|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
76.90.39.24
In Reply to: RE: My experience is the opposite posted by DAK on June 23, 2017 at 12:36:16
Roger Modjeski claims the HF87 output transformers are VERY good.
I use them in my PP 6b4g mono block amps along with Electra Print phase inverting autoformers (center tapped grid choke).
I use the single secondary, partial silver Electra Print OPTs in my SE 300b mono block amplifiers.
It would be interesting if you did the same experiment again using DHTs for the output tubes.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Follow Ups:
Hey Tre, i have sooo many power pentodes and beam power tubes that i purposely decided to restrict my amps to those power tubes. I have had 300b and 845/211 as repairs that had to be "tested long term" to verify the repairs and i could hear the difference between the power triodes of these vs power pentodes of 6550, KT66, EL37, KT90, KT120 power tubes and the differences are small. And if someone wanted to trade some 300b for tungsol 6550 originals, or some kt66 or el37 and mullard el34 i would be willing.
" i could hear the difference between the power triodes of these vs power pentodes of 6550, KT66, EL37, KT90, KT120 power tubes and the differences are small. "
That's interesting. I hear big differences between triode wired beam (or pentode) power tubes and DHTs.
Pentodes and beam power tubes wired in triode are far less linear than true direct heated power triodes.
"DHTs have about one-half to one-third the distortion of triode-connected pentodes" Lynn Olson.
But everything I build is free of loop feedback. I would think a little NFB would bring the sound of the two closer together.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
There is feedback but it is the plate to plate variety. I dunno if that is negative or positive fb. And that fb supposedly cancels some of the 2H which would lower IMD.
"pentode wired outputs"
I thought that might be the case after I posted.
Plate to plate FB is really plate to grid FB if you think about it.
A little of the output of the output tube is driven back into it's own grid through the coupling cap between the drive stage and the output stage.
That would make it negative feedback.
As far as pentode vs DHT is concerned, I really don't know what to say.
To me DHTs are a whole different world vs pentodes, with DHTs being far superior.
Each to his own.
Have you read much of Lynn Olson's stuff?
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
and of course we could escalate, and use DH tubes for the PP amps...:) Solid, Class A, PP amps are rather rare, even IDH ones...LOL
wishing y'all were closer,
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
"of course we could escalate, and use DH tubes for the PP amps.."
Yeah, that's what I meant. DHT for both SE and PP.
"Solid, Class A, PP amps are rather rare"
"Solid" as in what Lynn Olsen calls "deep" Class A?
To my way of thinking a Class A PP amp should run each output tube with the same load impedance (for each tube), same voltages and currents as the tubes would be run in a single ended amp where they HAVE to be run in "Solid Class A".
Otherwise, IMO, it's not really a Class A amp.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Power limiting Class A, as you mention, double the SE load for a-a...and keep the finals conducting enough that the load is indeed a-a/2.
I will refuse to exclude pentodes from this comparison; done with DH, and preferably Thoriated Tungsten. Am building a DHT amp now...looking forward to seeing it do as well as the 4E27 pentode amp. A high bar indeed...:)
cheers,
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
FAQ |
Post a Message! |
Forgot Password? |
|
||||||||||||||
|
This post is made possible by the generous support of people like you and our sponsors: