New Monster In the Basement

[W7SOE]

I recently picked up this transmitter.  It appears to have been built as late as the 80's, hard to tell.  It is two 811's modulating two 813's.    I haven't taken out the RF deck or the mod deck yet.  I suspect the 813's are grid driven.

My first task, as I have no documentation, is to clean it up and make a schematic.

I have the HV PS out, it weighs 175 lbs!!!  It consists of a large HV transformer, 110V in, 3150V out.  There are also two huge chokes.  All of these are Thoradson.  There is a variac on the mains and it appears that the is a multi-tap step down transformer on the mains before the variac, with a selector switch to select a particular tap.  Perhaps you select a stepped down voltage from mains and vary that with the variac.....

There is a 100K 100W bleeder resistor which is adjustable. It is adjusted near the end, perhaps I will replace this with a fixed 100K version as this one is looking tired.

The rectifiers are 866a's, nasty looking devices, I see there are non-mercury replacements, perhaps that would be a good idea.

Is marked to accept a 500 ohm audio input.

Anyway, I am in over my head for now and would be interested in opinions/ideas about this rig, how it may be designed to work etc.
Thanks

Rich

W7SOE

[W7SOE]

More pics

[W7SOE]

and more

[WA1GFZ]

very nice job.

[WBear2GCR]

Really excellent construction, do we know who the builder was??

Not to be too glib, but check the PS, the modulator with a dummy load resistor, then or also the RF deck for RF, dip the plate, then (turn it off first, and bleed down) reconnect the modulator, the audio input, antenna and then talk?? 

              _-_-bear

[W7SOE]

No idea who the builder was.  It may be some time before it is on the air...

Rich

[w3jn]

I'd first change out any and all electrolytics.  Those are almost certainly bad.

Second, I concur with ridding yourself of those 866s.  A 3B28 makes a good sub, and won't arc over and wreck your iron.

If you MUST use the 866s let 'em cook for a day or two with the fils on and no plate voltage.  If they've ever been tipped upside down or on thier side, they're gonna be prone to arcing over.

After this is done, give it some RF (doesn't look like it has an oscillator), feed it some audio, put it on the lowest HV tap, and go to town!

[WA1GFZ]

Go solid state and never worry about the ps again.
After a closer look that is a beautiful rig!
Might want to check all the high voltage wire and get a spool of packard 440 if it is cracked.

[WV Hoopie]

Rich,

Nice find, did I see that one on QTH.com? Location was some where east of Salem, I recall, and advertised to make about 800 watts input. If that's the one, it took a long time to be sold.

Hope to hear you on the air with that piece of heavy metal.

wd8kdg,
craig

[k4kyv]

If you MUST use the 866s let 'em cook for a day or two with the fils on and no plate voltage.  If they've ever been tipped upside down or on their side, they're gonna be prone to arcing over.

I've used 866A's and 872A's for years and they have always given good service if they were good tubes to start with.  I cook the filaments at least 24 hours like you said and that seems to take care of the problem.  You are never going to find a pair of tubes that have never been tipped over on their sides, unless someone picked them up directly from the factory brand new and kept them vertical as they brought them home and put them into the rig.  I'd say the overwhelming vast majority of stores laid tubes in their stock on their sides whilst on their shelves.  If they were ever shipped by a 3rd party carrier, rest assured they were in every conceivable position during transit.

[N3DRB The Derb]

I vote for the 3B28's. Never a problem in my HB rig. 866 are purty but I'd rather have no problems. I'd submit that unless you hand selected the diodes and built out a full Cap/rx balancing string on each diode, the 3B28 would be a better choice.

I would have something beefier to modulate 2 813's than 811's. You would have to run the 813's pretty piss weak in the plate voltage dept. and the 811's at the max.  I dont know the mod iron but it looks big. Read off the iron labels and we can get you some info on it. The mod iron most important.

The tapped transformer is maybe to give the 811's and the 813's different voltages from one supply? or maybe simple AC input adjustment to allow operation from 220? There's no way to know.

have fun and BE CAREFUL. You are now working with shit that can kill you dead really quick. That thing looks like a serious maw dropper.

After a good look at the pix, thats all medium grade Thordarson iron in there - the line below the CHT series. 800 watts input? not 100% modulated it's not. but builder was probably limited by the iron he had on hand. once you get it going change them out to 811-a's and dump about 1750 volts on em. Then you will swing the munky.

I bet you have too much plate voltage on the 813's as is. Need more audio headroom.

Damn, I sound like a know it all.    have fun and keep us updated, love dem HB rigs.

[W7SOE]

The modulation transformer is a Stancor A-3898.  The 813's are modulated by 811A's, not 811's.

Looking for the 3898 spec now....

Rich

[KL7OF]

 The rig looks great, well built....How is the screen voltage supplied for the 813's? .......what is the  RF driver,  what is the audio driver? Good luck hope to hear this rig soon.   Steve

[KB2WIG]

 Try this link....

http://www.bunkerofdoom.com/xfm/MSTANCOR/stancor2.htm

[W7SOE]

Steve,
    I am not sure how the screens are supplied yet.  The RF exciter is external, in this case it will probably be a Johnson Viking II.  I am not sure what I will use for an audio amplifier.  Perhaps I will use the audio section of the JVII after I have done the mods described by K6AD.  It will have to somehow be matched to the 500 ohm input.

I am open to other suggestions!

Rich

[N3DRB The Derb]

hmmm where all the metal tags on the iron? I thought it was thor because of them stamping the numbers on. Stancor used them metal plates that said "A Quality Product" on them. 811-A's, very good you R set.

 

[WA1GFZ]

The V2 modulation transformer has two secondary windings. To modulate the rig they are in series. 2000 ohms. Connect them in parallel and you have 500 ohms for a audio driver. That would easily drive a pair of 811s. The V2 may need reduced screen voltage on the final to get the output low enough.

Diodes of today don't need balance resistors and caps but it is good cheap insurance.

[W7SOE]

What is the "V2" transformer that you are refering to? 

I fired up the HV supply last night after conditioning the 866's for 1 hour on filaments only.  It seems to work ok, I get ~1600V out with the variac all the way up.  (3120VAC transformer) There is still the multitap transformer in series with the mains and  controlled by a multi-position switch.  It seems like this enables a bit of fine tuning of the voltage, not sure.  I will have to sketch out a schematic, perhaps that will help.

There is a toggle switch marked increase and decrease, the rotary switch is marked the same.  A clue?

Rich

[WD8BIL]

The VK2's (and later VK1s) mod transformer secondary is in 2 windings. They are wired in series for internal use. The common point can be used as a centertap and the entire secondary used to drive a higher level modulator.

If you have a manual for the VK2 the proceedure is documented there. If not let us know. I can scan mine in and get you the info.

[W7SOE]

Ahh VK2 = viking II!   Insert headslap here......

[W7SOE]

It looks like the "Figure B" schematic in the manual may be the way to go, it drives a 500 ohm input.  Thanks for the heads up on that. 

Could someone take a look at that diagram in the Viking II manual?  It shows a switch that you add to switch between normal operation and driving an external modulator.

With the switch in the DOWN position (driving external mod) the diagram does not make sense.  If you look at the bottom center of the diagram, it looks as though the line representing B+ should be connected to the line labeled "Gn-Yel" where they cross.

I have drawn it out and that seems to be the case, could someone verify this?

Also, there is an inductor on the output labeled L1 4-10 inch VHF choke.  What is a 4-10 inch VHF choke??

Thanks

Rich

[Ian VK3KRI]

There is a toggle switch marked increase and decrease, the rotary switch is marked the same.  A clue?

Rich

I'll bet the toggle switch reverses the phase of the transformer to either Add or Subtract from the mains voltage and the rotary swich will select the tap on the transormer to select how much you add or subtract .
                                                         Ian VK3KRI