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5687 op-point for IT coupled PSE 807 amp

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Posted on October 31, 2009 at 05:24:32
JANDG
Audiophile

Posts: 1564
Location: Washington State
Joined: February 27, 2004
 Can someone give me a starting point op-point for a 5687 driving a IT coupled PSE 807 amp. I am useing fixed bias on the 807's & have 4- 20k trimmers for adjusting fixed bias on those, & also am installing series glow tube shunt reg for the g2 on em. I have switches installed for triode - UL - & teterode operation. PS is seperate chassis & choke input. I would like to just hang NiMH batteries off the cathode of the 5687 if possible. I will try 300v plate/250v g2/ @ 83mA 1st then try 500v plate/200v g2/ @ 50 mA for the 807's. Signal chassis is wired up for the most part & PS chassis just neededing to be modified for this project. Reason for tube choices is I have Tungsol NOS 5687's allready & 807's also. Amp is completely a on hand closet parts build. Useing switchcraft XLR jacks for all PS umbilical duties, yes....I know that is probably a no-no but have them & used them. Source will be mostly a tuner & CD player for this amp.
Joe
Wisdom for today.........
A GREAT tube amp or speakers will allways be GREAT & bieng relevant today is irrelevant.
RE: 5687 op-point for IT coupled PSE 807 amp, posted on November 1, 2009 at 21:38:05
casouza
Audiophile

Posts: 485
Joined: March 18, 2008
 Hi
The driver op point depends on the output tubes grid bias voltage and the high voltage PS available to power the drivers.
We need that information in order to be more specific.

RE: 5687 op-point for IT coupled PSE 807 amp, posted on November 2, 2009 at 04:33:02
JANDG
Audiophile

Posts: 1564
Location: Washington State
Joined: February 27, 2004
 I am going to try 500v @ 50 mA w/ -14.5v on g1 & 200v regulated on g2 for the 801's in tetrode mode & parrallel with adjusting them individualy thru 20k-20 turn trimmers. Seems 5687 has a max plate voltage of 330v @ 65mA. I am building outboards supply for drivers & outputs. So the driver voltage I can build to what I need. I have many 250-0-250 PT's I could use on the 5687's & use SS diodes to keep close to 250v..? My OT's have 5 & 7k w/ 4/8 & 16 ohm taps also & have UL taps for 5 & 7k if wanted. But really wantto try to make these 807'ssound good in tetrode operation with the extra power as a bonus. I will regulate g2 on the 807's with simple glow tube shunts for starters. My signal chassis is wired up & ready to go & time for the PS to go together. Fixed bias on the 807 & whatever sounds best for bias on the 5687, I will try all avalible bias schemes on the drivers & listen to each.
Joe
Wisdom for today.........
A GREAT tube amp or speakers will allways be GREAT & bieng relevant today is irrelevant.
RE: 5687 op-point for IT coupled PSE 807 amp, posted on November 2, 2009 at 11:01:18
casouza
Audiophile

Posts: 485
Joined: March 18, 2008
 Hi
I see that according to the 807 data sheet you are shooting for maximum power in Class A: 500 V plate, -14.5 G1, 50 mA, 11.5 W per tube @ 12% harmonic distortion (probably more than 15% due to slight tube mismatch).
You may want to consider that the maximum power op point is not the minimum distortion op point. There is no free lunch in Mother Nature or electronics.
Usually, to my ears, the max power op point sounds strained. Lower voltage & higher current usually sounds more relaxed and "life-like", for lack of better words.

Anyway, with 807 in tetrode mode, the distortion may be too much and you will have to resort to negative feedback, which I believe you are trying to avoid.

Maybe fellow DIYers with SE 807 experience would like to contribute ?

As for the 5687 op point, it will drive two 807 to maximum power at practically any op point, because 14.5V is a piece of cake. However, you may want to verify the Miller effect of two 807 grids in paralell, which may or may not muffle treble output.
Again, a more experienced DIYer may want to comment.

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