DHT filaments on AC

[pre65]

I'm having another dabble with PT15, and for the sake of simplicity am going to use AC for the filament.

Trouble is my brain has miss filed the information that was stored, so,as the 6.3v AC has a centre tap, can I take the cathode resistor from there ?

Or is a hum pot de rigueur ?

[steve s]

I'm having another dabble with PT15, and for the sake of simplicity am going to use AC for the filament.

Trouble is my brain has miss filed the information that was stored, so,as the 6.3v AC has a centre tap, can I take the cathode resistor from there ?

Or is a hum pot de rigueur ?

best place for it phil

i would check the votage or the resitance on both windings, it wants to be equal, on a good transformer it should be
it will sound better than many hum pots...
but it will hum a little..

[pre65]

Thanks Steve.

I've just realised that the same 6.3V supply also heats the 6DN7, and the centre tap was grounded to make that quiet. Also, the two 6D22s damper diodes are on that supply as well.

So, that's buggered up my plan.

Spose I need a dedicated 6.3V transformer just for PT15, so much for simplicity.

I do have a couple of twin secondary 6v @ 1A AC transformers, but they have no centre tap.Secs paralleled would be man enough for 1.3A. Hum pots here we come.

[pre65]

Plan C

Use the "mycroft" filament supply from the existing PT15 amp and add a 240V AC outlet on the "new" PT15 amp to power it, then use the jumper wires as before.

Not so simple, as means semi dismantling two amps to get one right, but hey ho and who's a fairy, these things have got to be done. (in the best possible taste of course )

I need something to take my mind off tomorrows wedding events.

[andrew Ivimey]

she threw you aside for a big willy then did she!

Not finding a centre tapped 6volts or so was why I stuck to DC filaments ( a rather obvious variable dc supply, lm1085 ic, I think) with PT15 - it was cheaper! and it meant, with only a little re-soldering I could use the same setup with the delightful PX4s. If I'd a had a couple of centre tapped 6.3 sources I would have started with that. I would have used a hum-bucker and taken the centre tap to ground via cathode resistor and cap.

I reckon 6.3 must be on the cusp for AC/DC. 5volts 1 amp as typical for say 300b is easy to cure with a humbucker and I still prefer AC even though I am using DC more and more, aswell as on indirectly heated valves.

[Mike H]

she threw you aside for a big willy then did she!

Story of my life ..



 

[pre65]

The first one works !

This is (simply put) what was my KT66 SET (or EL34) amp modified to use PT15 as a triode. None of that Pentode malarkey here.

Driven by 6DN7 with CCS in first anode and cathode follower with choke in tail driving.