Got my Globe 500C up and running!

[ke7trp]

Thanks for all the help guys!

All new filter caps where installed. The replacement mod power transformer was installed along with New HV connectors and cables made up. 816s ditched for Sold state plug ins. 3b28s put in place of the 866s.

Fired it up and found the 811s would not light.  Open filiments on both.. DOH..  Checked voltages and found 1500V on the plates (no load) and filiment volts on the pins. Should be good to go once I get some new 811s. 

In repairing this rig, I learned that some previous owner decided to plug in some very odd tube into the place where the 816 rectifiers where located. These turned out to be some type of audio tube and not rectifiers at all. This toasted the mod power transformer, 811s and some wiring. It also shorted some caps.

Tuned and loaded it up to 250 watts on 40 meters with the modulator deck off. Seemed a bit low and Grid Drive seemed low. Went to swap in a fresh 6146 and found the center of the parisitic resistor broken.. DOh.. Someone must have mistuned it. The center is gone on the resistor and there is no evidence of it on the deck. Must have been like this for a while.

A fellow ham is going to come over tonight with two RCA 811s and a couple of 47 ohm 2 watt resistors. I will make up a new P-resistor assembly for the 6146 and install the 811s.

With some luck, Grid drive will come back up to 15ma where it should be and not the Touchy 5ma I am getting now. Maybe with the Drive section repaired I can get the 330MA I am looking for on the plate of the 4-400.  I figured output should be at least 300 watts. Its rated at 540 input. I was also running it off a 15 amp lamp socket near the test bench which the manual states not to do.. LOL.  I had a real 30 amp plug put in the radio room just for this transmitter so I shoud have plenty of power.

Thanks to Robert W0VMC for the parts and transformer and to the rest of you for the help on email.  W8QBG came over and helped me wire everything up and I am thankfull to the people will take the time to help me.

The goal is to have this thing on the air for the wednesday night AMI net!

Clark
ke7trp

[Steve - WB3HUZ]

Congratulations! Enjoy.

[ke7trp]

I put the 811s in along with making a new P-resistor.  No audio...

Went back and checked the work and found that the replacement transfomer is the wrong one..

This radio needs 1000volt HV and 400 volt LV taps.

What I got was a 1000 volt HV tap and a 2.5 volt tap... DOH!!!

The LV in the mod deck is not going to work at 2.5 volts..

Obviously this replacement transformer ran a Pair of 866s or other 2.5 volt rectifier tubes. This radio has seperate filiment transofmers for the Rectifiers. Must be for a 500A or 500B?

I cant seem to find the correct transformer anywhere.  We are thinking of trying to build an LV power supply off the HV supply.  Its running some mic preamp tubes and a 6l6GC.  Every other voltage is present in the radio and its keying up 250 watts of carrier.. Just NO LV modulator supply..  The mod deck is so full now that I doubt I can fit a second transformer anywhere. I would have to remove and relocate a ton of caps, tubes and large chokes.

We also thought about Driving the 811s with solid state externaly since the 811s have HV on them and are lit up. 

Not sure what to do!

Clark

[Jim, W5JO]

The 500A and B models all have the same transformer your C model has for the power of the mod deck, HV for the 866s and for the 5Y3.  You must have gotten a wrong transformer or one from someone who didn't know. 

If you have the bad one, you might send it to Gary WZ1M and have it rewound.  That way you know it is correct.

[ke7trp]

I confirmed this one came out of a 500. The problem I think is with WRL and the fact that they used all kinds of parts on this rigs. I also have two Filiment transformers that are not pictured on the schematic anywhere.

This transformer has HV and 2.5 volts for the filiments. Its clearly wrong. We might try using a dropping resistor and filter caps off the HV DC to power the LV section. Its two mic preamp tubes and a 6l6. I guess its worth a shot...

Clark

[WD5JKO]

Clark,

    In your situation I might look for a 120v/240v isolation transformer, and mount it underneath the modulator chassis. There are many options here, and a toroidal form factor might have an advantage. If you wire the primary for 120v, and the secondary for 240v, and then use a FW rectifier bridge with capacitor input filtering, the B+ will be around 275-300v depending on the load current, and AC line voltage.

    I'm not sure of the power needed, but I'd say a 50Va rated tranny will do fine, and maybe even a 25va. This rating mainly depends on the 6L6 operating point, which should be under 20 watts plate dissipation for that Class A stage. A 25va tranny should be small and inexpensive. If you have room, go for the 50Va size.

   If you use a dropping resistor from the HV B+, the resistor will be very hot. Let's say we pull 300v at 100ma (30 watts). You would need to drop say 1300 - 300 = 1000v, and at 100ma, that resistor would dump 100 watts (1000 volts X .1 ampere). To make things worse, the driver circuitry will see the full HV (~ 1400v?) until the 6L6 and low level stages warm up. Don't do it.

Good Luck,
Jim
WD5JKO

[w4fms]

Clark: 

I'm a litte confused since my 500c mod deck has plenty of room right by the mod transformer that would fit something like a Hammond 712.  Pricey but would work great.  http://www.hammondmfg.com/700.htm

Good luck

Frank, W4FMS

[flintstone mop]

I always wanted to get my hands on one of those until I heard of the major disease they have with wimpy iron.
A lot of RF power for such a small foot print.

Fred

[Jim, W5JO]

I always wanted to get my hands on one of those until I heard of the major disease they have with wimpy iron.Fred

They don't have to be if one makes a few simple changes Fred.  They can be made to sound as good as you want. 

[ke7trp]

I read the list wrong...

What I need is a new trans that has 1000 and 500 taps. The resistor is going to get real hot. I agree. Thats no the best way to go. 

My other option is to feed the 811s externaly with solid state. The rest of the radio is up and running.  What 10 to 20 watts would do it right?  I just need a transformer to feed the solid state audio to the 811s?  Any ideas? 

I already use a large diaphram condensor mic and mixing console for my 1000d. I could just output this to a small amp. Then into the back of the mod deck on the 500.  Can you guys help me with this?



Clark

[Jim, W5JO]

Put 1K ohm resistors to ground from each grid of the 811s.  Use a 600 ohm to 4/8/16 ohm transformer to feed the grids with the 600 ohm side.  Feed what ever your audio stuff will do, 4 or 8 or 16 into the secondary.

couple of people I know do it this way using an audio amp.  They sound very good.

[ke7trp]

I tried looking on the hammond site for the right transformer. Can someone suggest one for me?

If I dont drive it outboard I need to get 500 volts to the mod deck.

Robert was nice enough to call today and we went over the schematic.  I think I might bring 500 up from the Power supply deck with another HV connector cable. That would fix the problem.

Clark

[ke7trp]

Success!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

I found a 500 Volt supply at the bottom deck that runs the 6146 exciter.  Its a hefty transformer with choke and new filter caps. I ran a Line from this junction to the mod decks Filiment line on the 5y3(tube pulled out). This gave me 500 volts to the Speech amp section of the mod deck.

Also found one of the bottom wires on the 4-400 was loose.. Resoldered that.

Flipped it on, Tuned and loaded to 300 mills at 250 watts on the bird into a dummy. Nice and stable. Right on 3.900.

Grabbed the D104 and had audio!   Listened to it on another RXer while a friend spoke into the mic. No hum and clean audio. I could easily get the 200MA I need on the 811s.  240 or more if you want.

Keyed the transmitter off and on over a 30 min period with no issues. Just a warm dummy load..    THe transformer at the bottom where I got the 500V from was ICE cold.

Thanks alot to Robert for all the help on this! and thanks to W8QBG for comming over and helping with the Transformer install. 

I plan on placing each unit back in the cabinet later today and rolling it into the Shack. I hope to have it up and running on 3870 tonight!


Its been a long road!  Hope it continues to work! Later on, I am going to open up the audio a bit and change the resistor feeding the D104. Probably paint the cabinet also!

Clark

[ke7trp]

Thought you guys would like to see my working Globe king 500C!  SX110 sitting next to the 500 on the table. Its 90 degrees in this room 

Sorry for the low quality pictures.

Clark

[w3jn]

Outstanding!  You had 'er on the air yet?

[ke7trp]

Yep.. I talked a few hours on 3870 last night and an hour today on 7293.  Works great so far! 

Clark

[w3jn]

Looks like yer all set, even got a scope a dope!  Running AM without a scope is like flying blind, IMHO...

[ke7trp]

Yep.. Running just below 100%.  Going to do some work on the audio chain with Roberts help. Remove the couplates ect..  Should sound nice.  I also have a Condensor mic with mixing board I want to run into it one day.

My only real problem now is the PTT wont work. Need to trace it down. Keying the thing from the bottom switch is getting old.

Clark