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Old 15th September 2012, 10:54 AM   #31
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I'm just reviving this thread to see if there are any new views on the best SE OPT for a 300b amp. It's a very common amp, and it would be good to optimise the OPTs we use.

I've rebuilt my amps with a much better circuit - 4P1L in filament bias> LL1620/18mA > 4P1L in filament bias> Hammond 126C > 300b. So far I've compared Lundahl LL1660/80ma and Audio Note Trans 152. The AN is huge and has slightly better dynamics and bass. The Lundahl is slightly better (I think but not 100% sure) on vocals. I previously preferred the O-netics level 1 "commercial" 3.3K model to both, and am rebuilding this with the same circuit. Will post the results.

Meantime - any revised suggestions for a great sounding SE OPT?

Andy
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Old 15th September 2012, 11:06 AM   #32
Jaap is offline Jaap  Netherlands
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Amplimo Toroid (design Menno van der Veen) transformers, the best there is. I am definitely not saying this because I have a pair for sale for 60% of newprice. The same as Plitron I believe. Single Ended uitgangs trafo's
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Old 15th September 2012, 11:57 AM   #33
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http://www.amplimo.nl/images/downloa...dv/vdv3035.pdf

This has "saturation primary current 172mA". That seems pretty high for a quoted 28H primary inductance. Any idea of the comfortable working current? It's not too clear.

Which ones do you have and how were you running them? What did they sound like?

andy
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Old 15th September 2012, 04:02 PM   #34
needsp is offline needsp  United Kingdom
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Hi Andy

These talk the talk, but do they walk the walk?-

http://www.monolithmagnetics.com/ima...asheet_S-9.pdf

http://www.monolithmagnetics.com/ind...d=62&Itemid=60

Double C cores with impressive specs, but I've been unable to find any independent reports on them. Can anyone help?

I'm still using some old Audio Note "Spec B" 2k5 transformers than came with a Kit 1 in 1995! The only parts, other than the chassis I'm still using.... I think these are now the 152 types you mentioned.

I've considered Sowter's SA08- Rod Coleman uses them- and also could probably still get hold of the ones used in the Border Patrol amps (I use Border Patrol interstage transformers). But the Monoliths offer double C-cores at not much higher cost- tempting, in theory. I'm also keen to move to a 3k3 or 3k5 primary- the ANs' are 2k5, which Rod reckons increases distortion unacceptably

Thanks

Paul N

Last edited by needsp; 15th September 2012 at 04:04 PM. Reason: Hyperlink error
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Old 15th September 2012, 04:29 PM   #35
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Hi Paul,

Yep - 2.5K isn't ideal. I've wondered about using the ANs on the 4 ohm tap. Must try it. If you look at all the distortion evidence, the best primary seems to be 5k or even more. I have a whole chart of distortion values from this guy:

"For the 300B: The minimum actually occurs at 6.5K in one case and 10K in the other (because of the different operating points). The DCR = 0.1*RL. Adjusting the DCR has the same effect as adjusting the reflected load. Something I am contemplating: Is it better to compensate the transformer's IR drops to get the desired loaded voltage gain or to compensate the transformer for the desired impedance ratio. Note: . I have a hunch it may be better to be a bit on the high impedance side of the 3HD minimum. It seems that so that as the tube varies or the load varies, the 3HD doesn't seem to change as much being on the high side. (7K +/- 3.5K) AND most 8 ohm speakers are less than 8 ohms.
Very interesting. This effect is going 3 or 4 different directions at once... For the last investigation, I didn't publish the primary DCR used... I used a DCR formula of DCR = .1*RL, where RL is the reflected load. Repeating the last post:
300 volts,-54.3grid, 60 mils, 3500 ohms, 3.3 watts, -31/-51.5db
350 volts,-70.8grid, 50 mils, 5000 ohms, 4.3 watts, -30.1/-47.8db
The DCR was 350 and 500 ohms.
And in the last post, for the minima for 3rd I had:
300 volts,-54.3grid, 60 mils, 7000 ohms, 2.22 watts, -36.7/-88.9db
350 volts,-70.8grid, 50 mils,11000 ohms, 2.56 watts, -37.3/-93.8db
The DCR was 700 and 1100 ohms.
So...tried varying DCR. This time used DCR = .05*RL to see how this would effect the 3rd order minima. I used the same op points from Mike L (as before) but just changed DCR on the transformer. Then varied the RL until I hit the 3rd order minima. The results were interesting... The 3rd order minima doesn't occur until much higher effective loads. It moves way up by lowering DCR in both cases:
300 volts,-54.3grid, 60 mils,12000 ohms, 1.45 watts, -43.7/-87.3db
350 volts,-70.8grid, 50 mils,25000 ohms, 1.27 watts, -48.4/-104 db
The DCR was 600 and 1250 ohms.

So it looks like DCR actually helps us get a good 3rd order minima. Looking at the 11,000 ohm load case on the 300B with the 350v operating point, and a 1100 ohm DCR...the 3rd order minima was -93.8 db. With a 550 ohm DCR (half) and 11,000 ohm load... the 3rd order minima is only -64.8 db. So it is better by 29 db by doubling the DCR. Dave, and Mike, thanks for finding something very interesting. I meant to say in the conclusion that raising DCR helped to get a better (deeper) 3rd harmonic minima at a lower load. One thing that lowering DCR *may* do is that it may cause a deeper Null in the 3rd harmonic minima. So if you aren't concerned with power, a lower DCR *may* get less 3rd order distortion *if* you have RLoad at the minima." Mike

Can't remember who "Mike" was.
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Old 15th September 2012, 04:38 PM   #36
kevinkr is offline kevinkr  United States
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Sounds like prose from Mike LaFevre of Magnequest.

Magnequest iron was quite good, I'm not sure what is going on with MQ these days, but I recently tried to find a source for his plate chokes and was unable to do so.

I've used a small number of Electra-Print custom built output transformers in SE amp projects - without exception they've been excellent.

I also like the old Tamura F-5002 with the 300B, these apparently are no longer made, and when they were the price was pretty stratospheric - the most expensive OPTs I've ever purchased.

I was the maker of the KTA 3030 amp referenced early in the thread.. Ancient history..
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Old 15th September 2012, 07:30 PM   #37
Jaap is offline Jaap  Netherlands
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Quote:
Originally Posted by andyjevans View Post
http://www.amplimo.nl/images/downloa...dv/vdv3035.pdf

This has "saturation primary current 172mA". That seems pretty high for a quoted 28H primary inductance. Any idea of the comfortable working current? It's not too clear.

Which ones do you have and how were you running them? What did they sound like?

andy
I have both the 3K5 and 2K5 versions. They are super soundwise. I used them with 80 or 85 mA if I remember well.
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Old 16th September 2012, 08:18 PM   #38
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Choose a Transformer in Audio

This mentions Daburu which I've been trying to track down. They seem to have gone up in price a lot. DA-50X is already over 400 euros. I'm assuming this is 5K.

LOOK-AUDIO MATERIEL AUDIOPHILE - Mentions Daburu and some cheaper "45" ones.

Transfo Daburu DA-35x vs LL1664 : Electroniques - Cinetson - Hifi et Homecinema Bit of discussion here including the great quote "crois moi camarade les Chinois ont encore beaucoup de chemin a faire avant d 'égaler les transfos de sortie Chrétien que celà te plaises ou non."

Here's another thread:
Chinese Output transformer for 300B SET
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Old 16th September 2012, 08:26 PM   #39
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I svapped my Audio Note OPTs for a Daburu 3.5k... That was el cheapo AN - IE core I think.
The Daburu is better in every aspect and with great margin also. The amp is in fact en AN kit1 (heavily modified)
Great OPTs...

"Nano-crystal Double-C core output transformer 3.5k:4/8/16ohm Single Ended"


Click the image to open in full size.

Last edited by bambadoo; 16th September 2012 at 08:56 PM.
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Old 16th September 2012, 10:51 PM   #40
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Those are pretty expensive, no? What price did you pay and what was the cheapest supplier you found?

I'm using Audio Note Trans 152 right now, which sound like the ones you had.

andy
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