Who built this??? NEW pics added

[blaren]

19.89ohms....guess it isnt that?? ...now I forget what else I was gonna say and I gotta run to get coffee at Tims (you wouldnt understand unless you're from this God forsaken bagfreezing country).

OK...I'm back and now that I have some coffee in my gizzard I can stink thraight.
Now...why are the screens or grids or whatever, running at 100V less than the plates? Is that a kt66 thing??

[doctord02]

Off the top of my head, I think thats common for KT66's to have the screens substantially lower... Look at the data for AB1 push-pull:

http://tdsl.duncanamps.com/show.php?des=KT66

[RevD]

Just an FYI, I inquired on this amp on Hoffman and many agreed the layout STYLE was hoffman'ish but not a verbatim hoffman layout of anything known. Some said it looked like whoever made it must have been pretty versed in KOC (Kevin O'connor) concepts and design. I thought it might be Hoffman too just because of the way the ground side of the board had a twisted buss wire like is often done in a Hoffman layout. Sorry I could'nt provide more info, just that no-one over there knows anything about it.

Regards,

Rev. D

[blaren]

sheeeit...I hope no one's "sorry" for not knowing. I apreciate ALL this SO much.
I signed-up for the hoffman forums but am not yet approved. I looked at some layouts there and yes...they sure did look similar.

Thanks for enquiring over there.

the build sure isnt as sexy in real life as it is in the pics. Not BAD but coupleof the sozos are scarred by someone's shakey iron hand. you can see the foil through the "casing" of a couple of them. Does that kill a cap?
Agani fellas...I really appreciate all this info.

[doctord02]

The soldering iron scarred caps might be damaged, might not be working at their marked values.

One guess about the smaller circuitboard on the back; does it have DC heaters on the preamp tubes? From the description it sounded like that was a regulated DCpower supply. Another thought, could this have some sort of power scaling circuit? The galatic layout is from O'Connor, maybe its got scaling on it (in some form) as well?

[blaren]

The soldering iron scarred caps might be damaged, might not be working at their marked values.

One guess about the smaller circuitboard on the back; does it have DC heaters on the preamp tubes? From the description it sounded like that was a regulated DCpower supply. Another thought, could this have some sort of power scaling circuit? The galatic layout is from O'Connor, maybe its got scaling on it (in some form) as well?

How can I tell if it has DC heaters? I DID say I'm stoopid right?
I dont know a lot about power scaling either...I had always assumed that it was some sort of potentiometer controlled power reducer thing?? I dont see any "power scaling" knobs.
Sure would be nice though if it was running in 5W mode. Almost seems like about 5 watts...no, maybe 10. I dont think it's anywhere near my 18watter but I'll try them both tomorrow.

[doctord02]

>How can I tell if it has DC heaters? Embarassed I DID say I'm stoopid right?

you put the probes of your multimeter on the heater lugs of the first preamp tube (or safer, that third tube that has no other connections) with the amp powered up but in standby. Try it with it set to both AC voltages and then again with DC voltages and tell us the readings.

PS - we really need better close-up pictures to help...

[blaren]

I may have said I was stupid but did I say just HOW stupid? I almost electrocuted myself!..JUST KIDDING...NO fireworks. lol.
BUT....I dont know how to work my meter. I dont know which little symbol means AC and which means DC. I'm assuming that the side that goes to mV is the DC side. Anyway, I included a pic of the meter reading...which makes NO sense to me. I think this is on the AC side of the meter. I DID manage to get it to move the meter on the DC setting but BARELY. Tenths of a millivolt.
Please let me know if it's rude to have so many pics using-up this sites bandwidth. If so, I'll delete a bunch and replace them with links instead.
Sorry about my photographical skills or lack thereof. If there's anything else anyone wants to see (clearly), let me know.
Thanks again.
Here goes:


[IMG:800:600]http://i32.photobucket.com/albums/d42/b ... C02382.jpg[/img]

[IMG:800:600]http://i32.photobucket.com/albums/d42/b ... C02383.jpg[/img]

[IMG:800:600]http://i32.photobucket.com/albums/d42/b ... C02384.jpg[/img]

[IMG:800:600]http://i32.photobucket.com/albums/d42/b ... C02385.jpg[/img]

[IMG:800:600]http://i32.photobucket.com/albums/d42/b ... C02386.jpg[/img]

[IMG:800:600]http://i32.photobucket.com/albums/d42/b ... C02387.jpg[/img]

[IMG:800:600]http://i32.photobucket.com/albums/d42/b ... C02388.jpg[/img]

[IMG:800:600]http://i32.photobucket.com/albums/d42/b ... C02389.jpg[/img]

[IMG:800:600]http://i32.photobucket.com/albums/d42/b ... C02390.jpg[/img]
This reading was taken on the "extra" preamp tube and the one next to it. Amp was connected to an 8 ohm load in operate mode with all pots on "0".

[doctord02]

I'm still pretty sure that daughter board is some sort of attempt at DC heaters for the preamp; looks like just the first two tubes... BUT I'm not so sure it's correctly implemented...

I think it's time to have a qualified tech take a look. I'm not confident I can safely walk you thru testing and measuring things on a live amp - especially if you arent 100% certian of how to set your meter - no offense intended, but this stuff can kill you instantly.

[blaren]

lol...really though...I AM safe. I've been messing with this stuff for a lot of years. I've done a lot of FUSSY stuff on PCBs too. Nope...no worries with the soldering skills or the safety aspect. I know how to "operate" a meter...just dont know what the symbols mean...just like on a schematic.
No offense taken though.
The reason I "kinda" can fix amps (without knowing what I'm doing) is because there isnt a qualified tech for hundreds of miles. well...there is a tech within hundreds of miles...whether or not he's "qualified"...that's another story.
Even if I find a "qualified" tech, he'll use a scope to bias and he wont know how to play a guitar.
He wont be a hardcore tube amp junkie like you guys are.
It really sucks cause I've never had a KT66 amp and I have a feeling that this thing will sound SO awesome when it's up to snuff. There's no one anywhere NEAR where I am that I'd trust more than....uhhhh...ME. It's really that bad.
There is actually ONE guy but...oops...gotta run...
Thanks fellas

[Structo]

The V with the straight line over it is DC, the V with the ~ over it is AC.

Just be careful for heavens sake!

The doc expressed what a lot of us are probably thinking right now.
You said you almost electrocuted yourself then say you don't know how to use a multimeter correctly.....

Maybe time to read up on safe troubleshooting practices.
I

[blaren]

I was just joking when I said I almost electrocuted myself. I ALWAYS...ALWAYS drain caps before doing ANY work on an amp and if it has to be on, I ALWAYS use ONE hand.
I can do repairs if the problem is visibly obvious like a burnt resistor or a bad cap or something. I've done capjobs on some of my amps, tweaked some of my amps (bias resistors, nfb values, adding grid resistors........), bypassed/repaired pcb board traces, installed (and UNinstalled lol) mastervolumes....blah blah.. Did it all with coaching from online experts and layouts and stuff. Did some serious troubleshooting on a build from Nik with Richie. He (Richie) actually took the time to PHONE me and we found and corrected the problem...well HE did. That BLEW ME AWAY! I didnt buy the amp from Richie and he didnt know me from Adam and HE phones ME!! WOW.
Anyway yeah...dont worry, if anyone's into it, feel free to tell me where to check for how much of what kind of voltage or current, and I can safely do it.

And about a (semi) local decent tech...there is a guy in Edmonton that a lot of people like but I've seen a few things. He IS very into old tube amps and fixes a LOT of them, he doesnt PLAY though and I'm sure he still uses a scope to bias . I've seen a few amps that were brought to him for repairs. Amps that came back with ALL their nice old tubes replaced with EHs and biased...the bill?...$250!!! I kinda doubt if he even knows that there's a world of crazy bastards like you guys building some of the most amazing amps ever made. I'd hate to pick-up my amp and get an extra bag of parts that were removed because they were "unecessary". OR...to have him say..."I replaced the filter capacitors" as usual, only to get it back sounding EXACTLY as before.

Anyway yeah...keep it comming fellas...you wont be held responsible...lol. No...really though...no worries.

[Krinkle]

You asked about the discolored resistor. If it opens due to stress (it looks like a metal oxide, 2 or 3 watter, so it should be flameproof) then you will lose your B+, or at least part of it, and essentially your amp will not work. If you want to do a quick check (Cover my butt statement, don't do it if you can't keep from killing yourself), measure across the resistor using the DC volts setting (straight line over dashed/dotted lines).

Take your measured value and compare to this theoretical value.......

As one of the power formulas is P=Vsquared/R and assuming a 2W resistor;

V=square root of P*R

V=square root of 2*10

V=4.47

Given that the general engineering rule of thumb is to run components at half of their rating, then anything at or about 2.25 Volts is fine. Anything at or over 4.47 Volts will stress the resistor and cause discoloration.

My guess is that you will get a measured value that is higher than the rated value, or a value that won't be proper, when combined with the fact that there could be a fair bit of heat inside the chassis.

Also, even though the DC value may look okay, the caps are charging pretty fast and the current goes through that resistor, looking a little like a spike and driving the heat up that needs to be dissipated. These small value resistors (1 to 10 Ohms) are usually used in conjunction with capacitors as filters for spikes. Take a look in the TUT series by KOC and you'll see. If you're playing around with amps without a lot of knowledge and you don't have TUT1, then I would highly recommend it.

As for the board on the rear, if it is an attempt at DC heaters, it is not a real good one given the fact that the voltage rating on the caps is 10 volts. It may be a voltage rail intended to run a fan, another thing described in TUT1.

As for Power Scaling, I do not see any of the components required so it is not in there.

Darrin

[blaren]

Well....I cant get a resistor in this stupid town. Going to the big city today though...if something's not too far out of the way...
When I measured that resistor I got retarded numbers...cant remember exactly right now but the DC voltage was WAY higher than 2 or 4 volts.
Even if I FIND a resistor today and change-out the discolored one, I'm guessing that I'm in for a show. Either some smoke or another resistor doing the chameleon(?) thing. Should be interesting.
So yeah...I forsee me changing a resistor only to have the underlying "problem" cook the new one too. I guess that then I'll HAVE to bite the bullet and take it to a frickin "electronics" tech...GOD!
On the other hand...as quiet and dirty as it is, I could probably use it in the studio. We have a tune that's in dropped D (only ONE) and I dont have any gain monsters. This amp seems like it's only spitting out <10W but it's kinda scooped and REAL gainey.
In 20 years from now everyone'll be trying to emulate my tone and someone will try to build a "replica" line of my amp only to discover that it's BROKEN (think VH frankenstein axe pickup)...lmao.
K...I'm off

[Krinkle]

If that resistor is what I think it is (1 Ohm used with the next capacitor as a spike filter), then you can just remove it (and the cap, although you can leave the cap if you like). I'd be willing to bet a pretty large sum of money that you will not notice any change in tone or reliability of the amp.

If it becomes too big of a problem for you we can trace out the circuit, with values, and confirm so you can pull it out.

Is the big city Edmonton? My brother lives there and I may come out for a vacation some time. You'll have to bring your amp over. If you go there often I'll find out where my brother jams, he has the London Power Standard that I built for him with Dual DC Power Scaling.

Darrin