Tubelab Simple SE OPT Query (Hammond 1628SE vs 1629SE) - diyAudio
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Old 21st December 2009, 04:21 AM   #1
Junior is offline Junior  Singapore
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Default Tubelab Simple SE OPT Query (Hammond 1628SE vs 1629SE)

hi guy,
believe me. i had tried searching the forum for answer to my query.
please do also bear with my newbie question as i am very new to tube/valve.

i am in the process of building the Tubelab Simple SE, which is my first tube integrated project.
George stated that "The ideal primary impedance for this design is 5K ohms."
my question is : what is the consequences if 1629SE with primary impedence at 6.5k is used instead?
reason for asking is i have a very good offer of a pair of 1629SE.

one consequence that i can think of is the lower end of the frequency being affected. (5k has better bass control)
what other effect will one expect if 1629SE OPT is used instead of 1628SE.

thanks in advance.
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Old 21st December 2009, 05:56 PM   #2
rknize is offline rknize  United States
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Usually the trade-off for a higher impedance ratio is that you get less power output but a bit more dampening factor. To put it another way, it gives the tube more leverage against the speaker but it can't move it as far. That is a highly simplistic explanation as there are lots of other trade-offs as well, but they can be ignored for the most part as long as you don't deviate too far.

If you go with EL34s, they probably won't mind the higher impedance as long as you don't mind that reduction in power output. For example if you setup the SSE to run KT88s, they really want to see a 3-4k primary impedance to get the most power out of them. But people generally seem to go with 5k impedance as George recommends regardless of what tubes they end up using. So running a 6.5k primary with KT88s is starting to take things a bit too far, I would think. It would still work, but I would expect linearity would start to suffer more.

How sensitive are your speakers?
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Old 21st December 2009, 08:09 PM   #3
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My Industrial Amp (Simple SE) uses a pair of 3K OPT's with KT88's. I find that I prefer the sound with my 8 ohm speakers connected to the 4 ohm output taps which results in a 6K load on the tube.

It is true that the text book load for a KT88 and an EL34 is in the 3 to 4 K ohm region. This is optimum when the tubes are operated at 350 to 375 volts. The Simple SE can be operated at these voltages but most builders use a power transformer that generates 430 to 460 volts of B+. The optimum load for tubes operated at these voltages is around 5K ohms, although a KT88 will handle a lower impedance.

In general a lower load impedance will result in higher output power but increased distortion. A higher impedance will result in lower power and lower distortion.

As rknize explained the OPT functions like a lever and the winding ratio is the balance point (fulcrum). The Hammonds have multiple taps on the output which is like having the ability to move the fulcrum of the lever to three different places. The 6.5 K specification is valid only when an 8 ohm load is connected to thge 8 ohm tap. If the 8 ohm load is connected to the 16 ohm tap the transformer acts like a 3.25 K ohm load. This is why my 3 K transformers work like 6 K transformers.

It is highly probable that your "8 ohm" speakers are not 8 ohms. The actual impedance of most speakers varies as the audio frequency and power level changes. The documentation supplied with your speakers should include a graph of impedance VS frequency. If your speakers have significant portions of this graph below the 8 ohm line, the 6.5 K ohm OPT might be a better choice than a 5K.

If you can get the 1629SE's for a good price I would say to go ahead and use them. Get the amp working with everything connected up normally (8 ohm speakers on 8 ohm tap). Once things are working and you have had some listening time you can experiment with the choice of output tap, UL VS triode and feedback on or off to find the combination that works best for you.
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Old 21st December 2009, 11:39 PM   #4
Junior is offline Junior  Singapore
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hi rknize & george,
thanks for the replies and really appreciate it.

am using a pair of Usher X719 and currently driving it using // & bridged LM3886 chip amp with m7c preamp by my3c.net (site no longer exist).

since it is going to be my first built and right from the start i planned to use both KT88 and EL34 in the same amp (via switch to select the cathode resistance). i shall not skimp on the OPT then.

on top of that, george had already done alot of study supported by technical measurements with various type of tubes and OPT to go with it.
(how silly of me to have asked this question in the first place but thanks to the patience of those who replied )

one will not go wrong if one follow closely to george's recommendation.
this is especially so for newbie like me.

i believe that my valve journey will not end with simple SE as I had at the same time order the Tubelab SE too.

merry christmas in advance.......

Last edited by Junior; 21st December 2009 at 11:45 PM.
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Old 22nd December 2009, 02:59 AM   #5
rdf is offline rdf  Canada
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Make sure it's a 1628SEA and not a 1628SE if you go that route. A forum search will provide the details.
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Old 22nd December 2009, 04:18 PM   #6
kevinkr is offline kevinkr  United States
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Quote:
Originally Posted by rdf View Post
Make sure it's a 1628SEA and not a 1628SE if you go that route. A forum search will provide the details.
Bluntly the 1628SE has a design and/or manufacturing issue that places a resonance in the audio band, and has poor HF response as well. (It rolls off well below 20kHz.)

You might want to consider SILK or James transformers for both your SE amplifier projects, they're pretty local to you, and both make better transformers than Hammond IMHO..
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Old 22nd December 2009, 09:20 PM   #7
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In hindsight I should have kept my 1628SEA's. Their bass response is tight and thunderous compared to the tiny transformers I'm using now.
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Old 22nd December 2009, 11:12 PM   #8
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Quote:
Bluntly the 1628SE has a design and/or manufacturing issue that places a resonance in the audio band, and has poor HF response as well. (It rolls off well below 20kHz.)
The 1628SE does indeed have the "built in notch" effect. They are not all the same, but they all have the problem. The 1628SEA still has the resonant notch but it is moved out to about 28 KHz. The frequency response is down about 2 db at 20KHz. These transformers have the best bass of any SE OPT that I have ever tried. The 1629SE is not supposed to have the problem but I have not tested them. Given a choice of the Hammond 1628SE or the Hammond 1629SE the choice is easy, use the 1629SE.

The big Hammonds have a large magnetic structure which does consume a bit of the audio power. My listening tests (and those of a few others) agree that these transformers absolutely rock when used with speakers that require a bit of power to use. On 87 to 96 db (what I have tried) speakers where the average power level is in the 1 to 5 watt level they sound pretty good. We listened to them on a set of Lowther based horns that were 106 db efficient. Here the average power level was in the .1 to 1/2 watt range. We all agreed that the big Hammonds took something from the music no matter what we fed them with. We couldn't pinpoint exactly what was missing though. On these speakers a 45 tube feeding OPT's in the 3 to 5 pound size worked the best. I never got to try the little Edcors but I would bet that they would sound really good here.

Quote:
In hindsight I should have kept my 1628SEA's.
I still have a pair of the 1628SE's and a pair of the 1628SEA's. Neither is being used right now because I find that the big Edcor CXSE 25-8-5K's just sound better with my speakers. They are going into a 300B based Tubelab SE which has been half finished for almost 2 years now.

I think that the big Hammonds (either pair) would do best in the bottom half of a bi-amped SE system, probably a KT88 based Simple SE with a 45 based Tubelab SE on top. I may change my mind as I spend more time with some P-P amps.

Quote:
You might want to consider SILK or James transformers for both your SE amplifier projects, they're pretty local to you, and both make better transformers than Hammond IMHO..
I have never listened to either since they aren't too common in the US. Reports from users have been very positive though. I am not familiar with your speakers but if they are over 100 db efficient, a smaller OPT than the big Hammond may be a better choice. If they are below 90 db then the a transformer may be needed since a small one will distort on bass.
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Old 22nd December 2009, 11:42 PM   #9
Junior is offline Junior  Singapore
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[QUOTE=tubelab.com;2021804]The 1628SE does indeed have the "built in notch" effect. They are not all the same, but they all have the problem. The 1628SEA still has the resonant notch but it is moved out to about 28 KHz. The frequency response is down about 2 db at 20KHz. These transformers have the best bass of any SE OPT that I have ever tried. The 1629SE is not supposed to have the problem but I have not tested them. Given a choice of the Hammond 1628SE or the Hammond 1629SE the choice is easy, use the 1629SE. QUOTE]

hi george,
with 1629se, any changes requires (i mean the value of the resistors/capacitors) to accomodate the 6.5k primary impedence?

cheers...
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Old 22nd December 2009, 11:44 PM   #10
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No, just hook it up.
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