PT secondary question

[bigdaddy]

I see that some power transformers sold today like some from Webersvst have 2 sets of secondaries. One would be a higher voltage and one lower, like 300-250-0-250-300. My question is could you use both taps? Use one set of higher voltage for the power tubes and one for the preamp tubes. They even have a universal one setup like a Hammond 125 PP output tranny that you can mix and match to get the correct primary and secondary.

Or do you need complete different sets of windings separate so you might have something like a 300-0-300, then a 250-0-250, then a 5-5 and a 3.15-0-3.15 for instance.

[PRR]

You'd need two rectifier systems. Two first filter caps.

And in the low-power preamp, "excess voltage" is GOOD. You use a large dropping resistor, get more filtering for the same capacitance. Start with a "just-enuff" voltage, you have no slack for filtering, you might have to use oversize caps or a costly choke just for the preamp.

OK, when you need 660V for huge-tube plates and  250V for hif-fi preamp, it does maybe make sense to use tapped windings. (Though mostly when you actually need 330V for power screen grids, as is done in hifi/PA 100W amps.)

[bigdaddy]

I was thinking in terms of the high winding on the preamp and the lower on the power tube. Using a low powered pentode like a 6AK6 which does not want to see more than like 250V period. It's recommended at 180V by the dtat sheet but the plates can take 300V and the screens 250V.

[jjasilli]

But after rectification 250 will be 350; and 300 will be 420. 

[bigdaddy]

I was just throwing numbers out there not anything specific. I don't know yet what the secondary voltage would be with such a low load. How much drop would there be?

So that would be the second question, what would be the voltages needed to run a 2-12AX7s on one and a 6AK6 on the other? Or even make it a push pull amp running 3-12AX7s and a pair of 6AK6 tubes.

Those tubes do not put out much more wattage then the dual triodes used in these small low wattage amps but the triodes can take more voltage. I'm sure a power pentode would sound better then the triodes.

[PRR]

Here's how you do it:
  http://dilbert.com/strips/comic/1999-02-17/
Sorry, I just found that (linked from a salary site, of all places!) and got a giggle.

> I was thinking in terms of the high winding on the preamp and the lower on the power tube.

I wuz wondering, because you typed "Use one set of higher voltage for the power tubes and one for the preamp tubes." I was not sure you meant it that way, or if your keyboard fouled the words.

We use high voltage to force high power. You are bucking this trend. Still with Pentodes for power there is little reason to have preamp voltage higher than power amp. If preamp eats power-amp G2 voltage, or even near, the preamp can slam the power tube; more is moot. You may have to scale-down preamp gain in proportion to preamp voltage. The extra-clean first stage of some late Fenders with 350V-390V preamp supply allows gain of 50+ on guitar pickup; with a 100V supply you want to scale preamp for gain more like 12-14 (or embrace the extra input breakup).

Target 200V raw B+. Use 1K-470 and a second cap to drop and clean this to 180V for the 6AK6(s). Use 4.7K and another cap to get 160V for the preampery. Since first-stage gain of 50 works with 320V supply, aim for first-stage gain of 25 with 160V supply. The rest of your gain stages may be conventional gain and values.

[bigdaddy]

I do that a lot here because when I say what I am really thinking a lot do not understand. So some times I start backward so they get it. The nail in the wood is about what I know on how to design a power supply.... I admit that....

If I did as you say then the plate resistor would be a very low value, below 100K and I thought that would really mess up the way a 12AX7 works.

I talked with my pain management doctor the other day and I am going to try a new medication. If there are no side effects and it works it's possible it might relieve some of my inability to function. I am hoping that lets me at least tinker with an amp because right now I can't. I'm hoping but who knows....it might even let me sleep longer then 2 hours at a time...

A while ago I stuck a 6AK6 in a low voltage champ amp, the voltage was still a bit too high. But the amp sounded great and very low volume with a full tone stack and all. Just that I doubt the tube would have lasted very long at that voltage, which was pretty low by normal guitar amp standards today. I forgot what it was but I am thinking around 340V, that would fry a 6AK6 pretty quickly from what I read. I did change over an amp to a 6G6G which is the bigger bottle and more robust and it does sound good but still a little loud for my needs, it running at a little below 300v both plate and screen. The 6AK6 although said to be the same tube was not as loud and it was baised correctly. I played it a bit and stopped for fear of burning the tube out.

[zendragon63]

We use high voltage to force high power. You are bucking this trend. Still with Pentodes for power there is little reason to have preamp voltage higher than power amp. If preamp eats power-amp G2 voltage, or even near, the preamp can slam the power tube; more is moot. You may have to scale-down preamp gain in proportion to preamp voltage. The extra-clean first stage of some late Fenders with 350V-390V preamp supply allows gain of 50+ on guitar pickup; with a 100V supply you want to scale preamp for gain more like 12-14 (or embrace the extra input breakup).

Target 200V raw B+. Use 1K-470 and a second cap to drop and clean this to 180V for the 6AK6(s). Use 4.7K and another cap to get 160V for the preampery. Since first-stage gain of 50 works with 320V supply, aim for first-stage gain of 25 with 160V supply. The rest of your gain stages may be conventional gain and values.

Great explanation PRR.

BD, I struggled with the lower voltage preamp thing when I was designing ( ) and building with the both of those power tubes thinking the same notion that, unless you had upwards of 300 volts supply to feed the preamp, the headroom and tone would suck ditchwater. Not necessarily so though there is a limit to how low you can go before it sounds like a 12 volt powered 12AU7 distortion pedal. Using between 150V-250V as a preamp supply for 12A_7 works OK but there is a much narrower range for dialing in a sweet spot and an acceptable touch response of the amp. Just 'sounds' like you are running your speed boat in a smaller and smaller pool. YMMV

Back to work. Regards

dennis

[bigdaddy]

Right now my speed boat doesn't even fit in the pool. So either I get a bigger pool or a smaller speed boat.

Maybe I should switch to a canoe....

[jojokeo]

For what it's worth, my 269ex @ 190-0-190 w/ ss rect. turns into 270v B+ and is too high for either the 6ak6, or 6an5 which is a great little power tube. The 6an5 doesn't need a lot of voltage and a preamp voltage at 160 is ok too, just use a lower plate resistor like 56K so you don't drop too much voltage since B+ is lower already and you'll be fine. I suggest you use something like a Hammond 262D6 120V which will give you 180v B+. Seriously, for what you're looking for and at the power level, you'll be where you want to be.
btw, I saw your other trannies you were selling on eBay and from what I saw, were way overkill for what you were using them for or planning on using for also so you may be over thinking/designing this too? Those little tubes crank louder than you think @ modest voltages & amperage as you're beginning to realize w/ the 6G6. That tranny I suggest is only 22 bucks and all you need for your closet playing volume. Don't over think it, buy it, and build it. Good luck on your meds.

[bigdaddy]

That's why I am selling them, they were running bigger bottles like KT-88s and I don't need them.......DUH!!!!!!!

Sorry but do you think I'm like stupid? Of course those PTs are not right for what I am talking about. They were pulls from much more powerful SE builds. For instance the Chinese KT-66 will heat up one of those Hammonds to a point were you cannot even touch them, that's why I went with the higher rated 272 series for the KT-66 and KT-88 version of my SE amps. The old data sheets for certain tubes do not represent modern versions a lot of the time.

I'm looking at some Adcor trannys, they're cheaper.

Thank for you for your good wishes with my new meds, I should have them tomorrow and hopefully it will open a closed door for me and thanks for your advice about amp building.

But really dude.....you are talking to me like I'm a f**kin' moron and that's not appreciated, I'll just chalk that up to you not realizing it and leave it like that, by the way this is not the first time Joe. I guess it's just your way...I have some advice for you: reevaluate how you speak to people,  you're coming off like an egotistical jerk, to me at least.

[jojokeo]

Gimmee a break, you're taking what I'm saying totally wrong and negatively like you have some kind of chip on your shoulder. Instead of looking for something to take the wrong way and be defensive, why don't you take the opposite approach and if you suspect something is "off" verify it okay, before you jump any guns and fly off the emotional handle like a woman.

Why would I try to offend you when I offered to build an amp for you? Why would I say you were right about having a tone stack and then try to be an a-hole to you? That logic doesn't make any freakin sense. Now, I'm offended.

You are wrong in interpreting those trannies' uses now vs your ebay adds' desriptions. I was going by your adds and how you described them to be used. Not guessing you had other ideas like you say now. Again, you are lashing out for no reason. Take you attitude and shove it up your a$$.

[bigdaddy]

Give it up dude.....look in a mirror and ask yourself why would I feel this way about you. There must be a reason, you condescending jerk.

I am very nice until I am not nice anymore and for a good reason. You never offered to build me an amp. From the way I understood it you offered to SELL me an amp.

See you don't know how you come off to the people you are speaking to. As for my Ebay auction the information is for those who do not really understand things but want to build an amp. When they email me I go into more detail. If you looked at one auction someone does ask me a question and I answered them in more detail and with the correct information. But I don't owe you an explanation nor do you have the right to put me in a position to have to justify myself to you, another thing that makes you a condescending jerk.

So do yourself a favor and stop being a busy body and mind you're own business.......Also learn how to talk with people not down to them, that's another thing that makes you a condescending jerk. Be offended, be very offended.

[jojokeo]

  Wrong about many things here and I won’t go into it or indulge you any further, but I wonder what color the sky is in your murky overly medicated world? Through compassion I felt sorry for you because of your handicap and situation that you tell everyone about but now it's just sadness becuase you're handicapped in more ways than you're even aware of. Take care bigdaddy.

[bigdaddy]

You got the last word in I hope you're happy....

Nice of you to take a cheap shot at a person with a disability.......shows your true character or lack of.....you're a joke of a man dude.

I had you pinned from jump street. You are full of sh*t and have serious personality deficiencies, that's obvious. I never asked for anybody to feel sorry for me, just to understand what people with disabilities go through. Of course you twist that in your twisted mind and take a cheap shot at someone with medical issues because they call you for what you are.

[plexi50]

No finger pointing. This is not the gear page or another forum. This is a happy home!

[zendragon63]

Easy gents, the magic of 'email mis-interpretationus unintendus' is creeping in. You both bring way too much to the party. Chalk it up to a bad afternoon and let 'er go. Regards.

dennis