drhulsey wrote:Dave, how could anybody complain At least, you DID it with the best info you had at the time I really needed an excuse to use my new ConceptDraw program and thought adding some labels might be helpful to some- just a little sharing Thanks for all your sharing
Your energy inspires and depresses me Tim. I've got Visio sitting new in the box over there with my stack of stuff for 6 months and I really need to put it in the machine. Ya know? But the thought of learning a new program just kills me. I hate it. I hate it. I hate it.
Dan
The Last of the World's Great Human Beings
Seek immediate medical attention if you suddenly go either deaf or blind.
If you put the Federal Government in charge of the Sahara Desert, in five years time there would be a shortage of sand.
skyboltone wrote: Your energy inspires and depresses me Tim.
Dan, if you could see my mesh deck chair, leaned back at 45º, my studio flat panel monitor at the edge of the desk, a Contour Shuttle with programmed buttons! About the most energy I expend is drawing a LONG line As far as programs go, I just start using it and only go to the manual if I NEED to. Most Mac programs have a straight forward interface. Really, I'm L-A-Z-Y Re-drawing a schematic or layout just helps my atrophic brain understand the circuit better. It's nice to be able to produce a little helpful info, since I have gained SO MUCH from this forum I'm not knowledgeable enough to give electronic advice, so, I'll do some leg work
Jem, thanks for the suggestions. Appropriate changes have been made. The schem shows a center tap for the heater supply, therefore "virtual" center tap not shown. Either is acceptable as far as I know.
gcenker wrote:I thought the bias was to be set at -30VDC?
Most amps can work within a range of bias. Ken used -30mA and said "set it and forget it." Allynmey found bias at -49mA in two of Ken's amps. Some builders have found a better sound with a bias other than -30mA. The bias is tweakable
gcenker wrote:I thought the bias was to be set at -30VDC?
Most amps can work within a range of bias. Ken used -30mA and said "set it and forget it." Allynmey found bias at -49mA in two of Ken's amps. Some builders have found a better sound with a bias other than -30mA. The bias is tweakable
I was just curious because I installed a 1ohm resistor across the cathodes (ala Komet style) and created dual test points.
First I measured across pin 5 of the EL34(rated for 25W) and dialed it in at -30VDC. Then I measured the plate voltage which was 382VDC. Next I measured across the bias test points and it read 49.3mV (which correlates to 49.3mA). By using the formula (mA/watts) x plate = dissipation factor, then (0.0493/25W) x 382 = 75.33%
So by dialing in -33VDC makes me think the tubes may be biased too hot.
gcenker wrote:First I measured across pin 5 of the EL34(rated for 25W) and dialed it in at -30VDC. Then I measured the plate voltage which was 382VDC. Next I measured across the bias test points and it read 49.3mV (which correlates to 49.3mA). By using the formula (mA/watts) x plate = dissipation factor, then (0.0493/25W) x 382 = 75.33%
So by dialing in -33VDC makes me think the tubes may be biased too hot.
You haven't factored in that the screen current is being measured across your 1R cathode resistors as well. If you subtract the screen current (approx 5.5mA in mine) then you'll be down at 43.8mA which is 67% dissipation at your plate voltage.
They can be biased pretty hot as the plate voltage is fairly low compared to similar 2x EL34 amps.
I've never bothered to measure the negative bias voltage but I've ended up settling on 49mA across the cathode resistors, which is coincidentally what Allyn has found from some that Ken had serviced.
I think that I read here (UR12 perhaps??) that the third leg of the bias pot should be grounded per the schematic- in that case, shouldn't the layout drawing indicate this? I wired a jumper under the PS board on my build (which I have not powered up yet, waiting on tubes...)
The experts here will know if this change is correct...
Thanks for doing the layout, it was indispensable during my build!