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I built a 18 watt TMB. I was posting at 18 watt for a while. I got ALOT help from a guy named Phil over there. I've forged ahead on my own, but now I have a few questions. I know the site is coming back up, but I'm really close and would like to wrap this thing up.

My voltages are way off from a voltage chart I saw on 18 watt. I assume that chart is for an 18 watt (not TMB). My voltages are more inline with what I have seen on this site. My V2 voltages seem a little low though and I have a question about my V4/5 voltages and the wattage I calculated it to be dissapating.

The schematic I used is quite similar to the one here. I deviated from it in that I used a 1000uf cap on the V4/5 cathode bypass cap, it's one channel/one input (the TMB), 22uf cathode bypass cap on V1 instead of 1uf and V1 in parrallel with itself.

V2 voltages:
1 - 144
3 - .97
6 - 258
8 - 142.1
I checked V2 plate resistor and it measured 97.8 K whcih is well within 5% and if anything would make the voltage higher as opposed to lower.

I think my V 4/5 voltages are close to what I see here, but when I figure plate dissapation it's over 20, which can't be good. Hopefully my calculations are wrong.

V 4 voltages:
3 - 12.12
7 - 328
9 - 318

V 5 voltages:
3 - 12.12
7 - 329
9 - 316

B+ 345

Does anyone see anything here that's worth worrying about? I love this amp. I've finally got some decent volume and the response is incredible.

Things look pretty good there. Is the cathode resistor getting hot? You should have a 5W in there and it shouldnt get too hot at all.

To check the bias current in a cathode biased amplifier, measure the voltage across the cathode resistor and divide by the resistance value to obtain the cathode current. Since the two output tubes share a common cathode resistor, you must divide the current reading by 2 to get the bias current.

Calculate the wattage by (Cathode Current )^2 X Cathode Resistor
I^2 X R

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Thats what I wanted to hear about the voltages . Thanks a bunch coco.

I just read an article on aikenamps that said the same thing about a common cathode resistor. I was actually wondering about that as I posted, which prompted me to google calculating dissapation.

Nothing seems to be getting hot. I also figured if I were dissapating 20 watts per tube I would have noticed the tubes glowing some interesting shades. I'm actually running 10.21 per tube.

That's a source of a lot of good information!

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps