12.000 Finished!!

[Sral68]

OK.

I'll go with the 5.6k as in the 100 watt instructions then.

I've sucessfully solderes in the mainbord. Checked contact between the leads and tube sockes. Things are taking shape.

I'm sorry but I have another question about grounding the mainboard. If I go with the prescence control on a seperate ground (to the P.I. cap groundlug). I see that most people remove the busswire from the prescence and the bass pot. Does this have any negative consequence for the shielding of these pots?

The grounds for v1, v2 and the bias will be solderes to the busswire. The cap on the mainboard will be solderes to the groundlug (between the mainboard and the tonepots) as with the busswire.

[wdelaney72]

Even though it's how Marshall did it, grounding the backs of the pots together is not necessary and potential for ground loop noise. The pots are already grounded by the fronts being in contact with the chassis... the Marshall grounding scheme had other potential flaws as well.

A while back Rockstah posted a grounding scheme that I've stuck with:

1. AC input cord gets it's own ground lug. This lug is attached to the PT mounting screw closest to the AC input.

2. Filament (heater) center gets it’s own grounding lug on the PI Cap mounting screw that is closest to the front of the amp.

3. Bias ground from PT gets it’s own grounding lug on the PI Cap mounting screw that is closest to the front of the amp.

4. Bias ground from circuit board gets it’s own grounding lug on the PI Cap mounting screw that is closest to the front of the amp.

5. Mains filter gets it’s own grounding lug on the PI Cap mounting screw that is closest to the front of the amp.

6. Screens gets it's own grounding lug on the PI Cap mounting screw that is closest to the back of the amp.

7. PI Cap gets it's own grounding lug on the PI Cap mounting screw that is closest to the back of the amp.

8. Presence pot gets it's own grounding lug on the PI Cap mounting screw that is closest to the back of the amp.

9. Pot Ground buss. Run the ground buss through the lugs of the buts... not the backs. Normal Volume, Bright Volume, Middle. This should be run to a grounding lug on one of the choke mounting screws. I run this from a spot on the buss wire between the middle pot and treble pot... but again, the trebel pot is not connected to the ground buss. Also, leave a little extra buss wire open between the Normal volume pot and input jacks.

10. V1-V2 Cathodes ground on pot buss wire left open between Normal volume pot and input jacks.

[Sral68]

Thanks for the tips.

Here are some pictures of where I'm at presently. I've not had time yet to incorporate the ideas for alternate grounding. Hopefully I'll get some work done this weekend.

[neikeel]

Excellent stuff so far

[Sral68]

Thanks!

I've resoldered the pots and incorporated the alternate grounding scheme. I havent solderes in the bias pot on the stanby switch. Beside from that I'm ready to solder in the recistors.

Here are some pictures.

[Sral68]

The amp is finished. Hopefully I can begin testing this evening. I got to late last nigt. I'll try to post some more pictures this evening.

The powercord was hard work. I had to file the cord retainer down some to be able to pry it into the chassis.

[Sral68]

I started testing the amp today. I found the correct voltage on pin 5 of the power tubes. The bias voltage also varied when i turned the bias pot. I seems A bit out of range. It went from -56 to -41.

On the preamp tubes I got the correct reading on pin 4/5 of V1. There was no voltage on pin 2 and 7. Also there was no light in the preamp tubes. The tubes got warm though.

Also I could hear the transformer humming in the speakercab.

No blown fuses.

I went through the troubleseeking sequens in the 100 watt manual. There are no shorts and the diodes are in the correct direction.

I have to go trough the amp again tomorrow.

Here are some pictures

[Sral68]

I vent over the wiring. Cant seem to find anything thats out of place from the layouts. I also checked the solder and redid it in some places.

I have only inserted the preamtubes so far. Cant seem to find any current on pin 2 and 9. After powering down the amp and draining the caps, there dont seem to be any charge in the caps.

[Sral68]

I put in the power tubes. Their filament voltage is working. Have to assume the problem is in the preamp section of the amp.

[Omn]

Pin2 on V1 and V2 should be zero, as you have it. Pin2 on V3 should be (something - I do not remember exactly) 20-40.
Pin9 on all the preamp-tubes should read 3.15. And they are connected to pin7 on the power tubes. Try measuring pin7 on V7. If it shows 3.15 try V6, and so on.

[Sral68]

Hi!

I took mesurements all over the amp. Things seem ok. The NOS AB 56ks have drifted to 40k. Is this ok, or should I replace them.

My voltage readings on the heater wires are 2,9 and they are consistent through the tube sockets.. I have light in the preamp tubes. I use the 240 V. Maybe this has something to do with it?

Are the other voltages present ith the stanbyswitch turned off? My readings so far have been with the switch turned off.

[Sral68]

Its alive!!!!!!

Man what a feeling.

Now I need to adjust the low voltage option.

Thanks for all the help guys!

[Sral68]

Ive been playing it a while now. Here at home I only have a 4x10 cab with dubious speakers. Cant wait to try it out on some proper speakers. I can't dime because the speakers will be blown. I managed volum 8 though. I really dig it so far. Compared to the 73 SL it sounds faster and tighter. That could be the smaller speakers. Otherwise the sound is very smiliar.

[Sral68]

The amp sounds great. Cant wait to try it out in the studio and in reharsal.

next up will be instalng the ppimv.

Heres a final pic. Please excuse the quality of the shots. They are taken with my phone. Dont have a proper camera availeable.

[wdelaney72]

Looks great!