diytube.com

Very cool. What tubes does everyone recommend? There's quite a few choices for all about the same price. JJ, Sovtek, new production Mullards, EH, etc. Any favorites?

here's another source for the mpc2 cables:

http://www.monoprice.com/products/produ ... 1&format=2

I've ordered all sorts of stuff from them before, always had prompt shipping and their prices can't be beat.

HI All,
Compiling parts for the build-like to use stuff out of my parts box if I can-I also like to "parts" roll if I have the space.

Are the 475k resistors value critical? - it is a unusual and only available in 1/4 watt- Do you think a 470k 1% (1/2W) work just as well?
Same question about the 1.21K? How about a 1.2k 1%?
FYI-Also I noticed that Hammond has the same choke (158SA) same price - better tolerance 15%- a little smaller in width I believe.

Also question-On tube guitar amps I have always had the power and output transformers installed so the plates aren't parallel (in the same plane)-
Is this not required in HI-FI amps?
Thank!

Yes, you may sub resistors with low voltage across them. Just watch their voltage ratings if needed (like bleeders).
Hey - I like that Hammond choke! Yes, it's a perfect sub. Made in Canada.
The parallel transformer lams are necessitated by the tight layout, but no coupling noise occurs. I did a lot of testing to be sure.

Shannon

Hi,
Please confirm R-19 value. Conflict from schematic to mouser list (300k or 330k?)
Thanks,

MacL wrote:Hi,
Please confirm R-19 value. Conflict from schematic to mouser list (300k or 330k?)
Thanks,

Use the Mouser list. This is a non-critical value bleeder resistor.

Shannon

Hi,
I didn't notice 9 pin tube sockets on the parts list... Does anyone know if PC Belton's will fit the PCB holes?
Thanks again!

I used Beltons - they worked great!

The Beltons and the generic ceramic sockets both fit a .750" hole and will work fine. I've used them both.

Shannon

Hi,
Going through the schematic & PCB- and have question-regarding the 6.3v center tap.
I don't understand why it is located on "A" part of the cathode bias circuit on V3 & not grounded.
Thanks,

You could do that, but attaching it to 'A' gives the cathodes a DC bias instead of 0V. This is a common trick of the trade in a lot of old designs, and it worked out well enough in my testing to make it the standard build. It is meant to lessen AC coupling of 60Hz. A third method is to omit the center tap altogether and use a voltage divider to ground at R22 & R23 (currently unused). I think any of the three would work fine, but my noise readings were so low with the elevated heaters that I didn't even test the others.

Shannon

Thanks Shannon!

Any advice on adding adding a 3.5 mm stereo input in addition to RCA jacks?
Thanks!

Two methods:
1) You could drill two small holes in the back of the steel chassis near the RCAs. One would be the 3.5mm input and the other would be a DPDT toggle switch acting as a two source selector.
or
2) I'd get an adapter cable from Radio Shack or ebay.

Shannon

Hi all,
Grounding question.
Installing the PCB under metal chassis (not using top plate option).
Supply is grounded to chassis. Should I have a ground wire from chassis ground to one of the three "ground" holes on the PCB?
VCT power leads are grounded/terminated per instructions to (GND on PCB and Hole "a"). I am trying to be wary of a ground loop but it seems like I should ground PCB to chassis-not just transformer center taps.
Thanks All!

MacL wrote:Hi all,
Grounding question.
Installing the PCB under metal chassis (not using top plate option).
Supply is grounded to chassis. Should I have a ground wire from chassis ground to one of the three "ground" holes on the PCB?
VCT power leads are grounded/terminated per instructions to (GND on PCB and Hole "a"). I am trying to be wary of a ground loop but it seems like I should ground PCB to chassis-not just transformer center taps.
Thanks All!

1) Connect your safety ground to the chassis.
2) Connect a wire from a GND eyelet to the chassis at the same spot.
3) Make sure all other grounds are connected only to the PCB (like RCA grounds - be sure to use isolating wafers).

Let me know if all this makes sense in your build.

Shannon