18Watt.com

built my 36 watt its up and running sounds great, but seems to be lacking power. i used richies schematic. my 18 watt blows this thing away. i used quality parts. the only things im concerned with is the tubes are old, the feedback switch, and i used w**** 36 watt trannies. just not sure whats wrong i went over everything at least three times this is a head scratcher.
any suggestions would be greatly appreciated

How about posting some voltages?

what type of jacks did you use? I had a build a couple of years ago where I decided to cut corners and use cheaper Radio Shack Switchcraft-type phone jacks. Turns out I didn't even consider that the "pinout"(for lack of a better term) on the jacks were very different than that of Switchcraft's. Took me a quite while to figure that one out.

i used cliff style marshall jacks very quality

My hunch is that the tone problem lies with the OT and/or old tubes. Those are two key factors in any amp's tone....

the tone is great its the volume thats too low. but you are right i think its one of those two

here are my voltage charts notice tube 3 thats not a typo

You can pretty much ignore the readings for pins 2 and 7 on V3. Unless the measurements were taken with a VTVM or some other meter with an extremely high impedance, they will be incorrect.

Still something there doesn't add up. With 5.6V on the cathode, you're pulling 0.093mA through both halves of that tube combined. It should be in the 1-2mA range And the cathode voltage should be in the 50V range (IIRC). If you can post some pictures, that would help.


Matt

i will get some pics up soon but i also think that the ot is not running hot enough

i may have found the problem. im using ***** power tranny and i hooked the red /white wires to the rectifier tube and those taps are 540v the rred wires are 680v do you think this is why the output voltage on my chart seems a little low

twl wrote:i may have found the problem. im using ***** power tranny and i hooked the red /white wires to the rectifier tube and those taps are 540v the rred wires are 680v do you think this is why the output voltage on my chart seems a little low

I can't comment specifically on any ***** products, but if you used the 680V secondary, you would have ~450VDC after the GZ34. I think your tranny is hooked up right. I think you're pulling too much current somewhere and that's pulling down the voltage. It looks like something is also wrong with the PI voltages. Check the resistor values there and make sure they're correct. Measure the voltage at the junction of the cathode, grid, and tail resistors on the PI.

Matt

what would i need to check

i checked every resistor in the amp all fine except the two 68k tied into inputs they 34.4k each is that cause they are tied together

Can you post the voltage at the top of the PI tail? (47k or 56k resistor, probably). I think there's something wrong with the PI. Pictures would be great too.

Matt

i measured the 56k and got .06 volts

these are pi voltages 470k -2.34v, 470k-2.34v, 820-6.0v, 56k-.06v

Hi.

Take a closer look at the tail resistor. I'm not sure if I saw correctly but it looks like to me that the colours of the tail resistor you have are green-blue-brown. That would be 560 ohm.
Of course it could be that the picture is changing colous a little and it's actually green-blue-orange as it supposed to be. That low value resistor would also cause the the low voltage you have there.

-T

i checked and it is a 56k resistor

twl wrote:i checked and it is a 56k resistor

It looks like something significant is causing current to not want to flow through the PI. Have you swapped the tubes around to see if you got a bad one? If they're new, it's not likely, but possible. With all the under-board wiring, it's kind of hard to tell if the leads are properly connected.

Matt.

i am using old tubes but they work fine in my 18 watter