[Boatanchors] 6AU4 SS replacement?

[Richard Post]

Hi Eugene,

Short answer. No good reason why it won't work.  The 1262 at 4500 PIV 
and 250 mA is roughly the same rating as a 6AU4A.  A tube base from a 
broken tube, a diode and a resistor will do the job.  Several cheap 
1N4007 of recent manufacture and in series would also do the job.

However, the rectifier tube with its cathode allows a lag for 
filament heating of the 6550 pair.  The B+ doesn't hit them until 
they have had a bit of time to heat up.  The tubes may be fine if hit 
with B+ before heating up but not guaranteed in all circumstances.

Are the 6550 tubes used for RF finals or are they in a modulator circuit?

When you say you are powering up with a variac, are you powering the 
filaments along with the B+ supply or are the filaments separately 
fed?

There is a reason why the manufacturer chose a pair of 6AU4 as the 
rectifiers for only a 600 volt supply.

Knowing the circuit allows for a better answer.

73,
Rich KB8TAD

http://tinyurl.com/537ds


At 3:05 PM +0000 3/10/07, Eugene Hertz wrote:
>Hi All,
>
>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+.  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.
>
>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? Seems like embedded in this is a 
>(or more than one?) 1N1262. I wonder if they do anything else like 
>series resistance, good heatsinking or anything fancier. Otherwise, 
>why couldn't I just wire in a 1N1262? (maybe 2 in parallel for more 
>forward current?).
>
>Transmitter also has a 5U4 which I will probably replace with the 
>weber copper cap.
>
>Any thoughts welcome.