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Old 24th August 2009, 03:59 PM   #831
netbug is offline netbug  United States
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Quote:
Originally Posted by dupyv View Post
[snip]
I went back to anode-feedback on my current build of the baby huey.
With UL-feedback, I was unable to get the same focus and soundstage.
I went though several values of the feedback-resistor but each time voices
remained dull and flat.
[snip]
Did moving from UL-Feedback to Anode-Feedback require new feedback resistor values? I'd like to compare the two modes, so I was thinking about a wiring up a switch to quickly change between UL and Anode.
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Old 26th August 2009, 06:28 PM   #832
dupyv is offline dupyv  Luxembourg
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Netbug,

Going from UL-feedback to Anode-feedback will require a change of 3 resistors per channel and a different hookup of the ECC83 anode supply.

The anode-feedback variant is on post 602: http://www.diyaudio.com/forums/showp...&postcount=602
The UL-feedback is on post 604.

Compare and you see that instead of 10k-18k-10k you'll have to use 47k-16k-47k where 16k is the feedback resistor.

Kind regards,

Yves
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Old 26th August 2009, 08:21 PM   #833
netbug is offline netbug  United States
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Quote:
Originally Posted by dupyv View Post
[snip]
Going from UL-feedback to Anode-feedback will require a change of 3 resistors per channel and a different hookup of the ECC83 anode supply.
[snip]
bummer.

I really need to build a second baby huey in a much larger chassis. Lay everything out so that its easy to get to and change around. My current build is a real pain to make changes to.

oh well..
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Old 30th August 2009, 08:58 PM   #834
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I have just finished building (one channel of) the original EL84 baby huey, and i must say, i'm impressed

Instead of the ecc803s, I used the russian 6n2p, wich seems to work very well.
Another addition I made was a simple stabilised power supply with one mosfet and one high voltage transistor, if anyone is interessed, I can upload the schematic.
Also, the gNFB is not used.

Pictures and measurements will have to wait untill I finish the second channel.
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Old 31st August 2009, 04:06 AM   #835
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Yves (dupyv),
I messed about some more with the original CCS biased BH on the weekend. I changed back to sourcing the shunt feedback from the EL84 anodes as you have done. I decided I like the shunt feedback from the UL taps better BUT ONLY when I have linearised the speaker impedance by addition of a 10 Ohm + 2u2 zobel across the 4 Ohm secondary tap. (The speakers are VAF Research DC-X, 2 x 10" bass/mid with tweeter mounted between them "time aligned", and a simple series cap for the tweeter feed). That is I have optimised the amp / speaker interface for just one set of speakers. The amp seems to be much more susceptible to speaker impedance changes with frequency when using the UL taps so in general I think sticking with the anode connections makes sense, especially with speakers with complex impedance profiles or where you want to use the amp with different sets of speakers. Also keep in mind I deliberately went back to Hammond 1608 Output Transformers on this unit, trying to keep things simple and cheap.
P.S. I greatly appreciate your testing, suggestions and insights into the Baby Huey. Thank You. I hope you are enjoying your BH Amps.


hidnplayr,
Tube amps (in particular) suffer Intermodulation distortion. Using a simple voltage reg is something yves recommended (and posted his circuit) and it makes sense since you remove the ripple from the power supply and there is then one less "signal" for the sound signal to intermodulate with. I have'nt tried this yet but it makes good sense.

Cheers,
Ian
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Old 1st September 2009, 08:17 AM   #836
dupyv is offline dupyv  Luxembourg
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Ian (Gingertube),
>The amp seems to be much more susceptible to speaker impedance changes with frequency when using the UL taps so in general
>I think sticking with the anode connections makes sense, especially with speakers with complex impedance profiles

This seems to confirm the experiences I made with my Fullrange speakers, they don't have a linear impedance over 40Hz..20kHz.
The anode connection seemsto be the more universal & easy setup. To setup the UL-connection correctly, you need
an oscilloscope to check the signal, moreover it responds more critically to the type of OPT and speaker at the end.


>P.S. I greatly appreciate your testing, suggestions and insights into the Baby Huey. Thank You. I hope you are enjoying your BH Amps.
Thanks for your design Ian (and YvesM who I hope to see at ETF2009). Since I have the BabyHueys, I didn't touch my 2A3SE and 2A3PP much... (does that say enough?).
Just for the kick, I'm tempted to try that 6AV5-pentode screen-driven design yielding 80W that tubelab.com presented on this board.
It's a class B design, I doubt it can beat the BH sonically. But it has power (call it a muscle amp, with all the drawbacks).

Kind regards,

Yves
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Old 1st September 2009, 08:25 AM   #837
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Quote:
The anode connection seemsto be the more universal & easy setup
What does that mean in simple language? That triode connection is the way to go?
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Old 1st September 2009, 09:31 AM   #838
Yvesm is offline Yvesm  France
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I understand, "the simplest way to go".

The original design goal was to do not use UL tapped OPT (wich are not always"ideal") while having the power of pentodes and the damping of triodes.

Bas, do you plan to move at ETF09 ?
http://www.triodefestival.net/index.php?page=etf-2009

Yves, sure, I will be too !

Yves.
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Old 1st September 2009, 11:25 AM   #839
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Quote:
Originally Posted by gingertube View Post
Tube amps (in particular) suffer Intermodulation distortion. Using a simple voltage reg is something yves recommended (and posted his circuit) and it makes sense since you remove the ripple from the power supply and there is then one less "signal" for the sound signal to intermodulate with. I have'nt tried this yet but it makes good sense.
Yes that is exactly the reason why I decided to rebuild this old el84PP amp I bought.
The electrolyts where dried out, I replaced the rectifiers and put in some newer, bigger caps, but this raised the B+ to 390V and sound still wasnt as good as it should.
I didnt have any room to fit a regulated power supply in the original case.
Then I saw your circuit on here and decided to do a complete rebuild using your circuit,
wich also fixed the sound quality problems
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Old 1st September 2009, 02:16 PM   #840
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Quote:
Originally Posted by dupyv View Post
Ian (Gingertube),
>The amp seems to be much more susceptible to speaker impedance changes with frequency when using the UL taps so in general
>I think sticking with the anode connections makes sense, especially with speakers with complex impedance profiles

This seems to confirm the experiences I made with my Fullrange speakers, they don't have a linear impedance over 40Hz..20kHz.
The anode connection seemsto be the more universal & easy setup. To setup the UL-connection correctly, you need
an oscilloscope to check the signal, moreover it responds more critically to the type of OPT and speaker at the end.

(...)

Yves
Is the amount of feedback the same with both, anode and UL connections?

Could it be that the UL FB connection is giving you less feedback and lower
damping factor? The Zout must be higher for you to observer the greater
dependence on load impedance.

Are the g2 connected the same way in both cases?

Michael
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