Phase inverter

Orange Amps Technical Q&A's

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kars0747
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Phase inverter

Post by kars0747 » Tue Jun 20, 2017 10:19 am

Anyone has experience with diff pre amp tubes in the phase inverter
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Jondog
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Re: Phase inverter

Post by Jondog » Tue Jun 20, 2017 12:08 pm

Personally I think that tube should be left with what it's designed to be. It's main purpose is to split the signal into two. Optimally pass the preamp signal to the power section. Not saying you shouldn't experiment, but I'd rather play with the preamp tubes.
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Gladmarr
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Re: Phase inverter

Post by Gladmarr » Wed Jun 21, 2017 3:13 am

Whether you'll hear anything different depends on if your amp has any gain in the phase inverter stage. Usually the phase inverter is unity gain so you wouldn't hear much difference with different tubes. Hiwatts are the example that comes to mind of an amp with higher than unity gain in the phase inverter. You'd likely hear a difference in an amp like that.

jontheid
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Re: Phase inverter

Post by jontheid » Wed Jun 21, 2017 8:01 am

I take it that this is in reference to you changing the PI tube in your AD50 to a 5751.
Usually the phase inverter is unity gain
The gain of the phase inverter stage depends on the type of phase inverter:

'Cathodyne' or 'Concertina' type phase inverters, such as those used on OR80/120, GT120 always have slightly less than unity gain: http://www.valvewizard.co.uk/cathodyne.html
There's a nice simple (approximate) equation to work out what the gain of a cathodyne PI is: Gain = mu/(mu+2)

'Long tail pair' type phase inverters can have significant gain. This type is used on loads and loads of amps, including pretty much all modern Oranges afaik.
(The Retro 50 is the sole definite exception to this that I know of. I don't know what the AD50 uses).
http://www.valvewizard.co.uk/acltp.html

Bear in mind that, although a cathodyne PI will always have a gain less than unity, it only uses one triode to do this (LTP uses 2).

Thus in amps that use a cathodyne PI such as the OR120 the other triode in the 'phase inverter' tube is used as another gain stage prior to the phase inverter.
Hence changing the 'phase inverter' tube in an OR120 to a lower gain type will lower the overall gain of the preamp stage, but this is primarily because you are reducing the gain of the gain stage immediately before the PI.
You can see this from the equation above.
ECC83 mu=100, thus Gain=100/102 = 0.98
ECC81 mu=60, thus gain=60/62 = 0.97, so not much difference to the gain of the PI at all going from ECC83 to ECC81.

Whatever type of PI the AD50 uses, changing the PI tube to a lower gain tube won't mean you are able to drive the output stage harder. Quite the opposite.
They'll be driven less hard for the same settings on the amp. In my mind 'output stage' = 'power tubes', everything before this including the PI is 'preamp' to me.

Hope this is of use,
Jon

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Re: Phase inverter

Post by Jondog » Wed Jun 21, 2017 8:20 am

Ad50 has a long tailed pair.
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a.hun
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Re: Phase inverter

Post by a.hun » Sun Jun 25, 2017 9:55 am

kars0747 wrote:
Tue Jun 20, 2017 10:19 am
Anyone has experience with diff pre amp tubes in the phase inverter
Actually since your signal always passed through the PI (from all preamp channels in multi channel amps, unless they have a separate PI per channel like the AD30), it is one of the stages where valve swaps can have the most effect IMO. Probably second only to the first (V1) gain stage.

There is a lot of rubbish talked about needing 'self matched' preamp valves for the PI slot. Ignore that!
https://www.thegearpage.net/board/index ... st-3503931
Just try a few and stick with whichever sounds best there to you, simple as that.


BTW in some amps, eg most Mesa amps, it is even worth trying a 12AT7 in there instead of the usual stock 12AX7. It will alter the tonality (and gain slightly too), and may or may not be to your taste.


Andy.
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kars0747
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Re: Phase inverter

Post by kars0747 » Mon Jun 26, 2017 9:43 pm

Thanks for all the input. From my experience it seems the ad50 needs a 12ax7 or similar in the PI. I have tried a 5751 and a 12at7 and a ge 6072a. All of them seems to make the sound a bit too tame and dull. I am still not convinced which tube suits the amp the best in v1. I am facinated with the ge 6072a but it seems to be a bit too tame here. It definately cleans things up but I am not after that much more clean headroom. I tend to increase the gain 10-15 % when I use this tube.
Les Paul, Orange AD50 CS, ppc 212 ob with 3ow green back heritage (g12h 30) and a greenback (g12m), Boss tuner, Cry Baby, Electro Harmonix Electric Mistress, T-Rex replica and the orange sustain pedal

Farrerdale Records
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Re: Phase inverter

Post by Farrerdale Records » Fri Oct 06, 2017 7:50 pm

Sorry to bump an old thread but I've been experimenting with 12AT7s, 5751s, and 12AX7s in my AD30. With more digging I found that 12AT7s draw more current, and when in V1 I heard what sounded like the the power transformer working harder, a definite hum that disappeared when using a 5751 or 12AX7.

With researching the 12AT7 they are recommended for PI positions, and while not always designed with that in mind, is there any reason a 12AT7 is good for this?

I'm guess also that the AD30 is long tailed in this section, but I wonder if it's 3 stage gain or 2 stage?

When using a 12AT7 in the PI it sounds great, and no hum, so I really have no complaints or issues, just wondering about the technicalities.

As a side note the Tung-Sol 5751s are harmonic on every amp I've put them in (AD30, Blues Jr, Reeves 12) and I'm going to try an EHX 12AY7, they come out of the same factory in Saratov but has a shorter plate spacing.

Any thoughts?
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Re: Phase inverter

Post by Les Paul Lover » Mon Oct 09, 2017 8:30 pm

Farrerdale Records wrote:
Fri Oct 06, 2017 7:50 pm
Sorry to bump an old thread but I've been experimenting with 12AT7s, 5751s, and 12AX7s in my AD30. With more digging I found that 12AT7s draw more current, and when in V1 I heard what sounded like the the power transformer working harder, a definite hum that disappeared when using a 5751 or 12AX7.

With researching the 12AT7 they are recommended for PI positions, and while not always designed with that in mind, is there any reason a 12AT7 is good for this?

I'm guess also that the AD30 is long tailed in this section, but I wonder if it's 3 stage gain or 2 stage?

When using a 12AT7 in the PI it sounds great, and no hum, so I really have no complaints or issues, just wondering about the technicalities.

As a side note the Tung-Sol 5751s are harmonic on every amp I've put them in (AD30, Blues Jr, Reeves 12) and I'm going to try an EHX 12AY7, they come out of the same factory in Saratov but has a shorter plate spacing.

Any thoughts?
The hum you heard in V1 is most likely because the valve is microphonic.
V1 is in any amp is the most obvious place for a valve to show its faults.

Is your AD30 a single or dual channel? If dual channel, it has 2 V1 preamp valves, 1 for each channel - so you woukd expect that hum to disappear on the other channel.

The AD30 only has 2 gain stages per channel, all derived from their respective 1 preamp valve.

The PI slot is less taxing on valves, and a slightly microphonic valve will often perform just fine in that position.
Ant

Current Orange Gear: RV50 MKI, R30, AD15, PPC212
Previous Orange Gear: Orange AD30TC Combo, AD15, Tiny Terror

Guitars: Gibson Les Paul Standard Faded, Vigier Expert Retro 54, Gibson SG 70s Tribute, Aria Pro II RS X80, G&L ASAT Special Tribute

fiveightandten
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Re: Phase inverter

Post by fiveightandten » Mon Oct 09, 2017 9:43 pm

Les Paul Lover wrote:
Mon Oct 09, 2017 8:30 pm
The hum you heard in V1 is most likely because the valve is microphonic.
V1 is in any amp is the most obvious place for a valve to show its faults.

Is your AD30 a single or dual channel? If dual channel, it has 2 V1 preamp valves, 1 for each channel - so you woukd expect that hum to disappear on the other channel.

The AD30 only has 2 gain stages per channel, all derived from their respective 1 preamp valve.

The PI slot is less taxing on valves, and a slightly microphonic valve will often perform just fine in that position.
The PI slot is the *most* taxing position for pre-amp valves. It carries the highest voltage in the pre-amp and works that tube the hardest. Microphonics are the biggest issue in the V1 position because any stray noise at the beginning of the signal path gets amplified by every other gain stage in the amp.

Slight noise in V1 can turn into big noise by the time it hits the speakers. The same slight noise in the PI position will not be as noticeable. Though, the tube itself is working harder.

I agree that this sounds like a tube problem. When in doubt, swap them out!

-Nick
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Les Paul Lover
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Re: Phase inverter

Post by Les Paul Lover » Tue Oct 10, 2017 2:28 pm

fiveightandten wrote:
Mon Oct 09, 2017 9:43 pm
Les Paul Lover wrote:
Mon Oct 09, 2017 8:30 pm
The hum you heard in V1 is most likely because the valve is microphonic.
V1 is in any amp is the most obvious place for a valve to show its faults.

Is your AD30 a single or dual channel? If dual channel, it has 2 V1 preamp valves, 1 for each channel - so you woukd expect that hum to disappear on the other channel.

The AD30 only has 2 gain stages per channel, all derived from their respective 1 preamp valve.

The PI slot is less taxing on valves, and a slightly microphonic valve will often perform just fine in that position.
The PI slot is the *most* taxing position for pre-amp valves. It carries the highest voltage in the pre-amp and works that tube the hardest. Microphonics are the biggest issue in the V1 position because any stray noise at the beginning of the signal path gets amplified by every other gain stage in the amp.

Slight noise in V1 can turn into big noise by the time it hits the speakers. The same slight noise in the PI position will not be as noticeable. Though, the tube itself is working harder.

I agree that this sounds like a tube problem. When in doubt, swap them out!

-Nick
Thanks for the correction.

I always assumed the PI position was kinder as I put slightly microphonic valves there and didn't get the issues they were creating in V1.

One shouldn't assume....... :roll: :lol:
Ant

Current Orange Gear: RV50 MKI, R30, AD15, PPC212
Previous Orange Gear: Orange AD30TC Combo, AD15, Tiny Terror

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fiveightandten
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Re: Phase inverter

Post by fiveightandten » Wed Oct 11, 2017 12:20 am

Les Paul Lover wrote:
Tue Oct 10, 2017 2:28 pm
Thanks for the correction.

I always assumed the PI position was kinder as I put slightly microphonic valves there and didn't get the issues they were creating in V1.

One shouldn't assume....... :roll: :lol:
:lol: Truth. It is a little counterintuitive though.

Personally, I always put my noisiest tubes in the PI position, as it sounds like you've been doing. You can also put them in earlier stages of an amp's clean channel, as there's less gain to make microphonics audible. And any functional position in trem or reverb circuits is a good place as well.
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Jondog
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Re: Phase inverter

Post by Jondog » Wed Oct 11, 2017 1:08 am

I put noisy tubes in the drawer :lol: Anyone got a VT1000 I can borrow!!
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Les Paul Lover
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Re: Phase inverter

Post by Les Paul Lover » Wed Oct 11, 2017 8:58 pm

Jondog wrote:
Wed Oct 11, 2017 1:08 am
I put noisy tubes in the drawer :lol: Anyone got a VT1000 I can borrow!!
Image
Just a few i see!!!! :)

They should have those VT1000 on hire.
How many people, like you, have no real need for it, but would be happy to pay $xx to have it for a week or two and test all their valves?
Ant

Current Orange Gear: RV50 MKI, R30, AD15, PPC212
Previous Orange Gear: Orange AD30TC Combo, AD15, Tiny Terror

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Jondog
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Re: Phase inverter

Post by Jondog » Wed Oct 11, 2017 11:22 pm

Les Paul Lover wrote:
Wed Oct 11, 2017 8:58 pm
Jondog wrote:
Wed Oct 11, 2017 1:08 am
I put noisy tubes in the drawer :lol: Anyone got a VT1000 I can borrow!!
Image
Just a few i see!!!! :)

They should have those VT1000 on hire.
How many people, like you, have no real need for it, but would be happy to pay $xx to have it for a week or two and test all their valves?
I’d love one, but I can’t justify the cost of it. Yeah, I have a bunch of tubes sitting in a box, but probably not enough to amount to the cost of the VT1000. Just easier to buy new tubes. I use these as backups, some I know are good, just tubes that came stock in an amp, or were for projects.
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