OLD: Parks Audio Budgie SE - updated 8/21/14

a 3W single ended EL84 amp for home, work & school

Postby jollyrogr » Fri Oct 26, 2012 9:57 pm

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?
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Postby jollyrogr » Tue Nov 13, 2012 10:17 am

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.
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Re: Parks Audio Budgie SE - updated 10/25/12

Postby MacL » Fri Mar 22, 2013 6:42 am

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!
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Re: Parks Audio Budgie SE - updated 10/25/12

Postby Shannon Parks » Fri Mar 22, 2013 6:52 am

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. ;)

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Re: Parks Audio Budgie SE - updated 10/25/12

Postby MacL » Mon Mar 25, 2013 8:54 am

Hi,
Please confirm R-19 value. Conflict from schematic to mouser list (300k or 330k?)
Thanks,
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Re: Parks Audio Budgie SE - updated 10/25/12

Postby Shannon Parks » Mon Mar 25, 2013 1:56 pm

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.

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Re: Parks Audio Budgie SE - updated 10/25/12

Postby MacL » Wed Mar 27, 2013 7:09 am

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!
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Re: Parks Audio Budgie SE - updated 10/25/12

Postby jollyrogr » Wed Mar 27, 2013 8:15 pm

I used Beltons - they worked great!
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Re: Parks Audio Budgie SE - updated 10/25/12

Postby Shannon Parks » Thu Mar 28, 2013 2:59 pm

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

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Re: Parks Audio Budgie SE - updated 10/25/12

Postby MacL » Mon Apr 01, 2013 6:17 am

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,
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Re: Parks Audio Budgie SE - updated 10/25/12

Postby Shannon Parks » Tue Apr 02, 2013 4:53 pm

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.

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Re: Parks Audio Budgie SE - updated 10/25/12

Postby MacL » Fri Apr 05, 2013 11:39 am

Thanks Shannon!

Any advice on adding adding a 3.5 mm stereo input in addition to RCA jacks?
Thanks!
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Re: Parks Audio Budgie SE - updated 10/25/12

Postby Shannon Parks » Fri Apr 05, 2013 1:21 pm

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.

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Re: Parks Audio Budgie SE - updated 10/25/12

Postby MacL » Sun Apr 28, 2013 1:12 pm

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!
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Re: Parks Audio Budgie SE - updated 10/25/12

Postby Shannon Parks » Sun Apr 28, 2013 2:22 pm

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.

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