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VRD Tube Biasing


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About a year or so ago I emailed Craig at Nos Valves inquiring about his VRD monoblocks and I asked about the discount if I were an active Klipsch Forum member. Anyway, since I own Klipsh Cornwalls, I decided to sign up here and ask your opinions about various amps. At the time I owned a McIntosh MC275 and was fairly unimpressed with its performance - especially for the price. Pretty much everyone on the here agreed that the VRD amps were the way to go so I decided to give them a try. Then, one of the guys here pointed out that someone had a pair of used VRD's up for sale on the forums. I ended up purchasing the amps from user Smilin (can't recall his real name at the moment... Steve Milin? Can't remember...) and have been completely blown away by them ever since. They sound great on everything from my Cornwalls to my custom Selah Audio dipoles to my little Chinese made Compact stand mounts and everything in-between.

When the Smilin sent me the amps they worked great and he sent me everything I needed except for the user's manual. Now is the first time I'll really be able to set them up in a permanent setting since I bought them due to moving and other life issues but I don't know the proper tube biasing. I'd really like to get these babies up and running; so basically, this is my long-winded way of asking if any of you could send me a copy of the user's manual for the VRD monoblocks. PS I did email Craig at NOS Valves pretty much the same thing I’m posting here but haven’t received a reply yet so I’m hoping that one of you will have the info that I need. I'd really appreciate it.

EDIT: I guess I should have posted this on the "Technical Questions" board. Oh well, I guess a mod can move it there if they want to.

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STD,

contact CIGARBUM from the forum. He bought my VRDs earlier this year and he can give you the bias instructions from the pages I sent him. I could probably instruct you from memory, but I might leave out some detail. It is very simple, you just need a tiny flat blade screwdriver and a good multimeter.

Good Luck,

Darrell

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http://www.nosvalves.com/vrd.htm

Craig has moved in the last couple of months so his email address is different...I set my VRDs to 72 bias but Smilin' might have bought super VRDs or something like that...I thought I remembered him getting something different...anyway...I provided a link as well...good luck

Bill

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I have a multimeter to correct the bias and I know how, I just need the settings. Thanks, Lighting, I'll give CIGARBUM a try.

Silversport, unless I'm missing something that page doesn't have the bias settings, does it? Do you have Craigs new email address by chance?

Also, I think the VRD's that I got from Smilin were stock but he was thinking about buying some "super" upgraded version of the VRD's at the time.

Haha... I just noticed my join date here and checked my messages... I guess it was a bit longer than a year, more like two. Damn, time flies.

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.715vdc for kt88's or 6550's.

the below is from craig when i was asking about using el34's, which i never did.

EL34's can be used you just have to cool the bias down and watch em for
plate glow. Start at about .40 volts on the bias and inch it up if you
start seeing plate glow with the room dark then back it down a smudge.
It really depends on what brand EL34's you use some are better at taking
the heat then others. By the tube specs an EL34 should be able to have
.50 to .55 volts on the bias in a VRD but I have found with some current
production tubes they can't handle what say a Mullard XF1 or 2 would. I
have biased my XF2 up the 60mA in my VRD's with a 5U4 rectifier. A 5U4
rectifier is another good Idea to get the plate voltage down with these
tubes.

There is really no chance your going to hurt the amp using these tubes
but the tubes need some care taking when using them. The VRD push all
the lesser power tubes pretty hard. I personally always use a 5U4
rectifier when using these other tube types.

These above things are true of all tubes except KT88, 6500, KT90
and KT100's these you can bias from .65 to .80 without worries.

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STD,

Gald you're anjoying the amps. Not sure what email address you sent the request too but I never received it. All my old email addresses are still active so it must of been lost in cyber space. The current best email address for me is craig@nosvalves.com .

The proper bias setting for the configuration of the VRD's you own is .70 VDC

If you want a copy of the manual email me again and I'll get one to you.

Craig

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  • 5 years later...
  • 4 years later...
On ‎6‎/‎13‎/‎2009 at 4:20 PM, dbflash said:

EL34's can be used you just have to cool the bias down and watch em for
plate glow. Start at about .40 volts on the bias and inch it up if you
start seeing plate glow with the room dark then back it down a smudge.
It really depends on what brand EL34's you use some are better at taking
the heat then others. By the tube specs an EL34 should be able to have
.50 to .55 volts on the bias

 

On ‎12‎/‎29‎/‎2014 at 12:01 PM, eth2 said:

I just heard from Craig and am going to bias at .72 which is the low end of his range (.70 to .80)

Thanks, Craig

 

On ‎6‎/‎13‎/‎2009 at 4:20 PM, dbflash said:

There is really no chance your going to hurt the amp using these tubes
but the tubes need some care taking when using them. The VRD push all
the lesser power tubes pretty hard. I personally always use a 5U4
rectifier when using these other tube types.

 

Brining this old thread back to life as it has lots of info for my question. I found this while searching for an answer I can't yet find. I do have an email out to Craig at @NOSValves but figured with so many VRD owners here you all might be able to help.

 

I've got some EL34s that I want to try just because I have them on hand and never run anything but KT88s in my VRDs. I've acquired some vintage GE 5U4GB rectifiers so I'm good there. I have my original manual from when I bought the VRDs new. In it with respect to biasing it says bias them at .50-.65 and Craig said he ran his at .55. I've always kept mine at .55 since I bought them. This thread seems to suggest .70-.80 is the range.

 

  1. So what is the proper bias for KT88s and if EL34s need to be run lower what is a good number for them?
  2. Was there a few different version of the VRD thus my manual says .50-.65 the one quoted above says .70-.80?
  3. If there are two different types of VRDs and mine are the .50-.65 variety AND EL34s need to be run lower what would be a good number? 
  4. I've got some Russian military 6P3S-E (GL6GC equivalent ) inbound, what should I run them at based on the above answers?
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El34's... around .40 to .45

I don't know the conversion off the top of my head, but that's a safe number.

El34s should sound more balanced across the entire dynamic range, where as 88s and 150s sound more impactful,  but less balanced.

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30 minutes ago, Schu said:

El34's... around .40 to .45

I don't know the conversion off the top of my head, but that's a safe number.

El34s should sound more balanced across the entire dynamic range, where as 88s and 150s sound more impactful,  but less balanced.

 

Thanks. I know you have/had at least two pairs of VRDs did your manuals from Craig say 50-65 or 70-80? I'm looking right at mine and they say 50-65. I've always run mine at .55, what if any benefit to running them higher assuming this thread is correct?

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I've had long conversations with Craig, and while the circuit can handle the wear and tear of higher bias values, he recommends slightly more conservative settings... unless you love replacing tubes all the time. Manual says in the .55mV range.

I've never run mine in the .75mV range... I'm perfectly happy where she's at right now and don't really miss any of the higher output power tubes because most of my listening is done in the 85db range.

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