KAT6550 construction question - World-Designs-Forum

timsymons · #1 6th January 2007, 10:16 PM

I bought a KAT6550 kit way back in 2002 but for various reasons have only got round to building it recently. My question concerns the connection to pin 1 of the output valves. The circuit diagram has the label '1' by the envelope of the valve but the construction diagram has pin 1 connected to pin 8 (cathode). The 6550s I have (Russian re-issue Tung-Sols) have pin 1 connected to the metal ring around the bottom of the glass envelope, which is obviously exposed. Is it really advisable to have this ring at cathode potential (40v or so) or would it be better to either leave pin 1 unconnected or, alternatively, connect it to 0v?

Any advice gratefuly received.

Thanks,

Tim

NickG · #2 7th January 2007, 01:17 AM

I would leave 1 unconnected. I can't remember what I did when I built mine, too long ago :-)

timsymons · #3 7th January 2007, 02:23 AM

Thanks, Nick. That sounds like the best plan. Unfortunately, data sheets vary on the function of pin 1. Some say no connection, some say 'base shell' (clearly the case with the Tung-Sols), and one had pin 1 as the suppressor grid, with the cathode as a separate connection on pin 8. This may be why the construction diagram had them connected, although all the 6550s I've come across have the cathode and suppressor grid connected internally.

Tim

Baggy Trousers · #4 7th January 2007, 04:06 AM

Quote:

Originally Posted by NickG

I would leave 1 unconnected. I can't remember what I did when I built mine, too long ago :-)

I don't remember either but I built mine with GE 6550s and replaced these a couple of years later with the Tung Sols without doing anything at all. Never been a problem. I would follow NickG's advice.

Richard.

Richard Higgins · #5 7th January 2007, 06:14 PM

Hi Tim
Looking at the wiring diagram it suggests to me that i and 8 are joined inside the valve, and I cannot see any thing in the instructions saying join them externally. When I built mine I followed the diagram/instructions and it worked Ok.

Regards Richard Higgins

ScottF · #6 8th January 2007, 12:29 AM

Tim
I think unconnected is safest. As you've seen the datasheets have pin 1 either no connection or shell (shield?).
There certainly seems no point connecting pin1 to pin 8.
Good luck

Scott

timsymons · #7 8th January 2007, 01:31 AM

Thanks to all those that replied to my question. I'll leave pin 1 unconnected. The diagram I referred to which shows pins 1 & 8 connected is attached (I hope, not tried that before) so you can see how my question arose. I'll let you know how it turns out - looking good so far (famous last words!).

Tim