GT120 project that needs a helping hand

[R.G.]

Wow. I just looked at the schemo of the original. That is seriously messed up. I agree with JM - the person who produced that schematic does not know what they're doing.

The only possible "redemption" is that maybe the schemo was deliberately messed up to keep people from copying it. That's kind of a brain-dead anti-copying scheme, but I suppose it might happen.

What is certain is that the schematic provided for the amp will NOT work as an audio amp. In fact, smoke is likely. If it were me, I'd demand a refund and go get something from a competent supplier. Of course, a seller that clueless will not provide a refund; only endless exclusions and excuses.

I'm sorry that you're learning amp building in such a bad way.

[Jazz P Bass]

So we wire up the output tubes, in pairs, one pair to each end of the OT primary.

Rewire each separate screen resistor from each output tube, in parallel to the B+ node.

Reverse the bias diode.

Rewire the neon lamp across the switched line.

And 'Call it a day'.

[g1]

I'm still trying to figure how the choke would fry if the 1A fuse was properly in series with it. But I have no doubt the choke and OT primary could have had a bit of a fight if wired as in the schematic.

Is this schematic the one that was provided with the kit? Is there also a layout drawing you could post? I would think if this were the schematic provided for the kit, all the amps would blow up, so how could this guy still be in business?

[Jazz P Bass]

If I am not mistaken, the amp uses a PCB for the most part.
Excepting the tubes.

[J M Fahey]

Well, maybe the PCB is fine.

Why bother to supply a schematic at all?

The only ones who can understand it will spot gross errors ... those who can't and only follow a layout will not, simply won't use it at all.

The gut picture posted is out of focus at the tube line, but I see lots of parallel connections along power tubes.

Apparently:
* #1 & #8 pins together in all
* #2 pins
* #7 pins

so far so good.

What I'd like to see clearly is plates and screens.

And supplied layout.

As of how could the seller stay in business if amps are wired like in the schematic? (i.e. not working)

How can Penis Growth herbal pills sellers stay in business?

FWIW I've been taking the P.G. herbal pills for 3 years now, I think I grew around 1/8" instead of the 4" promised, but seller said I should insist (I already spent U$2000 on them) and next time should be more careful about the Moon Phase, that's why they seem to work poorly.

Oh well, it must be something I did wrong

USA is HUGE, if seller hawks his wares at some Net page, aided by the YT Video, he may sell quite a few, each unexperienced builder going slow and probably blaming himself for failure, until someday the bubble bursts and he gets burned at the stake at some well known Forums.

Pity is , the kit shown implies a reasonably important investment, mainly the expensive chassis, not forgetting the PCB, and "it costs the same to do it right than to do it wrong" .

I am baffled by that schematic, doubly so because it was drawn a year ago.
Plenty of time to correct it, specially after kit builders' complaints.

Back to the amp: I would try to get the layout for a real Orange and build that, using the expensive parts already bought.

On an eyelet or turret board, of course, following some tried and true design.

Doesn't Ceriatone or Hoffmann (or some other) supply an Orange compatible board?

Troubleshooting the build with that schematic is impossible, and the unexplained voltages measured and gross errors such as filaments not lighting, burning a choke, blowing fuses, can't be coincidence.

EDIT:
Look what the cat brought !!!!
Searching around found this 2007 post by the kit maker, Mr Nathan Hilbish himself.

Maybe this starts to explain what we are seeing here.
Cut and pasted from
http://forums.vintageamps.com/viewto...575963#p575963

Orange Voltage Levels

Post by NathanHilbish on Mon Apr 09, 2007 2:25 am
Hi, I recently finnished build a or120 clone, and im having some problems with it. It works at low volume/signal levels but when there is a hi signal it starts to crakle and pop very loudly. I have a hunch it may be the filter caps supplying power to the tube plates (the 32 uF caps), I wanted to know if any one could tell me the voltage i should be getting at that point, and other points in the filter section, like the point supplying power to the output and preamp stages and the first set of filter caps after the bridge rectifier (the 100uf ones), at that point i am getting about 1222 V from where the bridge, fuse and those two 100 uf caps come together, does this seem to high?? I do know i am getting good power to the preamp section because i sent a signal from it via the send jack to the poweramp input of another amp and it sounds very good. Thanks for any help in advance.

[Jazz P Bass]

Wow!
1222 volts.

Edit" he rewired it.
Well here are a few voltages. (if they can be trusted)

[R.G.]

I'm still trying to figure how the choke would fry if the 1A fuse was properly in series with it. But I have no doubt the choke and OT primary could have had a bit of a fight if wired as in the schematic.

It's axiomic in power electronics that expensive parts will *always* die protecting their fuse.
Seriously, fuses are fast enough to protect transformers and sometimes tubes, but other stuff?
The simple way for a choke to fry is for the bias to be implemented on the board the same way the schemo shows it. That's about all it takes. Well, OK, and a cheap choke.

Is this schematic the one that was provided with the kit? Is there also a layout drawing you could post? I would think if this were the schematic provided for the kit, all the amps would blow up, so how could this guy still be in business?

Who says he's in business? [Disclaimer: I know nothing about Hilbert or Hibbits or Hoomeever; he may be an amp god for all I know and my opinion may be crap on this, but] It is possible he's a QBA.

[quiettimer]

Ok, soooooo I have it up and running!
Using some common sense and ignoring the original schem I was able to get it to sound pretty good - However, I think I will be redoing the whole board and probably everything as per these schematics in the provided section.

As much as I can see error with the layout and schem, I'm not going to post the layout as it has been expressly labeled "do not distribute" and I would like to respect his wishes.
I believe the Oranges are slightly different to the Matamps - in any case, the bias diode is orientated correctly on the board and I'm getting regular voltages everywhere.

Only one problem now and it's a crackle / artefact that follows each note and really is apparent when you dig in on the strings.
I suspect a bad cap maybe but quite unsure what else could do this apart from a connection which I've triple checked for.

[J M Fahey]

Oh, he is in Business.

His main selling point is being in Facebook
https://www.facebook.com/hilbishdesi...53811272875389
and his ads go viral, with bait, hook and sinker headings such as:
@ https://reverb.com/item/310782-hilbi...p-orange-or120 it goes:

Hilbish Design GT120 Kit 2014 White Matamp Orange OR120
Listed by Hilbish Design
Condition: Brand New
584 Views

8 in stock

$80 + $15 Shipping

Offers a YT Demo
https://s.ytimg.com/yts/swfbin/playe.../watch_as3.swf
and a link to his page
GT120 Amplifier Kit / Hilbish Design

where you learn that the $80 sticker now reads

GT120 Amplifier Kit
$160.00

Still not bad, until you learn that for $160 you do not get a full kit but chassis, frontpanel and PCB.
Not bad, chassis and panel look very good, but not a crazy bargain any more.

So far so good and if I were an experienced DIYer would buy just that and fit inside anything but what he offers.

Might also buy the tolexed cabinet housing for U$ 325 although by now I would have spent close $500 for an absolutely empty amp.

He offers different stuffings, of course:

* Bare bones (shown above): $160
* Standard (electronic parts and jacks/pots/switches): $665
* + transformers: $1174
* + tubes: $1297
* "Everything" (includes cabinet): $1500

Small detail:

Customers will need to provide their own wire for each kit.

But don't despair, at least:

Each kit comes with a full schematic.

OK, let's just help our friend quiettimer with any doubts he might have

[R.G.]

Good to hear that it's running. Good work, especially considering the handicap you were presented.

Only one problem now and it's a crackle / artefact that follows each note and really is apparent when you dig in on the strings.
I suspect a bad cap maybe but quite unsure what else could do this apart from a connection which I've triple checked for.

Hmmm. Might be a bit of parasitic oscillation. Are there any grid stoppers on the output tubes?

Yeah, yeah, I know - R.G., look at the schematic. Right.

[R.G.]

Oh, he is in Business.
His main selling point is being in Facebook

Wow. Quite a read when you chase down what you get for the money.

I was fascinated by the note that:

Kit orders can take up to 4 weeks to fill due to the amount of custom parts.

From the pictures on the site at GT120 Amplifier Kit / Hilbish Design, I don't see a lot that could not be sourced from a supplier in less than 4 weeks. I know some custom sheet metal shops that would CNC cut, bend, weld, powder coat and silk screen in less than 4 weeks. 2-3 weeks is probably the order/receive time for transformers. I'm guessing that he doesn't metalize his own caps nor film-deposit his own resistors, nor wind his own transformers.

Having dealt with the just-in-time model of manufacturing in my first professional career, I'm mildly astonished to see it pushed down to the quantity-of-one scale.

Of course I am always amazed at what salesmen will do to make a sale. I like to stay safe behind the design curtain.

Let me once again add, I don't know the people there, nor the quality of the amps. But the technical view of the net presence sets off alarm bells.

[quiettimer]

I actually got the kit as the board, chassis and faceplate - all really well made and I think it was worth the asking price considering that to have a one-off chassis cut, bent, welded, powder coated and screen printed would cost more than $160.
I built my own headshell (which is much nicer than the typical orange picture frame and matches the full stack I built) and I think it would've cost me about $50 in timber at the most.

The artefacts I traced down to the V1 and V2 sockets and once prodded with some chopsticks I found a connection and rectified it.

All is working pretty perfectly now and I am using it split with my Laney AOR 50!

[J M Fahey]

Cool

And really, you did the best.

Counterintuitively, for the DIY the "electronics" side is the easier part , because parts can be bought from several suppliers and received at home; the BIG trouble is the "mechanical" part, mainly metalworking.

Plus plating/painting, silkscreen, etc.

FWIW I make my own chassis from scratch sheet aluminum, cut, bend, drill, punch, surface treat, paint, silkscreen, but had to buy a lot of expensive heavyweight machinery along years, had custom dies made, etc.

Only worth for series production but not justified for single ones or small lots.

I guess Mr Hilbish forte, rather than Electronics, is the metallurgical side.

Maybe Dad/in law works at/owns some metal fabrication shop, or he is in close/friendly/family contact with one, because the chassis design is complex, has lots of holes, standard mechanical punching is fast and cheap but relatively long setup time for each hole means that then you have to make many (say >100 units per job) while laser/waterjet can do any hole shape and size but is slow and expensive.

I saw he works in lots of 10/12 sets, then he runs out and has to wait, say, 4 weeks to have more available .

What he always seems to have, is PCBs and at only $20 each , so those are probably made in 50/100 lots.

Oh well, all is fine if it ends fine.

Glad you found the problem; intermittents are great time wasters.

[quiettimer]

I have to say, thanks a lot - means the world that people are happy to spend some time helping!
What a great forum

[Jazz P Bass]

Really glad to hear that you got the amp working.

As an aside, maybe you could send a word or two to the supplier indicating the frustration that was caused by bad documentation.
Who knows, maybe the supplier doesn't realize the gaffs on the supplied schematic.