<html><head><style type="text/css"><!-- DIV {margin:0px;} --></style></head><body><div style="font-family:times new roman,new york,times,serif;font-size:12pt"><div>Thank you for the very nice and comprehensive update. Just a very nice set of data to have and I will be adding a paper copy to my Ham notebook. <br><br>73<br>Bob Groh, WA2CKY<br></div><div style="font-family:times new roman, new york, times, serif;font-size:12pt"><br><div style="font-family:arial, helvetica, sans-serif;font-size:10pt"><font face="Tahoma" size="2"><hr size="1"><b><span style="font-weight: bold;">From:</span></b> Kenneth G. Gordon <kgordon2006@frontier.com><br><b><span style="font-weight: bold;">To:</span></b> Heath@puck.nether.net<br><b><span style="font-weight: bold;">Sent:</span></b> Wed, August 8, 2012 6:01:39 AM<br><b><span style="font-weight: bold;">Subject:</span></b> [Heath] Results of experiment with reactivation of 572Bs in SB-200<br></font><br>
My experiment, begun 2 years ago, in which I asked for used 572Bs has <br>finished, and I have discovered several things of interest.<br><br>First of all, those 572Bs which have been made in China by the Shuguang <br>company are very marginal even when new. Their filaments are not made at <br>all correctly, and have absolutely no reserve emission capability. Once they <br>are used up, there is absolutely no possibility of reactivating them, unlike <br>properly-made U.S.-made tubes.<br><br>The Chinese-made tube's plate dissipation rating is not 160 watts, as the old <br>Cetrons were, but is more like 125 watts per tube. Furthermore, the grids <br>appear to be unusually fragile, accepting no more than 30 mA grid current <br>per tube, whereas the original 572Bs were rated at 50 mA grid current per <br>tube. In fact, in the interests of longevity, I would not operate the Shuguang <br>tubes regularly or for very long at any grid current much above about 25 mA
<br>per tube.<br><br>Plate current, rated at 250 mA per tube for the original Cetrons, should never <br>be allowed to be above 200 mA per tube with the Chinese-made versions, <br>for very long.<br><br>Then, tuning and loading using the Chinese-made tubes is very different <br>from that using an old, but reactivated set, of Cetrons I have here. This <br>indicates to me that the plate impedance of the Chinese-made tubes is very <br>different from the originals.<br><br>Lastly, even 5 minutes of operation of my SB-200 with new Chinese-made <br>tubes installed, at 14 WPM CW and at a power output level of 400 watts, <br>resulted, routinely, in glowing red plates. This continued as the tubes were <br>used.<br><br>I received several sets of used and pretty well used-up, Chinese-made <br>572Bs, through at least one member of this list, with a view to attempting any <br>of several different methods of reactivating them.<br><br>Any attempt to reactivate the
Chinese-made "572Bs", using methods that <br>have always worked for me in the past with other thoriated-tungsten-<br>filamented tubes, resulted in complete failure of what was left of the Chinese <br>tubes.<br><br>I also bought, over the past two years, 4 complete pairs of new Chinese-<br>made 572Bs. I bought two sets directly from China, and two sets from R.F. <br>Parts. The R.F. Parts tubes were labled 'Taylor" but were very clearly the <br>same tube as those I bought directly from China.<br><br>In the two sets of tubes bought from China, one failed immediately with a <br>grid to filament short. Another worked OK, although it rattled when shaken.<br><br>The two sets of tubes bought from R.F. Parts worked right out of their boxes, <br>and none were defective. Obviously, R.F. Parts is very careful with their <br>tubes and tests each one before they accept it or sell it.<br><br>I have absolutely nothing to complain about concerning R.F. Parts service or
<br>warranty.<br><br>However, ALL the new Chinese-made tubes lasted no more than 9 months <br>of normal to light use in my restored SB-200.<br><br>At times, they acted very oddly. In one case, suddenly going into very strong <br>oscillations on 15 meters and above...for a couple of months, then reverting <br>to acting normally after that, until they finally and rather suddenly began to <br>lose output and exhibit both very low grid current and low plate current at <br>what had been normal drive levels.<br><br>After the output from my last matched-set of "Taylors" from R.F. Parts <br>weakened, I then installed a pair of very old Cetrons I had here, both of <br>which were very weak when I got them, but after I had reactivated them, they <br>showed normal output with very reasonable grid drive.<br><br>I am presently using these ancient, reactivated Cetrons in my SB-200. RF <br>power output is routinely between 700 (80 meters) and 550 watts (20 meters)
<br>with grid current of 30 mA per tube. If I overdrive the tubes to 50 mA per tube <br>grid current, I can easily reach 800+ watts output on 80 meters.<br><br>I normally run them at 30 mA per tube grid drive, and around 400 mA plate <br>current at 2100 VDC.<br><br>They never show red plates.<br><br>According to the Heathkit SB-200 manual, the operator should keep grid <br>current below 100 mA (50 mA/tube) and plate current should be no more <br>than 500 mA. and power input should never be more than 1KW. Obviously, <br>this information concerned new, U.S.-made tubes, and not these modern <br>Chinese-made semi-copies.<br><br>At this point, I am converting at least one of my SB-200s over to a pair of <br>4CX250Bs in a grid-driven, grid-swamped, Class AB1 configuration, with <br>regulated screen and grid voltages. I will use a 25 ohm 10 watt un-bypassed <br>cathode resistor at each tube to improve IMD.<br><br>These tubes will finally allow me to follow
Heathkit's recommendations as far <br>as using the SB-200 is concerned.<br><br>I MAY attempt to buy used, flat or semi-flat, worn out, U.S. made 572Bs such <br>as Cetrons, Dentrons, etc., with a view to reactivating those and using them <br>in my other SB-200, but I doubt if I will ever buy another Chinese-made so-<br>called "572B" unless someone can assure me that they have been <br>redesigned and built correctly, or if I can buy new ones for no more than <br>$10.00 each.<br><br>vy 73,<br><br>Ken W7EKB <br>_______________________________________________<br>Heath mailing list<br><a ymailto="mailto:Heath@puck.nether.net" href="mailto:Heath@puck.nether.net">Heath@puck.nether.net</a><br><a href="https://puck.nether.net/mailman/listinfo/heath" target="_blank">https://puck.nether.net/mailman/listinfo/heath</a><br></div></div>
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