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Author Topic: BC-799/SP-200 Hammarlund Recondition/Mod Project  (Read 39836 times)
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WBear2GCR
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« on: October 17, 2014, 09:23:39 PM »

Over in this thread - http://amfone.net/Amforum/index.php?topic=37139.new#new it was learned that I acquired a Hammer-land BC-799/SP-200 receiver. One I absolutely do NOT NEED. Or to be more precise, yet another radio needing work that I ought to know better than to bring anywhere near my shack.

Given that I have not yet finished all sorts of other radios and gear, test equipment, why should this one be any different?

It sort of is, because I had already made a running start at another one of these, acquired a few years back, in genuine rust-o-bucket condition. It was cheap. Yes. Cheap. The weak point of almost all hams.

So I had taken the front panel off, since it is engraved (stamped probably) stripped it of paint using "green" stripper (which worked surprisingly well). Was surprised to see that the steel front panel was actually nickel plated! Thanks to years of hard living the panel had quite a few scratches and dings. This meant bondo, sand, bondo, sand, primer, sand, spot primer, sand, and well it still had some tiny little pinholes. BAH!

This I set aside in a place of high honor, in the front area of the shack. Where it sat for the past several years. Mocking me.

After all those hours trying to get the surface flat and smooth. It sat there mocking me, all the same.

Oddly enough, as anyone who has visited this QTH will attest, it's generally a chaotic situation. Too much stuff, not enough space. The factor is now like 4:1 in favor of stuff. The oddly part is that when it comes to building things or repairing things I become nearly an obsessive perfectionist. So this panel was just NG. Not even close to perfect.

And, you know what? IF it was perfect? Throwing the paint, would have resulted in a wonderfully smooth glassy gloss finish, until the wet paint runs... sand, paint again...

Well the image attached is/was the inspiration. Now, I forget who did this. Whomever it was/is, please chime in and take credit! Of course that one is/was an SP-600 which has style. Maybe not the best receiver ever, but eye candy!

So I was going to do up the panel in a neat metallic color. Was going to pick another color, but did not have the inspiration on that. Besides, it was sitting there mocking me. Pinholes.

Anyhow, when Steve W2TRH got this BC-799 and it ended up here, I thought <hey I've got a PANEL for this already!>. I grabbed the paint and shot it, a nice metallic cranberry red auto paint. Yes I did. Pinholes and all!

----------

Then too I realized that this is still not going to be all honey and roses. The unit is stone cold deaf on all but one range, and is going to need to be gone through. Somebody had tried to recondition it and obviously got up to a point and no further. It's possible that the previous owner is going to see this post too.

My thinking is that I ought to take pix and do a blog as it goes along. We see a few before and after here, and of course people asking questions and getting answers. But not too much of the doing and the process shows up.

I'm going to try, for better or worse to document with pix and text whatever I do on this radio. Hopefully it will inspire and maybe even start a trend. Otoh, I might get waylaid and stalled, and this might end up being not much of anything. But, I'm going to try to do what I can, and we'll see how it goes...



* SP-600-Med.jpg (91.32 KB, 768x407 - viewed 755 times.)
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WBear2GCR
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« Reply #1 on: October 18, 2014, 09:57:35 PM »

Here's the receiver's front panel, as found.

The second shot - somewhat out of order as far as introducing the unit, shows the "tuning coils" from the bottom, with the cover plate removed.

The way this radio's front end works is that it has what amounts to two cascaded sections of tuned filters that track as you tune the radio. I'd expect that these are fairly wide. The one to the left in the photo is the same sort of coil that tunes, but this one is the "HF OSC", and amounts to a VFO.

Going to get back into this shortly.

Since the radio is stone deaf on all but the 10-20mc range, all of these stages will need to be checked out.

My plan is to grab an RF sig generator and input signal "in band" and see if it can be followed with a scope from stage to stage, down to the mixer. If one band works, then the mixer works.

The other half of this is to check the function of the "HF OSC" section. If the HF OSC is not functioning, the receiver won't tune or hear anything. That will be watching the output starting with the working band, and switching bands. If it doesn't work, then check the coils for continuity, then check the caps. Each stage has a series cap...

That's the idea.

 


* BC-779-A-AS-FOUND.jpg (229.63 KB, 1480x1043 - viewed 712 times.)

* TUNING-COILS-BOTTOM.jpg (399.75 KB, 1480x1110 - viewed 695 times.)
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« Reply #2 on: October 19, 2014, 05:33:56 AM »


   The information provided on this site may prove helpful..

http://www.radioblvd.com/hammarlund_super_pro.htm

  For the LO, I usually just use another RX. You can hear
em' loud and clear across the bench..

GL

/Dan
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WBear2GCR
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« Reply #3 on: October 19, 2014, 08:36:25 AM »

Dan,

Thanks. Think I will give it a shot and fire up another receiver! Cheesy
Heh.
Appreciate all the help.

Yes, I think I have found all the sites by now.

While cruising I came across this site with a recondition on a National.
Although he doesn't show more than the before and after, it's got to be one of the most
impressive clean ups I've seen online.  http://www.ohio.edu/people/postr/bapix/nc120rao.htm

This is my first time into a Hammarlund. Except for the eye-candy aspects of the SP-600 and the TMC GPRs I've not been very interested in them at all. Not sure what the sudden desire is all about.

Probably has more to do with the paint on the front panel than the radio itself!

Of course a whole ton of folks have been into these receivers. I'm late to the party for certain. Expected on my side are stupid mistakes and misunderstandings as I go along, assuming I can keep this going... but that's part of it.  the idea is more to document the process and steps along the way than to provide any sort of "definitive guide."

The previous owner, as I mentioned got just so far, and maybe got frustrated or stuck, sold the rig. I'm hoping this comes out as more of "how to get it done" rather than exactly what to do, the general plan of action, and an overview including talking about it and the thought process along the way. Like now. Cheesy
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« Reply #4 on: October 19, 2014, 08:51:26 AM »

Today I'll be checking the rusto-o-bucket rig to see what it really is, and what it covers. If I'm lucky I can "borrow" some coils.

Also picking up:
- "Magic Eraser"
- Goop (waterless hand cleaner)
- 409 + Ammonia
- Extra toothbrush

This is in preparation for cleaning the chassis, etc... the chassis has been cleaned a bit by the previous owner.

I'll be very curious to see how this magic eraser thing works. Found out that it is melamine foam!! Micro sized pores and fibers. Might be the ultimate thing for this sort of thing.

The other items are highly recommended and oft cited by folks who have posted restorations online, and by some here as well. The Magic eraser is new.

I'll also be trying out some other chemical preparations and applicators - on a "mule" chassis first.
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« Reply #5 on: October 19, 2014, 07:43:17 PM »

Later that same day, our hero and Spotty the RF dog...

... I picked up some brand X "magic eraser" thingies. That and a can of NEVRDULL. The GOOP, actual GOOP brand, and some extra toothbrushes at the dollar store.

Checked the rust-o-bucket rig, and it is the same one, with the useless VLF bands. Drat!

But got a lead on a 1004, which has the "good" bands. Might come through eventually. Also have access to a few NOS coils for the aforementioned "useless VLF bands" that might just get rewound if it comes to that.

So, it might not ever work, but it ought to look shiny!  Roll Eyes

Also grabbed an RF sig gen off the shelf...

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« Reply #6 on: October 20, 2014, 08:29:38 AM »

Well, you have to look carefully. Never know what you will find, or who has been where.

Looking down at the top of the tuning assembly, on the bandspread side, using some bright lights, noticed something was not looking quite right. two wires not touching? More inspection showed that three of these wires were clipped, one per section. Huh?

Without tracing the circuit to see what these were, was this the cause of the dead bands? Re-solded them - ok it's a "temporary" fix. I do not like a butt soldered connection. But no, this is not the cause.

Why were they clipped? Dunno, they are associated with the bandspread variable cap.



* CLIP-CLIP.jpg (224.22 KB, 1480x1110 - viewed 568 times.)
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« Reply #7 on: October 20, 2014, 08:37:26 AM »

  Maybe someone bent the rotor plates and shorted it out.
Visual inspection or an ohmmeter while turning it across it's
full range may tell the tale.

/Dan
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« Reply #8 on: October 20, 2014, 06:06:39 PM »

  I found this little "Blurb" in the TM...

/Dan


* BC-779_HF_osc.gif (20.48 KB, 783x198 - viewed 570 times.)
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WBear2GCR
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« Reply #9 on: October 20, 2014, 07:34:00 PM »

Dan,

Yes, possible.

I did run the radio after I reconnected them, and of course they may only be used on one or more bands... but the 10-20mc band worked as before.

I'll use the Arrf generator to determine the calibration of that band - as in, is it anywhere near where it should be. And then to see if there is any life on the other bands.

I'll also be trying to see if I can hear the HF osc on the bench receiver too.
Maybe even later tonight.
That was a really good tip.

After these preliminary diagnostics what to do next will be considered. It looks likely, based on what I saw on one of the websites, that I'll end up pulling the entire tuner assembly out anyhow. I've got to repair the band indicator on the main dial side - probably replace it with one from the rust-o-matic unit, the one in this one has a bend in it (how the heck did that happen??). Makes the band switching not so great.

Also cleaning the chassis surface will be far easier.

We'll see...
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« Reply #10 on: October 21, 2014, 07:11:32 PM »

So, I got the stuff to clean. Mostly things recommended by others on their websites where they did restorations.

Attached is the test.
I did it on the bottom plate.

The right hand upper set is Amonia + 409 with and without scrubbers, including the magic eraser (not terribly impressed, btw).

The upper two left are NEVR-DULL applied top with the magic eraser, and below that with the wadding.

Lowest right is the winner.
I did a better job with it on the lowest right, but that was after I took the pic, and you can't see the up close surface detail in the photo.

If ur going to rub on that old zinc plated chassis, use a thing that is totally soft, otherwise you will get scratch marks. That's the bottom line. I tried some of these microfiber dish towels, worked great, no scratches (unless you pick something up from the surface).

So, clean the surface carefully first. Alcohol or 409, Mean Green, Fantastic will likely get all the surface stuff off. The Alcohol + Ammonia seemed to work ok, could not say it was better than 409 alone. Might be. Good if you want just a cleaned, dirt free result.

I found that the NEVRDULL really polished well, but has some abrasive action in the wadding. Took the zinc "black" and bamm, gone in short order. Shiny result. Shiny is NOT always a good thing. Probably on things like aluminum IF cans, it could be, or things like that.

The Magic Eraser? Dunno, jury is out. Could not find the proper application for it. It's interesting, slightly abrasive, very slightly. Probably more than any rubbing compound, although maybe on par, but without the cutting action. So, could be a good tool. Might be best on painted surfaces.

But the basic Turtlewax Color Back, which is a basic auto polish with some polishing compound thrown in did the ultimate job IF you want to make the zinc SHINE. The microfiber towel left it shiny without any streak/rub marks.

Paper towel left rub marks. Ick.
The zinc is dead soft after rubbing. Beware.

Fingerprints (inevitably present) from the past do not come away fully with the polishing. And not at all with just the cleaner.

Still may experiment with some chemically active methods...

Turns out the chassis itself is painted! So that it will only require a regular cleaning, maybe a light wax. The IF cans are painted too. No sign the unit was re-done before, so this looks original. Actually this is a relief, less work.

What else?

The black oxide on the zinc sucks...  Angry

Thinking out loud now, it seems to me that the polish on a chassis would be excessive. Really good for mechanical parts though... if they are plated. I found that it may be possible to control the polish when I was experimenting with Color Back. You can find different grades and hardnesses of polishing compounds. The right grade and just the right duration of polishing would give less than a full shine and a clean look. Tricky. The Color Back goes from that to shiny rather quickly. So the thing that would work would in essence be a really really poor polish!  Roll Eyes

Ok, a wide shot of the topside from the rear of the radio too...

Next the bit with the Arrf generator and listening on the receiver for the HF Osc.

How much an hour do I pay myself??



* ZINC-CLEANER-TEST.jpg (265.73 KB, 1480x1973 - viewed 629 times.)

* CHASSIS-TOP-ANGLE.jpg (185.34 KB, 1480x1110 - viewed 675 times.)
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« Reply #11 on: October 21, 2014, 08:39:37 PM »


   Very Nice...
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« Reply #12 on: October 21, 2014, 09:25:32 PM »

"Lowest right is the winner.
I did a better job with it on the lowest right, but that was after I took the pic, and you can't see the up close surface detail in the photo. "

I could not quite figure out what worked the best from your post.  Could you clarify what worked best?  I have an SP-200(F270/FRR) & RA74-D PS to restore, eventually.

Thank you.

Jim
Anchorage Alaska
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WBear2GCR
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« Reply #13 on: October 21, 2014, 10:09:26 PM »

When I get the quad of rotating towers with 1/4 wavelength 75m beams, I intend to work you direct from here to KL7 land!! (yeah right)

I remain semi-comatose while doing all this... trying to do too much without any down time, and squeezing in this project. I did not write what I intended.

After doing all the the upper sections, I did the lowest right with the Color Back car wax and not the microfiber towel.

THEN, I did the lowest left, which is NOT in the picture using the Color Back and the microfiber towel and got almost no evidence of scratches.

In all cases the bottom plate had been cleaned with warm water and dishwashing detergent first.

I'm really not sure that I've found the best system. But if you want pretty shiny, this is sure a good way to go. I'd call it a bright semi-gloss result. The NevRDull comes off as more of a full sheen.

What I'd like is something chemical to "brighten" the zinc. But I'm not sure this can be done without dunking it into a vat and applying juice to it.

I've yet to try any acids or acidic substances. Maybe that's next.
I did do a search on "brightening" zinc and found very little online.
Somewhere I have a copy of Metal Plating Handbook, a yearly publication, from a decade or more back, it may have something on brightening chemically.

Perhaps this is getting "too fine".

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« Reply #14 on: October 22, 2014, 10:59:39 AM »

Bear, it is most likely obvious to you, but that wonderful Super-Pro 15-Watt hi-fi output is at 600 Ohms.

I've seen more than one ham feed it to an 8-Ohm speaker and wonder where the oomph went....

73DG
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« Reply #15 on: October 22, 2014, 11:16:37 AM »

At the modest volume I'm running, it woiks FB OM! Good enough for testing.

One possible solution is to take a "70volt" speaker distribution transformer - the one that is hung on the frames of those speakers up in the ceiling, and run that. It works out to be pretty much what you need to do the job. Some of them have multiple taps, I have a few around like that, so you could optimize the taps.

The way to do that without getting too heavy into test gear is to put a scope (best) or a voltmeter on the secondary that is being loaded by an 8 ohm resistor, or the secondar tap that you picked. Of course if ur using a 4 ohm speaker or a 16ohm speaker, use that resistor instead.

Now, put a steady tone on the output (BFO + carrier). When you have the right combination of taps you will see the highest voltage on the load.

Although pretty much anything close will be good enough.

I'd only use high sensitivity speakers with radios like this.
modern Hi-fi speakers not being high sensitivity. Old school speakers like from AM-FM-Phono living room consoles, or PA/SR pro audio speakers are the right sorts. Cheesy

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« Reply #16 on: October 22, 2014, 11:20:12 AM »

Tested the HF Osc.

NG except for the working band. Heard in the receiver on the 10-20mc band.

Put the scope probe next to the plate of the Osc tube, nice sinewave. Nothing on the other bands. Sad  Now have find out why.
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« Reply #17 on: October 22, 2014, 01:18:22 PM »

Some possibilities:

Dirty or bent knife switches on the cam switch, or slipped lobe.

Open coils due to bad caps passing B+, and that PSU can really have them over a barrel as in a pinch it can run two of those radios at once.

Soft osc tube.

73DG
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« Reply #18 on: October 22, 2014, 03:07:13 PM »

Betting on missing the B+... although maybe not.

Unlikely to be a soft tube since the 10-20mc band is higher than the low bands, and it's likely to run lower more than high, I'd expect.

Next time I'll probe the sucker!! C'mere ya b*****d!!

Good thoughts there Dennis! Cheesy

I do have the hammer handy in the drawer, just in case I need it!!  Shocked
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« Reply #19 on: October 22, 2014, 04:14:07 PM »


        An ohm meter from pin 8 (cath) of the HFO tube (6J7)
to chassis will check the Band switch. shouls be <2 ohms in
all positions.

        If the tube were soft, one would think since it works on
the 10-20mc band it would still work on the high end of band 4
the 5-10mc.

        You can also Inject the HFO signal into pin 8 of the HFO
socket (V4) and see if the rest of the stuff works..  Easier with
2 signal generators but an antenna should work too.

    RX Frequency + 465kc = Injection frequency.

GL

/Dan
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« Reply #20 on: October 22, 2014, 08:26:16 PM »

Well not quite, will pin 8 check the bandswitch.

It's trickier than that.
The bandswitch shorts out the unused coils on one side and the CT.
Each coil having three terminals.
When the band is switched IN the grounded CT of the coil is now connected on one side to the cathode, but IT is on ground through the bottom end of the coil.
The first side of the coil, the high side is connected through a cap back up to the grid, which in turn has a cap coupling it to the grid.

The tricky part, and it took me a bit to figure out what to do about it, is that the first side, with the blocking/series resonating cap is also shorted out when the bandswitch is NOT on that band - so all times other than when it is in use, it is shorted to ground.

So, what I just did is to put the probe on the side of the grid blocking cap (which resides above the main tuning variable cap (for those following along) and also checked  the output of the switch that goes to the series resonating cap on the first side of the coil, the other end of the meter on ground.

IF the cap is ok (not shorted) then the resistance measured when the band is switched in will be infinite - cap is good. If there is resistance shown when the band is switched in then there is a short across the cap.

Every band other than the good one shows a dead short!

You could just probe the contacts on the outside of the switch and look at that to ground
as you rotate the band switch too, but that won't tell you if you have continuity back to the grid cap...

So, it's looking like there are dead old micas in the oscillator.

I'll have to figure out how to get into those coils and pull a cap for testing, in the next installment!

I'll post up the section of the schematic in question and shoot some pix of the mechanism that does the switching. Pretty neat switch.

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« Reply #21 on: October 22, 2014, 09:39:02 PM »

We'll see if it's those caps or not.

Anyhow here is the schematic in question.
The area of interest is the set of coils to the right.
The bottom one is the lowest freq, and the top is the highest.
The trick switch is the thing directly above the coils.
The cap on the main tuning condensor is C15, next to the grid cap on V4, the HF OSC.

If you look at the switch, good idea to zoom it up big on the screen, the horizontal BAR is the bandswitch.
The things that go at a 45 deg angle and look like the usual switch schematic representation, those are the grounding contacts for the unused bands.

When a band is selected a shorting bar comes down and connects across the 2 pairs of contacts. On SW 1E that is shown connected in the second position from the top.

It shows the connection to the ground buss (one buss left and one buss right) open.

In reality it is not a single switch. Not a DPST at all. The way it is made is by using a phenolic guillotine that has silver plated brass wrapped around the bottom of a square piece - this rides up and down. In the down position it engages two pairs of fingers, forming two switches. The ground is accomplished by springy silver plated fingers attached left and right to the switch enclosure.These are NC contacts. (not North Carolina) When the phenolic switch blade rides down, it pushes past the spring contacts and opens the ground connection for the band being engaged. Wheee!

Anyhow pix of this Rube Goldberg operation after I get them off the camera and adjusted for size...

Imagine the conversation in the product development lab at Hammarlund?
"Sven, come here! Look, the design is very good, but we have a problem!"
"Ya vat dis it?"
"Vell, ve will need to short out the unused coils!"
"VOT DO YOU MEAN SHORT OUT THE COILS?? How can vee do dis?"
"Dat is your problem Sven! Make the coils short out!"

Which is probably why this design has these fingers outside the cage to do the grounding of the unused bands. Maybe. You decide!


* BCC-779 PG 104.pdf (96.63 KB - downloaded 257 times.)
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« Reply #22 on: October 23, 2014, 08:03:27 PM »

keep it up, fine , educational, and entertaining!
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« Reply #23 on: October 24, 2014, 10:47:22 AM »

I have a similar Hammarlund, a SP400 that I started and left off putting back in service.  The beautification effort is commendable but I'm more interested in your electrical restoration effort.  Does the receiver still have the original paper / wax caps in it?  If so, it is a fairly easy job to completely remove the tuning unit from the chassis and do your work on replacing those caps with orange drops.  

While you are at it, inspecting the tuning unit is much easier with it removed.

As we discussed on the air today, I'd be most interested in how you eventually restored the front panel

Al
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« Reply #24 on: October 24, 2014, 02:20:55 PM »

Al,

Nice signal - as always - emanating through the aether from ur QTH down to the netherlands of the northern Hudson valley in Noo Yawk!

This radio has an engraved (probably stamped in reality) front panel. As mentioned earlier, I had bought a rust-o-bucket some time back and had already stripped the panel (was surprised to see it is nickel plated underneath!) and primed it. I shot it with some metallic car paint, similar to the one in the first post.

What I mentioned in the QSO is that folks seem to often sell parts, including just panels on fleapay...

Patrick, thx.

Anyhow here are some shots of the deep interior.

First one is the place where the greed cap connects back through the requisite blocking cap. (mentioned in the earlier post).

Following that is the shot on the other side of the tuner section showing 'Sven's magic fingers'. These are the shorting contacts of the switch! When the (switch) blade is up the finger, being springy, touches the side of one of the three finger contacts that catch the blades on the bottom of the center of the tuner chassis (under the blades).

Next shot is the top view of that center section showing the cams on the shaft, the blades that go up and down, and you can probably see the silver plated spring fingers on the bottom that contact the bottom of the blades to form the switch itself.

One of the things that always strikes me is that they worked everything BIG back in those days. There is no reason that the same mechanism could not be easily shrunk down to 25% of that size, and work just as well. The coils too, IF and RF, wound on large forms, with big slugs. 20-25yrs later with miniature tubes, later receivers using the same design (essentially) like the SX-88 being the same as the SX-28 to a great extent used smaller cans and coils...  well, big it is...

My next step is to pull some screws from one of the HF osc's coil modules and see what it takes to get it out or get at the cap.



* GRID-BLOCKING-CAP.jpg (213.05 KB, 1480x1110 - viewed 641 times.)

* SVEN'S-MAGIC-FINGERS.jpg (210.93 KB, 1480x1110 - viewed 661 times.)

* WHEELS-GO-ROUND-AND-ROUND.jpg (292.21 KB, 1480x1110 - viewed 638 times.)
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_-_- bear WB2GCR                   http://www.bearlabs.com
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