Strip back a few inches of wire on each section and do a overlap spiral wrap of the 2 sections.  Solder the connection and wrap with a couple of layers of heat shrink tape or tubing (to assist in waterproofing and to add some rigidity and strain relief).

WX7G wrote:  ‘KI4VEO thank you for running the transformer test. So the thump is due to charging current and not core saturation.

This is good information and I have learned a couple of things from this.’


I also learned to check all the mounting hardware.  The posting of AD6KA put me on the track of checking screws and mounting hardware.

Today I loosened the cover side screws – 4 on each side but I left the 7 screws on the top in place and fully tightened.  Cycling the AC power switch on and off, after waiting for the meter to show a full discharge, resulted in a thump almost every time I applied power.  Waiting until a half discharge of the HV showed on the Plate Current Meter and then reapplying power made no real discernable difference to the sound of the thump – perhaps it was not quite as loud.  Placing one hand on the side panels allowed me to feel movement of the panel at the time of the dull thump.  With all the cover screws firmly in place the thump is quite muffled.

I then barely loosened the K2 primary relay mounting screws and the loud resonating thud returned that I had previously heard, prompting my original post.  Snugging down the relay mounting screws once again silenced the relay clamor.

Was the expanding field generated by the transformer the force flexing the cover side panels?

Could it not be a combination of the charging current to the capacitor bank AND core saturation and what takes place when the core magnetic field expands when a huge current surge occurs due to the capacitors charging?  Please explain your theory further…this has really piqued my interest.

Somehow my created document in MS Word and the subsequent cut n' paste got some info out of sequence.

Let's try this again.  Ignore the first attempt on this posting.  This is what I REALLY meant to post:

While none of my observations were terribly scientific, I attempted to satisfy my curiosity and find a method to resolve the “thumping.”

WX7G suggested disconnecting the secondary of the transformer, which I did. I proceeded to cycle the AC power to the SB-1000. No “thump”.

I repeated this more than a dozen times. Same result.

Reconnected everything - Thump returns. I waited until the HV meter showed full discharge of the caps, and also tried cycling power at half discharge.  I repeated this more than a dozen times. Same result.  Thump, thump and more thump.

Three things I found. The power switch relay (K2) on the primary was a bit loose in its mounting to the rear panel. The power transformer was also a bit loose where bolted to the chassis. Nothing overly significant, but enough to allow vibrations to occur when the 240 VAC was applied to the transformer primary thru the K2 relay. And third, the fifteen 6/32 X 1/4 cover screws all allowed for some additional tightening.

Once all the above were addressed, the violent THUD became a muffled and subdued sound. I am unsure of a major culprit, but I suspect the K2 relay closure was resonating soundly on the rear panel.

I plan to cut some sections of rubber sheet gasket material to put under the transformer mounting bolts and the transformer relay (K2) to determine what effect this will have. Or, I could leave well enough alone and live with what I have. It is certainly better now.

Sure...I did that back in the 70's with my "chirpy" Conar.

Check in to modifying the Johnson VFO.  I seem to recall a method of buffering the output so the oscillator doesn't get pulled.  A good source of mods and Elmers:

http://amfone.net/Amforum/index.php?board=27.3000;sort=last_post

While none of my observations were terribly scientific, I attempted to satisfy my curiosity and find a method to resolve the “thumping.”

WX7G suggested disconnecting the secondary of the transformer, which I did.  I proceeded to cycle the AC power to the SB-1000.  No “thump”.  I waited until the HV meter showed full discharge of the caps, and also tried cycling power at half discharge.  Still no thump.  I repeated this more than a dozen times.  Same result.

Reconnected everything - Thump returns.

Three things I found.  The power switch relay (K2) on the primary was a bit loose in its mounting to the rear panel.  The power transformer was also a bit loose where bolted to the chassis.  Nothing overly significant, but enough to allow vibrations to occur when the 240 VAC was applied to the transformer primary thru the K2 relay.  And third, the fifteen 6/32 X 1/4 cover screws all allowed for some additional tightening.

Once all the above were addressed, the violent THUD became a muffled and subdued sound.  I am unsure of a major culprit, but I suspect the K2 relay closure was resonating soundly on the rear panel.

I plan to cut some sections of rubber sheet gasket material to put under the transformer mounting bolts and the transformer relay (K2) to determine what effect this will have.  Or, I could leave well enough alone and live with what I have.  It is certainly better now.

WX7G wrote:
"An experiment to test whether the thumping is due to core saturation or if it is due to capacitor charging:

Disconnect the transformer secondary and power up the transformer repeatedly. Record the frequency of thumping (if any). Reconnect the secondary and repeat."
 

I shall try that this week and let you know what I find.

Thanks for the analysis.

Howard

This SB-1000 is strapped for 240 service (measured 245 VAC at the wall mounted outlet.)  I knew the relay was causing the sound but was unsure how to address this...and was it a "real" problem that could cause component damage, or was it just the result of the relay mounting method in the unit that some sound deadening rubber sheeting could solve.

The transformer lamination hum being picked up by the YM-34 Yaesu microphone was resolved by tightening up the lamination bolts and then applying some polyurethane to the lamination stack - top and sides (didn't have any varnish handy).  After drying overnight, the audible hum was silenced.  Of course, if the amp had been more than a few feet away from the mic, that would have solved the problem, too.

Thanks to all for the replies.

Howard

Often, when I apply the AC power to my SB-1000, a loud "thud" occurs when the AC primary relay closes.  But it doesn't happen all the time.  

Having some experience with zero crossing detectors in power supply circuits before, I began wondering if this method might be used.  Or should I just use a soft start circuit from Harbach?

Any thoughts?

Thanks...

Howard Walker

This won't help now, but when the antenna is dry and working correctly give it a spray coat of Krylon Clear Plastic spray after cleaning the joints and reassembling the antenna.

I have had good luck using the Burndy Penetrox Electrical Joint Compound between sections of Aluminum and Copper.  It works well with dissimilar metals.

Got mine from DX Engineering.

A bit of caution:  It does not play well with skin, so use some latex gloves when working with this stuff.  And wipe all the antenna joints well after assembly.

The usual disclaimers are on the reverse of the squeeze bottle.

Send an e-mail to Mal (NC4L) NC4LMal@aol.com and describe the problem.  He may have some suggestions.  He has repaired hundreds of the 102's over the years and has take good notes along the way.  I am sure he can help you resolve this.

It seems my observations and personal feelings have stirred up a hornets nest.

I don't think it wise to hold everyone in suspicion yet, reading some of the postings it is clear they were made as inflammatory statements.  The poster obviously knew the "Hot Buttons" to press.

Much like our old friend CharlieBaker in the MISC forum, these postings were meant to raise the ire of those who could be incensed - read "lose their cool".  An argument cannot survive without 2 participants, minimum.  And I will admit, I was foolish enough to take the bait with Charlie, as were many.  A few caught on really quick.

While the first posting in this thread seemed somewhat innocent in nature, others, posted by...anonymous "trolls" were not.

I guess my point in this is that everyone should encourage legitimate inquiry, nurture prospective members to this great hobby, and NOT respond to those who are obviously baiting and itching for confrontation.

With that, I shall close my "sermon" and see if any DX is available on 40M.  Now that my SB-1000 is working well I can "sit at the adult table."

I will be checking back to read other opinions.

73

Howard

Ken (AD6KA)...

You only can see the ill advised postings of some...what about those that just drop by to read?

Since this is the forum on amplifiers I may have overstayed my welcome and should have posted in the MISC forum.

Suffice it to say that I fear we are judging too harshly ALL based on the postings and ill advised comments of a FEW.

Let the flames continue.

The testosterone level in this forum edges up when some of the 11 meter crowd pays a visit?

Many of them come here because they want to learn about Amateur radio and don't really believe all the marketing spin that is put on the CB stuff.

Many of the present "respectable" Amateur ops came up through the ranks of CB.  The desire to go beyond those imposed limitations of "handles" and overpriced bargain basement equipment urged us from that shallow end of the electronic gene pool.

So let us not get so, "Holier than thou".  For as they are, we once were.

Not a sermon, just a thought.

I tried the White Out first and found that it, initially, worked OK.  After awhile the stuff seemed to shrink and fall out of the grooves because it did not make a good bond to the Bakelite knobs.

I tried the Testor's modeling paint-in-a-jar because I had some and it has held up well for several years.  Maybe I was lucky on the 2nd attempt but unlucky on the 1st.

A narrow tip artist brush and a small bottle of white Testors modeling paint for plastic models will work well.  You can get both at a well stocked hobby shop.

Clean the knob groove area well with a Q-tip dipped in rubbing alcohol and allow to air dry or wipe with a lint free cloth.

Some good lighting and a steady hand are required.

This should work well.  I've used this technique on some Hammarlund receivers I have.

Howard