Holy Cow!
So I finally got to the bottom of my Xformer humm issue...I replaced the PT with a BEEFY Edcor XPWR030: Power transformer for a 120V, 60Hz. or 220V, 50/60Hz. line to 700V (350-0-350) at 300mA center tapped, 130V at 100mA and two 6.3V at 6A.
NO MORE XFORMER HUMMMM
This was driving me crazy...especially as I have finally got my EL34 push pull in a form that I was happy with regarding the sound and power.
This Edcor is HUGE...it weighs a ton...Now I want to crank up the bias a little more...it is set with a 15 ohm resistor so 83mA per channel - B+ is running at 465.
I think I can get away with 100mA per channel with the correct CCS resistor.
Need to order some beefy 12.5 ohm resistors!!!
So I finally got to the bottom of my Xformer humm issue...I replaced the PT with a BEEFY Edcor XPWR030: Power transformer for a 120V, 60Hz. or 220V, 50/60Hz. line to 700V (350-0-350) at 300mA center tapped, 130V at 100mA and two 6.3V at 6A.
NO MORE XFORMER HUMMMM
This was driving me crazy...especially as I have finally got my EL34 push pull in a form that I was happy with regarding the sound and power.
This Edcor is HUGE...it weighs a ton...Now I want to crank up the bias a little more...it is set with a 15 ohm resistor so 83mA per channel - B+ is running at 465.
I think I can get away with 100mA per channel with the correct CCS resistor.
Need to order some beefy 12.5 ohm resistors!!!
Great thread, I've enjoyed reading the build progress, Woodturner-Fran. Looking at Broskie's EL84 version of this, I'm wondering why that would not drive a pair of EL34. I've used a 6N1P to drive a 300B, so I'm guessing, given the right setup, EL34's would be very possible, which would eliminate that second stage (and coupling caps, more complex power supply, etc.). I think I'll try that out today on the bench and see what happens. If not enough gain in the first stage I can always CCS load it. I read where you were messing with different feedback resistors, have you tried it with no feedback?
Dumbass moment...so I put the 10 ohm resistor in place and fired up the amp...to my surprise it sounded terrible...ugh!!!
That is until I remembered that the xformer for the power tube heaters was a 12.6v unit and the edcor has a 6.3v tap. DUH!
I rewired the heaters for parallel and back in action. I even went and ordered a quad of 6550 for grins.
That is until I remembered that the xformer for the power tube heaters was a 12.6v unit and the edcor has a 6.3v tap. DUH!
I rewired the heaters for parallel and back in action. I even went and ordered a quad of 6550 for grins.
The problem with no feedback is the high gain - too little and the gain (and hum etc) becomes unmanageable, too much and its dull.
Let us know how you get on with the 6n1p...
Fran
I tried it this weekend. Gain is just right with the 6N1P driving PP El34's. I can get 13.5w before clipping. No feedback used. No hum problem either. I have both monoblocks built, but only one tested so far. After I test the second one, I'll also try them with a bypass on first stage and see if that is better/worse. Right now, the one playing sounds very nice! Oh, I'm using about 430v B+, 300v on driver and phase splitter. Output transformer is recycled Fisher 500C iron (ca. 7k?).
Well folks...a little New Years update
I finally installed a couple test points on the tube plate for easier adjustments to the power tube bias - 10 ohm resistor across the test points.
Now running a 10 ohm resistor on the CCS for 125mA per channel. B+ is hovering around 420.
This amp is dead silent and so far sounds really really nice. No humm, no buzz, balance seems spot on.
I finally installed a couple test points on the tube plate for easier adjustments to the power tube bias - 10 ohm resistor across the test points.
Now running a 10 ohm resistor on the CCS for 125mA per channel. B+ is hovering around 420.
This amp is dead silent and so far sounds really really nice. No humm, no buzz, balance seems spot on.
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