Call Search
     

New to Ham Radio?
My Profile

Community
Articles
Forums
News
Reviews
Friends Remembered
Strays
Survey Question

Operating
Contesting
DX Cluster Spots
Propagation

Resources
Calendar
Classifieds
Ham Exams
Ham Links
List Archives
News Articles
Product Reviews
QSL Managers

Site Info
eHam Help (FAQ)
Support the site
The eHam Team
Advertising Info
Vision Statement
About eHam.net

   Home   Help Search  
Pages: [1]   Go Down
  Print  
Author Topic: heathkit sb 200 moded to use ccx800a7 tube info  (Read 1355 times)
N3JBH
Member

Posts: 2358




Ignore
« on: October 14, 2005, 01:21:07 PM »

hello kind folks i heard  threw some talk that there is a mod to use the sb-200 with the 3cx800a7. i did a google did not find much information. and the guys i heard it from knew nothing other than it was done some where. so with that all out of the way does any one no anything about this interesting mod?

i did notice peter dahl sells a new transformer for the fillaments  for this mod  but gave no details. and steve and alan i know you two know plenty so whats up?
jeff/n3jbh
Logged
WB2WIK
Member

Posts: 20561




Ignore
« Reply #1 on: October 14, 2005, 02:18:47 PM »

I've never seen this done, but I imagine it might be possible.  The plate voltage ratings are compatible; however I don't know why anybody would replace two inexpensive 572Bs with one very expensive 3CX800A7, unless they happened to have the 3CX800A7 laying around anyway.

The 3CX800A7 requires forced-air cooling, a special air system socket, a chimney and a centrifugal blower (to provide pressure), all of which the SB-200 doesn't have, so these are pretty major changes.

WB2WIK/6
Logged
N3JBH
Member

Posts: 2358




Ignore
« Reply #2 on: October 14, 2005, 03:30:07 PM »

thanks steve i wasnt sure myself why it was done? but it sounded intruiging. i thought maybe there where doing this to move it to 6 meters maybe aswell as that really be better tube. but i guess you have to weigh out the cost and work to see if this really have any advantages aswell.
Logged
WB2WIK
Member

Posts: 20561




Ignore
« Reply #3 on: October 14, 2005, 04:40:29 PM »

Maybe.

If I was going to modify an SB-200 for a 3CX800A7 in order to use it on six meters, I'd start with a blank chassis and just build a six meter amplifier -- it's easier.   And if I were starting with a blank chassis, I'd use a different tube than a 3CX800A7, mostly because that one's expensive.

My last 1500W 6m amp used a 4-1000.  Not that it's such a great tube, just that it takes an inexpensive socket, cooling is easy and the tubes are available surplus everywhere for $100 each.

For a baby kilowatt, I'd just use a 3-500Z.

WB2WIK/6

Logged
W9GB
Member

Posts: 2613




Ignore
« Reply #4 on: October 15, 2005, 03:41:10 PM »

I very much doubt that this conversion was performed on a stock SB-200 (Two Hundred) which uses the 572B tube ....

It is more likely that the SB-220 (Two Hundred Twenty) which uses the 3-500Z woudl serve as the basis for such a conversion.

Also likely that this is another urban legend or rumor -- ask for photos or web pages.

w9gb
Logged
PA0FRI
Member

Posts: 31


WWW

Ignore
« Reply #5 on: October 17, 2005, 04:01:03 PM »

If you want to replace the inexpensive 572bs do it with one or two GI-7Bs.
Frits, PA0FRI
www.xs4all.nl/~pa0fri
Logged
W8JI
Member

Posts: 9304


WWW

Ignore
« Reply #6 on: October 18, 2005, 02:56:08 AM »

That mod is NOT performed on the SB200.

It is performed on the SB230.

The SB230 uses a tube similar to the 3CX800 except the tube is air cooled. The tube in the SB230 is an obsolete ceramic metal heat sink cooled tube.

Since the 230 has room you can easily change things over to use the 3CX800 by adding a blower, air box, and other minor changes (like a grid current overload circuit and proper filament voltage adjustment if you want to do it right).
Logged
K3XF
Member

Posts: 3




Ignore
« Reply #7 on: October 23, 2005, 04:30:59 AM »

The SB-230 has pros and cons in a 3cx800 conversion. It has a pretty wimpy power supply so utilizing the tube to its fullest would be almost impossible. On the other hand it would probably last a long time if you don't allow drive w/o B+. My favorite conversion for the 3cx800 is the MLA-2500. The tube is mounted in horizontal plane on the back of the amp with the stock fan on a spacer to allow the input circuitry to be mounted to the bottom of the tube. 1000W PEP and no problems at all (120VAC) 160-10M (10 required one less turn on the output coil). The tube heat sensor works well when I use the amp on AM. I put a (somewhat undersized for inrush limiting) R/S filament transformer in the RF section under the T/R relay.
I have a SB-230 and may put in a pair of GI-7s and convert it to 6M. That should prove  interesting. 'thinking of machining anode coolers like the tubes that were in the MLA and using the same type of fan as the MLA on the back of the SB-230. I expect it will do about 600W PEP output. 'could do the same kind of conversion as the MLA and put in a 3cx800 but am convinced I wouldn't get any more out of it .. .  $250 used 3cx800 vs $40 for a NOS pair of GI-7s is the real driver for working the pair vs a known entity . . . The perfect tube might be the GI-7 on steroids . . . GI-46?. Maybe I will look into that tube before starting work on the two holer . . . 'would probably use the MLA cooling scheme (horiz tube) in that case . . . Considering the upper freq capability of the GIs, a good VHF suppressor might be wise . . . . . .

-ap
Logged
PA0FRI
Member

Posts: 31


WWW

Ignore
« Reply #8 on: October 23, 2005, 09:28:47 AM »

To replace a SB200 with GI-7Bs is a matter of skill and conversion, see what I did with a Dentron GLA1000:
www.xs4all.nl/~pa0fri/Lineairs/GLA1000/gla1000eng.htm.
A SB200 can be converterd accordingly.
Logged
K3XF
Member

Posts: 3




Ignore
« Reply #9 on: October 23, 2005, 12:27:07 PM »

Nice work . . . the GI-7 conversion is very professional. I see you put in a sub chassis to support the sockets . . . Where did you get the sockets? I was  going to 1.5" hole saw a 6X6X2" chassis and use retaining clips on the lip. Now that seems rather crude.
The tool clips for grid connections is a great idea too.

Have you done power output at 2100V tests yet? I think the GLA-1000 and SB-230 have about the same power supply capability from a VA perspective. The '230 runs about 2500V no load. I'm guessing about 500W CW output.

The GI-7 or GI-46 are too tall to fit into the '230 in the vertical plane as you did with the GLA-1000 so my horizontal single tube method is how I will proceed. The GI-46 is looking better all the time.

All the best,
Art
Logged
PA0FRI
Member

Posts: 31


WWW

Ignore
« Reply #10 on: October 24, 2005, 02:30:10 AM »

Hi Art (K3XF),
I purchased the sockets via eBay.de.
Output test with 2100 V supply:
Unloaded 2150 V (mains=221VAC)
Loaded 1600V/750-850W (CW). With SSB the plate voltage was average 1900V.
I reduced the output to 700-750W with a 25 Ohm feedback (cathode) resistor.
73, FRits, PA0FRI
Logged
K3XF
Member

Posts: 3




Ignore
« Reply #11 on: October 24, 2005, 03:54:06 AM »

Hi Fritz,
Thanks for the info . . . I will check out eBay and see if any more of the sockets are around. The power output is more than I expected and should make a good conversion for the SB-230.
73,
Art
Logged
Pages: [1]   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.11 | SMF © 2006-2009, Simple Machines LLC Valid XHTML 1.0! Valid CSS!