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#1 2009-11-25 15:11:16

Gary
New member
From: SoCal
Registered: 2009-11-25
Posts: 1
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12BH7 phase inverter

Been lurking for a week and decided to join. I want to shout out a "thank you" to hangman for the 180K resistor fix for the non-working standby indicator light.

After getting my late 70's master volume V4 working this week, I got to swapping tubes to make it sound better. (I got it in a trade and it came with all the original Magnavox branded tubes.) A big surprise came when I tried a 12BH7 in the phase inverter. The amp's tone opened up in what I would describe as being more "3 dimensional". The effect was most pronounced when palm muting clean notes. Playing chords, each individual string stood out more clearly. This was playing my 335 copy.

I did try many different PI tubes and had almost settled on an RCA clear top 12AU7. But the big bottle 12BH7 really sounded glorious. A GE was real nice but I settled on an RCA.

Anyone else ever try a 12BH7 PI?

Gary in SoCal

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#2 2010-08-18 20:22:22

gsb
Member
Registered: 2010-02-10
Posts: 58

Re: 12BH7 phase inverter

This is an old thread but, have one of you else tried 12BH7 is phase inverter (e.g. in V4-B) and did it increase the clean volume (later breakup?)

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#3 2010-08-19 04:02:39

hangman
Banned
From: Seattle Washington
Registered: 2006-09-04
Posts: 1848

Re: 12BH7 phase inverter

The 12BH7 is electronically similar to the 12au7.  their specs differ only slightly.   

I have tried it and they certainly sound different than the 12au7s  but its a textural difference,  not a difference in gain or volume.

to be more clear on this topic as i have been in the past.  The V4 distortion that you hear coming from the v4 is not the preamp,  it is the power amp.  The power amp is distorting because it has reached its limits.  there is nothing you can do to make your amp louder save for plugging the ext amp jack into additional amplifiers.
and there is nothing you can do to make your amp distort at higher volumes,  because your amp doesn't get louder than 100 watts.
it doesn't matter if you put 12au7s or 12ay7s or 6cg7s or 12bh7s. 

That being said... if you use KT88s your output power will increase to about 110-115 watts max,  but that translates into only marginal increase in headroom because in reality it translates into practically no additional volume.    trust me i've done the mod to many amps.  i prefer the sound of KT88s,  but thats because to my ears they just sound bigger.  (but not louder) 

to get back to the 12bh7,  it really is quite remarkable.   i can't say for sure if i like it better than my clear top RCA 12au7,  but it has a really sweet sound to it.   I certainly recommend it to anyone trying to get a more earthy/open sound to their V4.   
The 12au7 sounded tighter to me...  which i do like...  but I feel like the v4 sounds so tight as it is, that to have it open up a bit is pleasing and i can almost feel my shoulders loosen up.   it really effected the way i played.

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#4 2011-09-14 09:39:36

nitraus
Member
Registered: 2012-02-22
Posts: 55

Re: 12BH7 phase inverter

It sounds interesting, I'm always after a more "open" tone. Is there any 12BH7 brand/type you would recommend?

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#5 2011-09-20 00:58:14

Godofbass
Member
Registered: 2006-05-17
Posts: 17

Re: 12BH7 phase inverter

I have an old battered "Mcintosh" by RCA greyplate 12bh7. Tried it, sounds good to me...

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#6 2011-09-21 17:57:55

Liquids
Member
From: CT
Registered: 2010-08-01
Posts: 491

Re: 12BH7 phase inverter

I have a BH in there just for kicks but haven't A/B'd with a 12au7.  I think I've said it here before but in terms of SPECS, the BH has more heater current...obviously it's a bigger bottle...

In the end I sound like me no matter what tubes are plugged into the Ampeg, and I feel the Ampeg is not as tonally dependent upon / affected by this vs that tube as a Fender might be so long as you keep the tube's gain levels per spec, obviously.   That is, IMO because the V4 has 1) plenty of drive stages, 2)little to no resistance into preamp grids 3) lots of preamp negative feedback (unbypassed cathodes). 

But if for nothing else, I like the IDEA of running the 12BH7 - seems more like a man's tube than a 12AU7. wink

Last edited by Liquids (2011-09-21 18:08:38)


Matthew

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#7 2013-09-25 23:13:37

nitraus
Member
Registered: 2012-02-22
Posts: 55

Re: 12BH7 phase inverter

I finally tried a TAD 12BH7 as PI, but sincerely I didn't like that much and ended up in putting the TAD 12AU7 back in.
I found the 12BH7 a bit harder/drier, than the 12AU7. Maybe because I run 6550s?

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#8 2013-09-26 17:07:58

hangman
Banned
From: Seattle Washington
Registered: 2006-09-04
Posts: 1848

Re: 12BH7 phase inverter

could be the TAD too...  I was using a NOS RCA if memory serves.  the 12au7 was a NOS GE

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