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Old 9th May 2012, 09:20 AM   #41
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Hello,
I recently built a SE KT88 triode class A, and really loved the sound, but 5W of output power seems a bit on the low side for my low efficiency speakers. I would like to make a push-pull KT88 triode based amplifier in order to get the sound as close as possible to my other design, but aiming for more power.
How much power? I am not sure, you tell me. My knowledge about tube amplifiers is a bit scarce at the moment, so maybe I can make a push pull paralleling 2 or 3 tubes per channel.

What are your thoughs? Can I use this board to drive that? Could someone point out an schematic with a P-P KT88 triode output stage? Is it feasible to run valves in class A or even convenient?

Best regards!
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Old 9th May 2012, 12:29 PM   #42
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Quote:
What are your thoughs? Can I use this board to drive that? Could someone point out an schematic with a P-P KT88 triode output stage? Is it feasible to run valves in class A or even convenient?
Look at Pete's web site. The only amp that he has built with this board IS a P-P KT88 in triode amp.

You can run this (or most any P-P amp) in pure class A but you will get about 12 watts (twice the SE class A power). Doubling the number of tubes will double the output power. Most P-P amp builders set the bias and load such that the amp will remain in class A up to a certain power level where it transitions to class AB. In this manner 35 to 40 watts from a single pair of tubes is possible.

Maybe Pete can post his complete schematic. I have not had time to work on this or any other amplifier this year, but I have some big amps planned for this little board. KT88's are on the list. I will be away until June, so it won't be soon.
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Old 4th September 2012, 12:36 AM   #43
tomlang is offline tomlang  United States
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Has anyone made any progress with these boards?

What is the dimensions of each board?

If one uses the "Schade" feedback similar to Pete's other red board is it fair to say the input stage won't be necessary?
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Old 4th September 2012, 02:26 AM   #44
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My board is sitting on the shelf looking exactly like it did in post #36. It measures 6.5 X 4 inches.

Petes big red board gets along without an additional drive stage in stock 18WPC form. When squeezing 125 to 250 WPC out of it there isn't quite enough gain. I swapped in some higher Gm driver tubes, which helps but a CD player may not get you to full power. In my case it doesn't matter since with 96 db speakers and 250 watts its like being in the front of a Metallica concert, except you don't get burned by the pyro!
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Old 4th September 2012, 11:58 PM   #45
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Quote:
Originally Posted by tomlang View Post
Has anyone made any progress with these boards?
Unfortunately, I just haven't had the time to do anything more with this one, beyond the KT88 triode amp I breadboarded. I made some improvements to the PCB after my first proto, but have not had the opportunity to build anything yet.

I have a pair of Tango FX-40 OPTs and a monster UTC power transformer that are just begging to become an amp...

Pete
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Old 6th November 2012, 03:01 PM   #46
wicked1 is offline wicked1  United States
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Anyone want to start a winter build w/ these boards? Mine have been collecting dust for a year. Last year I had a crazy idea of using it for some bright eimac tubes, but have come back to earth and simply want a decent powerful amp. 50+ watts would be great! (I have far too many 1-25 watt amps now)
Basically, I haven't picked out the tubes yet, and if someone is considering a similar project, we could do the same thing.. I guess I'll start reading the old "big read board" thread, as that seems like the best starting point.
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Old 6th November 2012, 04:44 PM   #47
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I had a crazy idea......
I have a really crazy idea........use Petes shiny red vacuum tube board to drive these.....as followers. I have some of each.

I found a top secret driver tube that drops into these boards and can deliver 10 watts of audio power by connecting an OPT up to the board. They are essentially an EL84 with a tighter wound control grid for double the Gm and an odd pinout. I kept quiet about them until I managed to collect over 500 of them (for 35 cents each!), so....the number is 6HA6/6HB6, yes they are on the dollar menu at the usual places. Sylvanias pictured in post #36. All seem to be Syl or GE regardless of the name on the box. Both work good.

I figure that the 6HB6 can deliver all the voltage gain while the big mosfet follower deals with current gain, sort of like a PowerDrive on roids! Not sure when I will get to it, but both my boards are built and working, I have the mosfets, and I have a 0-650 volt 1.7 amp power supply. OPT?????? maybe a big power toroid. I don't see why this board couldn't be used to drive a Circlotron output stage........

If I choose to do a tube output...it will be sweep tubes....BIG sweep tubes....at least 4 BIG sweep tubes per channel, and I have the OPT's already.....400 Watt Plitrons.
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File Type: pdf 2SK3675-01.pdf (41.6 KB, 28 views)
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Old 6th November 2012, 07:55 PM   #48
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Originally Posted by wicked1 View Post
50+ watts would be great! (I have far too many 1-25 watt amps now)
I was looking at this the other day and had the same realization. I was planning on finishing this up as I prototyped it (triode KT88s), but I think it would be more useful if I cook up something in the 50-100W range. Though I would really like to use my Tango FX-40 OPTs. Maybe I could trade with somebody for something beefier...

So many choices... I guess the first question is output tube. Something conventional (KT88?) Sweep tubes? Transmitting tubes (push-pull-parallel 807's?)

In any case I'd like to make it straightforward enough that it could be built by normal folks...

Anybody got any ideas?

Last edited by pmillett; 6th November 2012 at 07:58 PM.
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Old 6th November 2012, 08:44 PM   #49
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The obvious choice to appeal to the masses is KT88's, EL34's or 6L6GC's since you can get them anywhere. Maybe a parallel pair per channel. The 807 is a repinned 6L6GB, so whatever you can do with the 807 you can also do with the 6L6GC, except the plate dissipation is higer and the voltage rating is lower for the 6L6GC. Your driver board would drive any of these to full tilt. An OPT in the 5K range could use any of these with only a bias tweak, and even work with a triode / pentode switch. Maybe a bit too much for the expensive Tangos though.

The 6HJ5's that I used in the big red board amps are still $5 to $7 each but aren't available outside the US. I have two 125 WPC red boards and my boss is building one now since none of my amps will drive his Maggies. I loaned him a red board and he was convinced. I will be looking at something different, just because I like different! I still have about 20 6LW6's and a set of big Plitrons, so it has to be done sooner or later.

Maybe a big sweep tube that is still relatively common world wide? The 6KG6/EL509 comes to mind. 40 watt plate dissipation....got to be good for a 200WPC amp. You could also build a little sweep tube amp that just fits the Tangos, but....you have already done that.
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Old 6th November 2012, 10:11 PM   #50
pso is offline pso  Spain
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Hi, the first step could be the PP triode of your website, if you publish a detailed list of parts, tubes and PT ( edcor?) today, I will buy your boards tomorrow, I have no experience to build for my only, and over time can be changed to one of these beast who are planning...
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