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Old 1st June 2009, 07:40 PM   #11
rknize is offline rknize  United States
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Quote:
Originally posted by PaulyT
I'm confused because I don't know all the jargon here, no idea what "new design with one sec" means... clues?


It means the new design has one secondary. I don't quite follow what he is saying about the secondary taps, but he just needs to know what you want. As for the input impedance, you can read about what George has to say here:

http://www.tubelab.com/AssemblyManua...ormers_TSE.htm

If you plan is to go and stay with 300B, most folks would get an OPT with a primary impedance of around 3k. This gives you the most power from a 300B. You can sacrifice some of this power for a little better distortion characteristics and go with a 5k input impedance. This also opens the door for running 45s if you have a power transformer that supports it. Since you are buying a quality transformer, you don't have to worry as much about the large turns ratio of the 5k affecting performance of the OPT.

Bottom line is that the primary impedance has to do with the type of tube and circuit, not so much the brand of a particular tube.

Quote:
Does it matter how close the impedance of the speakers matches the rating of the output transformer?
It should match as close as you can guess. The impedance of the speaker load is reflected back by the transformer at the tube. It's really about the turns ratio of the transformer. For example, if you get a 3k:8ohm OPT and then put a 4 ohm speaker load, the tube will "see" a 1.5k load from the OPT primary. This also puts the OPT, which was designed for 3k:8, into a less efficient operating region.

Speaker impedances vary with frequency too and this depends on the design of the speaker and crossover. An 8ohm speak is 8ohm at 1kHz, typically. This information should be available for the speaker in question. Even so, you want to be in the ballpark.

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Would this 80uF from Mouser work? I'm guessing the exact capacitance value isn't critical (100 vs 80 uF)? Could I hook up two 50's in parallel?
Yes, that works too. The value is not too important, but most folks get something in the 80-100uF range. You can get that same cap off of eBay for about half that price or less.
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Old 1st June 2009, 07:45 PM   #12
boywonder is offline boywonder  United States
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Quote:
Originally posted by PaulyT
Thanks!

2) Cool, I'll contact Edcor and see if they can sell me one of those.

3) Got a response from Jack from EP, asking about "Albert Pagan" and TM3KB, quoting directly his response:



I'm confused because I don't know all the jargon here, no idea what "new design with one sec" means... clues?

I guess there are two load impedances - the tube side (~2.5-3.6kOhm) and the speaker side (8 Ohm or whatever), and the total current throughput (e.g. 100mA) right? I can figure out the impedance of the speakers (from the specs on the drivers), but how do I know what impedance value is best for the tube side? Do I need the detailed specs of the particular 300B tube I'm getting in order to make this decision?

Does it matter how close the impedance of the speakers matches the rating of the output transformer?

5) Would this 80uF from Mouser work? I'm guessing the exact capacitance value isn't critical (100 vs 80 uF)? Could I hook up two 50's in parallel?
The "one secondary" impedance means that you order 4 ohm or 8 ohm, instead of getting two (or more) speaker taps on the transformer.

For the primary impedance most folks opt for 5K or 3K for this project; check out tubelab's site, George has lots of transformer info for the SE board over there.

Speaker impedance is reflected from the secondary side of the transformer to the primary side, so if you get a 5K/8 ohm transformer, it's primary impedance will be 5K with 8 ohm speakers connected. with 4 ohm speakers connected to the 8 ohm taps, the primary impedance will be 2500 ohms, and so on.

You will not need specific specs for an EH300b or whatever to order a proper output transformer; a transformer designed for 300b's will work with any 300b.

Sorry for the redundant post, it appears that rkinze and I were typing in parallel
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Old 1st June 2009, 08:56 PM   #13
PaulyT is offline PaulyT  United States
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Thanks, gentlemen, this is beginning to make a little more sense now. Since I will be driving only efficient (Klipsch) horns with these (>~800Hz only), high output power is not a major issue, so I would probably go with the 5k primary. I will try to find out - or measure - what the impedance of these horns is.

I'm trying to find out from Jack@EP if he can do a single secondary that's a little cheaper, George (I think) says that's the case in his documentation.

It looks like the One Electron UBT-2 would also be a reasonable choice in this case, since it has a higher primary imedance (4.8k)?
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Old 1st June 2009, 09:18 PM   #14
rknize is offline rknize  United States
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Quote:
Originally posted by PaulyT
It looks like the One Electron UBT-2 would also be a reasonable choice in this case, since it has a higher primary imedance (4.8k)?
The UBT-2 is what I am using in mine.
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Old 1st June 2009, 09:24 PM   #15
agent.5 is offline agent.5  United States
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Quote:
Originally posted by PaulyT
[B]Thanks, gentlemen, this is beginning to make a little more sense now. Since I will be driving only efficient (Klipsch) horns with these (>~800Hz only), high output power is not a major issue, so I would probably go with the 5k primary. I will try to find out - or measure - what the impedance of these horns is.

Because you don't need any bass, you may consider an OT with limited inductance, such as Tango m757

http://www.eifl.co.jp/index/export/ISO.html
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Old 1st June 2009, 09:39 PM   #16
PaulyT is offline PaulyT  United States
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Quote:
Originally posted by agent.5
Because you don't need any bass, you may consider an OT with limited inductance, such as Tango m757
Interesting. Not a money saver though, a pair of those is about as much as a pair of UBT-2's. Any particular advantage to the Tangos? I don't know anything about these "boutique" brands, if you can call it that...
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Old 1st June 2009, 09:56 PM   #17
agent.5 is offline agent.5  United States
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Quote:
Originally posted by PaulyT


Interesting. Not a money saver though, a pair of those is about as much as a pair of UBT-2's. Any particular advantage to the Tangos? I don't know anything about these "boutique" brands, if you can call it that...

Because you don't need any bass, an OT with less inductance may have better mid and high. Furthermore, Tango makes some of the best OTs in the world. I am certain that an Tango OT sounds better than a UBT-2.
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Old 1st June 2009, 10:02 PM   #18
Tubelab_com is offline Tubelab_com  United States
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We sure do get orders from this Albert Pagan design over the years. never seen it!?
Albert is a friend of mine. He used to work here before they laid him off. He wanted to build a "top notch" 45 SE amp about 6 to 8 years ago. He called Jack to inquire about OPT's. Jack's response was that his standard product had multiple secondaries to allow for different speaker impedances. Jack stated that he could make the same transformer with only an 8 ohm secondary. It would have a greater bandwidth and cost less than the standard product he was selling at the time. Albert said "great, make me two". I believe he also ordered a power transformer and a choke at the same time, but I am not 100% sure. Albert built a 45 amp from a schematic that he got on the internet. I believe it was called the Bugle 45. It worked very well.

I was in the process of designing the Tubelab SE and I needed some good OPT's. I heard Albert's amp, and called Jack. I asked him to make me "two OPT's just like Albert's." At the time I paid $100 each for them. I explained that people would be calling and asking for more since I was planning to put my Tubelab SE on the internet. I inquired how people should order these transformers and he replied to "ask for the Albert Pagan design." I know at least one other person who got some "Albert Pagan" transformers from Jack because I built his amp. I guess Jack doesn't remember this. Feel free to remind him or forward this email to him. It really doesn't matter since it sounds like that is what he is building now.

At any rate these are very good transformers (possibly the best that I have used). The specs were a single ended OPT gapped for about 60 mA (a compromize between 45's and 300B's) rated for 10 watts with a 5K primary impedance and a single 8 ohm secondary impedance. Other impedances to match your speakers were available. Mine still live happily in my Lexan amp visible on the Tubelab home page.

The Electra Prints, the One Electron and the big Edcor CXSE25-8-5K are all good full range OPT's they will all operate over the entire audio frequency range. I prefer a 5K impedance in this amp. It will cost you a bit of output power (maybe 20%) over a 3 K transformer, but improves the distortion and damping factor. Any primary impedance from 3K to 5K will work. The lower impedances allow for a bit more power from 300B's or 2A3's but are not suitable for 45's. The 45's to me have the most detailed sound of any DHT, so I will sacrifice some power from the 300B's to allow for their use.

You state that you are only interested in this amp operating above 800Hz. If this is the case you can use a much smaller OPT at a reduced cost. I am sure that jack can make you something, but several users have had great results with the $20 Edcors when used with a subwoofer to relieve ths transformer of bass duty. The Edcor number is XSE15-8-5K.

Quote:
Personally I would avoid the Hammond transformer.... I had a custom transformer made from Edcor for this amp and it seems to work very well for both 45s and 300Bs. Here is the thread on it:
There have been issues with some Hammond transformers. The custom Edcor that rknize looks like a good choice, but I haven't tried it yet since my budget is negative right now. My small Lexan amp uses the Allied 6K56VG which is just right for 45's but quite under powered for 300B's. I have been using it anyway and it works well but only gives me about 4.5 watts per channel. I have another amp with a Hammond 272JX whick works well, but like all Hammonds it delivers more voltage than the published specs. If it delivered the rated voltage, it too would be a bit low.
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Old 1st June 2009, 10:48 PM   #19
rknize is offline rknize  United States
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Quote:
Originally posted by PaulyT


Interesting. Not a money saver though, a pair of those is about as much as a pair of UBT-2's. Any particular advantage to the Tangos? I don't know anything about these "boutique" brands, if you can call it that...
If you are certain that you would never want to drive a full-range speaker of some sort, then I suppose you might as well put some of the $$$ from the iron into quality rather than quantity or put it towards something else, like tubes. However if you think that your speaker setup could change, I would at least leave plenty of space on the chassis to mount a bigger OPT later.
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Old 1st June 2009, 11:08 PM   #20
PaulyT is offline PaulyT  United States
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Thanks guys! Yes, that's the beauty and one big attraction of DIY, that I can design and build something now, and still be able to tweak it later if things change. Right, as of now I forsee this only being used for the HF in an active system; I have a (DIY) 3-way active crossover, where the subwoofer and woofer will be amped separately (not with tubes).

George, you've said repeatedly how the 45's are the most detailed tubes. What do you think about them being used in the application I'm describing? I really can't judge whether the power would be sufficient... I'm guessing not, hence my interest in the 300B. But you've got me at least considering the 45 as an alternative.
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