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Post subject: HRD re-bias question
Posted: Mon Mar 11, 2013 3:12 am
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Hi guys!

Want to re-bias my HRD for the first time. Just a basic "how do you do it?" question.

What is the factory recommended setting? Where do you set all of the knobs?

Anything else I should know?

Thanks!

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Post subject: Re: HRD re-bias question
Posted: Mon Mar 11, 2013 3:36 am
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Easy if you have do some work on tube amp before .

On the Deluxe Reverb Deluxe schematic look at note 5 ; Bias adjustment. Everything is there.

http://support.fender.com/schematics/gu ... ematic.pdf


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Post subject: Re: HRD re-bias question
Posted: Mon Mar 11, 2013 3:27 pm
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Cool! I have biased my Egnaters before, although Egnater makes it a little easier because they put the test points on the back of the amp.

What setting would you recommend for the extremes, meaning, what setting if I wnated the amp to run cool and be very clean, and what setting if i wanted it to run hot and distort more?

Thanks!

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Post subject: Re: HRD re-bias question
Posted: Mon Mar 11, 2013 9:08 pm
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I don't care for their tubes, but they do have some good how-to bias videos. After reading, scroll down and select "#1. Fender Hot Rod Deville / Deluxe Bias". Personally, for this particular amp at 430 Plate volts, I like about 75 to 80 mV at the test point. The range would be, about 70 mV cold to about 100 mV hot.

http://www.eurotubes.com/eurotubes-how-to-bias-video-probe-Pro-One.htm

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Post subject: Re: HRD re-bias question
Posted: Tue Mar 12, 2013 1:16 am
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I never work on this amp and did not know best bias. Follow shimmilou advice he know a lots.


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Post subject: Re: HRD re-bias question
Posted: Tue Mar 12, 2013 8:48 am
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Hi Len,
I think I've seen you on the Rig Talk Egnater Forum.

I had a HRDlx. It depends on the tube manufacturer to some degree. I ran JJ's in mine and ran them pretty warm around 82-85mv. The hotter you run them the warmer the tone. My HRDlx came from the factory pretty cold around 62mv and it sounded pretty harsh with icepick in the forehead highs. I always had reliability issues with mine, that's how I wound up with a Rebel 20 and a couple of amps I built myself.

Biasing is pretty easy just be careful. Here's a video from Eurotubes. I know a couple of guys that bias by "ear". I wouldn't recommend it though. IMO, A bias probe is a real handy tool.

http://www.eurotubes.com/eurotubes-Hotr ... lts-mA.htm

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Post subject: Re: HRD re-bias question
Posted: Tue Mar 12, 2013 4:00 pm
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Thanks for all the replies! I will check the videos. Where do you set all the various knobs- 12 o'clock?

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Post subject: Re: HRD re-bias question
Posted: Tue Mar 12, 2013 4:37 pm
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Volumes at 0 no signal.


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Post subject: Re: HRD re-bias question
Posted: Wed Mar 13, 2013 1:09 pm
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stratele52 wrote:
Volumes at 0 no signal.


+1 no guitar attached volume at 0. Let it warm up too, then recheck the bias a little later. If you want it a little cleaner I'd go 68-72mv. I wanted mine to break up early so I went 85-88mv.
It's still better to use a bias probe get the plate voltage and do the calculations. But you can still use the bias test point. Just don't go too hot or you'll really shorten the life of the power tubes.

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Post subject: Re: HRD re-bias question
Posted: Thu Mar 14, 2013 2:56 am
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What about the EQs and reverb controls?

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Post subject: Re: HRD re-bias question
Posted: Thu Mar 14, 2013 4:47 am
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Turn them all down. The video explains it all.

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Post subject: Re: HRD re-bias question
Posted: Thu Mar 14, 2013 12:07 pm
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lenrabinowitz wrote:
What about the EQs and reverb controls?



Any position does'nt matter.


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Post subject: Re: HRD re-bias question
Posted: Thu Mar 14, 2013 12:30 pm
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Thanks! Gonna try it this weekend.

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Post subject: Re: HRD re-bias question
Posted: Sat Mar 16, 2013 7:35 am
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Done! It was reading about 64, which is cold. That's what I thought I wanted, but I decided to gas it up to the other end and brought it up to about 86. Just for the hell of it- since the amp was open- took out the V1 Sovtek and the groove tubes in V2 and V3 and put JJ's in V1 and V2 and and a PentaLabs in V3.

Likin' it so far! We'll see.

Question: Can I replace the Groove Tubes 6L6's with Tung Sol 6V6GT's? What would be the bias settings for those?

Thanks!

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Post subject: Re: HRD re-bias question
Posted: Sat Mar 16, 2013 9:00 am
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lenrabinowitz wrote:
Done! It was reading about 64, which is cold. That's what I thought I wanted, but I decided to gas it up to the other end and brought it up to about 86. Just for the hell of it- since the amp was open- took out the V1 Sovtek and the groove tubes in V2 and V3 and put JJ's in V1 and V2 and and a PentaLabs in V3.

Likin' it so far! We'll see.

Question: Can I replace the Groove Tubes 6L6's with Tung Sol 6V6GT's? What would be the bias settings for those?

Thanks!


You need to be careful running the stock GT 6L6s so hot if you are not also measuring the plate voltage. Look for the original lable (printed directly on the glass of the tube). If it says "SOVTEK 5881WXT" there is some debate as to if those are 25 watt tubes or 30 watt tubes.

Proper biasing is accomplished by measuring an idle power dissipation that is between 50% and 70% of the maximum power dissipation of the tube. In order to do so, you MUST measure both cathode current per tube (done by measuring at the factory test point and dividing by 2; i.e. 86 mv at the test point equates to 43 ma cathode current per tube) AND plate voltage for the tube. You then multiply the two values together to get an idle plate dissipation of X watts. That number is then divided by the max plate dissipation to come up with a percentage. Do not go above 70% or below 50%.

If you are measuring 43 ma cathode current (its really plate current you need but cathode is close enough for govt work) and your plate voltage is 430 VDC, your idle plate dissipation is approximately 18.5 watts per tube. If your power tubes are 30 watt tubes, you are at a bias setting of 62% (good). If they are only 25 watt tubes, your bias setting is 74% which is too hot and you risk burning out the tubes early.

The only 6V6 type tubes that will handle the plate voltage of the Fender HRD are the JJ 6V6S and GT 6V6S. Possibly the EH 6V6GT will work also.

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