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Duke of Metal
01-29-2006, 11:20 AM
hey guys,
So I retubed my VHT 2/50/2 tube poweramp just recently with all new tubes:

- Chinese 9th Generation 12ax7s (balanced triodes) in Phase Invertors
- GE JG-5814WA(12au7) (balanced triodes) in Drivers
- 4 Matched SED Winged =C= EL34s in power tubes

Previously I had:
- VHT branded 12ax7As in Phase Invertors
- Sovtek 12ax7WA in Drivers
- 4 SED Winged =C= EL34s in power tubes

After the retube, I noticed some improvments such as:
- A bit more clarity (even with lots of gain)
- volume knob is smooth and controllable

The only 2 things I wasnt too happy with after the tubes replacement but I could definitly live with are:
- Volume drop: the level of the poweramp dropped a bit of volume.
- Gain drop: I had to use a bit more preamp gain to match the level of gain where i was at before the retube.

I am assuming those things are caused by the 12au7 but hey, I can definitly live with it.

overall i am pretty happy with the results.

thats it for now.. clips will be coming soon :-D

EDIT - I forgot to mention that I personally prefered the tone of the Chinese 9th generation over the VHT branded 12ax7A tube in the phase invertor. I tried both in there and the Chinese 9th generation 12ax7 seemed to add a bit of fatter tone and an aggressive edge to it.


Cheers

ChrisPtacek
01-29-2006, 04:33 PM
What made you (a metal dude) want to put 12au7s in there? Sometimes changing things just to change them doesn't do a whole lot of good.

Duke of Metal
01-29-2006, 05:13 PM
What made you (a metal dude) want to put 12au7s in there? Sometimes changing things just to change them doesn't do a whole lot of good.
hey Chris,
I actully called up VHT and talked to Steve himself and we even had couple of e-mails going back and forth between me and him.

he said that the driver tubes are suppose to be 12au7s in the 2/50/2. He didnt explain to me why or anything. he just said it has to be a 12au7 for the amp to function at its best. I went with that because I didnt want to do any damage to the amp.

but I still wounder.. would it do any damage if I put a 12ax7 instead of a 12au7 in the driver socket? or will it have to be modded? cause if it wont do any damage at all and doesnt need any modding, then I'll probebly put a 12ax7 in there instead.


Thanks

SteveVHT
01-29-2006, 05:26 PM
As per a discussion me and Steve had last week....
That is the way the amp is designed. PI tubes are a completely different beast than a 12AX7...They run on different voltages etc...
I bought a second UL from a HC member....
I wondered why the amp was about half as loud as my other UL...
I popped out the tubes and he replaced the PI 12au with a 12ax...
Put in the right tube, and back to full power...

Trust me...Steve knows what he's doing and there is a reason behind his tube specs...
Steve

Duke of Metal
01-29-2006, 07:29 PM
As per a discussion me and Steve had last week....
That is the way the amp is designed. PI tubes are a completely different beast than a 12AX7...They run on different voltages etc...
I bought a second UL from a HC member....
I wondered why the amp was about half as loud as my other UL...
I popped out the tubes and he replaced the PI 12au with a 12ax...
Put in the right tube, and back to full power...

Trust me...Steve knows what he's doing and there is a reason behind his tube specs...
Steve
Oh.. believe me.. I didnt & I dont doubt Steve @ VHT a moment for his recommendation.

I am using a 12ax7 in the PI and a 12au7 in the Drivers. When I had a 12ax7 in the driver, the amp had a bit more volume and I didnt need to use as much preamp gain as I do now. Thats why I sorta wouldnt mind using a 12ax7 in the Driver socket along with the PI.

But if its not a good idea, then I mean I am not gonna arrgue with that.

Metalaxe
01-30-2006, 03:12 AM
had the same question a few days ago.
the 12ax7 give u a little bit more gain and volume (and noise), but steve said it does decrease the headroom of the amp due to different impedences, here's his mail:

"
I do not recommend using 12AX7. Yes, more gain, but serious loss of headroom as 12AX7 impedance is not compatible with the circuit in this location.

Please let me know if I can be of further assistance.

With Best Regards,
"

Duke of Metal
01-30-2006, 10:26 AM
had the same question a few days ago.
the 12ax7 give u a little bit more gain and volume (and noise), but steve said it does decrease the headroom of the amp due to different impedences, here's his mail:

"
I do not recommend using 12AX7. Yes, more gain, but serious loss of headroom as 12AX7 impedance is not compatible with the circuit in this location.

Please let me know if I can be of further assistance.

With Best Regards,
"
Ok.. so it doesnt do damage to the amp.. but just decreases the clean headroom? is that all?