Phase Inverter

[EnGl]

Which tube will be better for PI ?
Sovtek 12AX7 LPS or maybe Jj ECC803S ? Or maybe there is better tube for this slot ?

 

[Ventura]

Which tube will be better for PI ?
Sovtek 12AX7 LPS or maybe Jj ECC803S ?

All depends on the amp.

I've had god luck with LPS matched and balanced; Ei Yugo; and C9s.

 

[EnGl]

Amp is Peavey 6534.
At this time I have Ruby 12AX7HG in PI slot.

 

[Mr. Willy]

You might wanna try a lower gain tube like a 12at7 or even 12au7. That amp has a ton of preamp gain and one of those tubes might clean it up a bit.

 

[Ventura]

You might wanna try a lower gain tube like a 12at7 or even 12au7. That amp has a ton of preamp gain and one of those tubes might clean it up a bit.

Agreed. Something more open could really give it teeth. Less compression.

Might be a good idea to pick up 4 or 6 preamps tubes and roll 'em on through the slot.

 

[EnGl]

You might wanna try a lower gain tube like a 12at7 or even 12au7. That amp has a ton of preamp gain and one of those tubes might clean it up a bit.

You know , I don't want to reduce gain , I like the current gain characteristics.
I have this tubes in preamp:
V1-RFT 12ax7
V2,V5,V6 - JJ ECC83S
V3,V4(PI) - Ruby 12ax7HG

I don't know if the PI has the impact on tone , but I found somewhere it should be very robust tube.

 

[TrueTone500]

5751 tube. So let it be written... So let it be done.

 

[EnGl]

Hmm , what kind of effect I will achieve by putting lower gain tube in PI ? For example 5751 or 12AT7 ?

 

[stephen sawall]

Hmm , what kind of effect I will achieve by putting lower gain tube in PI ? For example 5751 or 12AT7 ?

More headroom & clarity to name a few things ...

TrueTone500 is very right about the 5751 - Because a 12AT7 draws double the current of a 12AX7 it could cause damage to many amps. It is best to contact the builder to see if it can accept other tubes than the 12AX7 family....

For reference purposes only!


12AX7
This is the original version of this tube. The earliest ones were all made in the USA by the usual manufacturers like RCA, Sylvania, GE and Tung Sol. Very early ones have rather large size plates. The "plain" version without the "A" suffix can only be used in parallel filament circuits, not series, unless the filament circuit is DC powered.


12AX7A
This later version has improved noise specs, mostly due to the improved filament design and can be used in series or parallel AC or DC filament circuits. Many manufacturers produced plain 12AX7's well into the 60's and 70's, but many of those could be 12AX7A's marked 12AX7. Current production noisy or untested tubes are often labeled 12AX7 while tested and selected ones are usually designated 12AX7A.


7025
This is the "hi fi" low noise version of the 12AX7. All other specifications are the same as 12AX7. Tubes marked with 12AX7 and 7025 both should be low noise, too.


ECC83
This is the European equivalent to 12AX7

ECC803, ECC803S E83CC
This is the "premium" version of the European 12AX7. The "S" on the ECC803S means "select" version. These are usually found on Telefunken brand tubes.


5751
This is the "milspec" version of the 12AX7, but is also slightly different. The 5751 has the same plate resistance as the 12AX7, but the gain factor is only 70 compared to 100 for the 12AX7. The 12AT7 also has a gain factor of 70, but since its plate resistance is lower, it draws more plate current than the 5751 and 12AX7, making it less suitable for use in low current high gain stages. The older "real" 5751's have extra thick mica spacers and extra support rods to minimize microphonics.


6681
Mobile version of the standard 12AX7. These are usually standard 12AX7's which have been specially tested to assure they will perform well in circuits with +/- 20% variation in filament voltage. Amperex Holland 6681s are a great example of this tube, and very well suited for use in guitar amps.

Any of these tubes should be fine. Also be very aware every tube is different even if made by the same manufacturer on the same run. They are like snowflakes. Some have more or less gain. Also the tonal balance can be very different.

This is a very complex subject ... best thing to do is get a few from the family & just try them. ..... By the way the tube that will change the voice the most in most amps is V1. Swapping this tube can make a huge difference.

 

[Ventura]

I don't know if the PI has the impact on tone , but I found somewhere it should be very robust tube.

Probably one of the biggest impacts on the tone of any amp.

In addition to a plethora of supporting documentation, here's a good read:

 

[TrueTone500]

Locate a NOS 'blackplate' 5751. I think they are Philips, or RCA... Don't remember which?

If you happen play a Boogie MKIIC+, place a 5751 @ V1, and another @ PI.

 

[se7en]

PI tube probably has the biggest impact on an amp besides V1.

 

[fek]

5751 tube. So let it be written... So let it be done.

+1. Seems to add some clarity to my tone. I keep about 4 or 5 JanGE 5751's around for this very reason.

 

[Anonymous]

my ears like the sovtek LPS for PI.

i've tried others.

my 2nd choice to tighten up a sloppy amp would be the mullard cv4024