[Boatanchors] 6AU4 SS replacement?

[Richard Post]

Hi Eugene,

Thanks for the link to the rather complex CE-100V schematic.

Since you are using the variac, I'm back to my "no good no reason why 
two or three cheap 1N4007 diodes in series and maybe a resistor, all 
in a tube base, wouldn't do the job well."  Extra RF bypassing in the 
way of a small  high-voltage cap across the diodes would be of value 
to protect the diodes from RF.

The 6AU4, as a now-cheap television damper diode, piqued my interest 
because I have given thought to using just one of those fed by two 
solid state diodes as a cheap replacement for the expensive GZ-34/ 
5AR4 for hi-fi amps.  The diodes would provide the full-wave 
rectification and the 6AU4 or similar damper diode would provide the 
slow warm-up and voltage drop.  The 6AU4 filament would be fed by the 
5 volt line increasing the warm-up time a bit.

Be sure to check for possible carbon trails on the socket of the 6AU4 
that died. Those tubes can handle a PIV of 4500 volts, overkill in 
this circuit.  Makes me wonder what happened, such as did RF got into 
the B+ line.  Also check for any leakage in the separate 6 volt line 
to ground.  Should be absolutely none.  That 6 volt filament line 
feeding the 6AU4 pair carries B+ bias on it.

Of course, solid state diodes would allow for the B+ connection to 
the 6 volt line to be cut.

73,

Rich KB8TAD


At 7:54 PM +0000 3/10/07, ehertz wrote:
>Hi Richard. Some more info that I sent to greenkeys that might be 
>interesting (or not!)...The 6550s are the finals and the whole 
>transmitter is on the variac A and B voltages together, not 
>separable.
>
>1. transmitter is a central electronics 100V. I have also posted 
>this issue to the central-electronics qth group. Yes, I have a very 
>nice schematic scan you can find here (if you are so inclined!)
>http://www.hertzmail.com/ce100v/CE100V-PDF.pdf
>
>
>
>2. 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 
>(a 6au4 has no pin 1) but instead a tiny hole in the bakelite. I 
>also observed actual smoke lingering in the pin hole of the socket 
>under where pin #1 would be. Pin number 1 actually has a structural 
>support to hold up the guts of the tube.

>mains is a good one and one I hadn't thought of. Here's an 
>interesting point to note. The successor to the 100V is the 200V. 
>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! Even more interesting