SS #002 No Reverb Build Questions

[dorrisant]

I have a wonderful set of iron for a 4x 6550 SSS. I acquired a non-functional KMD XV100SD for dirt cheap. Screen grid resistors burned and took their toll on the PCB... Cost of repair far exceeded the pricetag from the local gear store, so I scored cab, chassis and HUGE iron. This project is now burning a hole in my brain.

I'm using one of the #002 schematics (attached below) as a base to go by. Maybe I should be considering a different schematic, please advise.

- I want to add PAB, OD and FET boost as well as a built-in Dumbleator.

- I want to remove the reverb from the circuit.

- I feel like I should use Martin's values for the tone filter circuit. (See attached below)

I am wondering about disconnecting the reverb, is it just as simple as disconnecting the 220k resistor at the mixer and disconnecting the reverb input from the bright switch?

I think it will be pretty straight forward when it comes to adding PAB, OD and FET Boost. Same for the loop.

I realize there are a few differences implementing Martin's filters but it doesn't seem to be much at all.

That's it for the moment. I am trying to create PCBs for this one, board-over-tubes style and just need a little help to confirm or redirect my design before I process it through and let the CNC do it's magic. Thanks for looking!!

[martin manning]

I am wondering about disconnecting the reverb, is it just as simple as disconnecting the 220k resistor at the mixer and disconnecting the reverb input from the bright switch?

You might want to keep the 220k reverb mix R or something like it to get the right level going into the loop.

II realize there are a few differences implementing Martin's filters but it doesn't seem to be much at all.

Different R and C values all around, plus moving the 3n cap, and ditching the inductor.

[dorrisant]

You might want to keep the 220k reverb mix R or something like it to get the right level going into the loop.

Are you saying to keep the 220K coming off of V2B cathode? That was what I was thinking... removing the 220k passing signal from V3B cathode and all associated with V3. Right?

[martin manning]

Yes lose V3, and V5, and maybe the easier way is to replace the 1M level pot with a 250k. You have V2b as the send buffer, and you could reconfigure V4a as the loop recovery stage. That leaves V4b for?

[dorrisant]

That leaves V4b for?

Parallel 4A for the recovery, maybe?

Should I completely reconfigure V2 for the Dumbleator? Or use V4a & b for the Dumbleator?

Thanks for your answers Martin, but now I have more questions. I was thinking of preserving V2 as is and using what would have been V3, V4 or V5 for the loop... as near to original as possible. I have 6 preamp tubes to play with as I see it. Leave V1 and V2 as is, V3 for OD, V4 for the loop, V5 and V6 for the PI. Does that sound right?

[talbany]

If you lift the filters from the circuit you get (guess what?) a pretty cool Overdrive

So this amp your doing will have a total of 9 preamp tubes..
BTW. Be my hero and put it in a combo.
Good Luck!
Tony

[martin manning]

I have 6 preamp tubes to play with as I see it. Leave V1 and V2 as is, V3 for OD, V4 for the loop, V5 and V6 for the PI. Does that sound right?

Stepping back a bit, the overall topology would be V1 clean, V2 OD (ala ODS), then the filters (same place as SSS, except the OD is inserted), then V3 CC gain and CF loop send, then V4a CC gain loop recover followed by master volume. Then you need V5 LTP PI, and V6 CF for drivers. That leaves half of V4 unused. That could be a reverb recovery stage if you added one more tube for the reverb driver.

[dorrisant]

Tony - Nine preamp tubes... that sounds like my evil plans I have for my Super Twin Reverb. Stay tuned. This is just a head. Not enough room for the reverb. Six preamp tubes max.

Martin - Yes...maybe something closer to what you said. The reason I suggested what I was planning was for two reasons. One, the 47k .22µF connection between the cathodes of V1b and V2b. This along with the Board Over Tube thing is easier if I keep it like the original #002, connecting those stages like HAD did on the board.
(See pics below, one is HAD other is CHIP.) I was wanting to keep the loop in one tube, one board by itself and mount it closer to the back panel. The way I'm thinking, V2 would be the same in the original #002 and with a Dumbleator inserted after V2 I could use two different bypasses for the loop. One to completely bypass the loop circuit and one to bypass the actual loop between V*a and V*b of the loop. I have been playing with a Dumbleator that has send and return trims with good results. Even without effects in the loop I can set it up for various levels of boost which is really kinda nice. Let me know if I am doing anything stupid. I don't think it will turn out bad though. I always appreciate the input.

Next question: Does anyone here know how to copper clad some wood-grain Formica? Just kidding... Maybe.

[martin manning]

Next question: Does anyone here know how to copper clad some wood-grain Formica? Just kidding... Maybe.

It would be easier to wood grain some copper-clad, wouldn’t it?

[dorrisant]

I will build something Dumble-ish with these TXs soon. They are branded Tranilamp - Bury St Edmunds England. Does that ring any bells?

What kind of wattage can I expect with an OT secondary of 1k8 with plates at around 470?

Would I use the formula: (B+) x (B+) / OT Primary Impedance?

If so, it would be around 122 Watts. Does this sound right?

Merlin's formula is: (B+ - 50) * (B+ - 50) / OT Primary Impedance.

That comes out to around 98 Watts... I would think that for the sake of availability and price that 6L6GCs would be better. Am I missing something here? I'd love to squeeze more than 100 Watts out of this setup, but it is what it is and I'll still use them. I am just trying to justify the extra weight and redesign compared to a Twin Reverb TX set.

Also, at what bias point?

I've attached the original KMD schematic for reference.