telefunken: 686WK (T686WK); Super

Regarding replacement of the AD1's in the T686WK, I found an easy solution that works very well. If you can buy two good AL1's (they appear sometimes in eBay Germany), installing them in the 686 chassis is very easy. All you have to do is add a small wire joining the screen grid at the AL1 sockets to the corresponding plates, i.e., you are connecting the tetrodes as triodes. The grid bias, currents, etc are perfect without changing anything in the circuit and they work very well, with just a bit less power than the AD1's. The AL1's are considerably cheaper than the AD1's. 

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