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Old 6th January 2016, 12:46 AM   #1
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Default Which James output for a Lacewood SE

hello.

I have ordered locally the Hammond power transformers for a Lacewood amp project but i am not sure about the Hammond output transformers.

6V6 Lacewood Amp

But am waiting to the price of two James 6123HS from a taiwanese resident, it is OK for the lacewood amp?

There's also bigger transformers available from James at a higher price but i read bigger is not always better.

Best regards.
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Old 6th January 2016, 11:15 AM   #2
316a is offline 316a  England
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6123HS is multi tapped and has 4,8 and 16 ohm outputs . I have a pair of these . The 2k5 and 3K5 taps are fine but the 5k tap has poor HF response . To me , the 'Lacewood' amp is not a good design . UL output stage but no feedback so damping factor will be low . This may restrict the types of speakers that can be used . Volume pot on the grid of the 6V6 is also an issue , this should be at the input of the amp . I would suggest building something else to be honest with you

316a
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Old 6th January 2016, 11:17 AM   #3
zman01 is offline zman01  Bangladesh
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Hi,

The James 6123HS should be fine.

The design shows the Edcor GXSE10-8-5k (10 watss, 8 Ohms secondary impedance, 5K Ohms primary impedance; the James 6123HS has 4,8,16 Ohms secondary taps and 5K Ohms primary taps.

Not to sound pedantic, but building a tube amp means you will be dealing with lethal high voltage - make sure you follow all necessary safety guidelines. If you are not familiar with working with high voltage or do not understand the precautions, make sure you learn first, and/or get someone who has the necessary experience/knowledge to help you.

Edit: With reference to comments from 316a, for a DIY SE Tube amp project with 6V6 tubes, you can look at the Tubelab SE also.

www.tubelab.com

316a,

What amp do you have the James 6123HS in?

Last edited by zman01; 6th January 2016 at 11:20 AM.
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Old 6th January 2016, 12:18 PM   #4
316a is offline 316a  England
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Originally Posted by zman01 View Post
316a,

What amp do you have the James 6123HS in?
300B with E280F driver on the 3k5 primary . The 6123 works best on the 16 ohm tap but I use the 8 ohm secondary . The 5K primary has poor HF . Squarewaves come out more like sine waves and it sounds very dull on this tap . I would recommend a minimum of 7 sections : 5k to 8 ohm output transformer with at least 25H of primary inductance rather than a multi-tapped unit which inevitably will have unused sections and worse HF

316a
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Old 6th January 2016, 01:13 PM   #5
hpeter is offline hpeter  Slovakia
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Originally Posted by 100decibels View Post
he calculates triode curves (which 6v6 has nice) and then he wires it as UL..
At least Shade please
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Old 6th January 2016, 11:18 PM   #6
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Well, i already buy all the parts for the Lacewood amp, my idea was to use the James JS-6115HS l already own but on an other blog one guy said the max bias current is 45ma too close for the Lacewood. I can also buy the Hammond 1628SEA locally at a reasonable price and maybe i can get a good deal for the James JS-6135HSF from someone in Taiwan.

I have plenty of 6V6 tubes in stock, i will stay with them.
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Old 7th January 2016, 01:19 AM   #7
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Quote:
Originally Posted by 316a View Post
To me , the 'Lacewood' amp is not a good design . UL output stage but no feedback so damping factor will be low . This may restrict the types of speakers that can be used . Volume pot on the grid of the 6V6 is also an issue , this should be at the input of the amp.
I find this to be an interesting set of comments. And I would like to address them so that the design of the amplifier in question is more clearly understood.

The note about damping factor being low is correct; relatively speaking. But this is a small pentode amp and not a power house, so it should be paired with relatively decent efficiency drivers. However, I can say from experience that, even with middle of the road two way speakers (BIC DV62si), this amp has excellent acoustic performance with not a hint of booming. If it is paired with "sloppy speakers" then the inclusion of a 5kΩ resistor and 0.01f capacitor in series across the output transformer primary should temper performance w.r.t. the speaker resonant peak. I know that Leonard Tulauskas did his original work in this area with a pure pentode configuration but my experience has been that the process works almost as well in UL topologies. If any are in doubt, I recommend a reread of his article on the method in the October 1931 edition of "Electronics".

As for the placement of the volume control, I will have to disagree. This placement of the volume control has several distinct advantages. First it lowers the amplifier noise figure by at least 20dB and greatly reduces control noise due to the potentiometer. Second, the driver stage is specifically designed to provide enough 2nd harmonic to keep the amp warm. Specifically because pentodes in UL configurations tend to be a little "cold". However, as everyone knows, the 2nd harmonic level in triode stages is roughly proportional to drive level. Because most amps spend the vast majority of their lives in the mW range, by attenuating the signal after the driver, the tonal shaping designed into the driver is not lost at lower volume levels. Third, it could be argued that without the volume control on the input the risk of bias excursion (due to overdrive) increases. However, the driver for the lacewood is biased at 4.25v and uses cathode degeneration to further extend the allowable input. The risk of bias excursions due to line level input in this design is very remote.

Finally, I understand that there are those who will always look for negative feedback to "improve" amplifier performance. However, the inclusion of negative feedback, while decreasing overall noise, tends to promote non-choral harmonics over choral harmonics and decreases the overall quality of sound reproduction. If one desires the sound of a feedback topology, I suggest a good transistor amplifier. If one desires the classic warm tube sound rich in choral harmonics, I recommend leaving out the feedback loop and designing the amplifier for proper open loop operation from the start.

Please understand that I don't wish to discourage open discourse. However, in light of the comments made, I thought that some thoughts on the design philosophy associated with the 6V6 lacewood design were in order.
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