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Old 9th April 2013, 02:56 AM   #1
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Default RH84 power output

Hey All,

The RH84 specs B+ of 300 volts and at this voltage the EL84 has an output listed in the data sheet as 5.7 watts. Yet I've read here the amp only has about 2 watts of output. Why is this? Can anyone tell me? The RH is not triode connected. Is it an effect of the feedback?

Kevin
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Old 9th April 2013, 04:30 AM   #2
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Most likely a function of THD. You'll notice that the data sheet says 10% THD at 5.7 watts output with 250v plate & screen. Less distortion equals less power out, simple as that.

jeff
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Old 9th April 2013, 10:48 PM   #3
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So the design limits the output to limit distortion?
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Old 9th April 2013, 11:23 PM   #4
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Whoever said 2w got it wrong.

Our RH84 (B+ ~ 285V) outputs 3.9w at clipping.

One of the reasons for building RH84 is that it puts out much more power than the ~2W output by triode strapped EL84.

dave
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Old 9th April 2013, 11:46 PM   #5
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Maybe that's where the 2 watt figure came from, a triode strapped EL84?

jeff
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Old 10th April 2013, 12:03 AM   #6
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Likely, triode strapped EL84 typically makes 1.5-2w.

dave
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Old 10th April 2013, 01:06 AM   #7
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Thanks guys. I had a feeling someone had confused it with a triode amp. But the original schematic is not strapped. I was trying to use a 6P15P instead of a EL84. But 6P15P is too sensitive for this amp. It lays really loud and is seriously distorted. It needs to be redesigned for 6P15P with a different preamp tube. I was thinking of 6922.
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Old 10th April 2013, 07:29 AM   #8
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First of all what output transformer are you using there and what is your Uplate, Uscreen value?
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Old 10th April 2013, 08:20 AM   #9
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Quote:
Originally Posted by mr2racer View Post
Thanks guys. I had a feeling someone had confused it with a triode amp. But the original schematic is not strapped. I was trying to use a 6P15P instead of a EL84. But 6P15P is too sensitive for this amp. It lays really loud and is seriously distorted. It needs to be redesigned for 6P15P with a different preamp tube. I was thinking of 6922.
If you are going to do that consider substiting a small signal pentode. Using a triode in this circuit creates distortion. In the original RH84 it seems this is balanced sonically reasonably well - but if you attempt to change the output tube its a whole different design.
Something like the excellent 6AU6 fits the bill nicely.

Shoog
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Old 11th April 2013, 12:18 AM   #10
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Kosmin, Plate voltage 305 and screen 150. Originally I was using a pair of Motorola vintage OPT's. I tried a pair of Eico AF4 OPT's recently made by Heyboer. Same outcome.

I went back to a pair of EH EL84's and the original values and the amp is fine now.

Shoog, I'm planning another amp using 6P15P, have a bunch of them. I'm going to use a 6922 to drive two 6P15p SE in parallel. I had Arlen at Heyboer build me a pair of ten watt 4k OPT's with a 6ohm secondary. I plan to use fixed bias and hope for between 8-10 watts.
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