WAD 6550 rustling

[KC Jones]

Going back a few weeks I had another issue with my WAD 6550, it started with a few hours of gentle rustling over both speakers, I didn’t know what was causing it or the significance, followed by a few seconds of loud rustling a day or two later. Then a very red glowing 6550 valve, and a burning smell. I not so quickly switched the power off and gave Bob Orbell a call and dropped it off at Bob’s on my way to work.

The following day Bob informed me the valve was most likely duff and had caused the associated resistors and caps to blow. Bob kindly offered to replace and fix with new innards and 2 days later it was back working again.

Due to the unknown age of the 6550 valves Bob thought it best to replace them all. So the hunt began for replacements.

The amp itself has had a few upgrades (something along the lines of 2 large Ansar capacitors, some Rubycon Black Gates, a Heart Of Music, Jupiter Beeswax caps and an Alps Blue vol pot) The resulting sound is what I would call powerful, smooth but detailed. I really enjoy the sound so didn’t’ want to change it in any way and decieded to stick with the same make 6550s – Tung-Sol. ( the rectifier valves being Harma and the signal valves mullard’s) Incidently if anyone knows where to get mullard ECF80s from?

After a hunt ‘round the ‘tinter’, the only place I could find Tung-Sol’s was at HOTROX in Nottingham. So a matched quad was ordered (100 squid delivered) and 2 days later they arrived; popped them into the amp and ….Blimey what a difference, I thought the sound was good with the old valves, but now seem to have been a bit wobbly. With these new ones the sound is more refined, level and tight, still sounding like 6550’s with the same smoothness and detail, but just better. To my ears anyway.

It will be interesting to see how they evolve over the next few weeks, as I’d say there is a bit more detail to revel itself yet.

Anyway once again thanks to Bob for sorting me out so quickly with his skilful electronic tonic, no doubt he will update it with a bit more technical detail.
Hope all is well Bob and the new knee bending well.

Best wishes
Kevin