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Post subject: 65 DRRI - Phase Inverter
Posted: Sat Apr 25, 2015 1:46 am
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Should the phase inverter tube in a 65 DRRI be balanced?


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Post subject: Re: 65 DRRI - Phase Inverter
Posted: Sat Apr 25, 2015 2:39 am
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IMO yes, just as with any phase inverter tube installed in a class AB amplifier.

Arjay

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Post subject: Re: 65 DRRI - Phase Inverter
Posted: Sat Apr 25, 2015 1:21 pm
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Thank you.

I know next to nothing about audio electronics but have read that there are 2 main types of phase inverter. A long tailed and a cathodyne. What type does the DRRI have?


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Post subject: Re: 65 DRRI - Phase Inverter
Posted: Sat Apr 25, 2015 3:18 pm
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The main difference in the circuitry between those two types of PI, is that the long tail (aka Schmitt), such as in the DRRI, uses both halves of the tube for the PI, whereas the cathodyne (aka concertina), such as in a Princeton Reverb, only uses half of the tube. So, it makes sense to use a balanced PI tube for the DRRI, while a balanced PI tube is not necessary for the PR.

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Post subject: Re: 65 DRRI - Phase Inverter
Posted: Sat Apr 25, 2015 10:43 pm
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shimmilou wrote:
The main difference in the circuitry between those two types of PI, is that the long tail (aka Schmitt), such as in the DRRI, uses both halves of the tube for the PI, whereas the cathodyne (aka concertina), such as in a Princeton Reverb, only uses half of the tube. So, it makes sense to use a balanced PI tube for the DRRI, while a balanced PI tube is not necessary for the PR.


+1

Excellent dissertation, shimmilou!

8)

Arjay

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Post subject: Re: 65 DRRI - Phase Inverter
Posted: Sun Apr 26, 2015 2:13 am
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fifty4 wrote:
Should the phase inverter tube in a 65 DRRI be balanced?


Yes and ....no :lol: ,

You won't ear " small " unbalance tube . Like output tubes you don't need perfect match pair .

But this is my opinion .


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Post subject: Re: 65 DRRI - Phase Inverter
Posted: Sun Apr 26, 2015 2:55 am
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Thank you for the comments.

The factory fitted phase inverter in my DRRI is a Premium GT-12AT7 but there are no obvious markings to suggest that it is balanced (no dot between the pins). Or does the "Premium" label mean that is is balanced?

I did try a balanced NOS Mullard CV4024 in V6 but to be honest I prefer the GT tube. The Mullard seemed to give more headroom which is not what I wanted as I like the power tubes to break up earlier rather than later. Would you expect this from the Mullard?


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Post subject: Re: 65 DRRI - Phase Inverter
Posted: Sun Apr 26, 2015 3:01 am
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Premium ; I don't know .

Any problem with DDR ? Or you just do some test ? .

You may improve tone with V1 more than Phase Inverter


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Post subject: Re: 65 DRRI - Phase Inverter
Posted: Sun Apr 26, 2015 4:28 am
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No problem with tone in fact I am very happy with it. However, I do like to experiment, particularly with tubes to see what impact different brands have.

In V1 and V2 I have tried Tung-Sol 12AX7 RI and GT-12AX7M (the Mullard clone). I also tried a JJ ECC803S in V4 and the Mullard NOS CV4024 in V6 as mentioned in a previous post. For my tastes, none of these swaps changed the tone for the better so I am now back with all the factory fitted tubes where they were. The only other change I am considering is putting a 12AU7 in V3 to reduce the reverb but have not yet tried it.


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Post subject: Re: 65 DRRI - Phase Inverter
Posted: Sun Apr 26, 2015 4:41 am
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Gt12AX7M Mullard clone ? Poor copy IMO

A mix of different brand may sound better


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Post subject: Re: 65 DRRI - Phase Inverter
Posted: Sun Apr 26, 2015 5:08 am
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Done that. I tried various permutations of the stock GT-ECC83S, Tung-Sol and GT-12AX7M in V1 and V2. I've got plenty of other tube brands/types but don't intend to experiment any further for the time being.

The most effective thing I have done is to use a Radial Twin City ABY Switch (with 180 degree phase shift) so that I can easily switch between channels or use them both at the same time. That gives a tone that is not available through either of the channels in isolation.


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Post subject: Re: 65 DRRI - Phase Inverter
Posted: Sun Apr 26, 2015 7:18 am
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shimmilou wrote:
The main difference in the circuitry between those two types of PI, is that the long tail (aka Schmitt), such as in the DRRI, uses both halves of the tube for the PI, whereas the cathodyne (aka concertina), such as in a Princeton Reverb, only uses half of the tube. So, it makes sense to use a balanced PI tube for the DRRI, while a balanced PI tube is not necessary for the PR.


Had a tube vendor once tell me that balanced PI was'nt necessary in long tail circuit because woud'nt be audibly noticible, and that due to imbalance output transformers and other circuitry achieving a balanced output is'nt realistic anyway. And then there's suppose to be the desirability of achieving better harmonics with imbalanced output.
I'm sure these are all simply go-to reasons to push their stock, which I suspect are rarely balanced from the factory.
I further suspect that.....since I don't ave a tube tester to verify.......even those upcharged "balanced" PI tubes could very well be actually unbalanced.
That said, I'm for balanced PI's for sustain. And even though I suspect not all "tested and balanced" PI tubes are actally balanced, but occasionally you get one that really is balanced, and THEN you can definately hear the difference.


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Post subject: Re: 65 DRRI - Phase Inverter
Posted: Sun Apr 26, 2015 7:30 am
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ckmckool wrote:
shimmilou wrote:
The main difference in the circuitry between those two types of PI, is that the long tail (aka Schmitt), such as in the DRRI, uses both halves of the tube for the PI, whereas the cathodyne (aka concertina), such as in a Princeton Reverb, only uses half of the tube. So, it makes sense to use a balanced PI tube for the DRRI, while a balanced PI tube is not necessary for the PR.


Had a tube vendor once tell me that balanced PI was'nt necessary in long tail circuit because woud'nt be audibly noticible, and that due to imbalance output transformers and other circuitry achieving a balanced output is'nt realistic anyway. And then there's suppose to be the desirability of achieving better harmonics with imbalanced output.
I'm sure these are all simply go-to reasons to push their stock, which I suspect are rarely balanced from the factory.
I further suspect that.....since I don't ave a tube tester to verify.......

Most tube testers can't show that

even those upcharged "balanced" PI tubes could very well be actually unbalanced.
That said, I'm for balanced PI's for sustain. And even though I suspect not all "tested and balanced" PI tubes are actally balanced, but occasionally you get one that really is balanced, and THEN you can definately hear the difference.


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Post subject: Re: 65 DRRI - Phase Inverter
Posted: Sun Apr 26, 2015 2:21 pm
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fifty4 wrote:
...I prefer the...


That is all that matters. 8)

There are so many varieties (flavors) of tubes, and an equal variety of amp types, with various positions for preamp/PI tubes, so a tube that sounds perfect in one amp might not put a smile on your face when used in another amp, or even in another position in the same amp.

You might realize that trying different tubes can be kind-of an addiction after you have amassed several boxes full of dozens and dozens of tubes. I have my favorite tubes, but not one favorite that is perfect in every amp or every position.

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