bigjppop;-
A 50W amp just using a single pair is alot simpler for beginners.
Going to parallel pairs over 100W sounds great to fame but costs begin to rocket. If you encounter problems with this big game and big power supplies, youll' goin' to need a good clear undrunk head, work expertly and methodically.
BTW. More for less.. A 100W amp sine wave rated using p-p-p-p (parallel-pairs-push-pull) on a square wave is quite able to fork out 200W. That is one of the reasons these amps sound so fantastically loud.
richy
I'm with SY. The original question was how to get horsepower - 807s provide one answer and are readily available relatively cheaply. The Class A, U/L - triode bit came in later and significantly changes the rules. Money spent on getting over the 50W mark with good quality in a tube is probably better spent on better more sensitive speakers imho. Then you don't need stratospheric output.
Aim at 25 to 30 well controlled, cleanly and amply fed watts from AB1 for a simple effective amp. If you need more, bi-amp it and go to sand for driving the floor shaking bits.
Aim at 25 to 30 well controlled, cleanly and amply fed watts from AB1 for a simple effective amp. If you need more, bi-amp it and go to sand for driving the floor shaking bits.
So, has anybody got any good schematics for EL34 UL or KT88 triode? How about a fixed bias triode KT88 with a CCS? Not to thread-jack, but this is something that I've been looking for.
Bigjppop: Are you comfortable with a P2P scratch build or are you looking for a kit?
I've never build something P2P but everyone has first time sometime, right? A kit would be great, but all I've found so far is the Dynaco MkIII at 60W. For a pair of those I'd be looking at at least 1K which is a touch on the high side. I don't really need/want monoblocks (just an extra chassis to build!) so I'd love to find something that could work in a single chassis. I'm sure I could probably figure out a way to build the MKIII's into a single chassis but I'd love some other options.
From what has been said so far, it sounds like my best bet is some KT88/6550s done in parallel (at least two per channel). So I guess now its just a question of finding a design and then deciding am I going to be happier building my own or going with something commercial that on the used market could probably be had for the same money (or even less). Like I mentioned up top, I'm still torn on building from scratch vs. modding a commercially available unit.
From what has been said so far, it sounds like my best bet is some KT88/6550s done in parallel (at least two per channel). So I guess now its just a question of finding a design and then deciding am I going to be happier building my own or going with something commercial that on the used market could probably be had for the same money (or even less). Like I mentioned up top, I'm still torn on building from scratch vs. modding a commercially available unit.
You can't build a good PPP KT88 stereo amp for less than $1K. Just the power tubes will be $200 minimum. You'll spend at least $200 just on the power transformer. 120 watt output transformers don't come cheap either. The driver stage needs to be decent, or it'll let you down when it comes to the finals.
It isn't worth it, either. You're buying an extra three clicks on the volume dial, as compared to a nice manageable 6BQ5 amp. Start with a more realistic project. Play with it for a year. If it makes you happy but you still want more, then sell off the little one and pursue the big amp.
There is an old saying in the automotive hotrod industry, "Horsepower costs money, how fast do you want to go?" There is a curve of power VS cost that is nearly logrithmic. It is similar whether you are talking horsepower, computing power, or (tube) audio power. Class A power will always cost more (and be far less efficient) than class AB power. A SE amp is by definition class A, but a P-P amp can be class A, AB or even class B.
The 807 is a 6L6GB (360 volts max on G2) in a big bottle with a plate cap. The plate cap allows for much higher plate voltages but the low G2 rating makes the 6L6GC a better tube for higher power in triode or UL modes. In either case the most power that you can safely extract from a 6L6 type tube is 10 watts per tube in class A. Likewise the KT88 is good for about 14 watts per tube. You can push these numbers a little bit at the expenxe of tube life and reliability. So if you want a class A amp with big power you are goind to need a lot of tubes, or some bigger tubes (expensive transmitting types). There was a thread dealing with wiring up a bunch of 807's to make a big amp. I don't think any amps got finished but it is worth reading. This thread got me started on building a big amp, since it provided me with some monster OPT's.
http://www.diyaudio.com/forums/tubes-valves/100852-eight-807s-push-pull.html?highlight=plitron
I am commited to building a big P-P amp, but I have re-evaluated my power goals several times. I lucked into a pair of 400 watt Plitron toroidal OPT's so I planned to build a monster P-P amp to make full use of these transformers. A few other forum members got the same transformers over 2 years ago. The expense and complexity involved in making an amp of this magnitude has prevented me from building the beast. AFAIK no one else has completed their beast either. So several pairs of choice OPT's have been idle for over two years because the beast was too hard to tame.
I came to the realization that the beast would be a cool show piece, but it would likely wind up on the shelf next to my 40 WPC 845 SE amp that hasn't been turned on in over a year (too big and makes too much heat). My 87 db Yamaha speakers are only rated for 60 or 70 watts, and my 96 db big speakers are really loud when fed with a Simple SE, so why did I need 400 WPC? Maybe I should think about something realizable in the 50 to 100 WPC range. An amp in this range can be realized with two output tubes per channel if class A output is ruled out. I really like the sound of triodes, so I would like to do a triode (or triode wired pentode) output stage if possible.
A simple SE owner posted a thread about running 6L6GC's in AB2 a while ago. That thread got me thinking, and even got me to design a driver board, build it and get the big OPT's out of their box. This is a long thread (350 posts) but it goes from a simple idea to a working amp. Neither one of us has finished our amps yet due to other priorities, but the thread will get started back up again as time permits. So far we have seen 90 WPC from ordinary Chinese 6L6GC's in pentode mode, and 55 WPC in triode. The Electro Harmonix KT88's seemed happy running at 75 WPC in triode! And, despite what others say AB2 can be used in HiFi, and it sounds good if it is done right. The schematics are posted in the thread and a 75 WPC triode amp is breadboarded on my workbench and is operational. The power supply is not finished yet, but the amp sounds great on my bench supply.
http://www.diyaudio.com/forums/tubes-valves/133034-6l6gc-ab2-amp.html?highlight=6l6gc
It might be wise to look at the prices for 50 to 100 watt P-P OPT's in the 3 to 5 K ohm impedance range, one big or two medium sized power transformer, and 4 or 8 6L6GC's or KT88's, then compare them all to your budget. Figure that the finished amp will cost 1.5 to 2 X the cost of the major components, but we all know that things can get out of hand when you start dreaming.....
Still want 807s? How about modifying this RCA PA design...
The Shrine of the Ancient and Most Excellent RCA MI-12188A Power Amplifier
According to the site author:
" As-is, These amps are adequate public address voice-range drivers, capable of about 65 watts at clipping from 200 to 15,000 Hz. They also run near class-A, and consume the 807 output tubes quickly. They are definitely not designed as "Hi-Fi" amps, but can be tamed and reworked into a fast, transparent 45 watt amp, and trained to be conservative with those costly NOS WWII JAN-807's. "
A " ...fast, transparent 45 watt amp..." maybe just what you want...
: )
The Shrine of the Ancient and Most Excellent RCA MI-12188A Power Amplifier
According to the site author:
" As-is, These amps are adequate public address voice-range drivers, capable of about 65 watts at clipping from 200 to 15,000 Hz. They also run near class-A, and consume the 807 output tubes quickly. They are definitely not designed as "Hi-Fi" amps, but can be tamed and reworked into a fast, transparent 45 watt amp, and trained to be conservative with those costly NOS WWII JAN-807's. "
A " ...fast, transparent 45 watt amp..." maybe just what you want...
: )
he's also hugely experienced, winds his own transformers to suit, and by his own admission finds it almost impossible to get a buyer who is prepared to pay the price. No disrespec' to Patrick - he is an oracle vis-a-vis this technology - but his high power designs are about as relevant to the op as blueprints of a Ferrari are to a 100cc kart builder...
Gotta love his use of sweep tubes in one amp though!
Gotta love his use of sweep tubes in one amp though!
Did you see the stereo 50 Watt design using 2x kt88 per channel. The original requirement was for a 50 watt amp suitable for someone relatively inexperienced who didn't want mono blocks and didn't want a kit, quads were considered inappropriate.
This thread was started by bigjppop to find a design.I'm sure he'd rather hear what works not what wont.
I've got a pair of those OPT's stashed away for a PPP monoblock project,Just waiting for George's Universal PP driver boards.
Don't forget cheap. When other workable suggestions were made, he said that $1K was a lot to pay. I'd suggest he go to eBay and look for one of the Yaqin MC-100B amps. They're 65 watts a channel, single chassis stereo, require no experience, and can be found for around $600 shipped.
I don't know if I necessarily said "cheap." If 1000 bucks is the price of entry into the push pull world via DIY, I think the Chinese are going to be calling my name!
That Yaqin amp you linked looks interesting. Also the Onix SP3 and some of the Jolida stuff might work well.
I'm curious, and I'm being totally serious and not trying to be an A$$, am I just cheap? I make a good living but the wife only gives me so much allowance per month. 1K seems like a pretty serious investment to me for a DIY amp, especially something that doesn't seem to be too incredibly outlandish/esoteric; a basic P-P amp making 50-60 watts per channel with KT88/6550 tubes doesn't seem like it should break the bank. Is everyone else spending that kind of cash?
That Yaqin amp you linked looks interesting. Also the Onix SP3 and some of the Jolida stuff might work well.
I'm curious, and I'm being totally serious and not trying to be an A$$, am I just cheap? I make a good living but the wife only gives me so much allowance per month. 1K seems like a pretty serious investment to me for a DIY amp, especially something that doesn't seem to be too incredibly outlandish/esoteric; a basic P-P amp making 50-60 watts per channel with KT88/6550 tubes doesn't seem like it should break the bank. Is everyone else spending that kind of cash?
amazing value what's the quality of the OPTs like? i saw that thread too. Even if the circuit was a dud you'd get a great looking amp and could rewire, maybe replace the OPT's if necessary...or probably not need to do anything...
1.5k is a reasonable amount to spend especially if you've got a good source and speakers
1.5k is a reasonable amount to spend especially if you've got a good source and speakers
Last edited:
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.