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Post subject: Noob Here- HRD retube
Posted: Sun Jan 01, 2012 11:19 am
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I had a stock HRD FAT I bought in 97 and played intermittently. Earlier this week I fired it up and it sounded like crap (clipping low end at any volume in clean).

So I thought speaker: Installed Celestion Vintage 30. Still sounded bad.

Couple days ago, I installed the JJ 6L6GC and replaced all 3 12AX7's with Sovtek 12AX7WA's.

I left the amp on for about 8 hrs in standby.

I then checked bias - 68mv steady.

I rebiased to 71mv. I've left the amp on since (in standby) and just started goofing with my Strat which have active pups.

The tone now is incredible. Stock, I was really hard pressed to notice "good tone" from playing with knobs - it didn't make too much of a difference.

Now - 24+ hrs into burn-in it seems each increment for the various knobs makes a very noticeable difference in tone - the clean vs. drive vs. more drive is markedly noticeable (for the better that is).

MY QUESTION FOR THE EXPERIENCED GUYS HERE:
Did I setup OK?
... and please advise when I do fire up the amp to play (after a 8-10 minute warmup in stdby) how long should I leave the amp on per session? I've always had a concern that turning the amp on for 1 hr or so and playing, then turning it off between playing for a couple hours actually does harm? Is it better to leave the amp running for 2-3-4 hours per day vs. on and off?

Thanks all!


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Post subject: Re: Noob Here- HRD retube
Posted: Sun Jan 01, 2012 12:14 pm
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Ya done good GoochMan!

The HRDlx is known to be biased cold from the factory, and the stock output tubes sound can be improved with the proper bias setting. My HRDlx is a '98 model. :)

I think that you could bump the bias up some more if you wanted. I run mine at about 78 mV with the stock output tubes, many others go 85 mV and more. Check your Plate voltage and multiply times the Plate current to get the idle bias in watts (Plate current for a 6L6 typically 5 mA lower per tube than Cathode). It is generally acceptable to set the idle to between 50% and 70% of the tubes rating, and in the case of the JJ it is rated 30 watts. Assuming about 430 volts on the Plate, a 30 watt tube would be set between 80 mV and 108 mV at the test point. Adjust according to your actual measured Plate voltage.

I used the stock GT preamp tubes (Sovtek 12AX7WA) for years, and the clean sound is great, I used pedals for drive and didn't use the drive channel in the amp very much (sounded a little harsh). I now use the GT12AX-C for preamp/PI and the drive channel is much improved, while maintaining great clean channel also.

I hear this same scenario a lot; amp sounds bad so output tubes are changed then the bias is set for the new tubes. Why not try it? Reinstall the stock output tubes and set the bias on those to the same setting as you have for the JJs, and see if the sound doesn't improve for the stock output tubes. :wink: Some tubes will only draw so much current even with the bias pot all the way up, this is normal and tube dependent.

I agree with turning amp on and leaving in standby for a few minutes before switching to play. The real damage to most any electrical components in the amp, is not just the heat, but by the temperature extremes of heating and cooling of the components when the amp is turned on and off. It is better to leave the amp on and in standby, if you are going to play in a hour again. A car running would be similar, leaving it running for a few is much better than turning it off and restarting. I guess that energy conservation would be the only reason to shut it off if you are going to use it again an hour later. So, IMO it is better to leave the amp on for 4 hours rather than turning it on and off several times a day.

P.S.
You should check the bias immediately after changing output tubes, don't wait for it to stabilize before checking, you just might red plate the tubes if you don't.

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---> "The amp should be SWITCHED OFF AND UNPLUGGED before you do this!" <---

Por favor, disculpe mi español, no se llega a la práctica con mucha frecuencia.


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Post subject: Re: Noob Here- HRD retube
Posted: Sun Jan 01, 2012 12:25 pm
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Thanks for the reply. I'd researched on the net and read varying opinions - that I'd thought I'd take the plunge and thankfully, you've validated what I'd done. Appreciate it!


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