New Octal Build

WRC34 · Post by **WRC34** » Thu Apr 16, 2015 11:38 am

Looks excellent

chordball · Post by **chordball** » Thu Apr 16, 2015 12:31 pm

Beautiful!

fusionbear · Post by **fusionbear** » Fri Apr 17, 2015 5:08 am

Thanks for the kind comments. I already made some minor changes to the circuit. I adjusted the B+ string value between the choke and B2+ (Screens) and I changed the cap going to the Treble pot from 3.9n to 2.2n. The James tone stack is really fun to play with and the mid shift, while subtle, really makes a difference in all the right ways. Really happy with the amp. This weekend I will get an opportunity to play it louder and see how it does cranked up... So far I am really pleased with it. As I was playing it this evening, I was amazed and the delicious bloom and sweet feedback it would get at a reasonable volume... I haven't measured the output, but I am guessing that it is about 30 watts. The volume seems to max out at about noon on the LAR/MAR MV and just gets thicker from that point on.

Here are a couple of parting shots:

[IMG:640:480]http://i169.photobucket.com/albums/u223/fusionbear/Wreckish%20Octal%20Build/IMG_0797_zpsbuolfqv9.jpg[/img]

[IMG:640:480]http://i169.photobucket.com/albums/u223/fusionbear/Wreckish%20Octal%20Build/IMG_0789_zpsyj1fkd7h.jpg[/img]

They don't show the changes I made, but you get the point. Honestly, this is the best sounding amp I have assembled for myself... I know there is no best as we all hear things differently, but for me, this is tops...

fusionbear · Post by **fusionbear** » Sat Apr 18, 2015 4:59 am

final adjustments to the circuit pics:

This shows that I added one more step down resistor for the Screen supply:

[IMG

768]http://i169.photobucket.com/albums/u223/fusionbear/Wreckish%20Octal%20Build/IMG_0078_zpswozxelgv.jpg[/img]

I ended up with a 24pf fizz cap:

[IMG

768]http://i169.photobucket.com/albums/u223/fusionbear/Wreckish%20Octal%20Build/IMG_0080_zpsayrtq1e6.jpg[/img]

This one shows the change from a 3n9 to a 2n2 on the treble control and a 100k grid stopper on V2b from 56k:

[IMG

768]http://i169.photobucket.com/albums/u223/fusionbear/Wreckish%20Octal%20Build/IMG_0070_zpsgfpp42er.jpg[/img]

fusionbear · Post by **fusionbear** » Sat Apr 18, 2015 5:41 pm

Question: Any issue with putting the so-called "fizz" cap right before the inputs of the power tubes? Let me know...

dorrisant · Post by **dorrisant** » Sat Apr 18, 2015 6:05 pm

fusionbear wrote:Question: Any issue with putting the so-called "fizz" cap right before the inputs of the power tubes? Let me know...

Does it sound good? I don't know of any I'll affects but seems that you could get more drive out of the preamp by leaving the treble turned up there and cutting it out in the PA. Kinda like the cut control in the Vox or Rocket circuits. In those, I turn the treble up and notice a hotter signal... Then cut out some with the cut control to make it play nice. Don't know if that helps but there it is.

We need a well organized gallery of your builds. I know that neatness during a build facilitates easy modding and troubleshooting. Newbies and veteran builders can appreciate and learn from your builds... I do.

Tony

fusionbear · Post by **fusionbear** » Mon Apr 20, 2015 12:49 am

Le clip:

https://www.youtube.com/watch?v=u0QRkuGIhQU

Small disclaimer. V1 started going microphic on me right as I started making this clip.... oofta! I will make another clip once I get more tubes....

BTW, anybody know where I can get those rubber rings that go around tubes? I think I can make this one work with just that....

cbass · Post by **cbass** » Mon Apr 20, 2015 10:10 am

That sounds killer! Auto parts store maybe for some silicone orings

Bob S · Post by **Bob S** » Mon Apr 20, 2015 11:16 am

Great job Carl.
You & Tony have me wanting to build sumpin all octal with those strips.
The sickness is upon me - bad.
Very Cool.

fusionbear · Post by **fusionbear** » Tue Apr 21, 2015 4:33 am

Not quite satisfied, I changed things up a little and now I am content... at least for a few hours... LOL...

1. I removed the mid-shift as its range was more limited than needed, so I replaced with a resistor value that I thought was appropriate.

2. I also reduced the value on the Treble pot leg to ground from 1000pf to 500pf. This gave me a little more upper mids. Also went with a 3.9n Treble cap.

3. I added a cut circuit 500k/390pf

4. I reduced the value of the Treble out resistor to input grid of V2 from 20k to 10k.

Here is Samson again:

[IMG

768]http://i169.photobucket.com/albums/u223/fusionbear/Wreckish%20Octal%20Build/IMG_0188_zpsrlhxboio.jpg[/img]

Once I get my new tubes and silicone rings, I will make a new clip. I am even happier with the result...

WRC34 · Post by **WRC34** » Tue Apr 21, 2015 5:45 pm

The first clip you made was pretty great, ridiculous sounding hard rock amplifier! I'm really looking forward to the next one w/latest improvements.

It may be faux pas to ask (?) but this amp seems influenced by the Red Iron T-Rex you recently posted info about/clips of. Did you incorporate a choke input filter on this amp a-la T-Rex?

fusionbear · Post by **fusionbear** » Tue Apr 21, 2015 6:23 pm

WRC34 wrote:The first clip you made was pretty great, ridiculous sounding hard rock amplifier! I'm really looking forward to the next one w/latest improvements.

It may be faux pas to ask (?) but this amp seems influenced by the Red Iron T-Rex you recently posted info about/clips of. Did you incorporate a choke input filter on this amp a-la T-Rex?

No, standard config. Also, my voltages are different. Mine is closer to an express...

shane · Post by **shane** » Tue Apr 21, 2015 8:24 pm

Thats a cool looking build and the clip sounded great!

I'm confused about the values on the treble control though.

you say you've reduced the cap to ground to 500pF and have used a 3.9nF treble cap, the way I'm reading that is kind of 'upside down'. Isnt the smaller cap usually feeding the pot and the larger value on the ground leg?

Cheers
Shane

fusionbear · Post by **fusionbear** » Tue Apr 21, 2015 10:06 pm

shane wrote:Thats a cool looking build and the clip sounded great!

I'm confused about the values on the treble control though.

you say you've reduced the cap to ground to 500pF and have used a 3.9nF treble cap, the way I'm reading that is kind of 'upside down'. Isnt the smaller cap usually feeding the pot and the larger value on the ground leg?

Cheers
Shane

This is a James Tone Stack. The 3.9n feeds directly from the wiper of the gain. The higher the value, the more overall content. Too high and it adds bass. It is basically a coupling cap... Play with the Duncan tone stack program.... Really fun to see how playing with the different values affect the frequency response...

Post by **Colossal** » Tue Apr 21, 2015 10:42 pm

Carl,

How is the James stack working for you? I am thinking about using the James for a clean build. What value did you settle on for the mid resistor? Did you find the mid control to be of little value?

Great looking amp and it sounds killer.

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