Octal based Express

[fusionbear]

My amp has a head shell now...

[IMG768]http://i169.photobucket.com/albums/u223/fusionbear/Octal%20Express%20Build/Samson%20New%20%20Headshell%201%201_zps9s8xrmzh.jpg[/img]

[10thTx]

You've really done a nice job with that amp!

I like innovative designs & this one certainly turned out great.

With respect, 10thtx

[fusionbear]

You've really done a nice job with that amp!

I like innovative designs & this one certainly turned out great.

With respect, 10thtx

Your comments are always gracious and helpful. I hope to meet you someday and shake you hand!

[norburybrook]

I'm slowly coming to the conclusion that the 4x10 cabinet is the best cab for ANY amp.



MC

[Colossal]

I'm slowly coming to the conclusion that the 4x10 cabinet is the best cab for ANY amp.

I used to go see this bluesman (and his two henchmen) when I lived in California. He played a real 52 Tele (the neck worn black with use and the butterscotch mellowed to a honey gold that would make God jealous) into a real 4x10 Tweed Bassman. Wow, what a tone.

I've often wondered how two 4x10s (with two 10" Greenbacks and two Golds) would sound in stereo.

[fusionbear]

Hello Gents, after playing the amp quite a bit lately at louder volume, I came to the conclusion that it was a bit too tight feeling. I lowered the filtering. Please compare to the last revision. I lowered B1, B2, and the cap before B3 to 32uf each from 50uf each, respectively. The lowering of the filtering caused the voltages to go up slightly. Please note..

The bias is set at 97ma and 93ma per 6550A tube which works out to 76-79% dissipation which is right in the middle for a cathode biased tube.

Also, I really like the Scumback M75LD and the BM75LD with this amp. I am still on the fence with the WGS Liberator. I have to let that one break in before I make a decision.

[IMG768]http://i169.photobucket.com/albums/u223/fusionbear/IMG_0653_zpsleh4tmit.jpg[/img]

[PlinytheWelder]

Love the clips... One of the best sounding amps I've heard. Great work and playing!

[Colossal]

Carl,

In the latest schematic revision, you are now showing each power tube independently biased with 330R and 22uF. Previously and in your chassis photos, both power tubes were sharing 330R in parallel for 165R. Did you separate the cathodes?

[fusionbear]

Carl,

In the latest schematic revision, you are now showing each power tube independently biased with 330R and 22uF. Previously and in your chassis photos, both power tubes were sharing 330R in parallel for 165R. Did you separate the cathodes?

Yes sir, and added 1 Ohm resistors so I can check the current:

[IMG768]http://i169.photobucket.com/albums/u223/fusionbear/Octal%20Express%20Build/KIMG0033_zps2qszew8b.jpg[/img]

[Colossal]

Cool! Looks and sounds great.

[fusionbear]

Well, a little more tweaking as I have spent more time with it lately. I realized that lowering the filtering caused too much ghosting when turned up. I also decreased the values of the grid stoppers on V2a and V2b to decrease the overall gain, also decreased the plate resistor on V1 from 82k to 68k. I adjusted the B+ string values too. I redid the schematic to show the changes. I may do one more change. I may change the cathode resistor on the PI/V3 from 470 to 680. I tried 820 before, but didn't like how it sounded at all. I will report if I do. For now I will play it this week and decide....