Octal based Express

[fusionbear]

I played with three different values of "enhance cap on the PI entrance. 120pf, 130pf, 180pf. Liked the 120pf best. What a difference. Sounds much nicer than the snub cap. So, 10thTx thank you very much. I am really liking what I hear. I will make clips tomorrow.

You guys are awesome!!! Another reason to give thanks today!

[10thTx]

I am glad the enhance cap was useful to you. Thanks for letting us know!

It may not work well on every amp but it has been very useful to me to get smooth sounding highs.

You already had a great sounding amp so I look forward to new sound clips when you post them.

with respect, 10thtx

[fusionbear]

Here is the latest schematic, still learning to use the program. It is really cool!

Also, I noticed I have a 82k on the plate of V1, not 75k. I changed it some time ago, I guess I forgot. the schematic is corrected.

[martin manning]

Interesting the PPIMV sounds better that way. Mine is currently wired the normal way and I must say it sounds bad even if its only turned down a tiny bit. I'll try rewiring it your way.

Hmm... same bad behavior in a fixed bias amp! It'd be interesting if you can check this out. Maybe we can discover what is happening.

[caps8419]

just wanted to say this thread is bad ass. Thanks for updating it!

Are you using AC heaters for all tubes? any hum issues with the non-self balanced 6SL7's?

-Michael

[caps8419]

also what program are you using to draw up the .sch files? I've been editing mine from existing schematics via photoshop which is a pain.

Edit: Found the answer on accident. ExpressSCH if anyone else was curious.

Thanks!

-Michael

[10thTx]

I got to thinking about the power tubes cathode resistor? I am not sure I would want paralleled 330R resistors? That would give a 165R shared resistor value to the 6L6's.

Most 6V6 and 6L6 push/pull Fender amps that are cathode biased use a 250 ohm shared resistor.

Example: http://el34world.com/charts/Schematics/ ... RO_5E5.pdf

Look at the tube data sheets:

http://www.mif.pg.gda.pl/homepages/fran ... /6/6L6.pdf

With respect, 10thtx

[fusionbear]

I used this bias calculator and according to it, I am at about 78% for the 6550A's that are in it right now.

https://robrobinette.com/Tube_Bias_Calculator.htm

[fusionbear]

just wanted to say this thread is bad ass. Thanks for updating it!

Are you using AC heaters for all tubes? any hum issues with the non-self balanced 6SL7's?

-Michael

Very little, not enough for me to switch to DC on the filaments...

[10thTx]

I used this bias calculator and according to it, I am at about 78% for the 6550A's that are in it right now

Thanks for sharing that! With respect, 10thtx

[caps8419]

Thanks Carl

[Smokebreak]

Not to get all mathy, but 2 330r in parallel would be 165r

I've got a similar express-y amp here with 370 6l6GC plates(and all 12ax7s), and a 226r cathode resistor(lowest one I had on hand), and I'm at 71%. I imagine I could safely go to 180r or so in mine.
Sometimes I think Fender invested in 250r resistors.

As far as the PPIMV, this is the only amp I've ever liked it in. At all. It's all about the no NFB. I tried it both ways, and the "normal" way sounds best to me. The other way, with the outcaps feeding the wiper forms a highpass filter that kills low end when it's dialed low.

[fusionbear]

Latest Clip:

https://www.youtube.com/watch?v=_znpbiZ ... e=youtu.be

I will let you judge regarding the Bass response with the "backwards" PPIMV

[joeboo88]

WOW.......

that's awesome

[10thTx]

Great tone & very nice playing! Thanks for sharing it.

With respect, 10thtx