Hi all

I have finally completed to build a 18W TMB eF86, and I'm in the process of testing it ....and here we start with the problems...

I tried a shot and I notices the TMB chanel does not work at all, the EF86 sounds horrible and fade down.

I have been tested the connection several times and they looks right, but I can see some voltages that do not seems right to me.

With the tube rectifier and preamp in, all pot to zero I record an unbalanced Voltage at the two anode of the Phase inverter on the V2 - 12AX7.

V2
Pin1      162V
Pin 2      76V
Pin 3&8  80V
Pin6      239V
Pin7       70V

As the circuit is symmetrical I expect a similar voltage between Pin 1 and Pin 6

And the same for Pin 2 and Pin 7 when both channels Volume are grounded

This is the schematic I have followed
http://www.verelec.com/tijdelijk/images/Ceriatone%2018W%20TMB%20EF86.pdf

I have checked, re-soldered and replaced all the anode and cathode resistors and capacitors but nothing change, and I have tried to swap the preamp tubes.

Please some help
thanks
 

Some other things to check.  V2 10nF coupling caps can be leaky.  What is the B+ voltage measure feeding the two 100K plate resistors?   Also detailed pics would help.   It usually something constantly overlooked or assumed worked or was correct prior.  But on a new amp it can be anything until proven to work.   Broken wires, poor soldering, component out of tolerance, etc.

Good job!  Tube amps are such high impedance that it doesn't take much to be conductive and throw off the circuit.  I worked on an old amp once where a dust trail was conductive.  Birthing amps can be tedious.   2 out of 4 of mine had start up problems that were unique in some way.  And like you have been doing dig a little deeper and think outside the box.  But great job on hanging in there and not giving up.

I just use an Avatar G212 traditional cabinet (open back) with a couple of Scumback 12" speakers.  The speakers are rated 60W each and 16 ohm each wired in parallel giving effectively 8 ohm load.  I use other higher power amps as well with these speakers but sound great with the 18Watter.  The cabinet was delivered with Celestion mix rated 30W and 60W respectively and sounded OK but a little rough on the top with any amp.  Not sure how the EF86 comes into play with your amp.  With EF86 you may prefer Alnico magnet speakers which heighten the upper end response and good for "clean" distortion.  Power wise a couple of 12" speakers in the 15 to 60W range should work.  Celestion Greenbacks @ 25W each may work as well as Celestion Alnico Blues @ 15W each.  The Blues are pricey though.   Anyway to 18W TMB responds well with two 12".  I can get controlled feedback easily with this amp and speaker combo.

I like buying 16 ohm speakers as they seem the most versatile.  Two in parallel yield 8 ohms or four in parallel yields 4 ohms.  I generally don't like wiring speakers in series like two 8 ohm speakers (8 + 8 = 16) as one could fail and you would have no sound.  Speakers usually open circuit when they fail electrically.