[Heathkit] SB-200 Problem

[jbrannig at optonline.net]

> Id start by removing the Measures mods as they are voodo science. 
> Its not 
> easy to find 33-47 Ohm 2W carbons these days but Id rewind 
> original spec 
> parasitics.
I've had Measures parasitic suppressors in my SB-220 for years.
There is no switch arching, spitting or strange noises.
Voodoo, yes, effective, absolutely......
Jim

> Recently acquired SB-200 was refurbished and some mods added.  
> Worked FB on 
> 40 meters for about an hour and then would not load any more.  
> Readings when 
> working:
> 
> Tune Control:  Top of 40 meter range
> Load Control:  2.8
> Drive:  90 watts
> Output:  600 watts
> 
> Readings now (40 meters):
> 
> Tune Control:  Top of 40 meter range
> Load Control:  Almost full CCW
> Plate voltage, no load:  2390
> Plate voltage, 250 ma. (as high as it will load, regardless of 
> amount of 
> drive applied)
> Plate voltage, loaded to 250 ma.:  2280
> 
> Tune control produces barely discernable dip in plate current at 
> resonance. 
> Grid current remains well within the white arc at all times.  Grid 
> and plate 
> current both respond to drive power up to mid-scale for the grid 
> current and 
> up to 250 ma. for plate current.
> 
> On 20 meters, results are similar, except that resonance occurs 
> with the 
> Tune Control well to the right of the 10 meter arc (off scale).
> 
> The only parts that have NOT been replaced are the entire power 
> supply, 
> which checked OK, all the RF chokes, the plate tune and load 
> variable caps, 
> and the doorknob and other HV caps in the final tank circuit, and 
> the relay.
> 
> The Harbach softkey mod, the Richard Measures parasitic 
> suppresssors, a 
> 20-ohm, 25-watt glitch resistor in the plate voltage line, a 10-
> ohm, 3-watt 
> resistor between lug 8 of bandswitch wafer and C16 (to reduce 
> parasitics and 
> excess drive), plus two diodes for meter protection, have all been 
> installed.  Also, the filament voltage, which was excessive, has 
> been 
> dropped to the recommended 6.09 volts range.  Finally, the silver 
> mica caps 
> on the 10, 15 and 20 meter tuned input coils (one of which was the 
> wrong 
> value and the others missing entirely) were replaced.
> 
> Since the malfunction occurred, all the parts that can be checked 
> have been 
> checked and nothing can be found wrong.  The bandswitches have 
> been checked 
> for arcs and whatnot and are OK.
> 
> I am out of ideas.  Can anyone help???
> 
> Keith
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> _______________________________________________
> List Administrator: Duane Fischer, W8DBF        
> ** For Assistance: dfischer at usol.com **         
> $$ See the vintage area on the HCI web site - http://www.w9wze.org 
> $$ 
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