IslandPink wrote:What does the PY500A do, Steve ?
Also, where is the 40V toroid ?
It's on my list of essentials at Owston to listen carefully to this amp !
The PY500A gives a slow start to the driver stage and, I suppose, injects that valve rectifier sweetness into the part of the amp that has arguably, the largest effect on the final sound.
A second effect it seems to have had, is to improve the quality of the silence of the amp, that's the only way i can think of to put it.
The 40V toroid is the heater transformer for the PY500A and is mounted inside the chassis. These rectifiers are just the 40V heater version of the 6.3V EY500A half wave damper diode.
Sgt. Baker started talkin’ with a Bullhorn in his hand.
IslandPink wrote:Ah, OK , now I'm with you .
I'm surprised you haven't shunt-regulated the driver stage supply - that would be a very 'Lynn Olson' way to go
I'm not making any more holes in the top plate.
Something to think about if I do another iteration.
Sgt. Baker started talkin’ with a Bullhorn in his hand.
Aye, the driver stage has acquired a start up delay, courtesy of the PY500A damper diode.
A few posts ago I mentioned the injection of sweetness into the driver stage by the valve diode. I've changed by mind, perhaps it is removing some kind of distortion instead.
The treble tone is certainly more liquid and single endy, with the vacuum diode in line than it was with the driver PSU branch open, back to the solid state bridge.
It is however, the mid range instrumental tone quality that has seen the most change with the addition of the vacuum diode, not in the classic romantic way but in terms of presence in the room. This seems to have occurred without any moving forward of individual sound sources, ie none of that awful mid emphasis that is superficially impressive, but, in the long run, fatiguing.
Sgt. Baker started talkin’ with a Bullhorn in his hand.
colin.hepburn wrote:Yep I am using 6D222S damper diodes in the J.E.Labs EL34 SE Yep nice slow start up love the sound too
Aye, it's a lovely sound they give.
All I have to do now is fit cathode bypass caps across the common output stage bias resistors. Now the amp is running class AB1 they are going to be needed, if the amp is to work properly when it enters heavy class B, which at Owston, is bound to happen sooner or later
220uF should be a decent compromise between the theoretical optimum value and recovery time after overload.
Sgt. Baker started talkin’ with a Bullhorn in his hand.
It's been a while since I posted on this thread, but now that the amp is back running KT120s. I must say, it works rather well with EF184s as differential pairs, driving the output valves.
A nice refinement to the diff pair was to put a green LED in the tail to bias it.
Sgt. Baker started talkin’ with a Bullhorn in his hand.
SteveTheShadow wrote:It's been a while since I posted on this thread, but now that the amp is back running KT120s. I must say, it works rather well with EF184s as differential pairs, driving the output valves.
A nice refinement to the diff pair was to put a green LED in the tail to bias it.
Not sure a LEd will do what you think in the tail of a LTP, the roal of the resistor or better a CCS is to ensure that if the current in one half increases, the current in the other half will decrease by the same amount. A LED which is a constant voltage device won't care what he current in the two half's are.
Another way of looking at it is a cathode coupled pair, as the cathode is now a constant voltage, there is no coupling.
As you are feeding it a already balanced signal its no big deal, but you may as well have separate cathode components.
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
there is a small T03 package depletion mosfet CCS forgotten the number. Fatbottle probably stocks them. Might be worth a try in that tail. But with GaryP now on the forum he'll probably have better suggestions.
"Two things are infinite, the universe and human stupidity, and I am not yet completely sure about the universe." – Albert Einstein
