Help with Tuning a Ranger into a Thunderbolt

[W1TTL]

I'm looking for a little assistance from those of you with a Ranger and a Thunderbolt in CW Class C operation as I keep blowing the high voltage 10A fuse when I start calling CQ.

I finally finished restoring a "late model" Thunderbolt.  I cleaned it up, replaced all the electrolytics, checked all the resistors, oiled the fans, etc.  I also ran 220V to the shack for the Thunderbolt.  (I ended up running 8/3 with ground wire along with a 30A breaker.  It's probably way more than what's needed as the manual recommends a 15A circuit for 230VAC operation.  I also wired in a NEMA 14-30 receptacle.  For the power cable, I used a dryer cable with a NEMA 14-30 plug and put a Leviton 7565-C receptacle on the end of it.  The ground wire attaches to the chassis.  Just thought I'd mention it to add to the posts on wiring a Thunderbolt.)

As the VFO in my Ranger is stable on 80m, I have been using that band for my testing.  Initially, I was blowing the high voltage fuse when turning on the Thunderbolt plate, however, after I swapped in a pair of known working 3B28's from my Valiant, the 10A fuse stopped blowing.

I have the manual for the late model Thunderbolt and have been following the operation procedure by the book.  First, I preset the Thunderbolt's controls per Figure I.  Then, I peak the grid on the Ranger and dip the final.  With the Thunderbolt's plate OFF, I key down the Ranger in transmit and reduce the Ranger's drive so that the Thunderbolt's grid is at 10ma.  I then peak the grid on the Thunderbolt and reduce the Ranger's drive so that the Thunderbolt's grid stays at 10ma. I then re-dip the final in the Ranger.

I then turn the Thunderbolt's plate ON and while keying the Ranger in transmit (into a kW dummy load), I dip the Thunderbolt's plate.  I make sure that the Thunderbolt's grid current doesn't go above 10ma and the plate input power doesn't go above 1000W.

I don't want to increase the Thunderbolt's grid current to 20ma per the manual because the input power is already at 1000W when at 10ma and I can't go above that.  I keep the grid at 10ma, start calling CQ, and then after a few dits and dahs, poof goes the fuse.  What am I doing wrong?  Reading between the lines, when I am at 10ma of grid on the Thunderbolt, I am guessing the plate input power shouldn't be anywhere near 1000W.  I do not have the RF attenuator installed between the Ranger and Thunderbolt because the manual doesn't specifically say to use it for CW Class C operation (but it does for linear AM operation).  Is that my problem?  Should I have the attenuator installed even though it's not specifically stated?  (I have the parts for the attenuator -- I just haven't constructed it yet.)

Any advice from you Ranger/Thunderbolt veterans would be great.  

73,
Tony W1TTL

[W2PFY]

Just following. I have little to no experience running amplifiers.. I don't know how to "follow" without making a comment?

[K8DI]

First, you seem to be using two calls/logins..

Two thoughts: generally speaking, more grid current means more bias means less plate current. Strong grid current is a good thing. Try cranking it up to the 20mA the manual calls for. And, the grid current generates bias, along with the standing bias that has to exist between dits and dahs to keep the plate current from jumping to the moon.  You can run it for periods of time key-down to tune it but upon sending it pops the fuse. If there’s a problem with the bias circuit your drive/grid current could be enough bias to keep plate current in check…until you release the key during actual sending. Check the standing bias in CW mode — is it right/there?

Ed

[W1TTL]

Hi Ed,

Thanks for the reply.

I think I just figured it out.  I re-read the manual and I had an "aha!" moment.  The fuse was blowing every time the plate current was going above 500ma (1000W input).  Figure H gives the approximate operating values and the plate should be around 455ma.
 Figure I recommends that the coarse coupling should be at 3 and the fine at 75 for 4MHz to start.  Since I was transmitting at 3.6MHz, I thought... maybe I should reduce the coarse coupling to 2 or 1 to reduce the plate current.  And sure enough, setting the coarse coupling to 1 brought the plate current down enough so that I could increase the grid current to 20ma while keeping the plate current below 500ma and I am getting good output power (around 600W or so).

I didn't realize how touchy the Thunderbolt is with the plate and grid current if I am not paying attention to the Thunderbolt's meters when I am re-dipping the grid on the Ranger and on the Thunderbolt.  If the grid current goes above 20ma or the plate current goes above 500ma, then poof goes the fuse.  Which is a good thing.

The only thing left to address is the screen current.  It is at 90ma on key down.  (To read this on the meter, you have to divide the ma by 2 and multiply by 10, since the meter's markings are for grid current from 0-30ma and the scale for screen current is 0 - 150ma.) Typical operating screen current should be 50ma following Figure H.  In the installation procedure, step 5e recommends re-wiring the bias-screen transformer if your primary voltage is above 115VAC. Mine is 120VAC.  I will follow that rewiring procedure and see if it improves the screen current.  

UPDATE: I rewired the bias-screen transformer per the book.  It brought the screen current down.

Anyway, so far so good now when calling CQ on my G5RV on 80m.  (Antenna tuner is a Heathkit SA-2060A.) RBN is picking me up.  Looking forward to some QSOs on 80 when the sun goes down.

Oh -- that wasn't me using two calls/logins.  That was W2PFY.  W2PFY -- I'm not sure how to follow a thread without making a comment.

KC3LXJ -- if you're reading this... IT'S ALIVE!

73,
Tony W1TTL