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Author Topic: Heathkit HB-200 renovation  (Read 51381 times)
5B4AET
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Posts: 41




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« on: September 14, 2011, 12:23:42 PM »

Got an SB-200. Shipping cost me alot but I think it worths it.
Everything appears in good condition incliding the valves.
Im in the process of inspecting and checking everything before I power it.
The amp looks like it was owned at least from two people, the first one who built it, did a good job, the second one  Huh (from the mods/updates) seems he did not know what he was doing.
The Harbach soft start is actualy connected to the wrong pair of (black + red) wires - ending to the terminal strip where the A/C is connected.
It has all Harbach mods including a new fan. Will have check every possible mode made on it before any actual test  Undecided

Just out of curiosity, is there a way to know the year of production from its serial number?

Any sugestions regarding safety and mods are most welcome   
Appologies for the title................SB-200

Panicos  5b4aet

« Last Edit: September 14, 2011, 01:31:35 PM by 5B4AET » Logged
K8AXW
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« Reply #1 on: September 14, 2011, 09:00:00 PM »

Hey Panicos!!  Congratulations on getting an SB-200!!

Please tell me this.  Is the manual that came with it a yellow or a gray manual??

The yellow assembly manual is for the earlier SB-200s  --   The gray manual was for the later models.

The one difference I found with the two models is the wiring of one  bandswitch wafer that switches the load cap in or out.  The early model had the HOT side of the load cap. next to the metal switch mounting screw which in some circumstances (mostly mistuning) allowed the HV to arc to this mounting screw which melted the switch contacts.

The newer version wired the wafer so the HV side of the loading cap was further away from the switch mounting screw and he ground side of the cap was next to the mounting screw.

It sounds like you're on top of the situation Panicos.  I suggest you go over the whole amplifier just like you was going to build it. 

Good luck OM. Have fun!

Al

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A Pessimist is Never Disappointed!
5B4AET
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Posts: 41




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« Reply #2 on: September 15, 2011, 12:02:49 AM »

Many thanks Al.

Unfortunately I dont have the original manual so cant tell which version I have. Just got a copy from the internet. Any way can I find this info from the serial number?
Now Im facing a dilema. Shall I keep the amp as much as possible to its ORIGINAL state or change all possible parts to modern ones (caps + resistors)?  Not sure if all these old caps and resistors are still good for the job.

Panicos - 5b4aet






 
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W1BR
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« Reply #3 on: September 15, 2011, 07:32:26 AM »

I'm more familiar with the SB-220, and in that model the
equalization resistors are low enough in value to cause excessive
heating which affects the life of the filter capacitors.

It would be good engineering practice to replace any filter
cap that is getting on in age, especially ones that have seen
a look of service time. Can you see the date codes on the
capacitor shells? Do the equalization resistors look discolored
from use? 

You can replace the caps with a good brand, but replacements
will likely be snap mounts and require some mods to fit the
SB-200 capacitor board. 

Use 105 degree C. rated caps,
and avoid the Chinese junk on eBay. I believe there are
board kits available for the SB-200 if you wish to go that
route. There are better diodes available these days too,
but the old ones seem to work fine.

Pete
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W1BR
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« Reply #4 on: September 15, 2011, 08:04:47 AM »

Here is one ham's homebrew approach:

http://www2.wcoil.com/~tlee/GI7B%20Amp/SB200HV.pdf

here is a commercial option, albiet expensive:

http://www.harbachelectronics.com/main/page_products_sb200__sb201.html

I suspect you could make the new parts fit on the old board
with some ham ingenuity Smiley

Pete
« Last Edit: September 15, 2011, 08:07:15 AM by K1ZJH » Logged
W8JI
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« Reply #5 on: September 15, 2011, 10:05:18 AM »

Panicos,

There is one USA source constantly pushing the idea that the resistors across the capacitors cause a heat problem. If we look at that claim carefully and other claims from that same source, we find most of it is just an opinion or guess with no facts.

Based on the service life history of SB200's, there are very few design problems. There can be some bandswitch issues, the grid bypassing system is not good, and the relay runs very high voltage. If I used one with modern 572 tubes I would add a good fault current limiting resistance and some negative rail power supply clamping. I would also swap from carbons in the suppressor to metal composition resistors like the Ohmmite OX/OY series with no other change in the suppression  system.

Other than that you will find very few repeating complaints or problems that can be documented.

Most of the modifications are more to make people feel like they have done something, because they fix things that historically are never problems even though the amp is around 30-40 years old or older.

My opinion is the designers are almost always much more insightful into what they did than most people trying to re-engineer. In a 40 year life of something normally considered to have a service life of 10-15 years (consumer electronics), any problems show.

Most of things I pointed out are problems for obvious reasons.

For example the relay voltage of around 130 volts was never a problem with tube radios, when the 200 was designed. The band switch issues were an oversight and could have been planned better, so that was a miss. The grid problem with bypass values was created by strong industry influence to use a bad circuit. One person really pushed that mistake. The lack of a negative rail clamp and HV fault limiting was not an issue because back then tubes almost never arced. The carbon parasitic resistors were the only thing available, but now there are much longer life and more rugged metal compositions.

Everything is explainable and measurable. If it cannot be measured as a problem, or explained in a logical way with proof, it is a guess or opinion.

Much of that is driven by people making money, or being misled into thinking things that are not problems are issues.

73 Tom
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5B4AET
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« Reply #6 on: September 15, 2011, 12:50:26 PM »

Propably will do only the nessesary replacements.
Already removed the mods made from before.
Will check all caps and resistors and do the changes when ever needed.
Liked the Harbach mods so I wil replace the relay and the power supply module and add the soft key.
Hopefully will finish all checks by tommorow and power it on....... Embarrassed
Few pics of the beast!!


http://i1099.photobucket.com/albums/g399/5B4AET/Heathkit%20SB-200/P1020424.jpg
http://i1099.photobucket.com/albums/g399/5B4AET/Heathkit%20SB-200/P1020399.jpg
http://i1099.photobucket.com/albums/g399/5B4AET/Heathkit%20SB-200/P1020418.jpg
http://i1099.photobucket.com/albums/g399/5B4AET/Heathkit%20SB-200/P1020396.jpg
« Last Edit: September 15, 2011, 12:52:55 PM by 5B4AET » Logged
K8AXW
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« Reply #7 on: September 15, 2011, 08:21:40 PM »

Panicos:  Looked at your photos.  Looks like you might have a nice linear!  Just be careful.... look it over very close, read past posts on testing the SB-200.  There are many post here on eHam.com

Al
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K8AXW
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« Reply #8 on: September 15, 2011, 08:27:30 PM »

[quote author=W8JI link=topic=77494.msg538948#msg538948

Most of the modifications are more to make people feel like they have done something, because they fix things that historically are never problems even though the amp is around 30-40 years old or older.


73 Tom
[/quote]

Tom:

Do you have any specific modifications or upgrades listed on your website for the SB-200?

If not, perhaps you can suggest the proper grid grounding, negative rail clamping (I have no idea what that means) HV protection and replacing the anode supressor resistors?  
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KA5N
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« Reply #9 on: September 16, 2011, 03:57:43 AM »

Your amp has the Harbach power supply board installed so you have new components in the power supply. 
You have the Soft Start mod.  This is not necessary but doesn't cause any problems (unless it fails).  You have the Harbach fan mod.  Unfortunately this mod
doesn't improve cooling very much and the new fan motor is larger than the original and makes it difficult to get the cabinet off and on.  Since you didn't mention the soft key mod by Harbach, you either have to have this or some other keying interface or you may damage your transceiver.  The Harbach verison is a small
PCB that is placed near the center of the chassis toward the rear.  You need to
add a couple of pictures of the underside of the chassis.
You still have the original Cetron 572B's which (if good) will last a long time if not
pushed.  These are much better tubes than Chinese copies. 
I have two SB-200's and they put out an easy 500 watts day after day.
The only thing I notice in the photos that might indicate a problem is that the
Silkscreening above the tune control is worn, this might indicate that a previous
owner spent too much time tuning which might have stressed something.
Good Luck
Allen
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W8JI
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« Reply #10 on: September 16, 2011, 05:20:34 AM »

[quote author=W8JI link=topic=77494.msg538948#msg538948

Most of the modifications are more to make people feel like they have done something, because they fix things that historically are never problems even though the amp is around 30-40 years old or older.


73 Tom

Tom:

Do you have any specific modifications or upgrades listed on your website for the SB-200?

If not, perhaps you can suggest the proper grid grounding, negative rail clamping (I have no idea what that means) HV protection and replacing the anode supressor resistors?  
[/quote]

I need to work on that, but I've been waiting to get an SB200 in.

I'm not much like others in how I do mods and things. I always like to measure first and actually see if something is really a problem before fixing it. My policy with old gear, or even new gear, is to change only the things that really need changed. :-)

I don't really have statistics on this, but my impression is well over half of the modifications floating around do not make anything better.

G3RZP, you, and several others seem quite sensible. Some very prolific writers, however, just write nonsense about mods.
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W1QJ
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« Reply #11 on: September 16, 2011, 05:45:07 AM »

This is an interesting turn in the thread.  I was recently contacted through my website by a fellow ham who wanted to send me a Kenwood TL-922.  He requested a plethora of modifications done to the amp.  It seems he just bought it and simply wanted all this stuff done to it before he used it.  I questioned him about having any specific problem that the mods are suppossed to correct and I got no response.  I told him I would gladly perform the "soft key" mod and a "soft start" mod.  Above that I recommended nothing unless a specific problem could be identified.  I did not hear from him again.  Apparently he is looking for someone to just go ahead and do the many things he requested.  Many of which contained the west coast mods and the mods from Tulip land. 
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W8JI
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« Reply #12 on: September 16, 2011, 06:54:46 AM »

This is an interesting turn in the thread.  I was recently contacted through my website by a fellow ham who wanted to send me a Kenwood TL-922.  He requested a plethora of modifications done to the amp.  It seems he just bought it and simply wanted all this stuff done to it before he used it.  I questioned him about having any specific problem that the mods are suppossed to correct and I got no response.  I told him I would gladly perform the "soft key" mod and a "soft start" mod.  Above that I recommended nothing unless a specific problem could be identified.  I did not hear from him again.  Apparently he is looking for someone to just go ahead and do the many things he requested.  Many of which contained the west coast mods and the mods from Tulip land. 

I have a 922 here that has so many mods it never worked correctly after the mods. I have to undo all the mods and them see what is really wrong with the amplifier. The fellow paid to have all this done, and now has to have it all undone.

The nichrome was all added, the amp became unstable, so they removed most (but not all) of the nichrome and went back stock. Then it ran a while before giving up.

If you look at the latest QST, someone hacks an AL80 up by measuring voltage at the wrong place and using the wrong maximum voltage. Worse yet, QST tells readers to plug the amp in, push the interlock closed with a STICK, and measure filament voltage with the cover off and one hand holding down the interlock. Worse yet, they don't even give the cortrect voltages as a target. The reader puts himself, the author, QST, and even the manufacturer at risk doing something wrong.
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5B4AET
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« Reply #13 on: September 16, 2011, 07:31:32 AM »

The previews owner tried hard to make the amp better Undecided.
Added Soft start, soft key, new supply board and new fan. As mentioned in earlier post the soft start module was connected on the wrong pair of black+red wires  Huh. Actually it was connected on the ones that go the the mains terminal strip (ac) can be seen if you give a good look on the fotos. So i disconnected it. Not sure what result this "mod" had......hope did not make any damage (disconnected the soft key too).
The supply board seems to be ok...... but based on how the soft start was connected I will not use the soft key as well (which was on the amp). Cant risk my Icom!!! Will connect a new one.
I will also replace the relay and the output connector.
Will a computer fan do a better cooling than the fan replacement?

Was wondering what I can do to reprint the front panel lettering.
Thanks for the input + help. Will keep you posted on the progress and results.

http://i1099.photobucket.com/albums/g399/5B4AET/Heathkit%20SB-200/P1020403.jpg
http://i1099.photobucket.com/albums/g399/5B4AET/Heathkit%20SB-200/P1020402.jpg
http://i1099.photobucket.com/albums/g399/5B4AET/Heathkit%20SB-200/P1020401.jpg
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W1QJ
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« Reply #14 on: September 16, 2011, 08:51:00 AM »

IMHO....The single most NEEDED mod to Heathkit amps is the soft key.  You NEED that (in one form or another).  The soft start can't hurt but after 40 some years that many of these amps have been running it makes you wonder?  After many years carbon comp resistors change value just with age as well as heat effects.  Going to voodoo magic is not the answer.  Stay with a new carbon comp or a MOF and keep same design.  Fans, rectifier boards, capacitor banks, are GREAT replacement items since NOS parts are unavailable.  They are there "if" you need them.  Other mods need to be seriously considered, I suggest you read up very carefully about all of them and their credibility.  Some people have motives to push the mods.
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