Two screws are countersunk in the chassis and lay flush under the PT and OT. Getting everything laid out was a challenge, especially with those Spragues being so big. I recommend countersinking screws to get the power board in the right spot. It's easy and slick!
I am going to shorten the plate to V1 this weekend
I'm getting some great tones from the Express through my 412 with '79 Blackbacks, I have to knock it down -6 to -12db to get them at a reasonable volume. I am going to get a VVR from Dana.
I've been using inexpensive plastic spacers. Since they are not threaded, countersinking is not an option and I didn't think of doing that. Maybe I'll get some threaded aluminum spacers or see if I can find some in an old computer case at work in the storage room and do that instead of banging my head against the wall on this 4 gain stage express layout.
Use #6 or #8; 3/4 aluminun stand-offs with counter sunk flat head machine screws (1/4") long so the screw doesn't interfere with the PT and isn't too long so the top board machine screw has room to thread. Works well every time.
If I think there could be a problem with loosening then I use #6 star washer over the flat machine screw followed by the standoff so it locks down solid.
Yes you do have drill for PT and OT then figure out the board holes and counter sink the board standoff holes. Run the PT/OT mounting bolts from inside chassis to outside with nut on outside for more board clearance.
amplifiednation wrote:Thanks guys... I will try the 7025. I have a bugle boy in v1 now, its better, but still hissy. Put a "rogers" mullard, I think, in V2 and RCA 12ax7 in v3
I am getting more change with the presence control which is cool.
I put in a pair of Siemens el34s that I bought specificaily for the build and put that amp though the paces. Man is it loud! The controlled feedback is amazing. I cant wait to play with tubes more. Wife should be at work tomorrow...muhahahaha
Amp gets a little squeely at full volume when the presence or treble is cranked, that was a relief, I was getting nervous it was too stable. It is amazing you can tap the chassis and hear it through the speakers
I would shorten the plate wire to V1 , run it over the top of the socket. You can also go with a 1w plate resistor. A dale RN65 is 3/4w and very quiet, good mojo too.
If you really want low noise, Parallel the V1a/b, use 2 100k plates parallel for 50k, and use paralled 1.5k for 750 cathode resistors. move the second stage to the unused V2 1/2 . I guarantee it will be very quiet and sound even better. Might not be a true clone anymore.
I understand shortening the plate but how does paralled triodes cut down noise? Is it going to add gain? I don't think I need any more gain!
amplifiednation wrote:Thanks guys... I will try the 7025. I have a bugle boy in v1 now, its better, but still hissy. Put a "rogers" mullard, I think, in V2 and RCA 12ax7 in v3
I am getting more change with the presence control which is cool.
I put in a pair of Siemens el34s that I bought specificaily for the build and put that amp though the paces. Man is it loud! The controlled feedback is amazing. I cant wait to play with tubes more. Wife should be at work tomorrow...muhahahaha
Amp gets a little squeely at full volume when the presence or treble is cranked, that was a relief, I was getting nervous it was too stable. It is amazing you can tap the chassis and hear it through the speakers
I would shorten the plate wire to V1 , run it over the top of the socket. You can also go with a 1w plate resistor. A dale RN65 is 3/4w and very quiet, good mojo too.
If you really want low noise, Parallel the V1a/b, use 2 100k plates parallel for 50k, and use paralled 1.5k for 750 cathode resistors. move the second stage to the unused V2 1/2 . I guarantee it will be very quiet and sound even better. Might not be a true clone anymore.
I understand shortening the plate but how does paralled triodes cut down noise? Is it going to add gain? I don't think I need any more gain!
If you use a 50k plate load (2x100K) and 750 ( 820 is close enough)cathode resistor( I use 2x1.5k ), the gain is the same. The noise is 3db lower. Using 2 100k 1/2w resistors or 1 50k 1w resistor lowers the contact noise of the resistor too.
All I can say is try it, it is very easy to do and you lose nothing but noise. It does slightly fatten the tone due to the lower output impedance. Theoretically you should also raise the bypass cap value to double, but I don't hear any difference in the cap value so I leave it as is if it is 25uf.
amplifiednation wrote:So should I just jumper the triodes and then change the resistor values on the board?
I would just parallel the resistors on top of what you already have. Yes, you need to jumper across the tube socket. 3 wires , plate to plate, grid to grid and cathode to cathode. Move the 2nd stage over to the unused 1/2 of the V2 position.
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So having two resistors paralleled like that is quieter? I assumed you'd have to swap the resistor(s) for one at half the value. I am contemplating doing this for the express I'm doing now.
surfsup wrote:So having two resistors paralleled like that is quieter? I assumed you'd have to swap the resistor(s) for one at half the value. I am contemplating doing this for the express I'm doing now.
Using two resistors gives a higher watt rating, and that's another way to cut the noise. I think a resistor of half value and twice the watts would be the same thing, as you suggested.
Correct me if I'm wrong, but that is how I understand it
surfsup wrote:So having two resistors paralleled like that is quieter? I assumed you'd have to swap the resistor(s) for one at half the value. I am contemplating doing this for the express I'm doing now.
Using two resistors gives a higher watt rating, and that's another way to cut the noise. I think a resistor of half value and twice the watts would be the same thing, as you suggested.
Correct me if I'm wrong, but that is how I understand it
correct. report back to us after you are done and play tested.
Billyz, interesting that the wattage value is being quoted here. The reason i take note isnyou have suggested tomuse the dale RN series for plates and their wattage rating is 1/2 watt i think. I suppose that's a mil spec resistor though ao one could double or triple that though. Anyway, maybe i will go for the parallel first stage on the DBM and let ya know. I have some dale RN and PRP 1watt to use for this build.
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