VRL Globe King

[WQ9E]

I preformed HV testing today.

The plate voltage for the 811a's read 2kw, along with the plate for the 4-400.

That is kinda high for a 811a, so I have e-mailed The Perter Dahl Co. for information regarding what the voltage taps should read on the custom build transformers.

-Scott

Scott,

The Viking 500 was designed with the 811A modulators running at the same plate voltage as the 4-400A final, 2,000 volts under load.  Supposedly the Johnson design engineer got the official "OK" for this from RCA and they do run fine in the 500.  You need sufficient bias to set the proper idle current but the tube has no problem...At least with good quality U.S. production tubes.  Some of the Chinese brands may not stand up to this voltage level.

[KD8PIQ]

The HV power seems to come from the same xfmr, but separate winding's.

I read just shortly ago from here: http://amfone.net/Amforum/index.php?topic=16744.0
about the Johnson running the 2kw on 811a plates....

I have also just measured negative 12.5 vdc on the grid pin (3) on both 811a sockets.

I do have a very nice matched pair of NOS Made in USA for the US ARMY/US NAVY Sylvania tubes in the boxes.
My very favorite uncle in CA shipped me not too long ago for this project.  (WB6SLC)

I'm going to cross my piggies, and plug them in and power her up....

-kd8piq
  

[KD8PIQ]

It might be only 23 degrees outside, but my shack is heating up!

[VE3AJM]

From the pictures, I can't see a choke in the HV power supply. Perhaps its capacitor input configuration as opposed to choke input? Curious.

Al VE3AJM

[KD8PIQ]

From the pictures, I can't see a choke in the HV power supply. Perhaps its capacitor input configuration as opposed to choke input? Curious.

Al VE3AJM

The big gray box is a oil cap, tied into the 2kw, then grounded.  I do not know its value, the metal strap has it covered and down too far to see.

[VE3AJM]

Yes, I can see  the oil filled capacitor with the strap, I can't see any choke. If it were there, it would take up a lot of real estate on the chassis.

Al VE3AJM

[kb3ouk]

I thought that was a choke to the right of the oil cap, or is that a transformer?

[KD8PIQ]

I thought that was a choke to the right of the oil cap, or is that a transformer?

I think it is.  The deck is running right now, and I don't want to flip it over to look.  :-)

[KD8PIQ]

RF Deck, just opened.

[VE3AJM]

I thought that was a choke to the right of the oil cap, or is that a transformer?

There were 3 pics of Dahl iron from the PS chassis that we could see, and that we had closeup pics of. Plate, modulation,and a modulator filament transformer topside. So that transformer by the oil cap would be the filament transformer.

I guess we'll find out for sure in the course of time. Did this transmitter come with any documentation and or schematics?

Al VE3AJM

[KD8PIQ]

No information, no paper work.  You guys have the same information at this point, that I do.

[kb3ouk]

I see 4 transformers on the PS chassis: the HV and modulator transformers, the one by the big cap, and the other one in front of the modulator tubes.

[KD8PIQ]

Just got this E-Mail.  1/27/2013

Hi Scott,
Unfortunately, I can't find any info in my files on those units. They must have been special units Peter made for a customer or the design files were lost in the transfer when I took over. Either way, I do not have the design files or wiring diagrams for those units.

Jeff

Jeff Weinberg
Harbach Electronics, LLC

[VE3AJM]

I see 4 transformers on the PS chassis: the HV and modulator transformers, the one by the big cap, and the other one in front of the modulator tubes.

That transformer just doesn't have the size to be a HV smoothing or swinging choke rated for at least 2 KV, 5 H or so, and 500ma lets say, which would be needed in either or both the HV power supplies if they were choke input.
It doesn't look like a Peter Dahl unit. I wonder what the HV reading will do when there is a load on the HV power supply, from both the modulator and the final?

The use of that edge wound inductor in the final tank circuit was an improvement over the tank used in the WRL GK500s though.

Al VE3AJM

[WD5JKO]

I wonder if the VRL keys the high voltage transformer primary like the GK-500 did as a PTT, or if they just key the high voltage DC? Another possibility is they just use grid blocked keying, or some variation thereof.

If VRL has a common supply for modulator and RF PA, with appropriately sized parts, this is not a problem. Many broadcast transmitters use a common supply. When running AM, the RF deck acts like a huge bleeder so the power supply regulation can be quite good. Going to CW might be a different story however.

If I were to re-do the high voltage in my GK-500, I'd use a common supply, full wave voltage doubler or Full wave bridge, large amount of capacitance, and a safety bleeder; NO CHOKE. I'd key the high voltage with a 5KV rated relay which means the B+ is there all the time...up to the relay.. The RF final will provide the load, and the modulator will pull from there at an audio rate.

Jim
WD5JKO

[WQ9E]

A lot of ham gear uses a common HV supply for the modulator and final, both of Johnson's higher power rigs (500 and Desk KW) use a common supply. 

Although a well designed choke input supply certainly provides better regulation once SS rectifiers became available and cheap the high power choke input supply was on its way out.  Tube rectifiers, MV especially, couldn't withstand the high repetitive surge current from capacitor input filtering but that isn't a problem with adequately sized silicon rectifiers as long as the transformer is also designed to handle the repetitive peak charging current.

I haven't looked over the pictures that closely but I would pay close attention to HV insulation, adequate RF current capacity for switches and capacitors in the RF output circuit, and whether tube operating points (proper bias and screen voltage) and protection is addressed.

At the least you have some good quality iron and depending upon what you paid for this if it doesn't perform well you can always build a rig of your design incorporating the useful parts from this one.

[VE3AJM]

For sure, cap input common supplies can work in a plate modulated AM tx, if the tx etc is designed/built with the approprate components, etc. We'll find out if the VRL unit fits into that category, with how it was constructed.
Should be interesting.

Al VE3AJM

[Jim, W5JO]

I am afraid that he is going to find that the parameters you guys have so well stated are not met in this transmitter therefore the reason no more were produced.  I think he will find that the voltage sag under modulation will affect both the modulator deck and final.  I am curious too.

That is the problem that was addressed by others in attempts to repair these things.  I hope it works but we shall see.

[ke7trp]

2000 volts is fine on the 811's but wont run class B as in the GK500. They will be AB1 and will run hot hot hot. But they seem fine in my Johnson 500 even with no fan.

There must be a bias supply there if the voltage is 2K.  I see in the photo that you have some idle current on the 811's meter so that is great. Looks like its working.

No reason you cant stick in 572B's for fun if you have a pair. 

The RF deck looks like an upgrade over the GK500C.   The GK500 used two coils. one addative coil under the deck. Remember that the Loading cap does not need to be wide spaced, Its working at 50 ohms. Even the one in my big transmitter is very closed spaced high value/range cap and its fine.  The tune cap is where you need the spacing.

I am seeing some good construction and good parts.  The GK500 used a modulator power supply.  Are you saying this one has a single supply?

I would probably axe the Screen supply and use a Dropping resistor from the B+ line to the screens for the 4-400. This really made a big difference in my GK500. There was no question it sounds alot better this way and the wave form is much cleaner.  However, Get it running first, Then play around with things like that.

Thanks for posting the pictures and good luck. 

C

[KD8PIQ]

The HV comes from a single tap point on the VERY large "Multi" xfmr. Then through a rectifier and has the large oil cap filtering to ground.

From the cap, there are (2) wires that go to the "CUST. P/N 500 MOD XFMR".

 There are (2) inputs, and (3) outputs.  They all read 2kw.

The three outputs are as:  
One goes to the HV output on the back of the deck for the plate on the 4-400.
The other 2 are for the plates on the 811a's.


PS;
 I did just note an unused tap on the large multi xfmr, it reads 900VAC.  Might I have any problems in drop, I could try to use that point with a second rectifier and filter for the plate caps on the 811a's. Just a thought...

[ke7trp]

900 wont be enough to modulate the rig fully. 811s are just enough as it is.  The single supply is fine.  The idle current looked good on the meter.

C

[W4AAB]

The 572B's would give you twice the plate dissipation in the modulator. I did a mod for a ham who had a Gonset GSB-101 which used 4 as RF amps. The 811A's needed minus 4.5 VDC bias, but I was able to ground the grids of the 572B's. Worked much better. I am not sure that running the 811A's from the other tap would work well enough. The voltage on the modulators should be equal to or higher than on the amplifier tubes.I am running an original GK500, and I have had no issues with it, except I need to replace some HV caps as I have a hum issue.First, I need to get my antenna back up after the ice took it down.
                                                     Joe W4AAB

[VE3AJM]

2000 volts is fine on the 811's but wont run class B as in the GK500. They will be AB1 and will run hot hot hot. But they seem fine in my Johnson 500 even with no fan.

The 811A modulators in my Viking 500 run class B with 2kv on the plates, with a no signal current of about 35ma. They don't run red hot, and from the pics posted here of the VRL 500 with 2kv on the plates, its modulators are idling at approx. 25ma. The plates aren't showing any colour from the pics.

If one has 572B tubes, sure use them. I have used them in my Viking 500 modulator. Idling the modulators at about 35ma, I wasn't gaining anything though. Those tubes are running very conservatively though.

There appears to be a Peter Dahl choke underside chassis connected to the screen of the final tube. The screen could self-modulate that way.

Al VE3AJM

[ke7trp]

The GK500 should have 1500 volts on the plate of the 811s.  Did  you really measure 2000 volts?  Interesting.

I see the self modulating screen choke and that is how the GK runs. However, It produces distortion. If you modulate the screen in phase with the plate, the rig will work better and there is a very good difference in sound and signal quality.  It was a modification suggested by Robert W0VMC and it worked great.


C

[WQ9E]

It is best to think of the VRL Globe King as a partial replica that has some similarities but many differences from the original.  The cosmetic styling has similarities but the design, components, and layout are quite different.  Using documentation or even expectations about the original will likely be more misleading than helpful in getting this one in running order.

It would be similar to trying to use a factory service manual for an original car while working on a kit "repli-car".