How to tame the Express brightness

[mat]

I did read an advice from the forum: 'Put 250p between the PI plates and 120p on each plate resistor'. Does the latter mean that I should put a 120p cap in parallel on every preamp and PI plate resistor ?

Thanks,

[Shermock]

Hello,

Not necessarily. There is a basic goal of not adding any "band aid" type fixes in these projects, and construction methods do change some of the inherent instability and brightness that results from a less-than-perfect setup, which definitely was my problem at the outset.

So there's a few questions:

Do you have the bright switch installed? Have you installed a small cap (47pf) across the PI plates? What have you done with layout and lead dress? Which schematic are you basing your project on?

A little more info and there will be better help offered that pertains to your specific situation.

Shermock

[908ssp]

Darker speakers. Celestion Greenbacks or 55 Hz H's, or Tone Tubbys hemp cone Alnicos sound terrific with my CageWreck.

[mat]

You are absolutely right, I should have been more precise of my amp, sorry! But here it goes:

My build is based on Nik's layout:
[img894]http://www.pichotel.com/pic/16028B31e/105196.jpg[/img]

The power trannie is from my homeland and the OT is a Hammond 1650H.

The caps are OD 715P series and silver micas.

The filtercaps are 3 x JJ 47uF's and 3 x F+T 22uF's.

Voltages:
B+1 = 410V
B+2 = 399V (1k 25w)
B+3 = 313V (18k 3w)
B+4 = 292V (10k 3w)
B+5 = 274V (10k 3w)

Bias: -34.2VDC grid to ground

V1a 197V, 2.05V
V1b 173.3V, 1.5V

V2a 259V, 3.08V

PI pins:
1 193V
2 26.5V
3 39.5V
6 197.8V
7 25.2V
8 39.5V

Power Tube 1: (JJ EL34)
1 0.03V
3 408V
4 394V
5 -34.4V
6 399V
8 0.03V

Power Tube 2: (JJ EL34)
1 0.029V
3 409V
4 396V
5 -34.3V
6 399V
8 0.029V

I did try JJ6V6's and the overdrive is smoother with them so I left the6V6's in.

V1&2 are JJ ECC81's and PI is JJ ECC83 S. I tried several 12AX7's (Svetlana, Tungsol..) but preferred the mentioned JJ's in there.

Gut pic:
[img:800:600]http://www.pichotel.com/pic/16028B31e/74930.jpg[/img]

Close up pic with the MV removed:
[img1200]http://www.pichotel.com/pic/16028B31e/84118.jpg[/img]

Just finished the box (Finnish curly birch) :
[img:640:480]http://www.pichotel.com/pic/16028B31e/105195.jpg[/img]

Do you have the bright switch installed?

Yes, there is 100p and 500p caps in there. The switch is on/off/on.

Have you installed a small cap (47pf) across the PI plates?

Yes I have.

What have you done with layout and lead dress? Which schematic are you basing your project on?

I built from the layout picture without schem. I tried to wire as on the layout picture.

cheers,

[Normster]

I used Nik's layout as well. (The one corrected by Richie.) No problem with brightness, but I used Mallory 150's instead of OD 715's. Not sure if that makes a difference in these amps, but I've heard many folks say to steer clear of the 715's.

Beautiful cab, BTW.

[mat]

I used Nik's layout as well. (The one corrected by Richie.) No problem with brightness, but I used Mallory 150's instead of OD 715's. Not sure if that makes a difference in these amps, but I've heard many folks say to steer clear of the 715's.

Beautiful cab, BTW.

Hi Normster !

Do You think this (abowe) is the corrected layout ?

I will try Mallorys but I have to ask first what caps Humbucker is using (I like his tone alot!). I cannot say what they are from the picture https://tubeamparchive.com/download/file.php?id=736.

Some builders preferred the OD715 on this build + few originals was reported to use them also. Anyway I wan't mine to be more to the clips on the Komet site + the one of Humbuckers.

[gearhead]

For Francesca, KF used Mallory PVC series (PVC 601, 612, 622). They are now made/sold by Cornell-Dublier, but data sheets still have them as Mallory's. Allied Electronics sells them (as 601 for .1uf, 6122 for .22uf, and 6222 for .022uf).

PVC601 Allied# 862-0245
PVC6122 Allied# 862-0239
PVC6222 Allied# 862-0234

[Humbucker]

Holy cow mat! Your head cab is absolutely stunning! I made mine from maple and painted it reddish brown with a lot of lacquer. The face plate is flame birch with just lacquer - nice contrast.

But yours... Allyn's maple cab - the absolute top - somes to mind. Cheers!

[mat]

For Francesca, KF used Mallory PVC series (PVC 601, 612, 622). They are now made/sold by Cornell-Dublier, but data sheets still have them as Mallory's. Allied Electronics sells them (as 601 for .1uf, 6122 for .22uf, and 6222 for .022uf).

PVC601 Allied# 862-0245
PVC6122 Allied# 862-0239
PVC6222 Allied# 862-0234

Thanks gearhead for the info. Are these same as the Mallory 150's ? I have easy access to those.

Humbucker, thanks for Your kind words. I'm fighting now with myself if to screw a leather handdle on the top or not..

[Normster]

Nooo...!!! Not a handle!!!

BTW, I stand corrected. I did NOT use 150's in my TW.
I used Sprague 6PS ODs which are pretty close to Mallory PVCs.

Yep, that layout looks like the corrected one that Richie did.

[Humbucker]

Handle..... *passes out*
We don't need no stinkin' handle!

[gearhead]

For Francesca, KF used Mallory PVC series (PVC 601, 612, 622).

Thanks gearhead for the info. Are these same as the Mallory 150's ? I have easy access to those.

Have never used the 150s. The PVCs are polyester film/foil, and the 150s are metalized polyester. Have seen builds with the 150s, and some of those have said their amps are pretty bright. Others probably can say, but I can't solely attribute that to the use of 150s.

CD Data sheets:
http://www.cde.com/catalogs/PVC.pdf
http://www.cde.com/catalogs/150.pdf

[keithrick]

[quote="mat
I will try Mallorys but I have to ask first what caps Humbucker is using (I like his tone alot!). I cannot say what they are from the picture https://tubeamparchive.com/download/file.php?id=736.

Some builders preferred the OD715 on this build + few originals was reported to use them also. Anyway I wan't mine to be more to the clips on the Komet site + the one of Humbuckers.[/quote]

Mat,

That is one badass cab!! Very Nice!

BTW-It looks like the caps in Humbucker amp are Xicon MPP's but I could be wrong.

[mat]

[quote="mat
I will try Mallorys but I have to ask first what caps Humbucker is using (I like his tone alot!). I cannot say what they are from the picture https://tubeamparchive.com/download/file.php?id=736.

Some builders preferred the OD715 on this build + few originals was reported to use them also. Anyway I wan't mine to be more to the clips on the Komet site + the one of Humbuckers.

Mat,

That is one badass cab!! Very Nice!

BTW-It looks like the caps in Humbucker amp are Xicon MPP's but I could be wrong.[/quote]

Thanks Keithrick I'll try to hunt the Xicon MPP's also