Well, I've thought about it a bit more and I think (but could be wrong) that using just a relay before the pots won't work with either type of master volume. The problem as I see it is the pots will interact. If one is "off" then the other will be too. I think this will happen even with the setup that uses two sets of coupling caps. The AC signal will still hop to ground via the other pots 1uf coupling cap. I drew this up in the first pdf.
The second PDF has the two MV setups I think would work. I kinda prefer the upper one (with the bias voltage on the pots and relay) as it would present a 218k load to the PI and grid leak except durring switching where the grid leak is 2.2M (for a short time). The second setup seems to me to not have a 220k load to the PI (at least for AC) and I'm not sure if the grid leak is always 220k (at least for AC). Plus it has more caps.
In the end, I think I'm not gonna use a switched MV due to the fact I can not locate a DIN or XLR jack with a normally closed switch similar to a phone jack. I need the switch to disable the control panel mounted rotary switch. Using a 5 pin DIN I would have an extra pin I could jumper to another. But I don't see how I could use this to disable the rotary (without another relay .
Mike
You do not have the required permissions to view the files attached to this post.
You could still implement "normal" MV (pre-PI , off the tone stack)switching, if you want. On this 4stager I've been messing with, i've got both pre and post PI MVs, and when running lots of preamp distortion, turning the PPIMV below 5 or 6 just sounds awful. Fizzy fuzzy thin, you name it. I feel like I just wasted panel space, as the PPIMV has stayed on 10 since day 1.
I've finally *almost* finished the most painful stage of the build (ordering and waiting for parts). The chassis now has all the extra holes drilled and I've test mounted everything. Next step will be to drill the circuit board and mount the turrets and other components...
You do not have the required permissions to view the files attached to this post.
Reeltarded wrote:Jose and simple masters play very well together plus you can switch them in, out, double, whatever..
Simple master is easy to add a switched second 1M as boost as well..
Hmm... I've heard this enough times that I'm now convinced. . My current plan is to just build the thing (along with the PPIVMV for now). But I've yet to order the face plates (last item on my list). I think I'll label the holes "master I" and "master II" instead of "pre master" and "post master".
That way if/when I decide I don't like or need the PPIVMV, I can switch it for another simple pre master. I've got one spare relay still to play with. And I'm sure I will have to do some tweaking of the #39 gain stage. I will probably find that anther pre master is a better setup either to balance the switchable gain stages or as a boost. And the new face plate labels stay nice and vague as to what they actually are
Spent a bit of time in the hospital. So, it has been a while since I've worked on it. Oh, well, I'm not in a rush. The fun bit is the building.
Got it up to my "first light" stage. PT is in and heaters wired up and all tube filliments work. Like to check this right away to eliminate the terrible thought of having to redo heater wires after everything else is in.
Here she is all glowy...
You do not have the required permissions to view the files attached to this post.
Colossal wrote:Looks great! I like the choke location too..
Thanks. The only other inductive thing I got mounted is the transformer for the relay power supply. That is probably what you thought was the choke. The chassis is pre-punched to mount the choke after the OT over the board. Although I think you are right in that is make sense over closer to the main filter caps.
Just fired up the relay power board. Puts out a nice regulated 5V
Mike
You do not have the required permissions to view the files attached to this post.
Colossal wrote:Looks great! I like the choke location too..
Thanks. The only other inductive thing I got mounted is the transformer for the relay power supply. That is probably what you thought was the choke. The chassis is pre-punched to mount the choke after the OT over the board. Although I think you are right in that is make sense over closer to the main filter caps.
Just fired up the relay power board. Puts out a nice regulated 5V
Mike
Oh...ha ha, yeah that would be a teeny tiny choke! That looks good, solid voltage there.
Some progress has been made. Got all the transformers mounted for good and everything on layer 0 is done. The relays now work with both the foot and rotary switch. It has been a while since I've soldered to PC boards. So, far I've been careful with the heat
Now just need to mount and wire the pots then place in the board...
Mike
You do not have the required permissions to view the files attached to this post.
Coming down the home stretch. Board and pots are mounted. Now I just need to connect the mess of wires up. Every amp I build I always think that the next time I will not connect the leads to the board first. Somehow I never remember this when doing the board.
Mike
You do not have the required permissions to view the files attached to this post.
Well, its done. Just need to double check it against the schematic and then start
it up for the first time. I left the HV connections undone so I can bring up the bias
supply and main DC supply one at a time.
The plan is to test the relays again. Then the bias supply and finally the B+ supply (without and then with tubes). With luck there will be no smoke.
I may get into hum trouble running some of the B+ wires along the back corner of the
chassis. That way looked cleaner but does run 'em parallel with the mains. I guess I'll
reroute them if that is the case.
Couple of pictures:
You do not have the required permissions to view the files attached to this post.
Thanks! Powered and tested the relays and bias supply today. Got about -50 to -42 volts out of the bias supply. So, I think I'm good for el34s. Tomorrow I'll finish double checking the schematic and do a first start.
.
