In Reply to: RE: 26 DHT preamp posted by andy evans on March 14, 2012 at 14:38:35:
Just a few comments on the 26 preamp - the Hammonds 156Cs are a tried and tested plate choke option - not the ultimate but very good. However, they are prone to hum and must be kept away from any magnetic fields - in particular the filament supply chokes which should be as much as a metre away in a separate box. I use 3 boxes - filament supply, PSU and preamp. The cathode resistors are wirewound surplus Dale - quality is critical. Must be 50 watts - they get hot. I use 10 watters in a series/parallel arrangement and mount them on the top of the chassis. 26s can sound a little better in starved filament, but this alters all the voltages with filament bias. I have also used glow tubes, and others use Salas shunt regulators - it's all in the DIY thread. There are lots of other details and circuit options - many use Lundahl LL1660/5mA in 4.5:1 stepdown for instance. If you build a 26 preamp I do urge reading the thread.
andy
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Follow Ups
- RE: 26 DHT preamp - andy evans 15:27:38 03/14/12 (1)
- RE: 26 DHT preamp - Palustris 14:38:28 03/15/12 (0)