Who built this??? NEW pics added

[blaren]

Sorry for posting this in the TW discussion forum. Couldnt think of a better place. Couldnt think of a more "hard core" pile of amp building geeks (that's a compliment) either.

[IMG:800:600]http://i32.photobucket.com/albums/d42/b ... 001441.jpg[/img]

[IMG:800:600]http://i32.photobucket.com/albums/d42/b ... inotop.jpg[/img]

[IMG:800:600]http://i32.photobucket.com/albums/d42/b ... utshot.jpg[/img]

Anyway...anyone know who could have built this amp? It isnt a Cornell.
Sounds very cool so far. I havent gigged with it yet and have only messed with it for a few minutes but yeah....It's not overly loud (thats another compliment). The "gain" pot works as much as a gain as it does a volume...if THAT makes sense. All the pots are VERY ...uhhhh...useable? I mean...with marshalls, I usually have half the pots near zero cause they all either seem to add harsh highs or boomy lows. This one is cool cause the middle pot adds MIDS...the bass pot adds nice BASS...the treble pot adds nice treble...or too much if you want too much (all the pots are capable of adding too much but only when they're turned WAY up)...the presence adds sizzle, the gain adds GAIN and more GAIN..and volume...I'm still not sure what the "depth" pot does yet but I will find out. I dont know why there's an extra tube socket in there either (sounds best with a mullard in that position...lmao).
I havent even opened it up for a better look inside yet. These pics are the ones from the previous owner (who doesnt know what it is either).

So there it is. ANY help anyone can offer will be greatly appreciated.

Season's greetings.

[hairyandy]

Just taking a stab but I'll bet the 'Depth' knob is a PPI "resonance" control, kinda like a reverse Presence, that tightens up the bottom end without getting too flabby. Bruce Egnater has the same control in his Seminar amps, it's very cool for helping out the low end at low volumes...

Andy

[wsaraceni]

looks like a similar layout to a hi-fi amp someone on the gear page built. cant find the pics though

[Krinkle]

I don't see any wires going to the 3rd preamp tube except for heaters. Need more gut shots to tell, especially of the extra card on the rear. All high quality components from what I can see, metal film resistors, Sozo caps, etc.

It looks to have individual bias trim pots. The gain pot is a dual gang, simliar to the AX84 High Octane preamp maybe? Very interesting.

The grounding of the layout reminds me of a cross between the "Galactic" grounding in the TUT series and the way that the CAE 3+ is done (see gutshots in Rockstah's putfile section, on the Metroamp forum). Looks very nice to me, I wouldn't mind seeing close ups of the circuit to see if there's any layout tricks to learn. Is it quiet for the amount of gain it has? How much gain does it have?

It shouldn't be too hard to tell what is going on inside if we can see better.

Darrin

[CaseyJones]

The grounding of the layout reminds me of a cross between the "Galactic" grounding in the TUT series and the way that the CAE 3+ is done (see gutshots in Rockstah's putfile section, on the Metroamp forum).

It sure looks KOC inspired. I was hoping I could identify the builder because I see a lot of amps, I haven't seen this one.

[blaren]

...I KNEW this was the place to ask.
I'll open it up as soon as possible and I'll take some more shots. Anything in particular?
Like I think I mentioned. I know nothing about amps. When I saw the KT66s I was thinkin JTM45 clone with only one input and a master.
The extra tube...I'm ASSUMING that the builder had at some point planned on an additional gain stage? Maybe he changed his mind after he/she heard the stupid amount of gain already on tap...or...originally had another gain stage and it was just WAY too much???
I still dont have a lot of time on it but yeah...there is a TON of sweet (not fake/busy/shrill/preamp-ish) gain on tap. Reminds me of the real violinish dumble clips I've heard. It's weird cause everything comes on so gradually on this amp...(except the gain)...like, the master. On all my other amps, from silent to audible is like going from 0dB to one MILLION dB. The master on this thing is REAL gradual. The gain (pot) comes on pretty early though. Like if you run the gain and master on 5 it is VERY overdriven (lush harmonic feedback) but not too loud. On my 30watter for example (4XEL84), with the vols on 5 and 5 I get VERY loud, VERY punchy, tight, headroomy crunch. The gain on this mystery amp comes on at about 2 and just gets more "creamy" as you go SO....I "think" that if I wanted the kind of headroom I'm used to I'd have the gain on 2 and the master on 10...it wouldnt even be very loud. Weird. Rolling back on the guitar's vol cleans it up but there doesnt seem like there's a lot of headroom there in te first place.
The way the tone controls react DOES kinda remind me of the way a stereo acts. I almost want to dime everything and I could. With any other amp, as I mentioned, I usually have the treble pretty much OFF. The middle is real bright on my marshalls too. Not on this thing.
I'm thinking it could need a bias job to giv it the PUNCH I think it should have.
Wha's the max dissipation on a KT66?...or the max rated power or whatever you call it...you know, like, an EL34 is 25W. (70% = 17.5W).
Thanks for looking fellas. It's pretty irritating having an amp when you dont even know WHAT it is.

[jaysg]

To me, it looks like a Hoffman layout. Can you tell who made the transformers?

[Krinkle]

As far as pictures go, it would be nice to get close enough on each section to read the values on the caps, but far enough away to be able to identify what portion of the amp it is. If this is a typical/traditional schematic, then it will probably be pretty easy to tell what it is.

I'm interested in it because the quality of build looks very good to me. It looks like someone put a lot of thought and effort into it and there's always something to be gained from that.

This is my hobby (notice how I didn't use the word obsession, that's Wife speak for hobby) so I'd be glad to help you find out what it is. We might even be able to come up with a schematic, which is a possible way to identify where this came from.

I have to say again that it looks really good to me. If anything is bothering me it's the board on the back of the amp, that's the only sign of an afterthought in the design that I see (or that might just be the best place to put it, maybe we can figure it out and see).

Darrin

[Krinkle]

A quick look on the net tells me that a KT66 is 25W. Take a look at a few more sites to make sure though.

Darrin

[tunghaichuan]

A quick look on the net tells me that a KT66 is 25W. Take a look at a few more sites to make sure though.

Interestingly enough, the data sheet that comes with the Groove Tubes KT-66HP tubes (which seem to be the ones shown in first photo in this thread) say 22W for "Design" values and 30W for "Absolute" values.

FWIW.

[blaren]

didnt do much amp playing today. I DID go to Hoffman amps and yeah...his layouts sure DO look similar. I was looking last night and saw a preamp layout for an 18w of his and it had the 4 tubes like this one. Of course now I cant find the page for a better comparison.
The transformers dont have a manufacturer label...except the choke which is a merc.
The pt is stamped with W022798 and 1279 and has 0537 in white script. The OT has a white sticker on the top with HTS7751-8K 9960547. The choke says Merecury Magnetics and AXIOM JT45C-7H.
Now the caps....
They are (l to r): 1.0, .022 (I'm guessing...it's the same size as the .022s but no script showing), 1.0, .022, .022, 1.0, .022, .022, .022, .047, (2X) .1, .047, .047, and a .0047uF on the depth pot.
That other board with the 3 little big 2200uF 10V caps that has all the pre heaters wired to it also has 4 diodes and 2 resistors on it. Not much help I know. Better pics still to come.
Thanks again for all the help.

[ampgeek]

Looks like a Weber P/N on the PT.
Tweed Bassman if I remember correctly.
Dave O.

[blaren]

WOW I just threw a meter around in there. Those KT66s had 450V on pin 3 and 350 on pins 4. I'm used to seeing a 10V difference....not 100. I've never seen an amp with that much voltage on the plates of an EL34 either...other than my traynors. I know it isnt THAT unusual but I was surprised.
According to my calculations they should be biased at ~38mA but they were at 47 and 55 mA !! Now it's hitting the plates at 460V and I'm biasing at 37mA.
That oughta give it some jam right?


Weird!

Gotta wait for people to wake up before I can try it out. We had another turkey dinner tonight and everyone's passed-out still.

[blaren]

welllllllllll...it still doesnt have a lot of clean headroom. I can crank the master and turn the gain up to about 3 when the gain starts comming down in buckets and it isnt excruciatingly loud like it should be at that gain/headroom level. There's that one discolored resistor at the far right there. It's either a 20 or 30 ohm depending on whether that's a red or orange band on it. What can happen if that resistor is bad?

[billv]

Looks like the first dropping resistor in the B+ chain, based on position (next to the rectifier diodes & screen resistors). It could have a drifted upwards in value, which would drop voltages to the screens, PI and preamp stages.

Switch that meter to ohms, mister!