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Post subject: I Could Swear the Rectifier Made a Difference...
Posted: Sat Feb 25, 2017 7:23 pm
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I have a 2005 DRRI with a 75 lb, 10,000 Watt Weber California Ceramic (note that I may be underestimating those values) that plays very clean with the DRRI. BUT, it was breaking up real early on the volume knob with a Strat (around 4). Holding all of the tubes the same, I swapped the early breakup JJ GZ34 with a Sovtek 5AR4; and my ears think they hear a later breakup (more headroom?) around 7 with the Sovtek. The GZ34 and 5AR4 are the same tube n'est-ce pas?

Any way that the electronic calculations might correlate this, or should I re-test prior to taking my beer medication? :!:

Edit: I may have asked about this before, so apologize if this is a repeat. I'll go check now to see what you said.


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Post subject: Re: I Could Swear the Rectifier Made a Difference...
Posted: Sat Feb 25, 2017 7:27 pm
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Double down on your meds and repeat the test.

:lol:

Arjay

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Post subject: Re: I Could Swear the Rectifier Made a Difference...
Posted: Sat Feb 25, 2017 9:31 pm
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Every rectifier will make a slightly difference (sometimes, not so slightly) B+ voltage. Has a direct effect on idle bias point. Therefore, need to re-bias amp every time you change rectifier... then test the amp's tone.

:)


Last edited by BMW2002Ti on Sun Feb 26, 2017 4:33 am, edited 2 times in total.

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Post subject: Re: I Could Swear the Rectifier Made a Difference...
Posted: Sat Feb 25, 2017 11:02 pm
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BMW2002Ti wrote:
Every rectifier will make slightly (sometimes, not so slightly) B+ voltage. Direct effect on idle bias point. Therefore, need to re-bias amp every time you change rectifier... then test.


Correct.

Even minute variances in plate voltage can have a significant effect on the sonic performance of the output stage. Differences in the idle-bias current will have an even more dramatic effect. Both of these parameters are in large measure determined by the quality of the rectifier. The best GZ34 ever made IMO was the Amperex Bugle Boy. They were built like a tank and they lasted forever.

Arjay

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Post subject: Re: I Could Swear the Rectifier Made a Difference...
Posted: Sun Feb 26, 2017 12:41 am
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This is an interesting topic to me.
I wonder if the OP didn't mean he swapped out a 5U4 and replaced it with a 5AR4.
I've always thought the 5AR4 and the GZ34 had only minor differences, like in the way the heaters are wired or something but relatively equal in terms of values involved, no?

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Post subject: Re: I Could Swear the Rectifier Made a Difference...
Posted: Sun Feb 26, 2017 2:16 am
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The DRRI (the amp that the OP referenced) is not designed for a 5U4GB.

As to any functional differences between the GZ34 and a 5AR4, there are none -- merely two alternative designations for the exact same tube (much like the 6550/KT88 or the 6CA7/EL34).

Arjay

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Post subject: Re: I Could Swear the Rectifier Made a Difference...
Posted: Sun Feb 26, 2017 4:32 am
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GZ34 and 5AR4 are the same model rectifier. GZ34 = European designation. 5AR4 = US.

That in mind, you'd be surprised the range of B+ voltage from a bunch of various "NOS" GZ34/5AR4 tubes. That's why it's a good idea to check the B+ every time you exchange one.


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Post subject: Re: I Could Swear the Rectifier Made a Difference...
Posted: Sun Feb 26, 2017 9:07 am
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BMW2002Ti wrote:
That in mind, you'd be surprised the range of B+ voltage from a bunch of various "NOS" GZ34/5AR4 tubes. That's why it's a good idea to check the B+ every time you exchange one.


......And the C- (idle-bias voltage).

:wink:

Arjay

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