[geoffalter11]

I also have a couple on the way. A pair of matched Raytheon VT-231s, which are considered a holy-grail 6SN7 variant and are vintage 1945 tubes. I am so EXCITED for these to arrive end of the week. I also have a Telefunken 1950's 12AT7 Gray Wing Plate with Diamond Print on the bottom which is supposed to be sensational. The telefunken was only $59 which I thought was a steal for the quality and age of the tube. The Raytheon's were my biggest tube investment thus far and I will update the thread once they both come and I can roll them into my HP8. I imagine I will use a mixture of pairings for different music depending on my mood. Either way, the HP8 sounds incredible.

I love this amp! @Pharmaboy and I have one more tube forthcoming. A GE 12AX7 5751 NOS with triple mica plates. The 5751 is another great 12AX7 option as it has 30db less gain. Lots of fun to be had... After the 5751 I will stop and just try to enjoy and learn as the tubes evolve with the HP8.

 

[WorksUnit]

I keep stumbling upon mentions of OTL amps on head-fi, is there any value in owning one of these as well?

 

[Pharmaboy]

I keep stumbling upon mentions of OTL amps on head-fi, is there any value in owning one of these as well?

If you own high impedance dynamic headphones, there absolutely is value in owning an output transformerless amp. The ideal impedance match between one of these headphones and a good OTL amp sounds to me like a calmer, more stable sonic profile of the basic headphone sound you're already familiar with. It's a subtle thing, but as with so much in audio, once you hear it, you can't unhear it.

I have a modest OTL (Woo WA3) which does sound very good on my ZMF high impedance dynamics. You needn't spend huge bucks to get a decent OTL, though as with anything else, the more you spend, the more you'll probably get.

 

[geoffalter11]

I keep stumbling upon mentions of OTL amps on head-fi, is there any value in owning one of these as well?

You should talk to @Mike C . He is in the UK and builds OTL amps. He is a wealth of knowledge and an extremely nice guy.

 

[geoffalter11]

Tube Update:

I burned in the Tung Sol 6SN7GTB New Prod Cryos for 24 hrs and they sound sensational in the HP8. I have them paired with the Brimar CV455 12AT7 in the driver position and the combo is sublime. The TS's are extremely clean and silky smooth up top. This marries well with the warmth of a NOS Brimar tube. I cannot speak highly enough about this amp. it is slowly overtaking my Cembalo Labs Spring 1 as my go to amp.

 

[geoffalter11]

After owning an HP8 MkII SE for 12 months - with lots of use out of it - in a vinyl only rig into HD800S, I decided to try some new tubes.

My SE edition from stock came with Shuguang Black Treasure CV181s and an EH 12AX7 gold pin.

The Shuguangs never did seat very firmly, I have to say.

On considering new tubes, I telephoned Icon Audio and ended up speaking with David Shaw.

According to Mr Shaw, the circuit design of the HP8 has a wide tolerance for either less-than-perfect matching of the power tubes or degradation over time of tube performance.

Moreover, Mr Shaw made the point that the circuit as a whole - rather than simply the tube component - is responsible for the tonality, dynamics, and so forth of the amplifier. He even stated - and I hope I am not being indiscreet - that he "cannot hear differences" when tube rolling the HP8... Quite an admission, given that the SE version is sold as an upgrade in terms of tubes and capacitors (perhaps this is understood as capacitors influencing tonality, tubes only as a matter of mechanical integrity or longevity?)

Members here on Head-Fi - conversely - claim that tube rolling is VERY AUDIBLE in the HP8... What are we to make of this difference of opinion between designer and end user?

Well, today I rolled in Psvane CV181-T MKII (aka. 6SN7 GT) power tubes (the ones with the grey coating) and a Genelex Gold Lion 12AX7.

(Taken together, quite bit more expensive over the stock tubes with the SE version as shipped.)

What a disappointment! My HP8 is now rendered much, much worse!

Regardless of what Mr Shaw claims - and I mean this with all due respect - the HP8 is, very obviously, affected by tube rolling: noise floor is appears identical, as does the excellent channel matching (recall, I'm running a vinyl only rig). However, frequency response is HUGELY altered. To offer an example, the MoFi 45RPM "Brothers In Arms" is famously punchy in the low frequencies (to the extent that some turntable/cartridges had tracking issues on side 2). The HD800S are known for being bass shy. Yet with the stock Shuguang/EH tubes, my HD800S would literally PUMP on my head in with low frequency energy. Since rolling in the Psvanes/Genelex, the low end is now absent on "Brothers In Arms" - so imagine how insipid less bass-y recordings sound??? Moreover, the midrange is grainy and recessed.

Now, I appreciate some might cite the necessity of "burn in" - and no doubt this is quite true of capacitors (for example) that must undergo structural changes in the first tens/hundreds of hours, but is surely less relevant to tubes (which burn-out rather than burn-in, mechanically and electrically).

YMMV, of course - but my experience is that, yes, rolling tubes is audible in the HP8... and worsening is just as probable an outcome as improvement, in terms of system synergy even with putatively superior tubes. (Although at least the Psvanes actually seat firmly!)

I hope you find your right tube compliment. Try a NOS 12AT7. The Brimar CV455 can be had for 45 euro on eBay. I believe they are based out of the UK. @jonathan c turned me onto the CV455 Brimar Footscray, the Mullard 6201 and the Tung Sol New Production 6SN7GTBs. For a new production it is great.

 

[WorksUnit]

Found that Brimar CV455, mine should arrive in a couple of days.
No complaints with the David Shaw CV181 and Mullard 12AX7 combination I have, but for 50 quid why not roll some dice

 

[jonathan c]

https://www.head-fi.org/threads/the-reference-6sn7-thread.117677/post-17143824

 

[jonathan c]

For those interested in a great 12AT7 versus a 12AX7…

 

[gimmeheadroom]

I'm pretty sure you guys in America can buy from English shops cheaper than we can

 

[jonathan c]

I'm pretty sure you guys in America can buy from English shops cheaper than we can

Certainly with the strength of USD vs GBP and vs EUR…

 

[gimmeheadroom]

Certainly with the strength of USD vs GBP and vs EUR…

No, it's import duties, customs fees, imaginary charges du jour. Basically, when you buy "luxury" goods i.e. anything that costs more than 135 euros including shipping price, you become EU enemy of the state...

 

[JonT]

I wonder what the wider impact across the circuit is when swapping out the 12AX7 for a 12AT7?

As I understand it, it's not only that the 12AT7 has lower gain but also has different voltage and plate dissipation - this must then influence how the power tubes and transformer respond in the circuit?

Is there any potential for harm by rolling in a 12AT7?

 

[Pharmaboy]

I wonder what the wider impact across the circuit is when swapping out the 12AX7 for a 12AT7?

As I understand it, it's not only that the 12AT7 has lower gain but also has different voltage and plate dissipation - this must then influence how the power tubes and transformer respond in the circuit?

Is there any potential for harm by rolling in a 12AT7?

It says right in the Icon Audio manual's "Specifications and Features" page:

"• 1x ECC83/12AX7 first stage valve​

• Or use ECC81/12AT7 compatible for lower gain"​

I doubt Icon Audio would say this if an 12AT7 driver could harm the circuit.

After playing around with a couple 12AX7s to start with (one was a very good NOS Telefunken), I went to 12AT7s to drop the gain a bit (I have system gain issues to start with).

It's very subtle, but I think 12AT7s bring out a little more finesse, dynamics, and space than even great 12AX7s. I'm playing around with several top NOS 12AT7s (right now it's the 1056 Brimar CV4033), and the sound just keeps getting better.

 

[The Jester]

Is yours the “SE” version with factory cap upgrade ?