Johnson Thunderbolt restoration

[KC2TAU]

If I remember correctly from my perusal of topics on this forum regarding the Thunderbolt the 4-400's aren't run at a high enough B+ to really awaken them.

[ke7trp]

Very true.  Linear operation in class AB is pretty poor performance for AM.  However,  You can run the Tbolt in Class C for CW and get 800 Key down.  I think that was its main intentional use.  Remember that they had a limit for power input.. The Tbolt got right up to that limit.

At that time they did have SSB exciters on the market such as the CE20A, HT32 and others.  Those where all PW at 10 to 20 watts output.  So if you owned one and then got the Tbolt you would go to 600 to 800 watts which would be a huge step up.

For people using them as an AM linear, Its very poor output for weight and heat.  I am all about setting the gear up period correct and just enjoying them.  A ranger that now does 200 watts carrier is cool to me, Even if the room is hotter then hell doing it

C

[KC2TAU]

I certainly see a lot fewer Thunderbolts than I do of other vintage linear amplifiers. It's good to keep some stock so we know what they did back then. Preserving history is a must. Finally, 200 watts carrier isn't exactly peanut power, either.

[ke7trp]

True... He gripes come from people who have bc transmiters. The same twobtubes does 1000 carrier fully modulated.   The funny thing is tbe 800 lb weight is never mentioned... Only that the tbolt is heavy and only does 200 . Lol

[ke7trp]

Worked 12 hours and still found time to play with tbolt before bed. 

I swapped in another set of 4-400s.  Amprex.  Those where not happy in the tbolt.  Low power. little dip. 

Next I tried an old set of 4-400s. The ones without the fins. Just round ridges on the plates. 

Tuned up the ranger and tbolt again and power was up about 75 watts. Not bad. 

Playing around with the tuning, I tried turning OFF the ATTenuator.  I think this swamper is to heavy.  Maybe I can mod it. I never see much grid current.   

With the input in RES,   Then the ranger loaded down a bit, I found the best combo. I tuned for max peak on the Bird43P and the scope.  With some back and forth I got 900 watts pep!  The monitor reciever really perked up.   Carrier was 300!

The manual tells you to use the swamper and then the tuned input. When I do that, I cant get enough drive to hit past 500 watts pep and 200 carrier.   Maybe its cleaner?

I hope the built in resistor will take the ranger. I think it will as it is loaded loaded down. 

Plate current is 350MA with an upward kick on mod.  Grid is an upward kick to 8 ma.

I am MORE then happy now. 900 in AM mode is a wonderfull thing for this old amp.  I backed it off to 250 carrier and still hit 800.   So That is where i will run it.

The ranger has a slight hum in it. Not sure whats going on there.  Gotta fix it. 

Pete, Is it ok to run the range loaded down into the RES position on the Tbolt?

The manual talks about getting into Ab2.. Maybe thats what I did tonight.

C

[ke7trp]

More Tbolt work.

I put in 4 VR150s.  That got the screen volts up from 500 to 590.   That helped power output (Thanks to slab for the tip) but also raised the idle current.

The manual states 200 to 350 MA if idle current in Linear mode.  The Eimac PDF for the 4-400A shows 160 to 190 at this voltage.  I had 350MA at idle.  Insane heat and cherry tubes.

I guess for Linear operation with an SSB exciter of the day that would work.  However, I will only use the ranger in CW or AM mode.

I swapped the BIAS VR tube from a factory VR75 to a VR90.  That Got idle down to 250 MA.   Then I tried a VR105.   That got the idle down to 150.

HOLY MOLY!  that let the power out and killed all that damn heat!

Now, There is no more problem with to much carrier and not enough peak.  With the ranger loaded up by the book, the ouput is 250 watts carrier and 1100 pep.  MORe then the 90% mod I am putting into the Tbolt.

I can get a perfect linear pattern at 300 watts carrier now with the ranger

This plate current is 350 with an upward kick on mod.  The amp runs ice cold now.  The tubes dont even cherry with 150 MA on them.  I have the bias plug wired up to the Dowkey so there amp is in cut off when I am not keyed down. 

I am more the pleased with this old amp now!  Its clean, Clear and LOUD.   In tune postion on the mode swtich, You get about half power.  So you can run with 150 watts fully modulated for every day use and when you need it, Kick it up to linear mode and get double the power.  Cool

Foot notes:

Big HV caps, 33 MFD at 1400 volts each.
256 line volts on the input
Vr150s for the Screen regulators for increased voltage.
Vr105 for the Bias supply for more negative bias voltage and lower idle current
Plug in solid state rectifiers.
Tune for max signal on scope/pep meter using 1k tone or voice.
Hand picked 4-400A Eimacs pair.

The best part?  I did not modify anything but the replacement Screen supply/bias supply caps and HV caps.  The rest is simply plug in tubes or rectifiers.  Biasing the amp for AM use really helped alot.

I love my old Tbolt now!  Cant wait to put it on the air!

[N8ETQ]

Hey C,

   Nice Tale, I had one back in the day. Traded it
fer a GPR-90... Live and learn..   Congrats Man!

/Dan

[ke7trp]

Thanks man.  It was alot of fun working on it.  Kept my mind off other things.

Last night, I swapped the good fan out of the parts tbolt into the working Tbolt.  Took about an hour and a half. You have to remove the filiment transformer to get to the screws/nuts to remove the bleeder stack, fan.

I got a seringe and pulled a light oil up and then injected it into the felt pads through the hole on the fan case.  Should last a while now. It was bone dry.

The new fan runs smooth and produces alot more air then the old worn out fan.  Job done.

Adjustable Bias would be a good thing to add to the Tbolt.  Running in class A is just wrong.  Today the tbolt goes into the case.  I am going to wire up the bias cable i made to the dowkey.  Then take the ranger apart and figure out why it has hum in it. It was just rebuilt. It must be something simple..

C

[KE5YTV]

Clark, Thanks for the Tbolt updates and information. I have a nice one waiting it's time in the que. Reading your updates is getting me inspired to pull it out.

Mike

[ke7trp]

Mike, If you find you need some parts, let me know. I have the second Tbolt here.  Some good parts and some bad.

C

[ke7trp]

Going on the air tonight. I fixed the ranger. It took me all day to find fix the hum on the first audio stage. 

I ran new shielded cable to the back to the first tube, put in missing grid resistors, and cleaned up some stuff. Everything was perfect.  Still had hum.  My friend told me to put a 20 to 30 UF cap from plate resistor on supply side on first stage.  GONE!

Unreal.  No idea why that hum was there.. The Power supplys show no ripple on the scope.  But that first plate load resistor wanted some cap on it.  Audio is clear and I have full gain.

Next to put the ranger back in the case and hook it all up.  Hope I talk to some of you guys tonight on 75!

C

[ke7trp]

Not a good maden voyage.  It turns out, I mounted the fan upside down so the fan rubbed the case inside the Tbolt.  I had to take the tbolt back out of the case and spend an hour removing the fan again on to rotate it and put it back in.  DOH!

After that,  tuned up everything and got on 75.  Right off the bat I got bad reports of FM;ing and hum.  WTF!

I turned on the BFO on the NC183D and hear a motorboat signal along with the BFO tone.  I cant find any of my Xtals right now so I could not test further.  This happens with Tbolt OFF so it is the ranger VFO.

The thought of taking that ranger out of the case and spending more time on it is making me sick.  Its going to sit for a week now.  I am out of time dedicated to the hobby for now.  Maybe next weekend I can find time to look into it. 

In disgust...

C

[KB2WIG]

C,

No tears fer you here .... ..   I've had my ranger 2 out of the  case mor most of its last 8 years. But I'm getting better at them long screws.


klc

[The Slab Bacon]

Just FWIW, are you using a dynamic mic? ? ? And / or is the ranger real close to the t-bolt??

The plate transformer and swinging choke in the T-bolt put out a nasty 60Hz magnetic field. Mine drove me NUTZ with a hum problem. Then one day I was looking closely at the scope and noticed that the hum would change as I rotated my chair.
(I was using a dynamic mic!) I had everything apart countless times and was just about ready to grab the BFH when I noticed that it changed with the position of the mic. As I moved the mic around, you could actually see the amplitude of the hum change on the scope. Wired in a condenture mic and audio processor and all was good.

[ke7trp]

Good point slab.  I did turn the tbolt off and the ranger in vfo mode has a motorboat on the signal.  I am looking for another ranger now. This one needs aloy of work.  Maybe i will press my ce20a into service for now.

[ke7trp]

Had a saturday to spend with the ranger.  After measuring the entire radio I found the problem.  The PTT line was run with a 6 volt DC supply and that supply had 7 volts DC and 2.2 volts AC!

That AC went up and into the D104 and back out down the mic line into the audio stage and all over the damn radio. It was nearby the VFO supply. 

I did not do the PTT mod to the rig. The person used a 470mfd cap and a diode off the fil supply line.  That would normaly work but the relay coil was 27 ohms on that model relay. That put a huge current on the little DC supply. 

I added 1000UF and the ripple went down to 1.5.  Still there.  I then put a 4700mfd 16 volt cap in and that got it down to .800.  Hmmm.  Caps wont work here..

Rather then rip out the relay and redo the supply, I chose to use a TIP42 PNP transistor.  I got the transistor at rat shack for 1.50.   These are very simple and operate off Ground. 

Pin 1 goes to PTT line that hooks to the microphone jack socket.   This gets grounded when you squeeze the D104.
Pin 2 goes to ground. Case of transistor is also pin 2 so you can just screw the case to the chassis.
pin 3 goes to the 6 volt DC supply through the relay coil.

I put a 5K resistor across the 1 and 3 pins so the transistor does not switch on momentarly when you turn the radio on.

Now, When you close the D104, the transistor pin 1 goes to ground turning on, the relay latches and the radio keys up.

There is 100% isolation from the mic PTT line to the relay coil.  This took 5 minutes to install dead bug style.  It works perfectly, Has no heat at all.  And cost $1.50.

Success!  NO HUM.  AT ALL.   I cant even hear the carrier on the near by rxer.  I have to speak to notice it from the squelch

As for the VFO,  I swapped in new tubes, and put a 100UF cap on the VFO supply which got ripple down to nothing.  The main problem was the 6 volt DC supply and that was on the same terminal as the VFO supply.

JOB DONE!  Thanks to my friend Ted for helping me with the transistor!

C

[ke7trp]

Using the Ranger, Tbolt and NC183D on the 20 meter AM net now.  Everything is working great at 300 watts of carrier.  Got good reports from the guys!

C

[N6YW]

This has been an excellent thread.
My Tbolt is ready to put into service after doing basically the same things but with the stock HV cap.
The first thing I did was replace the regulator caps. It will be interesting to see how it works with my
HT-32B and CE-20 setups. My only other AM rig beside the ART-13 is a 32V-3 which I cannot use without
a pad.
My Tbolt is the later model. Which type of coaxial relay did you use on your setup Clark?

73 de N6YW

[Pete, WA2CWA]

Much too neat for an active ham shack. 

[flintstone mop]

Ahhh yes I remember the Rangers, when I was doing piece work for Howard W3HM.
And there is definitely an art to those long bolts.
They reminded me of the color TV days, when there were tubes. And the tremendous heat build-up inside of those "so-called" 19" portable color TV's.
Fred

[Pete, WA2CWA]

I have also used my Ranger to drive my Thunderbolt. I used a Dow Key relay for antenna switching.