of it in!   

Tomorrow I will take some pics of the deck and the supply.

AM and some QRP guys are the only ones building anything for the most part, other then maybe amplifiers.

We get to fool around with vintage gear, home brew, class E stuff, old buzzard antenna tuna's and sdr's along with all the modern radios.

You find some all vintage, even all pre ww2 stations, all home brew and all tube stations on AM.
Gives people something to talk about besides complaining about their gout or the government.

http://www.amwindow.org/tech/htm/813/813.htm (http://www.amwindow.org/tech/htm/813/813.htm)

So I went to storage a day sooner!

I am having problems loading three pics at a time...going to try only one?

Should be the back of the deck, okay and Top!

Bottom of Deck, and Filament transformer.  The two are the same in the bottom of the deck.

Front of Supply.

Inside Supply....Iron, caps...and so forth.

I should had took a pic away from it more.  It doesn't look as big as it really is!

I have more detail shots of the bottom of the deck if anyone wants them I can send them to your email address.

I figure no one wants all of them here?  But if so I can?

Old buzzardly but some good components and well built for the most part.
Looks like it could take plate modulation as well.
That looks like a bc610 transformer...

It looks like they ran high voltage to one of the meters, be very careful with that, it should be changed to not have high voltage on it.

This does look interesting.  Is this some sort of Modulator/RF Amp Deck?  Why I ask, it looks as if one would drive it with a separate transmitter where the 5-10 watt drive input is located?  Then there is the audio input that is throwing me off?
Where the 5-10 watt input is located, is this maybe where a VFO would be inserted?

I am Still learning here...what seems like a long ways to go. ???

That's a heck of a power supply. More than enough for AM on that amp, so you will get good regulation.  Looks like a nice grounded grid amp.

some random thoughts.

Looks like room for 1 or 2 more 813s even if you might have to move the fan and fil choke. The amp guts are big enough for legal limit. Power supply looks like it too.

Fil. choke is a 15A rating. One more 813. Transformers big enough for one more? That would make 187 Watts carrier/750 PEP.

Is there room to put the fan inside the lid but above blowing down directly on three or four 813s and still clear the plates and everything inside? The 813s have a lot of plate capacitance but it may not be an issue except on 10M. RF shielding could be a fan guard on the top of the lid w/ star washers.

A thought if you are really power-hungry, use four 813s, they are fast heating. To avoid overheating the filament choke and transformers, you could very softly start the filaments with a 1 second electronic ramp each time you key up (before HV is applied) and then run 4 tubes, transmit a short time like 1-2 minutes. Use a max. 50% duty cycle on transmit/receive, so the choke and transformers would stay cool, and all should be OK. -If you don't get too big a filament voltage drop at the socket.
"Horse Race" the amp. - but that's just a nutty thought. (sorry, been consulting a CB nut on his cheater). puts beans on the table. ahem.

note to self -Isn't there an old warning though about not running color on graphite plates?

Hello Al,

I would like to do whatever I can to make it all work on "AM" be it on 75, 160 or perhaps on 40 but I don't have the materials or the expertise.

I could search for the materials if I knew exactly what I needed, but then there's the expertise and lack of experience?

Right now I just need to keep it simple until I learn more of whats going on.

I wish I could make more of it though?

Thanks Al.
 

  

If this is the case, how would one go about connecting a meter to show the high voltages and would you have an idea why someone would had done this in this way?  Just trying to take all this in.

Hello Patrick,

Adding another 813 I could handle but having to change to many circuits to make all this happen might be?

Are you saying I could just drop in another 813...a thought just came to mind, would that mean I would need another filament transformer as well?  Looking at what is there, I gather the two filament transformer are there because there are simply two 813's!  One filament transformer per each 813? 

My original thought about this amp was to get it working on "AM", meaning using it as an Amp still, but on "AM".

Is this your intentions when you mention adding another 813 or two or are you suggesting converting it into a transmitter?

The issue here is , I don't have the experience yet to do a whole lot, but I am not afraid to experiment either?  I am mechanic incline I guess one would say.  I believe I do well on my soldering skills, I just don't have the head knowledge! (Darn! LOL)

Anyway I am still... "All Ears" !

Thank you.

Hello Tom,

Maybe this is all I need to do, change all the Caps?  It can't hurt anyway.  Would it be better to look for larger voltages then what is written on the original Caps?

Thank you Tom.

Hi Ken,

Yes, if one cap shorted, then they are probably all old and dried out, ready to go south -  and should be replaced as a group. It is always good to replace with higher voltage ratings and larger total capacitance values since it will make the supply more robust and have better regulation.

Another idea is instead of adding two more 813s, just pull out the existing ones and install a single 3-500Z. That is the cleanest tube going for linear operation (-40dB 3rd order IMD)  and would handle the increased heat. (500 watts dissipation = ~ 200 watts carrier out with the right plate voltage).   3KV works best with 3-500Zs and would need a chimney and air.  These mods may be more advanced  than you want at this time.  Just some food for thought to stretch.   I realize you are leaning towards staying with the 813s which will work FB too.

BTW, a simple parallel resonant circuit (Q of about 3)  from the RF input to ground will make the amp easier to drive and a few dB cleaner.  There are many on the web for reference. You can always add this later.


T

Thank you for the pictures. I think you have some good equipment there to work with.

I would suggest that you restore what you have to good working condition before making any modifications. I would give everything a good cleaning, a dirty power supply could lead to carbon tracks and shorts.
After cleaning I would take a lot of quality pictures for reference.
Then create accurate schematics of the RF deck and the PS.
If it was built as an ssb amp then get it working on ssb first.
Understand what you have before moving forward.

Of course there are deadly voltages there. Build a shorting stick. I also suggest buying a high voltage probe for your volt meter. They are not expensive.

I think at the point you will be in a better position to take advantage of some of the expert advice you have been getting here.

Rich

Hello Tom,

Adding all the "caps" capacity 240uf each in series equals 40uf with each having a 450 volts each handling capabilities.

My question here is, would it be better to add a bit more capacitance...say 45uf instead of the 40uf?  

Also would it be better to go with a higher value capacitor at 450 volts and use more then 6 of them so the value would equal the needed capacitance but making the total amount of voltages equal higher?

For an example: 390uf at 450 volts times 9 each would equal 43.3333uf and the total voltages adding up to 4,050 volts instead of having 6 in parallel equaling 40uf at 2700 volts.

Ken

Rich,

That sounds like a "Sound" idea!  I am already looking into some new "Caps".

There are some great ideas here, so after getting the amp back up and running and taking more pics and figuring how to draw up a schematics will be a good start.  This way if I do go another direction and it doesn't work out, then maybe I still can put it all back to its original build?

Thank You Rich
   

"For an example: 390uf at 450 volts times 9 each would equal 43.3333uf and the total voltages adding up to 4,050 volts instead of having 6 in parallel equaling 40uf at 2700 volts."


Hi Ken,

Yes, you have the right idea. To achieve  4 KV  of  capacitance voltage rating would make it bulletproof.  The difference between 43 uF  and 40 uF is insignificant, but the good news is they will be brand new and rated X2 your operating voltage which is what I normally like to do here.  Make sure your bleeder resistor(s) is working.   Be sure the voltage is reasonably split amongst the capacitors in series. Are you using separate bleeders that can double as equalizing resistors for the caps?

Rich's ideas to build a shorting stick and buy a HV probe for your VOM are important.  In fact, you should spend a session on defense and figure out ways you could get electrocuted and how to prevent it. Things like walking into the shack drunk, the cat starts pawing the rig, safety HV aids you need to troubleshoot it, etc.

Normally there is no reason to have an operating rig (with HV on) out of its protective case.  However, I have run across a few times that needed it. Once I had RF arcing that needed to be located. It plagued me for days when the cabinet was on. I ended up taking off the case, putting a large mirror behind the rig and turning off the room light. I stood a few feet away in the front - at a safe distance and keyed it up. It's a crazy idea, but I located the arcing in less than a minute - fixed it.

Don't sweat the fear of getting it working right. A grounded grid linear amplifier is the easiest amplifier to get working. Simple design and inherently very stable. You should not have any problems once you learn how it basically works.

T

Hello Tom,

That is great news!  I have a source for 9 of these at 450 volts so will start with these.

Also I do hear you on the dangers of the HV's and Rich's idea of the HV Probes and the shorting stick.  (Thank you Both)

Another thing you had mentioned....

"Another idea is instead of adding two more 813s, just pull out the existing ones and install a single 3-500Z. That is the cleanest tube going for linear operation (-40dB 3rd order IMD)  and would handle the increased heat. (500 watts dissipation = ~ 200 watts carrier out with the right plate voltage).   3KV works best with 3-500Zs and would need a chimney and air.  These mods may be more advanced  than you want at this time.  Just some food for thought to stretch.   I realize you are leaning towards staying with the 813s which will work FB too.

BTW, a simple parallel resonant circuit (Q of about 3)  from the RF input to ground will make the amp easier to drive and a few dB cleaner.  There are many on the web for reference. You can always add this later."
 

I guess after I get everything up and running I'll take a real hard look at all the ideas and then go from there.

With the more voltages from the new "Caps" when installed, do you think there is a chance the amp might work on "AM" ?

Or will I still be at square one not having enough capacitance in the supply?  I am not sure if it is the voltage or the capacitance to be concern about in the supply?   I just can't stop remembering what the builder said about not having enough capacitance for "AM".

Ken

I also think its a good idea to get it working as it was intended to work as a first step.
Then you can decide what you want to do with it or the parts.

As an amp for AM, its no good, not much power out stock, no real difference over a dx100 or other 100 watt carrier rig.
Great as an SSB amp.
Could be made into a class c plate modulated deck without too much trouble.
Not so easy for someone just getting into things and no junk box.

For an amplifier to be worthwhile on AM it should have a pair of 3-500Z's and a very robust power supply.
That will do 300 watts carrier out, a bit stronger of a signal then the 100 watt dx100.
Needs 220 volt outlet in the shack.

As a plate modulated rf deck you need to scrap the entire thing almost and build bias, screen, protection circuits, and a big modulator with a good mod transformer.

Not hard with a big junk box of parts and a lot of research in designs.
Building something is not easy, it takes a LOT of parts, some hard to find.

The old Bill Orr handbooks are VERY good at showing designs, rigs, and info about building them.
Everything you need is in those handbooks, except all the parts....

From the pictures, it looks like high voltage wire goes to one of the meters on the front panel.
If the plate voltage is on that, its a VERY bad setup.
You can put the plate current meter in the cathode circuit nad not have 2500 volts on the meter.
You can measure cathode current, or make it so the screen and grid current do not read on the meter by returning them above the dropping resistor in the cathode circuit.

2500 volts on the meter can arc through if you was to tap the glass and kill you.
2500 volts will be on the meter movement and even the pointer.
If you run it that way, it gets recessed behind glass so you can not touch it, some old rigs were built that way.

Also, I do not like electrolytic caps in series at high voltages.
You can find/get a nice 3000 volt oil filled cap that will last forever.
I have some that were old when I got them 30 years ago and they still work fine....

Hi Ken,

Yes, the amplifier will work just fine on AM with 40 uF of HV PS capacitance. That is plenty of "capacity reserve" to give decent regulation on AM. We must remember that AM has a build-in bleeder resistor effect due to the constant carrier. It's like pulling down an extra 200 ma or so of bleeder current which will help a capacitor input power supply better find its sweet spot.  (This assumes that the transformer can handle the average and peak currents - and yours seems pretty robust). Your planned capacitor voltage rating is X2, more than enough as is.

In contrast, on ssb we have a rather small idling current in class B with huge peak current swings that will cause the regulation to be more erratic with the load range.  So, you should be fine on AM.  If not, you can always add a filter choke to the power supply to make things even stiffer under varying dynamic current demands. (Or do I see a gray choke in there already?)

Like Brett, I'm not a fan of using a string of electrolytics in a power supply over say, 1200 volts or so, but it is commonly done in ham amplifiers for years and still done today. Just make sure they are overrated like what you plan and they are relatively new stock.  I use oil filled caps - or I just love using those compact "photoflash" caps. They are commonly found at 51 uF @ 5KV. I've used them for decades and never had one blow out.  They are a little smaller than a loaf of bread and might do the trick for you FB if you decide not to use electrolytics. One will do the trick.  I think the Russians still sell them. I've seen them on e-Bay too.

As Brett suggested, to measure high voltage, build a string of 1 meg resistors (HV divider) and tap off at the bottom with a 1K resistor to ground for a small sample to drive a meter.  (Juggle these values to get the circuit to work for your parts)  Lots of samples on the web.  No reason to have HV at the panel meter... bad idea.   To measure plate current, a meter in series with the fil transformer center tap works fine. (or some variation to exclude grid and screen current from plate current)

 T

Hello and thank you Brett and Tom.

Okay on the HV connection to the meter.  I will look into this and see what I can find to make it correct and safe.  
Again Thank You.  The thought of being Safe is far better then the thought of  6 feet under!

I searched for those Photo Flash Capacitors and I could not find ones close to 51uf at 5kv or close to what I need?  

I came across a few oil filled caps that were close to 40uf with high KV ratings but at $200.00 and up and with the shipping cost it made me back off from the monitor screen a few inches!  

I don't mind sometimes buying something at a high price if in the long run is worth it and if it's something that I will continue to use for a long time.  For this project I am not so sure?  

I will look some more for both oil filled and the Photo Flash capacitors but if I cannot find them, then I will just simply purchase the electrolytic capacitors?

Listening to everyone's input here does bring excitement and hope for some future builds, it's just I am not prepared enough to make any sudden moves on my own without any help.  But I do enjoy reading many posts in this technical section and else where, so many thanks to all.

When I get the new caps installed and rewire the meter I will post some pics!

Thank you to everyone for the "Enlightenment"!  I certainly needed it!

Ken


 

No my intention was just having thoughts on how to increase the power a bit. The filament choke will handle it three. I don't know about the transformers, you have to determine that. They seem to be in parallel? Anyway there is nothing wrong with the tube arrangement for AM as it is. 100-125W carrier, it's enough to work with.

Hi Ken,

Hmmm...  the photoflash caps must be getting rare. They certainly were in hot demand for a time. Keep looking. Check the Russian vendors for similar ones, not necessarily those values.

I had a chance to look at the 813 linear pictures closely. I realize that someone else built this rig long ago. To be honest, mechanically and parts-wise, you have a good RF deck and power supply to work with. But some of the wiring job and the mid-air hanging resistors, etc., need to go. I would draw a schematic of the rig and then strip out the sloppy wiring areas. The top of the RF deck is reasonable, the bottom of the RF deck is marginal - but the power supply needs rewiring bad.  Start over with some nice Teflon wire, and have at it. Get a bunch of copper silver plated connectors and go to work. Use Plexiglass and standoffs for HV mountings. Once working, you can use tie-wraps to neaten it all up. It will look beautiful.

While the rig is stripped, you can get in there with a brush and some Brillo pads and shine up all the metal. Paint the transformers.  Don't be afraid to give the rig a bath as long as you keep water out of the transformers.

Is that a filter choke I see in the power supply? If of adequate ratings and wired for choke-input configuration, with 40 uF of capacitance you will have great HV regulation on AM and ssb.

You may even consider sanding down and repainting the front panels. Or make the PS panel match the black RF deck.  There is nice lettering available.

What sometimes happens to new builders is that they skimp out on cosmetics to get the rig working fast and then either tear it down later or start from scratch and build their own after learning more. They soon become dissatisfied with its appearance. I suggest you reburbish the rig and make it your own, while you're in the mode. In the long run you will have a  rig that is more reliable and that you will be proud of to keep for a long time.

T

Hello Patrick,

As you might know now, I am new to all of this so it will take a while, but I will probably want to do more to it as I learn.
Even already listening to everyone here has enlightened me to think a bit more out side of the box.  I think it was you that mentioned that it would not do much better then a DX-100 ?  (In the "AM" Mode)  And so down the road I would like to have a decent carrier.  And besides I have a great desire to learn, but no real Elmer in the driver seat to steer me where I need to go?

But I am determined!  So I will get there!  I just wish I had started a lot earlier.  I have been into radio for some time, but mostly as an appliance operator?  I have experimented with SDR's and built plenty of antennas on my own and even taken down towers and installed them.  But to do what you guys do here in the "AM" world is a bit beyond me.  I had always had someone in the back ground (other SSB Hams)  talk down about boat anchors and such leaving me to believe there isn't any joy in them.

Yea right!  I have been finding out just the opposite and I can't wait until I have some real understanding to really get my feet wet!!!  Well maybe that's not the right terminology in this arena with all these voltages and such but I know that you know what I mean!

Anyway thank you for your help.  Also knowing that the amp will basically do the same as a DX-100, I will know what to expect.  And also it will help me to understand how much drive to input into it.

Thank you,
Ken

Hello Tom,

I will continue to look for a couple more days and then go from there as far as the caps?

Thanks for looking it over and mentioning about cleaning it up.  I never really gave that any thought?  And painting the supply to match the deck, I think is a great idea as well.  I have all these idea in my head thinking I may turn it into something better?  But who knows, maybe it should be a keeper and I should just start from scratch on building a transmitter?  Of course the build would be a clone of someone else due to the lack of experience.

But surely there has been a lot of great ideas that have been given here.

I am not sure about the filter choke that you are asking about?  Perhaps its the B&W Barker & Williamson gray box?  Shows how much I don't know!

You mentioned the lettering.  Where can that be found? 
I was in need for some at one time and I did not know where to buy?

Looking at some of the web sites of others here, there are some neat looking Home Brew "AM" gear.
They are very inspiring!

Thanks Tom,
Ken

K,

I'll tell you how I acquired my collection of oil cans. Go to the local ham fests. See what's there, and more importantly, talk to the real old buz zards. See if they have anything you might need. And always have plenty of money to throw around. You'll be in Valdez for shure.

klc

Hi Ken,

For the panel labels....  perhaps the best idea is to get some clear plastic adhesive 8 X 11" sheets. They can be found on the web or at stationery stores.  Then use your computer and printer to print custom lettering.   Maybe the guys have other ideas.   I do like the ability to create any words, colors or font size myself vs: buying canned labels.  The clear material is transparent and makes the lettering look like it was professionally paint stenciled on.

That gray box in the power supply may be a filter choke. If it has two terminals on top, it probably is. Where is it in the schematic?

BTW, if you like looking over homebrew rigs, here's a project of mine from 2 years ago.  It's a plate modulated 4-1000A rig. It is finished and currently works very FB after getting the last of any bugs out...  
http://amfone.net/Amforum/index.php?topic=33816.0


Stick with your 813 linear project. It is a good level to start at and then maybe tackle a plate modulated rig next.  



T

I got most of my caps and chokes at fests cheap, under $10.00.
I did get some 50uf at 2.5kv caps on ebay I think, trw Lighting, part number stb99003.
No pcb, made in 1997.

Anything sold new is crazy expensive these days.

Well I haven't bought any Caps yet off of flea bay, and there are some fest coming up.  Sounds like a good idea!

Hello Tom,
I haven't tried those transparent sheets yet.  I think when it is time I will give those a try.  I have another project from some time ago that needs labels too, so maybe this will be the way go.

There was not any schematics given for this amp, but the gentleman did give me a book that had amp projects in it and he did say this amp project came from this book.....Now where did I put that book!

Thanks for the link to your "AM" project.  You do some nice work there. 
To do nice work, one has to have some patience's! 
I had taken a look at your link before this site went down.  I was able to enlarge your pics, but now I cannot. 
There must be some more site issues here.  But I am sure we are all glad the site is back!

But anyway Tom, very nice work.  I really enjoy looking at other people's projects and learning new ideas from them.
In another post I mentioned I am basically an appliance operator, but I am comparing myself to everyone here.  I have built some small devices and such and I am not scared to jump in at anytime to learn. 

This is a great site to come and learn from that is for sure!

Thank you Tom.

Good inputs here! Appreciated the advice about derating a SSB GG linear for AM drive/service! Tubes really do take a beating just doing a carrier in this application. The idea of plate modulating an tube in RF Class C service drives me to the data sheets which of course consider the plate dissipation of the tube. I plan to do a 304TH/TL Class C plate modulated by a pair of 4-125A's in Class AB2. I hope to realize 750W carrier and 100% modulation. Plate on the mod will be 3KV and on the deck will be 2500VDC. Transformer is Signal Corp 7700VCT at 1 AMP!! Will do FW ...not bridge...and use variac to bring down the mod voltage. I can't do same 3KV on the deck as the mod sec Z is 8000 ohms. Need lower vdc and higher current to get that Z...and still have a carrier that can be 100% by the mod. You can see the need to 'jiggle' the RF deck to properly load the mod transformer. It is true the mod transformer can likely do margins of maybe 2:1 but I don't want to deal with possible distortion or clipping low/high end audio response due to improper loading of mod xfrm. Love the triodes in Class C for AM plate mod service! No screen. Maybe neutralization...but that screen supply is more parts that I can't well find these days. BTW: I even think I will do no choke input on the ps...using solid state. Just do high cap filtering. An even bigger AM rig will be a pair of 833A's modulating a pair. Now we are talking baby!!