[Central-Electronics] SS rectifiers? 100V/200V?

[K6JEK]

My 100V had the tube rectifiers replaced with solid state plug-ins by  
none other than Wes Schaum,  President of Central Electronics.    
After he left Zenith he did a little business refurbishing CE gear  
and my 100V went through his shop way way back when someone else  
owned it.    This made me think SS rectifiers are not anathema to  
100V's, that plus they put them in 200V's.

However, I suspect that the LV is so high it's driving the voltage  
regulator out of regulation.   I was getting frequency hopping and  
I'm not getting it now that I run it at 110V.   I'm not sure about  
this, it's just a theory.

Like Eugene, I wonder if the 200V had a different transformer to go  
with the silicon rectifiers  to take the HV down a peg.

Jon, K6JEK


On Mar 10, 2007, at 2:18 PM, Eugene Hertz wrote:

> Hi All (long email-apologies up front),
>
> While trying to set the FSK shift on my 100V last night, it coughed  
> up some smoke. I am pretty sure the smoke was from one of the 6AU4  
> rectifier tubes used in a 600V supply (for 6550 finals).
>
> Reason I think the tube gave up the smoke was because after I saw  
> flashing in the tube, there was soot at where pin number 1 would  
> be . I also observed actual smoke lingering in the pin hole of the  
> socket in which pin #1 would be. Pin number 1 actually has a  
> structural support to hold up the guts of the tube. This support  
> does not protrude beneath the glass envelope, but is held in place  
> by the glass. Observing this with a magnifier, I can see  
> discoloration at the point at which the support is affixed in the  
> glass. And last but not least, the base of the tube stinks! Just  
> like the smell when the smoke was emitted.  Of course, a very valid  
> question is, could something have failed and caused too much  
> current through the tube to destroy it? I will put it on the bench  
> to make sure nothing else has suffered.
>
> So, I am thinking about replacing the rectifiers with solid state.  
> You may ask why? Simple answer is there are 3 rectifiers in the  
> transmitter consuming a total of 37W of filament power and heat.  
> For those concerned, I always run the transmitter through a variac  
> and can adjust it down to lower the B+ if necessary. Also, as far  
> as inrush through the power transformer, I think I'm ok because the  
> power transformer does not directly feed filter caps, it first goes  
> through some mighty chokes. So I think the choke will moderate the  
> current filling up those capacitors.
>
> On the subject of reducing the mains voltage to compensate for the  
> higher HV—Seems the 200V had solid state rectifiers for all  
> rectification. I will also note that the HV supply in the 100V  
> model is 600VDC and on the 200V model its 680VDC! Given that the HV  
> in both models is used for the 6550s and the CRT tube, this leads  
> me to think that even if my HV B+ went to 680 as a result of  
> replacing the tubes with ss rectifiers, there should be no reason  
> to worry. I also checked the resistors and caps in the HV sections  
> for both models and they all remain the same values and ratings. Of  
> course, this may be an oversimplification.
>
> I looked through the manual of the 200V and looked at the schematic  
> as posted on bama and could not find this. Can any 200V owner tell  
> me what the B+ voltage is? 100V is 340VDC. Looking at the 200V  
> diagram, it looks like it should be ½ HV can anyone confirm?
>
> In any case, the real question is, does anyone have any experience  
> with SS replacements for the 6AU4? My google research has only  
> located one which can be found here: http://tinyurl.com/2crs5e
>
> This is the only one I've located. Anyone ever use this brand?  
> Anyone know of any other product? Transmitter also has a 5U4 which  
> I will probably replace with the weber copper cap.
>
>
> If I replace the rectifiers with solid state and if HV ends up at  
> 680V as a result, can anyone think of a reason why this would be a  
> bad idea?
>
> I am particularly interested in what other folks have used to  
> replace the 6AU6.
>
> Has anyone tried to completely replace the power supply section of  
> the 100V with the same circuit as the 200V? Remove all rectifier  
> tubes, put in a standard solid state full-wave-bridge tap the  
> center and be done?
> Thanks!
>
>
>
>
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