DRRI are rock solid

Here's my story,

I was working on my DRRI. I took it apart to take pictures of the mods the previous owner did. Then, I had to take it to another room to take clearer pics. Suddenly, my cat bit me at my leg (he's young so we forgive him...) and makes me fall. The DRRI chassis falls on the floor, tubes first ! I told myself : Great, now you probably need a set of new tubes and fix what's broken... I plug it in to see if it was still working and hell yeah it was ! Unbelievable. It fell from about 3 feet high and it still working.

End of my story, here are some questions I have to DR experts :-) Once again, I call the A-Team of fender amps to rescue me, the TDPRI forum !

The previous owner has made a couple of mods on this DRRI. The one that annoys me is the Master Volume. Here's what the shop (CMW amps) who did the mod says :

I mostly did/do use so called post pi mastervolumes in such amps so you have to re-install the bias-splitters. I also did install grid- and screengridstoppers on the tubesockets if I'm not mistaken.
If the installed MV is on 10 the circuit is like stock.

What is the advantage of those extras resistors ?
The master volume doesn't sound good to my ears that's why I want to remove it and put a negative feedback variable resistor instead.
Do you think there's a difference between PPIMV on 10 and the stock circuitry ?

Here the link the photo gallery to see the guts of the amp.
http://imageshack.us/g/42/dsc2452s.jpg/

There's a photo of a Silver Mica cap on a preamp tube socket, does someone know if it's stock or not ?

One last question, is a bias pot a linear thing that bias the tube from 0 to 100% ? I guess the answer is no... But we never know until we ask.

Once again thank you in advance !

Have a nice day,

Wil.

the master volume should not cause any loss in sound quality if is indeed a properly-installed post-phase inverter design.

The added resistors at the grids and screen grids of the power tubes are pretty much standard practice for all Fender amps with 6L6s.

I believe the grid resistor prevents ultra-high frequency interference; and the screen grid resistors maintain the proper relation between plate and screen voltages. I don't think that there is any negative effect from adding these components.

I have added them to my Princeton and PRII amps and not noticed any change in the sound of the amplifiers..

I'll manage to see where all those new wires go. And I hope someone would be able to say if it's a proper PPIMV or not.

Thanks for the answer !

I finally followed every wire and here are the results :

It's of course a stereo pot.

Lug 1 : linked to lug 4 and goes to lug 2 on the BIAS POT.
Lug 2 : Pin 1 V7
Lug 3 : Wire from PCB marked V7-Pin5
Lug 4 : See lug 1
Lug 5 : Pin 1 V8
Lug 6 : Wire from PCB marked V8-Pin5

V7 and V8 have pin 1 and 5 linked with what I think is a 1k resistor.

A wire, that is not stock, goes from one end of R62 on the PCB to pin6 and V7 and V8.

So is this a proper PPIMV ?
And how can I get back to the stock configuration ?

According to what I see on google, there are two 2.2M resistors missing.

Thank you very much !

With a little help from my friends...

I-Wil: I will try to figure out those wires, but I can't do it before next week because we are taking a trip to Paris. If nobody else helps before then, send me a PM next week and I will try to help.

Have a nice trip !
I think I'll get back to the stock config. I analysed the schematics and I don't think it's gonna be difficult. Plus, I'll change all electrolytics and coupling caps because this amp doesn't sound like a Deluxe... Preamp tubes looks goods, power and rectifier tubes are new... So there's got to be a ball in the meat as we say here in Belgium...
Thanks for the help.