Looking back thru the notes I made on the 807 I owned for a short while I found differences that I will list.
Where your amp has the 470K resistor from grid 1 to ground mine had a 680K. Yours has a 500ohm cathode resistor and mine had a 250 ohm and 64mA of bias. Mine had no bypass cap and yours does. Mine had no 200 ohm resistor to G1 either.
Interesting to note that when mine had a 500ohm bias resistor it was more distorted. Mine didn't have coupling caps either between stages.
Mine couldn't get past that magic watt either. Wait!!! Anyone have Joel's email address? He likes those amps less than 1 watt. They go with his Altec speakers.
J
Where your amp has the 470K resistor from grid 1 to ground mine had a 680K. Yours has a 500ohm cathode resistor and mine had a 250 ohm and 64mA of bias. Mine had no bypass cap and yours does. Mine had no 200 ohm resistor to G1 either.
Interesting to note that when mine had a 500ohm bias resistor it was more distorted. Mine didn't have coupling caps either between stages.
Mine couldn't get past that magic watt either. Wait!!! Anyone have Joel's email address? He likes those amps less than 1 watt. They go with his Altec speakers.
J
Quote:
The problems with the original circuit are manyfold in that the anode resistor for the 12AU7 are too low in value, the cathose resistor for the 807 seems off too and the screengrid is swinging along with the plate....Add to that that the 807 likes a higher B+ and you get the picture: distortion.
I can hear the wheels turning in Frank's head and I believe the answer is near. Maybe even a full blown schematic headed our way.
J
The problems with the original circuit are manyfold in that the anode resistor for the 12AU7 are too low in value, the cathose resistor for the 807 seems off too and the screengrid is swinging along with the plate....Add to that that the 807 likes a higher B+ and you get the picture: distortion.
I can hear the wheels turning in Frank's head and I believe the answer is near. Maybe even a full blown schematic headed our way.
J
Hi,
You give me way too much credit, Joe...
Sure, I see it in my head already but that's easy for me, I don't have to build it, neither do I need to fund it...
Thanks for the nice compliment anyway...
When the person starting the thread wants to build a very good SE amp he'd better realise that he can easily end up spending alot of money even if the hand holding is free.
If memory serves Thorsten Loesch says the exact same thing...
SE is not the free lunch some people think it to be....I don't mean the member with the same initials either.
Cheers,
You give me way too much credit, Joe...
Sure, I see it in my head already but that's easy for me, I don't have to build it, neither do I need to fund it...
Thanks for the nice compliment anyway...
When the person starting the thread wants to build a very good SE amp he'd better realise that he can easily end up spending alot of money even if the hand holding is free.
If memory serves Thorsten Loesch says the exact same thing...
SE is not the free lunch some people think it to be....I don't mean the member with the same initials either.
Cheers,
based on the rich input i've seen so far, my amp was obviously ILL-designed.
i already had the G2 resistor bypassed to ground, and my findings were:
- it sounds awful with 500R cathode resistor,
- i substituted 390, then 270 and heard it sounded better with 270 cathode resistor.
my next steps are as follows:
- raise B+ to 450 volts,
- use regulated supply for G2,
- use 417A driver, KYW gave me a nice operating point for that tube which sounded excellent on my UX-245 direct-coupled amp,
- get myself an oscilloscope! the signal generator is already sitting here doing nothing
i was nowhere in tubeland when the sound practices and similar magazines were available. i despise the day when WE300B (1940's) were available in the philippines like apples and costs so cheap, and all i do is build (not design) solid state amps as a hobby.
can i series VR tubes 0D3 (150V) and OC3 (105) to get 255V? and is 255V workable instead of 250V for the G2?
i can't thank all of you enough for the experience and knowledge shared on this thread.
happy new year to all!
ps.
joel... joel tunnah? he's in audio asylum...
i already had the G2 resistor bypassed to ground, and my findings were:
- it sounds awful with 500R cathode resistor,
- i substituted 390, then 270 and heard it sounded better with 270 cathode resistor.
my next steps are as follows:
- raise B+ to 450 volts,
- use regulated supply for G2,
- use 417A driver, KYW gave me a nice operating point for that tube which sounded excellent on my UX-245 direct-coupled amp,
- get myself an oscilloscope! the signal generator is already sitting here doing nothing
i was nowhere in tubeland when the sound practices and similar magazines were available. i despise the day when WE300B (1940's) were available in the philippines like apples and costs so cheap, and all i do is build (not design) solid state amps as a hobby.
can i series VR tubes 0D3 (150V) and OC3 (105) to get 255V? and is 255V workable instead of 250V for the G2?
i can't thank all of you enough for the experience and knowledge shared on this thread.
happy new year to all!
ps.
joel... joel tunnah? he's in audio asylum...
OK folks, I have a couple of comments, just one being a minor complaint.
Someone here said that tetrode or pentode SE amps sounded bad. and not worth building unless using UL connection. Holy mmoly.
The first two SE amps I ever heard were pentode and both sounded excellent, that with garden variety mass produced iron. The first was a 6BQ5/EL84 one, and the next was a 7868 one.
I get rave reviews for my 6L6 SE amp. Granted, it does sound a bit better UL, but it is a kicker even without UL. That with the Hammond OPT. The One Electron has no UL tap and is superior sounding. And I do have several other amps of various components and configurations to compare, including the venerable 300B.
So, ArnoldC, don't be too discouraged by your bad experiences now. You are learning from them. The end result will be vastly superior to any mid level solid state amp you have ever built and heard, and at the worst (once distortion clears up) equal to high end SS stuff.
Keep at it. You won't be disappointed.
Gabe
Someone here said that tetrode or pentode SE amps sounded bad. and not worth building unless using UL connection. Holy mmoly.
The first two SE amps I ever heard were pentode and both sounded excellent, that with garden variety mass produced iron. The first was a 6BQ5/EL84 one, and the next was a 7868 one.
I get rave reviews for my 6L6 SE amp. Granted, it does sound a bit better UL, but it is a kicker even without UL. That with the Hammond OPT. The One Electron has no UL tap and is superior sounding. And I do have several other amps of various components and configurations to compare, including the venerable 300B.
So, ArnoldC, don't be too discouraged by your bad experiences now. You are learning from them. The end result will be vastly superior to any mid level solid state amp you have ever built and heard, and at the worst (once distortion clears up) equal to high end SS stuff.
Keep at it. You won't be disappointed.
Gabe
arnoldc
I will have to agree with Gabe. Your 3/4 there now so why think about scrapping it now? Before anyone gets carried away with the merits of the Solid State amps lets review several things. Those fantastic distortion figures that are posted are obtained mainly at or near full output. Those figures are very dependant upon the bias setting of the output stage. Performance changes with the age of the unit/parts inside.
What can we actually hear in terms of distortion? It is said/written that we don't really hear distortion until it reaches 1%. Before anyone gets carried away with distortion figures around 12% one should realize that the amp is probably not going to be used in that range of output and therefore won't experience those distortion figures.
I have owned/repaired/played with some of the most expensive Solid State amps on the market but I have never experienced the realism displayed by tube amps.
Just my .02, ducking for cover now.
J
I will have to agree with Gabe. Your 3/4 there now so why think about scrapping it now? Before anyone gets carried away with the merits of the Solid State amps lets review several things. Those fantastic distortion figures that are posted are obtained mainly at or near full output. Those figures are very dependant upon the bias setting of the output stage. Performance changes with the age of the unit/parts inside.
What can we actually hear in terms of distortion? It is said/written that we don't really hear distortion until it reaches 1%. Before anyone gets carried away with distortion figures around 12% one should realize that the amp is probably not going to be used in that range of output and therefore won't experience those distortion figures.
I have owned/repaired/played with some of the most expensive Solid State amps on the market but I have never experienced the realism displayed by tube amps.
Just my .02, ducking for cover now.
J
hi j, i was thinking to use my variac for the screen grid supply. however, firing up the B+ (i have standby switch) and the variac (also has standby) could be a hand coordination challenge. i was wondering what will happen to the 807 tube if one of the other was on first.burnedfingers said:
i also have it wired using 125ESE, though i have one pair of custom transformer (5K) and a pair of Tango U-808 at my disposal.
will you be using the 450 Vp, 250 Vg2, -30V bias, 60mA operating point as suggested by the others in this thread?
hi frank,
whenever you're ready
Quote:
hi j, i was thinking to use my variac for the screen grid supply. however, firing up the B+ (i have standby switch) and the variac (also has standby) could be a hand coordination challenge. i was wondering what will happen to the 807 tube if one of the other was on first.
Your variac is running a DC source correct? I would set the screen voltage roughly at 250 volt with the variac. I don't think there is much current draw on the screens so that shouldn't be a problem. I'm not an expert but I don't thin the .5 difference will matter much in getting both power supplys turned on.
Will let you know shortly what I come up with. Thanks for letting me know the correct color for B+ as mine isn't marked.
J
hi j, i was thinking to use my variac for the screen grid supply. however, firing up the B+ (i have standby switch) and the variac (also has standby) could be a hand coordination challenge. i was wondering what will happen to the 807 tube if one of the other was on first.
Your variac is running a DC source correct? I would set the screen voltage roughly at 250 volt with the variac. I don't think there is much current draw on the screens so that shouldn't be a problem. I'm not an expert but I don't thin the .5 difference will matter much in getting both power supplys turned on.
Will let you know shortly what I come up with. Thanks for letting me know the correct color for B+ as mine isn't marked.
J
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