Audio Valve RKV mk2 bias question?
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Rob N

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After using the excellent Earmax for a several years I have decided to try the RKV+Impedencer.I have it for approx. one week trial.

Firstly, roughly how long does it take to 'burn in'?

Secondly,if I decided to keep it and tried some tube rolling how critcal is it to buy matched sets of tubes?

I know it has an automatic bias circuit but does this affect all the tubes together or just individual channels, ie if you had say old tubes (with say a lower output) in the left channel and new ones (with a higher output) in the right would the sound be balanced or would the right hand channel be louder?
 
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88Sound

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I've had my RKV MK II for almost 2 months and just received the impedancer a couple of days ago. I've tried Polamp, Mullard, & Telefunken tubes and the differences are slight to non-existant. Judging from what the manual says matched sets are not required, the automatic bias circuitry takes care of everything and you can even use tubes of different ages as long as they are the same brand and type and it will still sound fine.

I also have the EMP, tubes are everything for this jewel, I'm running Telefunken NOS tubes in this now and it's incredible. The RKV is more versatile however because it's a lot more powerful. With the impedancer my low impedance cans have zero backgroud hiss and sound great (Grado 325, RS1), With the W2002 although it works fine with the RKV/impedancer I prefer the EMP/Telefunken combination probably because of the more delicate, crystalline high end. The 32 Ohm Grado phones sound better to me with the RKV/Impedancer than the EMP, my EMP has some difficulty controlling the bottom end with the 32 Ohm Grados, this seems to be no problem for the RKV.

If you want a tube amp that can properly power every phone you have the RKV/Impedancer combo is hard to beat. If you can get your hands on a K1000 for your RKV trial this is a must hear combo.
 
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Gariver

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I am also using my AKG K-1000 and RKV amp with NOS Telefunken PCL805s. What can I say? Those Telefunkens are simply fantastic! Great sound from top to bottom. The original Polamp PCL805s don't even come close in the high frequencies! Actually, that's the problem with the Polamps: They lack HF extension.

88 sound...
I have to correct you a little bit. You said: "You can even use tubes of different brands and ages and it will still work and more importantly sound fine, and it does indeed sound fine." OK! That's half right, half wrong.

The people at Audio Valve warned me NOT to mix brands of tubes. That is, if you are using Telefunken, all 4 tubes must be Telefunken. If you use Polamp, then all 4 tubes must be Polamps. However, you are right on the age of the tubes. You can use an old Telefunken PCL805 tube mixed with new Telefunken PCL805 tubes. These are easy rules to follow.

RKV and AKG K-1000...
Here's my warning: Watch out for too much heat! The AKG K1000 headphones push the RKV too much. So the amp heats up. Solution? Use a fan to keep the amp cool.
 
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88Sound

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Quote:

[size=xx-small]Originally posted by Gariver[/size]
88 sound...I have to correct you a little bit. You said: "You can even use tubes of different brands and ages and it will still work and more importantly sound fine, and it does indeed sound fine."


Hey, I never said that. [size=xx-small]Pay no attention to the statement at the end of my last post saying it has been edited, I have no idea how that got there![/size]


Seriously, thanks for the correction.
 
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Gariver

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That was funny! I appreciate your sense of humor!

A little more on the heat...
I blew a 4.7 Ohm resistor-fuse (2 to 4 watt) due to excessive heat! So I got in touch with Mr Becker. He told me what to check and how to replace the part. Since then, I found a big Mills 4.7 Ohm wirewound 12 watt resistor for replacement. The Mills can take up to 400 volts. Great! The section that fried my resistor fuse goes up to 350 volts. Anyway, I've got to write Mr Becker about all this.

Once again: Be careful with excessive heat! Some resistors fail due to a combination of high heat and high current. Yes, it's the fault of the AKG K-1000's inefficiency! The K-1000s simply need more power than other headphones. So they do put a strain on the RKV.
 
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Rob N

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88Sound,how do you find the sound compared to the EMP with the Grados?

Here are some brief thoughts after listening for 2 days.BTW the Impedencer is essential if you're going to use Grados.

I find the sound of the RKV with Impedencer to be pretty neutral,much less 'tube like' than the EMP with more extended highs and a tighter bass.The best thing about the RKV is it's soundstage which is vast,the best I've heard (I've also tried EAR HP4 and Sugden Headmaster) this side of Stax,the EMP by comparison sounds closed in. The EMP doesn't have the depth that the RKV has and so sounds a little 'flat'.

The RKV isn't perfect but it's definetely better than the HP4 (and much cheaper) but I wish it had more of the EMP treble smoothness (it sounds brighter by comparison)

I'm beginning to think it's not possible to have a large soundstage,full sound,deep bass and EMP-like tubiness.
 
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88Sound

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Quote:

[size=xx-small]Originally posted by Rob N[/size]
88Sound,how do you find the sound compared to the EMP with the Grados?

I find the sound of the RKV with Impedencer to be pretty neutral,much less 'tube like' than the EMP with more extended highs and a tighter bass.The best thing about the RKV is it's soundstage which is vast,the best I've heard (I've also tried EAR HP4 and Sugden Headmaster) this side of Stax,the EMP by comparison sounds closed in. The EMP doesn't have the depth that the RKV has and so sounds a little 'flat'.

The RKV isn't perfect but it's definetely better than the HP4 (and much cheaper) but I wish it had more of the EMP treble smoothness (it sounds brighter by comparison)

I'm beginning to think it's not possible to have a large soundstage,full sound,deep bass and EMP-like tubiness.



I prefer the RKV/Impedancer with the Grados over the EMP. The RKV is much more powerful and controls the phones better. The RKV still maintains the characteristics that I like with tubes, a glassy, smooth quality although on a tubiness scale of 1-10 the RKV is a 2 and the EMP is an 8.

My impressions of the RKV vs EMP in the treble department are just the opposite of yours. My EMP has better treble extension, more delicate but better. The RKV sounds slightly rolled off in the treble, this works quite well with the AKG K1000 and also the Grado 325. The NOS Telefunkens give the EMP an incredible sound stage and depth, nearly as good as the RKV IMO which is huge, this is a big difference over the stock tubes but this is also with the EMP/Telefunken/W2002 combo and although it sounds good with a short warm up period, it sounds incredible with a long one, 2 hours plus. The only phone I have tried so far with the RKV that I don't like is the W2002 (probably because the EMP sounds so much better to me with this phone)

Have you tried the Telefunken NOS tubes in your EMP? They are expensive but worth it and to my ear are going to do exactly what you want in the soundstage/depth department anyway. With the W2002 and this combo you also get a full deep and very articulate bass, like you can tell what kind of pickups an electric bass player is using, just great.

Quote:

[size=xx-small]Originally posted by Gariver[/size]
The AKG K1000 headphones push the RKV too much. So the amp heats up.
I blew a 4.7 Ohm resistor-fuse (2 to 4 watt) due to excessive heat!
I am also using my AKG K-1000 and RKV amp with NOS Telefunken PCL805s. What can I say? Those Telefunkens are simply fantastic! Great sound from top to bottom. The original Polamp PCL805s don't even come close in the high frequencies! Actually, that's the problem with the Polamps: They lack HF extension.


I have not noticed additional heat with the K1000's over any other phone, maybe I'm not pushing them as hard. My RKV , although it has plenty of space around it is enclosed on a shelf inside a rack.

I also blew that same 4.7 Ohm resistor-fuse on one of my channels but it had nothing to do with heat. I rolled some Mullard tubes into the RKV and the instant I turned on the amp one of the tubes flashed blue and that blew the resistor out.

I purchased 8 Telefunken tubes. Upon inspection 3 were diamond bottom, 1 seemed older but still not diamond bottom and 4 looked newer non-diamond bottom and on these the boxes all had the same #5 along with the PCL805. When I rolled the 3 diamonds and one older the amp made this incredibly distressful sound, a very loud hum. I removed these tubes immediately and have some apprehension in using the RKV to test which tube/tubes might be bad (I don't own a tube tester). This horrible sound was in both channels BTW. When I rolled in the #5's they did indeed sound like they had a little more treble but it sounded edgy, not smooth so I removed them and went back with the Polamps.

Do you think this treble edgyness will go away with these Telefunkens if I let them break in for a while?
 
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Rob N

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88Sound,are all 3 tubes in your EMP Telefunken?

I've not tried these myself but I have tried various Sylvania,Mullard,Brimar,Philips,Siemens,RFT,Russia n military,Chinese,RCA and GEC and the differences they made to the sound was not that great.No way near enough to give the EMP an RKV sized soundsatge.

Are the Telefunken tubes so much better?
 
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88Sound

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Yes,

Two ECC88's and one ECC81 (if I remember correctly) and I think the difference was night and day. These are the only tubes I've tried other than the stock tubes in the EMP.

I liked them so much I bought four sets!. I sold one set but am not selling anymore, if you want a contact for getting them directly let me know and I'll give you my source for them.

Got to go, late for work!
 
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Gariver

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88sound:

We had some electrical problems in my neighborhood. A loose cable finally broke, and they had a crew fix it. Maybe this was the cause of the RKV's heat. People around here say the electricity was not up to par. Hmm...I didn't notice!

You have a Furman AC Voltage Regulator. Maybe that's what I need for my RKV to keep it from heating up.

Anyway, my RKV sounded great as soon as I put in the NOS Telefunken. There was no burning period! My experience is very positive compared to what you are telling me. Maybe you experienced problems due to too rapid turn on.

RKV Turn on procedure...
1. Turn volume all the way down.
2. Turn on the amp.
3. Wait for the red light inside the amp to go out in one minute.
4. Once the red light goes out, you can use the RKV.

Diamond? I'm not sure what you mean by this. My NOS Telefunken PCL805 all seem fairly new, and they do not have the diamond bottom.

Sorry if I'm a little bit vague. I do suggest that you contact Audio Valve. They are quick to respond to any question you ask them. I'm sure they are familiar with the Telefunken tubes.

audiovalve@aol.com
helmut@audiovalve.info
 
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