18 watt trouble

[C Moore]

I have been here before with this, but.....
I have:
1. Motor-boating problems.
2. Leas dress noise.
3. Bias adjust causes noise as the voltage goes more positive.

V2 (is that the PI in this amp.?) has LOTS of lead dress noise. I can move the blue wires and make the noise worse, butt cannot make it better if you know what I mean.
At first, I had a 50-50-500 JJ can cap. It was on my shelf for a few years, so I replaced in to see if that was a player in the motor-boating. I thought it might be an issue, so I replaced it. In its place I installed two 22-500 radials. It had no effect on the MB. I have checked and reworked all the PS grounds a few different ways. Nothing has effected the motor-boating.
I realize these amps are typically Cat Biased, but I thought I would try my hand at creating a fixed bias circuit. Turning the bias pot really increases the hum/noise floor of the amp.
This was a Crate V18. I gutted the chassis and installed all new parts, including the PT and OT.
Some of the lead dress looks disheveled because I have been moving wires around A Lot.
So, where do you start with something like this.?
Is my whole layout a disaster.? Should I ditch the fixed bias at this point.? Although, why would that be a problem.?
What should I tackle first.?
Thank You

This is how I had my first two caps in the JJ can.
http://i111.photobucket.com/albums/n143 ... l18004.jpg
http://i111.photobucket.com/albums/n143 ... l18003.jpg

Then I tried this.
http://i111.photobucket.com/albums/n143 ... all004.jpg
http://i111.photobucket.com/albums/n143 ... all003.jpg

[jestaudio]

Your build is similar to my 36dual tmb build with the exception of the grounding scheme, it may be worth grounding everything from on point, i'm not a expert but i know poor grounding can cause all sorts of problems

[ToneMerc]

Here's what I've seen with this 18W circuit when folks build them, with two things generally happening, either it comes out golden or it riddled with troubles. The lead dress is terribly critical and it helps to understand the circuit layout. Yes V2 is the PI, now the the fact that lies in between V3 the oscillator circuit and V1 doesn't help matters. The MB might actually be oscillations. If it was mine, I would gut it and redo it as stock. I laid mine out differently, which it won't do you much good. However, maybe these will help you.

TM

[C Moore]

I really appreciate any and all advice at this point. A SMALL part of my troubles may be that I am trying to use a chassis that was set up for a much different layout. It is cool to make one thing out of another, but this example might be out of my ability/skill level at this point.
I think it would be best to try and emulate the Ceriatone layout or the other one posted.....Is that the work of Richie Hall.?
Perhaps if I can first get it to work from a more "classic' layout, I can worry about things like fixed bias later on. Again, probably out of my league there.
And yeah, it seems the PI position is VERY sensitive.
Let me go back to the drawing board then.....and kind of "start over".
Thank You

[Richie]

Is that the work of Richie Hall.?

Well yes and no. their were a few mistakes in the drawing, that i don't know if they ever got changed or corrected. If i remember correctly someone asked to post the drawing to help them and we said it wasn't completed yet.
And it went on from there.
People copied it put it on other forums, then people came back in and said the drawing had mistakes. Well yeah it wasn't finished, and you learn not to put any drawings up that aren't finished.

But yes, the 18 watters have made even seasoned amp guys scratch their heads. As in the listing Nik has for the sovtek. Then mostly finding out it was the gain of the tube that would or could make the trem work or not work.. You think all 12ax7 are alike or should work. But in "SOME" not 'ALL" 18s thats not exactly true. I think at the time the sovtek worked best without as many problems as others.
Thats been quite a while ago.

But first what you should do is, pull the trem tube,which is also the other channel.
Does the normal channel work without problems?

There are all kinds of tricks to help the amp not have alot of the quirks it has. Like adding a grid resistor on the tube pin of the trem. I belive a 1k or 820 has worked.

If you can get the normal channel to work,then the trem channel can also be made to work. The lead dress is important.
Look at any pics of the real 18s or the hand built ones.

The wires going to the plates of the PI, and also the input leads to the PI are areas to keep an eye on. Lead dress there is very important.

If you had acess to 18watt.com, im sure every question has been asked about those amps. And it would eb easy to check out some things. I very seldom go there anymore.

[C Moore]

Hey Richie -
Thank You So Much.
Did not realize these amps were kind of "tricky". I think I had less trouble with my Express. But again, I was using a chassis and boards that were set up for an Express layout.
Considering my skill level and experience, I think it would be wise for me to use a chassis that accommodates the 18 geography better.
I think I will try an AC15 with what I have here.
To finally answer you question.....Yes I have trouble on both channels.
In the words of Jack Nicklaus....."I knew I was not going to be able to get this one through the trees, so I chipped out of the woods, layed up, and saved par."
Thank You All

[epis]

Hi,
your layout isn't disaster .Your problem is grounding scheme.
What I would do is : unscrew all input jacks and let them hang in the air.Remove ground buss connection to that bolt close to input jacks and connect it from other side to your main ground.
This way PI isn't gonna be grounded close to input jacks what is causing your problem.
If it worked, replace metal input jacks with some Marshall type insulated jacks.I hope it helped.Best regards.

P.S.

Just for test unsolder tail resistor of PI from turret witch goes to ground and connect it to main ground point. If it improved, you know what was problem.

[C Moore]

Hi,
your layout isn't disaster .Your problem is grounding scheme.
What I would do is : unscrew all input jacks and let them hang in the air.Remove ground buss connection to that bolt close to input jacks and connect it from other side to your main ground.
This way PI isn't gonna be grounded close to input jacks what is causing your problem.
If it worked, replace metal input jacks with some Marshall type insulated jacks.I hope it helped.Best regards.

P.S.

Just for test unsolder tail resistor of PI from turret witch goes to ground and connect it to main ground point. If it improved, you know what was problem.

OK I will give it a shot, and learn something, regardless the outcome.
I have said it before, but.....My efforts are 10 times what my abilities are at this point. It is so disappointing to have this much trouble on something I TRIED so hard to do right.
Give me a few days and I will let you know.
Thank You

[Phil_S]

I was not anxious to show mine -- I'm not the most experienced or tidy builder -- but my 18W is quiet. My first thought was the ground scheme.

There are some obvious and not so obvious differences. Mine is a TMB18W. You built it with tremolo. Mine is a head. Power tubes are 6GK6 so don't go nuts over the pin out -- BTW same tube as EL84, different pinout. There are a few obvious gaffs that were fixed (like the yellow wire to nowhere), but I didn't update my pictures.

See if you can get a look at the way I did the grounds. I know guys swear by grounding the buss bar near the input jack. I just can't get my mind around that.

At the right, the buss starts with the cathode of V1 and the input jack. At the left, there is a black wire to the one and only chassis ground bolt. Anything not grounded to the buss goes directly to the chassis bolt. The chassis bolt ground is below the lower left corner of the board.

Group your grounds by section. Each section ends with a preamp cathode. Sometimes, both cathodes in a single tube should be considered one section. The PI is the last section in the preamp, so, even though it is V2 in the layout, try to put that on the buss closer to the power tube end.

I was also a bit surprised to see the other end of the buss unsupported. I'd do something to stabilize it at both ends.

You can fix this. I don't think it's that hard to do. Do the thing with the jacks in the air for testing. I stopped using Switchcraft style jacks because of the grounding issues. Good luck.

[epis]

Hi Phil,
I do agree with you 100% about grounding.All my builds were done same way - preamp section (ground buss) at input jack, all power including PI at main ground close to power transformer.
In this case problem is PI ground close to inputs, simply, it's about poor layout (or maybe just unusual), so this way for grounding doesn't work.
Cheers, Damir

P.S.

Just one thing, only important thing is to separate preamp and poweramp grounds as far as possible, not where you are connect it to the chassis

[epis]

Even when I do Marshall type builds with insulated input jacks, I allways ground buss bar at input.Here are the images of my 6v6 plexi with post PI MV.

[/img]

[C Moore]

Thanks for the additional info....I appreciate it.
Some of this goes back to what I was saying earlier about the difficulty of taking one amp (Crate V18) and trying to make another amp (18 watt) out of it.
I wanted to use Cliff jacks, but there is real estate problems with both the chassis and the combo cab. I just could not see a way to make the Cliff Jacks fit.
Thanks Again.....I will try some of these suggestions also.

[epis]

You're Welcome , and good luck with your amp

[Phil_S]

Hired: when you hang the jacks in the air for a test, if you find that's part of the problem, they make nylon bushing washers. These have a little lip that goes inside the hole and will insulate the jack. You may have to enlarge the hole. They look like this. http://www.aspenfasteners.com/Shoulder- ... 041-14.htm I get them in the loose screws aisle of the Ace hardware store. You might find them at the Home Despot, too.

[C Moore]

Hey Phil -
Thanks for the tip. I know Doug Hoffman sells or did sell shoulder washers for Switch-craft Jacks.
I will keep that in mind.
Unfortunately, I am still pretty wiped out from knee surgery. Will get on these suggestions ASAP.
Thanks Again