Hi George, I'm beginning to think that this project will be a lot for me, it seems no one else is interested in the triode-KT88, only think of great powers.
I do lot of questions and you just answer me, so I will store my tubes and to retake my first choice, your SSE ( Just ordered your board ), is very easy to start, instructions and detailed parts list, to many people who built and much more willing to help.
One more question:
I will order the custom transformer, if one day I come back to this board, will have twice the capacity than necessary for the SSE, there may be
a drawback in that ( Vibrations, hum, etc...)?
Thanks.
I do lot of questions and you just answer me, so I will store my tubes and to retake my first choice, your SSE ( Just ordered your board ), is very easy to start, instructions and detailed parts list, to many people who built and much more willing to help.
One more question:
I will order the custom transformer, if one day I come back to this board, will have twice the capacity than necessary for the SSE, there may be
a drawback in that ( Vibrations, hum, etc...)?
Thanks.
I don't know what your experience and skill level is, but Pete cautioned that this was not intended to be a plug and play board. Some degree of experimentation and tweaking will be needed for any implementation until someone builds something and documents it. I have the equipment to turn knobs and take readings that can be used to provide a starting point for someone to build from. This is what I just attempted to do with the 13GB5's. Maybe Tomlang will document his build such that others can duplicate it, I don't know.
This situation just happened with Pete's big red board, I stuck the 6HJ5's in it and cranked them up, forum member Rknize made an amp using that concept, then several similar amps were built.
I fully intend to test KT88's with this driver board, but my work situation is rather busy right now, so I really can't say when. Odds are that this board will not be powered up again this year after this weekend.
Almost 5 years ago a thread was started discussing 6L6GC's in AB2. Over a 2 year period I assisted a person on the other side of the world to design his amp. He did all the building and testing, I directed and performed a few experiments. There were set backs and successes, and finally he built a pair of very nice mono block amps. I built a breadboard that used trioded KT88's. I have never had the time to build a completed amp. The entire design and build is chronicled here (schematic in post #460):
http://www.diyaudio.com/forums/tubes-valves/133034-6l6gc-ab2-amp.html?highlight=6L6GC+AB2
The SSE is a good choice for a first build since it is pretty much plug and play. You can use KT88's in it. One of my SSE's uses KT88's. I will take the board to the post office this morning. They are open on Saturday morning.
I know that there is another box with more big transmitter tubes in this house somewhere, but I can't find it. I did find a box full of 828's but they aren't as pretty.
Lately, all I have time for is being a designated hitter.....I just smack it out of the ballpark, then stand back and watch while someone else does the running!
Here are my plans at present (with big asterisk) that I will get to in a minute.
First off, here are the output transformers I plan to use in a 13GB5 triode strapped amp: 70.7 VOLT-4,8 ohm LINE TRANSFORMER 4 lbs. Buy It Now $16.00 172812 HT-327 | eBay
The seller will negotiate for large purchases. I (stupidly?) bought several of these to play with. Specs are attached. Why this transformer? With 8 ohms on the 4 ohm tap will be 1250 ohm primary. Also dirt cheap in keeping with the 13GB5 price.
I looked for a power transformer with the "proper" low voltage for the B+ and found one that should also do duty for the 13GB5 filaments, etc, pic attached. Hard to find a transformer that yields less than 300 VDC. 240VAC secondaries are easy to find but yield way over 300 VDC.
I should be able to "overload" the 14.8 vac at 2 amp winding with 4 parallel 13GB5's drawing a total of 2.4 amps.
The 390 VCT should yield about 260 VDC or so. If you put a FWB on it, you'd get over 500 VDC so this trans should be useful for other builds.
I'll run a voltage doubler on the 195 VAC winding for the phase inverter and of course the 64 VAC for bias.
New Tortran 750VA Toroidal Power Supply Transformer TN741-M390-CPE new * | eBay
Now for the big asterisk. I own Pete's other red board, not the two separate ones so this build will be different. I'm posting in this thread because of the 13GB5 testing done by George. I hope that is okay.
First off, here are the output transformers I plan to use in a 13GB5 triode strapped amp: 70.7 VOLT-4,8 ohm LINE TRANSFORMER 4 lbs. Buy It Now $16.00 172812 HT-327 | eBay
The seller will negotiate for large purchases. I (stupidly?) bought several of these to play with. Specs are attached. Why this transformer? With 8 ohms on the 4 ohm tap will be 1250 ohm primary. Also dirt cheap in keeping with the 13GB5 price.
I looked for a power transformer with the "proper" low voltage for the B+ and found one that should also do duty for the 13GB5 filaments, etc, pic attached. Hard to find a transformer that yields less than 300 VDC. 240VAC secondaries are easy to find but yield way over 300 VDC.
I should be able to "overload" the 14.8 vac at 2 amp winding with 4 parallel 13GB5's drawing a total of 2.4 amps.
The 390 VCT should yield about 260 VDC or so. If you put a FWB on it, you'd get over 500 VDC so this trans should be useful for other builds.
I'll run a voltage doubler on the 195 VAC winding for the phase inverter and of course the 64 VAC for bias.
New Tortran 750VA Toroidal Power Supply Transformer TN741-M390-CPE new * | eBay
Now for the big asterisk. I own Pete's other red board, not the two separate ones so this build will be different. I'm posting in this thread because of the 13GB5 testing done by George. I hope that is okay.
Attachments
Don't give up yet... indecision is starting to get to me!
I just set up the breadboard for split supplies (lower voltage for driver + screen if needed, higher for plates). Played with the 829B some... it worked well, though it was difficult to make the feedback stable, especially with a big Tamura F-2012 OPT.
Having realized that the KT88 is actually rated for 600V in triode mode (!) I went back to the KT88 trioded, running 250V on the driver and 450V (as high as my bench supply goes) on the plates. Biased class-AB with 50mA total idle current. Getting 0.06% THD @ 1 watt and clipping around 28 watts (5k load).
I'm thinking 250V for the driver and 500V for the KT88 would be a nice operating point.
Hmmm....
Last edited:
That transformer looks just about right for MELTING some big sweep tubes, so I bought one. I'm sure I can find something to do with it. The seller said it would be good for a guitar amp.....I think he might be right...a really LOUD guitar amp.
The 70 volt line transformer you are planning isn't listed on Ebay right now (listing expired). My experience with line transformers as OPT's has been hit or miss. Many do not heve enough inductance to handle bass. They are designed to be driven from a low impedance constant voltage source. Triode tubes with plate to plate feedback may be the best bet. Remember that the blue wire is the CT, not orange.
You can sky wire the 9 pin sockets just above the board. I did this to run some bigger 9 pin tubes.
I remember getting about 50 WPC from the KT88 in triode, but I don't remember the load. Probably 3300 or 2500 ohms.
Got to go back to mowing the yard.....we have to do that all year round here, but I also get to jump in the pool! Sherri is in West Virginia. It is snowing there. I can't repeat the words I got when I texted her a picture from the swimming pool. May get to melt some tubes tonight.
Hi Pete,
Seems not to have ruled out the KT88-trioded, I'm really interested in your PCB, not need the exact values of the resistors, only in some points measures (mA, Volts) and some specific part (LED), I understand the scheme, but neither would I go only for that configuration.
I suffice with 30W in triode mode and here seems to opt for more than 100, much more...
But it seems that your prototype sound good, if it continues to develop, I will buy your PCB's.
Even was asking coucil to order a custom transformer (EDCOR), but will wait if finally just the prototype, and like the results, to order one to your specifications.
I build a SSE of Tubelab, but I want to have your boards.
I'll be waiting for news.
Seems not to have ruled out the KT88-trioded, I'm really interested in your PCB, not need the exact values of the resistors, only in some points measures (mA, Volts) and some specific part (LED), I understand the scheme, but neither would I go only for that configuration.
I suffice with 30W in triode mode and here seems to opt for more than 100, much more...
But it seems that your prototype sound good, if it continues to develop, I will buy your PCB's.
Even was asking coucil to order a custom transformer (EDCOR), but will wait if finally just the prototype, and like the results, to order one to your specifications.
I build a SSE of Tubelab, but I want to have your boards.
I'll be waiting for news.
Good reminder on the CT. Like I said I have a few here right now. I measured 3H across the primary p-p. I measured another OPT I had here, about twice as large and got 8H. So we will see, will be an interesting experiment for cheapskates.
Good thing it's not about power.....cause you aren't going to get much. I Googled a bit and everything I read said you need at least 850 volts to get these tubes going, and thats in triode, you need over 1000 in pentode.
My biggest power supply only goes to 650 volts, and I had it maxed. I was getting 35 watts in triode with all feedback removed. Clipping set in when the capacitively coupled driver attempted to drive the 813's grid positive. That big grid is like a clamp diode across the output of the driver. What we need here is a mosfet driver and some more voltage.....lots more voltage.
Well at least it looks cool, and lights up the room.
Attachments
Need more power! (Ok, need is definitely the wrong word there).
And, does the world need another kt88 design?
Last edited:
I'd be happy with 5 watts. Triode.
Scary volts, I was thinking about 500. Too young to die.
I'm going to sim the circuit in SE CAD and report back. Thanks for the info.
Attachments
Last edited:
Damn, that tube is not in the library. OK, this is Pete's place anyway soooooooo..... this is my last interruption to an otherwise nice thread.
Just for giggles I did it with the 845. Look at those numbers..... lovely, aren't they? Too bad it's only one watt haha, that wouldn't stop me though what stops me is the fact that I'm not in love with the 845. 813 is my babe. I will build it even if it ends up being a super Champ. See ya.
Just for giggles I did it with the 845. Look at those numbers..... lovely, aren't they? Too bad it's only one watt haha, that wouldn't stop me though what stops me is the fact that I'm not in love with the 845. 813 is my babe. I will build it even if it ends up being a super Champ. See ya.
Attachments
Lets see.....100 watts of heater power for 5 watts of audio.....The GREEN POLICE are watching you
I was getting 30 watts on 650 volts, and about 24 when I was using the 550 volt supply. Cranking the bias up to 200 mA per tube (class A) actually lost some power since the lower bias voltage meant that the grid went positive earlier. I am sure that more power can be had with A2 or AB2, but that will have to wait until I have a mosfet driver board. Maybe 8 years ago I got that simulator. I plugged in 845, 5K load, A2 with as much drive as the tube can eat, and 1100 volts of B+. SE cad said 42 watts of power, which nobody including me believed. I built it and the simulator was right, I get 42 watts.
Remembering the "stuff" scattered all over the house, I decided to take several boxes outside and sort tubes today. I found a pair of really BIG Eimac triodes (3-200A3) and I was tempted to bring them inside and play, but they NEED A2 and want about 2500 plate volts. A pair will make only 750 watts.
I have found lots of tasty sweep tubes to melt.....OH and a shiney Mullard GZ34.
Going back outside....later.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.