18w Tremolo issue...

[SleepLess]

Hi guys!
Well, you're now getting used to my builds that look good but don't work...  Here's one more for you guys.
I have just finished a 1974 build (GDS chassis and trannies, the guts are sourced from other various parts, board from Brian Haberman) and here are the symptoms:
- Normal channel works perfectly. Loud and good sounding as it should.
- Tremolo channel works but the tremolo effect doesn't, either on the manual mode or with a footswitch plugged in
- The second thing is that the tone knob on this channel acts as a hum maker and when on 10 it completely turns off the signal. I mean, if the volume is on 10 and the tone is on 10, the amp doesn't work. If I roll back the tone to 9 then it's real loud and hummy. Ain't that strange?
- This 1974 comes with a LED/switch for the tremolo effect. The LED lits up fine despite the fact that the tremolo effect isn't there...

I have retraced my wiring multiple times. I have rechecked my component values multiple times. It all seems good to me, but obviously, it's not. I need you guys.

Here's the Voltage chart (VDC) I have on this thing, with power ON and standby ON, all tubes in and 240V wiring (I'm in the EU, wall voltage at home is 228V):

PIN        V1        V2        V3                              V4/5                            V6
1          146       213       99                                                             289(VAC)
2          0           55        00.4
3         1.145      80.6     1.016                          11.05                          337
6          144       209       145-179
7          0          55         -0.09/-0.500 (2V range)                               325/323   289(VAC)
8         1.14       80.3      1.2   
9                                                                   317

The necessary gut shots to help you:













Thanks a lot guys! 

[phsyconoodler]

Can't see enough in those pictures and they are too dark.Concetrate on the trolo oscillator tube and the foot switch jack are.
  Hoffman says:" if it was wired right it would be working"

[HotBluePlates]

Verify the wiring indicated on the attached photos. Intensity pot wiring is incorrect; see this layout.

Do yourself a favor and unhook the manual switch from the footswitch jack for now. See if hum goes away.

Triple-check that your underboard wiring connects the proper turrets.

There may be other problems, but these items jump out at me.

[SleepLess]

OK thanks, I will try this other layout. This is actually the one I followed... I didn't think it would lead me to problems... This is taken from the GDS 18w instruction manual. The thing is that this is page 30. Page 25 shows another layout... Looks like I'm gonna have to undo some connections...

[SleepLess]

OK. I have ruled the tubes out by replacing each of them one at a time.
So far I have rewired all the wires on the pots side of the board. I still have the same issues.

I have noticed that my layout puts the wires on pin 7 whereas on yours it's on pin 2 and vice versa...
I'm off to the tubes side now...

Damn amp. 15 hours to build it, 15 hours to debug it and counting... 

[SleepLess]

Do yourself a favor and unhook the manual switch from the footswitch jack for now. See if hum goes away.

Just did that and the hum went away... I don't know what that means. I was supposed to solder a 390ohms resistor across one of the LED legs and pin 4 ov V1 but I only had a 330ohms carbon comp... I thought it was OK since the resistor just prevents the LED from receiving too much current.

So the amp is now silent but of course I don't have any tremolo effect even with the footswitch... What would you advise? 

[SleepLess]

OK guys. I have redone all my wiring as per the layout you provided. The amp emits loud extraterrestrial noises. I'm think I have a bad componenet somewhere but I don't know where... I need you guys!

[SleepLess]

I have replaced the 3 tremolo effect .01 ceramic disks, to no avail...

[Willabe]

I had problem with my bias very trem on a 5G9 I built. I did get it working but I never did figure out what was wrong.   

Doug and a lot of the guys here print out a copy of the layout drawing and go through it wire by wire, part by part with the amp in front of them and a marker. Cross out each wire, part, 1 by 1, after confirming it's correct. Without using a marker it's easy to miss something.


                   Brad     

[SleepLess]

OK, I'll do that then. In the meantime, the newest pictures, with good lighting this time:

[Willabe]

Well, you're now getting used to my builds that look good but don't work...

FWIW and it's just IMO, but you really do some of the nicest, cleanest work that I've seen. So I'm thinking        hmm....  that maybe you are having build problems not in wiring/soldering up the amp, but in/or your following your drawings. Either your drawings have a mistake or 2 or your not following your drawing exactly. We all can and sometimes do make these same mistakes, certainly I do.

HBP said not long ago that he thought part of what the difference is between a newer builder and more experienced builders is that a more experienced/seasoned builder will know what to look for if the amps not working at start up and will be able to find it and fix it much faster? (I think I got that right?)

I did 3 scratch builds in the last year. All with my own eyelet/turret boards/layout. I used Sch to do my drawings, both the schemo and layout, to scale. I spent A LOT of time on them and still had a few mistakes. I choose to spend more time on the drawings hoping that I wouldn't have to spend any time tracking down any mistakes. As I wired them up, I crossed off each part/wire on the layout with a marker, 1 by 1.

I forgot the grid return R's on the output tubes in the 5E3 and Fender stand alone reverb. Left them out of the drawings, but I found them quickly after I fired them up. Now I know darn well that an output tube has to have a grid return R. And I still missed them.      

On the 5G9 Tremolux the trem wouldn't work and I re-checked that part of the circuit 12 ways to Sunday against both of the drawings. The trem pots speed and depth controls were wired backwards, but that was a mistake in my drawing.     I still think other than that, it was wired correctly and never did find what was wrong. I had chiped the term tube ceramic socket and after I changed it out for a new 1 it worked.

FWIW, I've seen a # of guys here have a problem with the trem on a new build, including myself.       I don't know why this is. It's realy not a complex circuit, it's got a few parts in it, but.....      

I know you'll find what's wrong, just want to help encourge you.


                 Brad      

[SleepLess]

Thanks a lot Brad! That's very kind of you!

Unfortunately I spent 6 hours on it today, rewiring stuff, trying this and that and I haven't found what's wrong yet. Things have even got worse since I can't even flip the manual/footswitch switch to the footswitch position anymore or the amp emits a loud loud squeal that resembles a large boat's horn, pretty much like the Titanic's call when it left Southampton...

My wife even asked me today if I had built a police siren or a guitar amp  ... This noise is unbearable, I can't even let the amp ON for two seconds because of the loudness of that honk.

I'm desperately lost and I haven't got a clue about what I should try now. No more tests come in mind... You are right Brad, the more I build amps the more I realize that a real good builder is not reckoned by how well he builds, but by how fast he debugs... 

I have:
- Rewired the pots and tubes and grounds.
- Ruled out the tubes.
- Measured all my resistors.

I may have a bad cap somewhere but I don't have anything to test them, besides replacing each of them individually one at a time i.e...

[Willabe]

Things have even got worse since I can't even flip the manual/footswitch switch to the footswitch position anymore or the amp emits a loud loud squeal that resembles a large boat's horn,

Somethings wired wrong. Go back and look at what you changed. IIWM, I'd give it a rest for a day or two and then take another shoot at it. Make sure your layout drawing is correct and then use it with a marker as you go through the amp again.

You are right Brad, the more I build amps the more I realize that a real good builder is not reckoned by how well he builds, but by how fast he debugs...  

HBP said that as I pointed out.

I may have a bad cap somewhere but I don't have anything to test them, besides replacing each of them individually one at a time i.e...

Yes you do. If it's a blocking/coupling cap, if it's good it will block any dcv from one side to the other. Look for dcv on the other side with your meter. If you find dcv the cap is bad.


                  Brad      

[HotBluePlates]

Do yourself a favor and unhook the manual switch from the footswitch jack for now. See if hum goes away.

Just did that and the hum went away... I don't know what that means. ...

It means the current for the LED to indicate your manual switch is on is sourced from the filament wiring... That gives a good chance of placing hum right next to the hot lead of the footswitch, which could pass hum along to other parts of the amp.

I haven't checked over the layout you linked, but I was looking closely at the layout and schematic in the Hoffman Schematic Library... and they matched quite well. Seems curious that there is different control wiring in the layout you had available. 

You'll have to triple-check the wiring and components, wire-by-wire and component-by-component while comparing to the schematic. Don't put lots of faith in a layout cause they can be wrong.

You'll eventually find the wiring error(s).

[SleepLess]

OK gonna rewire everything and strictly use this layout:



Can you confrm that this is 100% perfect? It's the same guy who made the one you posted earlier but with a later update.
Gonna use a floating buss bar as well...

Thanks!

[SleepLess]

Hi.
The amp has gone through a whole rebuild. I took out the board, unsoldered the pots ground bar, unsoldered all connections on both sides of the board. I unsoldered the underboard connections and installed them on top of it for a clearer reference.

Don't ask me what was wrong but the amp works. I'll go through all the tests tomorrow but I turned all the knobs up to 10 on both channels with a strat plugged in and the amp works, the tremolo as well, and it's quiet...

The only thing I suspect is a bad input jacks connection, but I'll never know 100% what was wrong on that one... This amp represents to me the biggest loss of time for the smallest lesson...

Thanks again for all the help guys. I'll post a picture of the newer amp tomorrow. You'll see it's a whole rebuild with a floating buss bar and stuff. I can hardly believe it's the same amp myself...

I'm starting the most complex build since I started amps building this weekend: a blackface super reverb replica... Damn... There's a tremolo in it... 

[Willabe]

All right!       

I'm starting the most complex build since I started amps building this weekend: a blackface super reverb replica... Damn... There's a tremolo in it...  

                             It'll be fine.


                        Brad                    

[tubeswell]

Don't ask me what was wrong but the amp works. I'll go through all the tests tomorrow but I turned all the knobs up to 10 on both channels with a strat plugged in and the amp works, the tremolo as well, and it's quiet...

Probably a mis-wire somehow. When I build a complex circuit, I use a hi-lighter pen to mark off each link in the circuit on the schematic and layout as I assemble it.

[bnwitt]

From reading this thread I think there is a distinct possibility that the orginal layout had an error in it.  It's always best to use a layout that has been proven correct.  Where did you get the original layout you used?

The attached layout is the Richie's improved tremolo layout that I revised with corrections and have used several times to build the 18 watt.  Also attached is the turret board layout, last revision of the original amps schematic and a voltage chart.  This layout works great.  I know the 18 watt site has been down for a while so save these files on your computer in case it never comes back or dissapears again.

Edit:  It appears the intensity control is wired incorrectly in that GDS layout.  That blows me away.  Graydon knows the amp better than anyone.  He taught me all I know about it for sure.  It just goes to show we all make mistakes and it doesn't matter how many proof readers there are they can get into print.

[phsyconoodler]

It'a all about lead dress.I had a thumping,squealing 18 watt trem in the other day that a guy built from a Weber kit.I had to rearrange everything in the tremolo circuit and had to add shielded wire to the footswitch jack as well to stop the thumping and the noise.
 Richies layout works perfectly almost every time.Usually it only takes a chopstick to find the offending thump in the trem if you follow Richies layout.
 However,I have built one with Trinity's layout too and did not have an issue.It was a kit.
 Weber's kit layout is funky!

[SleepLess]

Absolutely. 18 watters are definitely very demanding about lead dress... A 1/4 of an inch can make a difference...
Thanks guys!

[HotBluePlates]

Another tip:

I'm guessing from your pictures that you didn't sand the back of your Alpha pots. Or, if you did, you used an iron smaller than 40w.

You know how solder wicks into wiring and down turret holes when you get the wire/turret hot enough? The soldering to the back of the pots doesn't look like it achieved that kind of "wetting" action. The pots often have some kind of coating that prevents good soldering, and needs to be sanded/filed off. If you do that and have a hot iron, the solder will flow down onto the pot's surface. I think I have a 60w iron with a huge copper tip for such chores.

The test I used to do to confirm good solder joints on pots and the chassis was to use a large screwdriver on the solder blob like a chisel. If the solder joint is bad, it doesn't take much force before the whole solder blob pops off the surface in one piece. A good solder joint won't come off.

This won't make/break your build, but was a detail I noticed.

[SleepLess]

I forgot to post pictures of it but the buss bar across the pots is gone anyway. But it was well soldered. They had been sanded. The amp now has a floating ground bar atached to the board. Newer style. Played the amp yesterday for two hours. No problem, great sound.

By the way bnwitt would you also have the best possible layout and documents on the 18w TMB (Non master-volume)? I'd be interested in that one...

[bnwitt]

Why yes indeedy I do have the TMB files.  They are attached.

[bnwitt]

And while we're at it, here are the files for the 36 watt version of the TMB as well.  The board drilling guide was made to use in a hammond chassis so it might be a little fat for a small chassis.  I've added a gut shot photo of the last one I did in a Hammond chassis

[bnwitt]

and here are a couple of photos of the chassis of that 36 watt.  As you can tell I used a Vox style PT and a MM OT and choke on that amp.  It is a very sweet sounding amp still with the original owner.  It was a head amp of course and boy was it sensitive.  I had to put an AL shielding plate that came with the Hammond chassis under the bottom before putting it in the cabinet to prevent massive squeal from the 4X12 cabinet underneath.  With the plate in place it was dead quiet.