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Post subject: Re: Taming the ice pick in a HRD
Posted: Wed Aug 01, 2012 8:45 am
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I don't think so, you'll likely never get 136 mV at the test point. And the export models only differ in the input voltage, 120 V for domestic and 230 V or 240 V for export models, but the Plate voltage, and most everything else, will be the same for either. It should be close to 430 VDC on the Plate.

The reasonable explanation is; 68 mV at the test point, 430 VDC on the Plate, approx 50% idle per tube. I would bet on it. :wink:

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Post subject: Re: Taming the ice pick in a HRD
Posted: Wed Aug 01, 2012 10:03 am
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fenderela wrote:
shimmilou wrote:
Either you misunderstood, or gave the wrong numbers, or your tech's math skills are seriously lacking. :o Also, if you have only 300-325 VDC on the output tubes' Plates, something is very wrong with your amp. You should have closer to 430 VDC on the Plates in a HRDlx. The HRDvl is closer to 485 volts on the Plates. The BJr has a Plate voltage closer to 330 VDC, but of course uses EL84 output tubes.

Consider that the test point reading at the output tubes' Cathodes in mV, which can be directly translated to mA since the reading is across a 1-ohm resistor, is for two tubes. The Cathode current for one tube will be half of the test point reading. To calculate the wattage dissipated at idle, use the following simple formula, and numbers are for one tube. Plate voltage times Plate current equals Plate wattage. Typical idle wattage for most amps will be between 50% and 70% of the tubes max Plate wattage dissipation rating. For the purposes of this discussion, Cathode current can be used in lieu of Plate current as it is "close enough". So, 70 mV (70 mA) at the test point equals approximately 35 mA of Cathode current per output tube, or .035 A.

Using the numbers that you provided, 300 x .035 = 10.5 watts per tube, which is beyond cold, it's freezing at approximately 33%, and would result in very sterile, harsh or "ice-picky" tone. 325 x .032 = 10.4 watts per tube, same as above.

Using numbers that would normally be found in a HRDlx, 430 x .035 = 15.5 watts per tube, which is about 50% and is at the lower end of the range, on the cool side but still acceptable. Raising the current can provide a warmer fuller tone, but too much can result in shorter tube life.

In any case, 68 mV at the test point of a HRDlx is not hot by any reasonable measure, and I hope that you just misquoted the numbers for the Plate voltage, otherwise something is very wrong with your amp, or something is wrong with the tech.


Thanks shimmilou. I don´t know... Maybe he wanted to say 68mA per tube (so 136mA at the test point)??? So 325 x 0.068 = 22,1 watts per tube??? Does it has any sense?

By the way, mine is an European HRDII, if it has sth. to be with the plate voltage...


No, it does not make any sense. Both shimmilou and I told you what the typical measurements are and what they mean. It being a European amp only means that the primary side of the power transformer (the side that gets plugged into the wall) accepts the different European voltages and frequency. The voltages that are fed to the tube are the same regardless if it is USA or European spec. If your "tech" cannot adequately explain all this, it is time to find a new, competent tech.

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Post subject: Re: Taming the ice pick in a HRD
Posted: Wed Aug 01, 2012 10:05 am
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shimmilou wrote:
I don't think so, you'll likely never get 136 mV at the test point. And the export models only differ in the input voltage, 120 V for domestic and 230 V or 240 V for export models, but the Plate voltage, and most everything else, will be the same for either. It should be close to 430 VDC on the Plate.

The reasonable explanation is; 68 mV at the test point, 430 VDC on the Plate, approx 50% idle per tube. I would bet on it. :wink:


Which is exactly what we both said at the very beginning of this thread. For some reason it is not sinking in. :roll:

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Post subject: Re: Taming the ice pick in a HRD
Posted: Thu Aug 02, 2012 5:08 am
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shimmilou wrote:
I don't think so, you'll likely never get 136 mV at the test point. And the export models only differ in the input voltage, 120 V for domestic and 230 V or 240 V for export models, but the Plate voltage, and most everything else, will be the same for either. It should be close to 430 VDC on the Plate.

The reasonable explanation is; 68 mV at the test point, 430 VDC on the Plate, approx 50% idle per tube. I would bet on it. :wink:


Thank yoy very much shimmilou, you´re always helpfull :)

By the way, my power tubes are stock GT 6L6C (red label) which are supposed to be only 25w... and I read it´s not recommended biasing them more than 70mv


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Post subject: Re: Taming the ice pick in a HRD
Posted: Thu Aug 02, 2012 5:26 am
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That sounds reasonable, I've also considered the stock tubes to be 25 watts, in the case of them being Sovtek 5881 (my original tubes are). Look for the original label, not the GT label, in black lettering. You can still go higher on the bias if you feel the need, 80 mV would still be OK in the case of Sovtek 5881, but 68 mV is about where mine were running, maybe 70 mV.

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Post subject: Re: Taming the ice pick in a HRD
Posted: Mon Aug 06, 2012 8:29 am
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mikibhomi, Shims pretty knowledgeable about this stuff.
Also you should edit your post and get rid of the advertisements. Many of us including myself, own our own businesses and are not allowed to advertise them here. Linking to your site is against forum rules. Take them down before you get yourself reported. :wink:

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Post subject: Re: Taming the ice pick in a HRD
Posted: Mon Aug 06, 2012 10:42 am
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Why don't we all send mikibhomi's company's customer service department a nice email? :mrgreen:

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Post subject: Re: Taming the ice pick in a HRD
Posted: Mon Aug 06, 2012 1:28 pm
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Good idea! And one to the moderator here also. :wink:

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Post subject: Re: Taming the ice pick in a HRD
Posted: Mon Aug 06, 2012 2:16 pm
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Lou, somebody beat me to it. :shock:

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