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Post subject: HRD hissing
Posted: Thu Mar 10, 2011 8:08 am
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Hi all,I was wondering if anyone would be so kind as to possibly give me some idea of a solution to my problem with my brand new HRD mkII (clearance sale).
It hisses (at zero volume), more than I've been used to with my SS amps and more than my friend's mk II which is older(but still hisses).Mine's fitted with GT all round, 6L6-r powertubes 12atx7-r preamp.I've checked the bias and it's normal Fender 74mv but even decreasing or increasing this there's no difference in the hiss level. I've noticed the 500v condensers buzzing,is this normal?
I've got a 30days or money back offer, plus a three year waranty.My Mustang V head should arrive very soon and then I'll have a better way of comparing.I do love that real tube sound shame about the hiss.
Cheers all.


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Post subject: Re: HRD hissing
Posted: Thu Mar 10, 2011 9:14 am
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There is no "solution".

Regardless of what you do, that amp will never idle at dead quiet. They're the world's most expensive white-noise generators.

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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Post subject: Re: HRD hissing
Posted: Thu Mar 10, 2011 9:28 am
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GT george wrote:
Hi all,I was wondering if anyone would be so kind as to possibly give me some idea of a solution to my problem with my brand new HRD mkII (clearance sale).
It hisses (at zero volume), more than I've been used to with my SS amps and more than my friend's mk II which is older(but still hisses).Mine's fitted with GT all round, 6L6-r powertubes 12atx7-r preamp.I've checked the bias and it's normal Fender 74mv but even decreasing or increasing this there's no difference in the hiss level. I've noticed the 500v condensers buzzing,is this normal?
I've got a 30days or money back offer, plus a three year waranty.My Mustang V head should arrive very soon and then I'll have a better way of comparing.I do love that real tube sound shame about the hiss.
Cheers all.


You might try lower gain tubes in V1, V2, or V3. I run a 5751 in V1, a 12AX7 in V2, and a 12AT7 in V3 of my Blues Deluxe reissue which greatly reduces the hiss and improves the clean sound. These tubes will make the Drive/More Drive less useful, but depending on you opinion of those settings, it may be a benefit. I run my amp clean and use a pedal for drive (currently a FullDrive 2 MOSFET).

Or you could just return the amp.

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Post subject: Re: HRD hissing
Posted: Thu Mar 10, 2011 1:35 pm
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Another option is using fender's great warranty (5 years). I had a great experience with getting my amp replaced.


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Post subject: Re: HRD hissing
Posted: Fri Mar 11, 2011 9:06 am
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Bluesky's solution worked.I had a spare 6211 and placed it in V1 swapping out the stock GT12ax7-r. Hissing is tremendously reduced and a very nice clean sound up to about 6 then the shortcomings of that valve come into stake.Volume is also reduced but that's fine by me and my family! Thanks guys, really helpful.
GT


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Post subject: Re: HRD hissing
Posted: Fri Mar 11, 2011 9:13 am
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GT george wrote:
Bluesky's solution worked.I had a spare 6211 and placed it in V1 swapping out the stock GT12ax7-r. Hissing is tremendously reduced and a very nice clean sound up to about 6 then the shortcomings of that valve come into stake.Volume is also reduced but that's fine by me and my family! Thanks guys, really helpful.
GT


Just wanted to say welcome, George. Glad to hear that your problem has been resolved.


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Post subject: Re: HRD hissing
Posted: Fri Mar 11, 2011 10:26 am
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JOC... is that really a 6211? Or a 6201 (mil spec/industrial 12AT7)? I don't think I've ever heard of someone using a 6211. Pinout is the same (6211, 6201, and 12AX7), so you're prolly not going to do any harm to the amp. I think it had original use in computers (imagine the size of that computer!). And RCA receiver manual said it specialized as "Multi-Vibrator" app. Interesting... :oops:

If your amp sound much happier, maybe she's a female.

http://www.wps.com/archives/tube-datash ... 04B/16.JPG


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Post subject: Re: HRD hissing
Posted: Fri Mar 11, 2011 11:12 am
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GT george wrote:
Bluesky's solution worked.I had a spare 6211 and placed it in V1 swapping out the stock GT12ax7-r. Hissing is tremendously reduced and a very nice clean sound up to about 6 then the shortcomings of that valve come into stake.Volume is also reduced but that's fine by me and my family! Thanks guys, really helpful.
GT


I'm not familiar with the tube you are using so you might want to double check its specs. A 5751 has about 70% of the gain of a 12AX7 and is very useful in quieting things down. The amp will still play just as loud as before, you just have to turn the knobs a little higher. :D

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Post subject: Re: HRD hissing
Posted: Fri Mar 11, 2011 1:00 pm
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I live in the north east of Italy and valves are hard to come by unless ordering via the net.6211 is what's printed on the glass but no brand name.I bought it and another 2 at a swap-meet (big one at that) and the guy had a case full of these for 3 euros each.An interesting observation of the amp's behaviour when connected to two 16ohm spkrs though:- low frequency feedback once I hit 6 on volume(with the 6211 fitted).When hooked up to two 8ohm spkrs I could max out without any of that feedback(I'm talking clean channel).Dirt channel is much more controlable too.What damage could it do anyway?I'm no electronics expert but if it fits in the hole I'll stick it in!:) With the noise floor lowered so much the clean channel is obviously far more enjoyable.
Thanks again guys(and maybe gals)


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Post subject: Re: HRD hissing
Posted: Fri Mar 11, 2011 2:13 pm
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Rock Star
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Joined: Mon Apr 05, 2010 2:37 pm
Posts: 8708
Location: Natural Bridge, Virginia
GT george wrote:
I live in the north east of Italy and valves are hard to come by unless ordering via the net.6211 is what's printed on the glass but no brand name.I bought it and another 2 at a swap-meet (big one at that) and the guy had a case full of these for 3 euros each.An interesting observation of the amp's behaviour when connected to two 16ohm spkrs though:- low frequency feedback once I hit 6 on volume(with the 6211 fitted).When hooked up to two 8ohm spkrs I could max out without any of that feedback(I'm talking clean channel).Dirt channel is much more controlable too.What damage could it do anyway?I'm no electronics expert but if it fits in the hole I'll stick it in!:) With the noise floor lowered so much the clean channel is obviously far more enjoyable.
Thanks again guys(and maybe gals)


A Google search on "6211 vacuum tube" came back with this:

From http://www.tejastubes.com/NOS12AT7ECC81E81CCECC801S.htm

"6211:
A less common vacuum tube, this is a class A amplifier twin triode with medium mu; lower gain than the typical 12AT7, even lower than even the 5965 (see below). It usually has larger, flat plates with diamond shaped points at the corners bent inwards. This construction adds rigidity to the plate structure. This vacuum tube is slightly lower in plate voltage and current ratings, but is still very usable in hi-fi stereos.Often used in preamp circuits with lower gain, lower microphonics, and mellow sound. Somewhat uncommon but this medium-mu tube sounds very good in place of the standard 12AT7. Great for making the gain on a guitar amp more usable or eliminating harshness in your stereo system."

From https://www.tubeworld.com/6005.htm

"6211 / 6211A Medium-Mu Dual Triode
(6211=computer rated 5844)

MAX RATINGS:
-----------
Vplate = 200V
Plate Dissipation = 1.5W

Typical Operation:
-----------------
Class A Amplifier
Plate Voltage 100 V
Grid No. 1 Voltage Derived from Cathode Bias Resistor 470 Ohms
Amplification Factor 27
Plate Resistance 7500 Ohms
Transconductance 3600 µ
Plate Current 4.6 mA"

You should compare this to 12AT7 specs.

Personally, I did not like the sound of a 12AT7 in V1 of my Blues Deluxe Reissue. The sound of a 5751 was much smoother to me and is better suited in preamp applications than a 12AT7 type in my opinion. I don't think the 6211 will cause any problems with your amp, but it would not be my first choice. I forget who I bought my 5751 from but it was one of these two sellers:

http://tubedepot.com/nos-5751jan.html

http://thetubestore.com/sylvania5751.html

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