Why So Many EL34 and KT88 amps??

rollo · « **Reply #40 on:** 30 Jan 2010, 03:33 pm »

Quote from: Niteshade on 30 Jan 2010, 03:32 pm

Do you have another address? I got this:

Sorry, the page you requested was not found.

Additionally, a 410 Gone error was encountered while trying to use an ErrorDocument to handle the request.

Please check the URL for proper spelling and capitalization. If you're having trouble locating a destination on Yahoo!, try visiting the Yahoo! home page or look through a list of Yahoo!'s online services. Also, you may find what you're looking for if you try searching below.

try it again, just correted it, sorry.

charles

rollo · « **Reply #41 on:** 30 Jan 2010, 03:42 pm »

Quote from: Niteshade on 30 Jan 2010, 03:32 pm

I think this is what you meant: http://www.audiokit.it/ITAENG/Trasformatori/Bartolucci/Bartolucci.htm

The other link didn't work. I never tried them before but will look into it.

I know Wytech uses them in lieu of the discontinued Audio Notes. I use 211s now and am looking for alternatives. Need more juice. I'm finding this thread very interesting. One day YOU are going to build me a dream amp. When I sell my AR 250 servo and Classic 60 for the mulla.

charles

JohnR · « **Reply #42 on:** 30 Jan 2010, 03:43 pm »

Quote from: Niteshade on 30 Jan 2010, 03:26 pm

The trick is to use DC biasing, around 400v on the plates and roughly 300v on the screens. Your idle current will be low.

I don't really understand/believe you can have a single-ended amp with low DC bias. Could you provide a link to further information?

Niteshade · « **Reply #43 on:** 30 Jan 2010, 03:53 pm »

Do you mean that the tubes should run hot?

I do not have a link, but know tubes in SE or SEP configurations do not have to operate hot. The SE's & SEP's I have made run just as cool as tubes in a push-pull circuit. It is possible to operate with low idle currents. If the bias is too low, you will clip early. By low, I mean -38 instead of -35 or whatever is appropriate for your circuit.

FullRangeMan · « **Reply #44 on:** 30 Jan 2010, 08:37 pm »

Quote from: Niteshade on 30 Jan 2010, 01:23 pm

The B+ isn't so bad. A voltage doubler can be used with a 500v transformer. There are outputs rated for up to 35 watts off the shelf, but getting one for 50, single ended is what bothers me the most. Edcor won't make one! So it's off to find someone who can make it. The 35 watt transformer can be pushed a little and get really close without any issues. They can easily hit peaks of 50 without damage of sonic degradation. What damages outputs is usually sustained excessive current or when a tube shorts out.

Hello NiteShade,
Do you think this Voltage Doubler is a second class solution??

Niteshade · « **Reply #45 on:** 30 Jan 2010, 09:11 pm »

No, voltage doublers are not second class. When done properly, they work superbly. There are multiple cases where doublers, triplers, etc.. are best for producing high voltages. They can keep transformer costs down without compromising performance. A doubler is only as good as the parts that make it. It's possible to make poor, inefficient, unstable ones just like it's possible to make any kind of circuit poorly. Fisher used doublers all the time. Most of their power transformers had an output of only 225v or so. The Fisher 500C, 800C and many others use a very good doubler circuit.

FullRangeMan · « **Reply #46 on:** 30 Jan 2010, 09:22 pm »

Thanks NiteShade, I was think the power transformer reduced the outlet voltage, but by you said it raise the wall voltage more yet.

Niteshade · « **Reply #47 on:** 30 Jan 2010, 09:30 pm »

Don't forget that my line voltage is 120v. Most tube applications require a step-up transformer for us. If you needed 500V or so for a project, a doubler and a 1:1 isolation transformer could work. But- you would also require filament voltage, so you would be better off just getting a tube amp transformer with a 240v primary. When in need of 1kv or more, a 500v transformer w/ a doubler will work great for those large RF tubes.

FullRangeMan · « **Reply #48 on:** 30 Jan 2010, 09:39 pm »

Toroidal power transformers are cheap here, I know a small garage builder, he made only industrial and audio Transformers(silicium and nickel toroids, hand wound) at low prices, there is a waiting time due many orders etc. I see could be better two T. per channel, one for B+ and other for filament, huumm
Thanks

JohnR · « **Reply #49 on:** 31 Jan 2010, 01:27 am »

Quote from: Niteshade on 30 Jan 2010, 03:53 pm

Do you mean that the tubes should run hot?

Uh... no. You suggested that I build a single-ended amp using push-pull ultralinear transformers, and then said that it would be OK because the DC bias would be low by putting 300V on the screen. This doesn't make any sense to me - a class A amp needs the DC current through the transformer otherwise it's not class A. No?

baldrick · « **Reply #50 on:** 31 Jan 2010, 01:34 am »

Just a minute, a single ended amplifier is class A by definition right?

JohnR · « **Reply #51 on:** 31 Jan 2010, 01:39 am »

Sure - as far as I know...

Niteshade · « **Reply #52 on:** 31 Jan 2010, 01:48 am »

Ah... I see what happened: The thread is about single ended amps and I thought the transformers you mentioned were for single ended applications. I didn't pay much attention to the transformer model you mentioned.

Note: You can use push-pull transformers in single ended apps IF you couple the tube's anode to the output's primary with a capacitor & ground the other end of the primary & leave the center tap disconnected. (I don't recommend it, it's inefficient- but it can be done.)

Yeah- SE & SEP's are Class A by definition.

Quote from: JohnR on 31 Jan 2010, 01:27 am

Uh... no. You suggested that I build a single-ended amp using push-pull ultralinear transformers, and then said that it would be OK because the DC bias would be low by putting 300V on the screen. This doesn't make any sense to me - a class A amp needs the DC current through the transformer otherwise it's not class A. No?

JohnR · « **Reply #53 on:** 31 Jan 2010, 02:04 am »

Quote from: Niteshade on 31 Jan 2010, 01:48 am

Note: You can use push-pull transformers in single ended apps IF you couple the tube's anode to the output's primary with a capacitor & ground the other end of the primary & leave the center tap disconnected. (I don't recommend it, it's inefficient- but it can be done.)

Oh right. I guess that's a parafeed topology then. Here's an interesting example:

http://www.tubecad.com/may99/page9.html

baldrick · « **Reply #54 on:** 31 Jan 2010, 04:38 am »

So if you could get say 5 watts out of a couple of El34s in parafeed topology with a B+ of 435V what kind of output could you expect with two 813s in parafeed topology and a B+ of 1100V?

Niteshade · « **Reply #55 on:** 31 Jan 2010, 11:55 am »

Your example is good since it eliminates the expensive plate choke.

I do not like parafeed circuits at audio frequencies. Here is a big RF amp that's similar to a parafeed AF design: http://www.mykit.com/kor/ele/circuit/3-500Z/3-500Z%20Amplifier%20example.htm

It uses a plate and cathode choke and grounds the 3-500z's grids. I have worked with these and can verify this design works great. Gain is approx 12x. It takes 100 watts in to get 1.2Kw out.

Notice that it's a SEP design. I have used this kind of amp in SE & SEP configurations. The SEP version has a much hardier output because it's capable of sustaining high output demands for much longer than the SE model. A similar improvement goes for audio SEP amps. I notice bass frequencies are better pronounced and mids are well formed.

Since your transformers are push-pull, try a push-pull parallel topology.

Quote from: JohnR on 31 Jan 2010, 02:04 am

Oh right. I guess that's a parafeed topology then. Here's an interesting example:

http://www.tubecad.com/may99/page9.html

JohnR · « **Reply #56 on:** 31 Jan 2010, 12:15 pm »

Right. Thanks.

Ericus Rex · « **Reply #57 on:** 31 Jan 2010, 05:02 pm »

I like how this thread has morphed into a very interesting subject!

Niteshade · « **Reply #58 on:** 31 Jan 2010, 11:13 pm »

RF tubes are wonderful creatures if you have the $$$ to make amps with them. A small percentage of these tubes have ever seen audio applications. The two major setbacks are output transformer cost and filament transformers. As stated above, the extra high B+ isn't an issue.

The best tubes to start with if you're a DIY'er will be the 811, 572B or 813 pentode. I highly recommend the 813 to start with. I'm anxious to begin an 813 project myself! I've worked on an 845, 813, 4CX350B and 3-500z based amps, but want to make one from the ground up. Well, actually- I did make a 4CX350B SEP amp from the ground up. It was RF, but what an awesome project! It had a Peter Dahl B+ supply transformer that was nearly the size of a loaf of bread!

iGrant · « **Reply #59 on:** 1 Feb 2010, 01:30 am »

Great thread, back to the OP's question. It is what most people want, affordable with decent power, basically bullet proof designs and builds, new to tube types can hear a vast improvement over their existing SS gear with EL34 and KT88 amps. Any other tube type amp generally requires some knowledge of tubes to match to their other gear and some skills to keep them running. The 'experienced tube consumer' is basically few and far between and they already have a few amps licking around and a pile to choose from, building the next greatest big bottle or flea powered SET or exotic tube flavour isn't going to drive enough customers to your door to keep the door open unless you have been doing it a long time.

Not saying this is right, maybe with this current return to tubes by many, the other tube types will get their chance as the new to tube types get their feet wet and start exploring. I do almost move 300B amps on par with KT88 and EL34's, only a small percentage of those that have grabbed a 300B amp have done so as their first tube amp.

Cheers,
Ian