TUBENEWB - Quad KT88 Monoblocks

[Adrculda]

Hey everyone...
went for a listening sesion this past long weekend and fell in love with the sound a friends twin KT88 setup ( not sure exactly what hes got but its a homebrew of sorts )
which got me thinking at possibly starting another amp build :P
Something that has a lil bit more "punch" than his as it sounds a bit "weak" down bottom. Thinking of a Quad KT88 in a PP configuration.

I know good iron is expensive, but what even worse is trying to build a tube amp when you know nothing about tubes !!!

Found output trannies at hammond, but dunno what power requirements would be for such a monstrosity...

[kenpeter]

Either of these should do it...
EDCOR - CXPP100-MS-2.5K
EDCOR - CXPP100-MS-3.3K

[aardvarkash10]

lordie...

Whats wrong with just a pair in AB1 pp? Isn't 70-100 watts enough for you?

TDSL Tube data [KT88]

[taj]

Originally Posted by Adrculda

I know good iron is expensive, but what even worse is trying to build a tube amp when you know nothing about tubes !!!

You'd better stick to a project that is well tested and well supported. At least until you learn about tubes.

Yeah, Quad KT88's (parallel PP) is a little extreme isn't it? 2 usually nets you about 75 watts. If you need more, maybe using tubes isn't in your destiny.

If your pal's rig didn't have enough bottom end grunt for you, it may just have been a design limitation of the amp he built. There are plenty of [cheap and easy] methods of reducing the bottom end. Cheap output transformers is a good start. Too small coupling caps, etc. etc.

..Todd

[Adrculda]

Nothing wrong with overkill, at least in my point of view...
The way I always look at it is to have plenty of headroom

Thanks for the Edcor links but already have a local supplier that can get me both Hammond Outputs for well under $250. The ones im worried about is to find the specifics of what kind of current is needed for 4 x KT88's as i always like a "stout" power supply as its the foundation of every amp.

What I'm trying to figure out is where i can find a stable circuit that i can start with and slowly gather parts. In the meantime i have ordered the sockets and 2 sets ( quad ) of matched Gold Lion KT88's through a "friend" a that lives a couple of blocks away

Any ideas or pointers ???

[aardvarkash10]

there are plenty of competent designs for the KTs. Similarly, lots of horror stories!

If you are going for a quad, power supply is going to be... well, you've already identified it as critical.

If you are spending like a drunken sailor, there are the usual suspects in terms of voltage amp/splitter/driver set-ups. If you want to get a bit more funky, a few here will help you in the "how to drive a high power output" stakes.

Check out chrish's now infamous 6L6 thread which has almost become a primer in pentode circuit design.

[Andrewbee]

Triode Dick has a PPP KT88 amp. Look under projects and KT88 (surprise!) and on the second or third page he has the PPP version. I have not built it so have no idea what its like.

I did build a stereo KT88 PPP amp ~ 20 years ago, UL using 100W Massicore OPT's (not really the correct OPT's for PPP but what the hey and 800V on the anodes with the then new "Golden Dragon" tubes from Shuguang (sp). Lots of pops and clicks and pretty colours until I lowered the voltage / current. I used them to drive Infinity Kappa 8's. The lights in the apartment would dim with the bass transients. Great fun at the time but as others have questioned, do you really need KT88 PPP or is it something you want to do.... just because?

[Adrculda]

The way i want to set it up is to have the heater transformer separate from the HV circuit.
This will also allow me to run a regulated heater supply along with a preheat function to the tubes for 15-20 seconds prior to blasting them with HV.

So with a bit of quick math...
1.6A per tube will need a transformer capable of 6.4A without any other tubes in a circuit !!
I would say a 10A should be plenty of juice for 8 tubes and a few more left over for "driver" heaters.

[Adrculda]

And hopefully my power transformer is somewhere in this list :P

[gingertube]

Old PPP KT88 design of mine from a few years back but may give you some ideas.
I ran these monoblocks with both Hammond 1650T and some expensive Plitron PAT4006 Torroidal Output transformers and actually liked the sound of the Hammonds better in some regards.
See here:
Evatco Hammond Project Page
4th project down.
Schematics for amp and power supply and a "designers comments" document I put together which included some power output and frequency response measurements.
Cheers,
Ian