MY OPUS

[TIMBO]

Hi Guys, MY OPUS is up and running but with a problem.It starts ok but the EF86 section fades to nothing after strumming a few chords. The other sections all sound good so far
Voltages
       P1        P2       P3       P4      P5      P6      P7      P8      P9
V1  26.4     0         .47                           153              .47      0
V2  116      .015    .71                           196    116    117
V3  90         0        1.03                          95     .008    .95
V4  100       0         1.09                         109   .001    1.06
V5  183       0        1.35                          112     0        1.06
V6  285      24.3      70                           250     24       70
V7                          320     390    .009                          34
V8                          390     390    .009                           34

[loogie]

Does it come back to life when you switch it to triode?  You might want to consider something considerably smaller for the screen resistor.  A good ballpark for starters is 5:1 -- Rg2:Ra. 

[LooseChange]

V2a - You have a blocking cap between the grid and the volume pot. Add a 1M grid leak to that grid. Problem solved?

And what's the deal with the effects loop after the reverb?  When using time based effects in the loop, they sound a LOT better in front of the reverb. (This was copied from a design Tubenit provided with his one tube reverb amps and has not accepted my wisdom yet. )

[sluckey]

V2a - You have a blocking cap between the grid and the volume pot. Add a 1M grid leak to that grid. Problem solved?

Or maybe even better... Put that cap between SW7 and the top of the gain pot. The gain pot becomes the grid return for V2A and the blocking cap will now keep dc plate voltage off of the gain pot when SW7 is in the down position.

I see another 'dc on pot' issue too. V2B pin 8 has a big dc voltage on it. This voltage is connected to your volume pot (after tone stack) when SW7 is in the up position. This dc voltage is also passed on to the effects loop jack and to the reverb dwell pot. A blocking cap between points "#" would fix this.

[TIMBO]

Thanks guys for your ideas. The problem still exists in both "T" and "P". As i am not up with the technical side of amp building but always wanting to learn,if you could supply me with drawing it easier to understand. One other think ,when the VVR is turned to max it reduces the voltage of D and E by 10-20v and produces a hum. Thanks

[sluckey]

The changes I spoke of are in red.

[TIMBO]

WHAT CAN I SAY!!!!!!! Well done.How do you guys know this stuff.Something as simple as that fixed the problem. I do thankyou very much. Some pics are on the way

[TIMBO]

And what's the deal with the effects loop after the reverb?  When using time based effects in the loop, they sound a LOT better in front of the reverb. (This was copied from a design Tubenit provided with his one tube reverb amps and has not accepted my wisdom yet. )

Can i get some opions on this subject before i put this one into its cab Thanks

[tubenit]

Since I have not tried it both ways, I don't have an opinion.  The only pedal I use in the loop is a Boss digital delay which sounds very good to me. I am not much of an effects pedal player. I've given away a half dozen pedals and currently only have 3 & only use two of them.

I was purely arbitrary in drawing it up that way; but since it worked just fine,  I continued to use it.

The one tube reverb does sound different to me than the Fender reverb, so I don't know if that would play any type of factor in this or not?  The one tube to me is a warmer more mid tone accented reverb.

However, I would guess LooseChange has far more experience using pedals and I would trust his opinion on this. Should be easy enough to switch around. Why not try LC's approach and report back how it sounds?

With respect, Tubenit

[LooseChange]

IMO it sounds best that way.

And....
It's not my way, It's everybodies way. Fender, Marshall and Peavey all do it that way.

Thanks!

[TIMBO]

Doing some last checks . When doing the valve voltages i noticed the volt meter was reading the voltages in the negitive, is this right as the amp is sounding great with very little hum. thanks

[sluckey]

The amp would not work if all your voltages were negative. Do you have your black meter lead connected to chassis?  Is the black lead plugged into the negative jack on the meter? Does your meter have a polarity switch that may be in the wrong position? Does your meter indicate a negative voltage when connecting the red lead to the positive post of a battery and the black lead to the negative post of a battery?

[TIMBO]

Thanks Sluckey , Some dope put the test leads in the wrong sockets(ME)!!!!!

[TIMBO]

HI Guys, Just doing some more checks before i finish . I was fine tuneing to overdrive section by adjusting the 100k trim . In the starting position it had lots of white noise. then turning clockwise to almost a dead short between the 220k and 68k resistors the noise was almost gone. the overdrive sounded good with a slight vibro effect . Which leads me to ask the question is the 100k trim necessary or is there away of reducing the snow