Power but no sound

[PhatTele]

The trouble shooting continues.

I'm building a head version of the 18 Watt using the Mark Durham Head Layout, the Pedal Monkey schematic, and the GDS chassis/PT/OT.

MarkH helped me confirm that my connections for the Heyboer PT were correct. I also ended up moving the leads for the lamp as described in the layout so they are now connected to the two green 6.3 volt PT leads...like in a Fender tweed (no wonder the bulb filaments were vaporizing before ) The lamp now turns on properly without cooking the bulb.

In Standby the tube filaments all glow appropriately. With the Power cut on, the tubes all seem to be warm and wonderful. However, I'm not getting any sound. No hiss. No hum. Nothing. No bad smells either which is a good thing.

I checked all the leads from the OT. They seem to be correct. I noticed that on the layout the speaker jacks are not grounded. Is this correct? This seemed odd to me given my experience with Fender speaker jacks. So, I tried grounding the jacks. That didn't have any effect. I also tried bypassing the impedance selector (in case that was bad). That didn't have any effect either.

I'm just guessing now. I need a more methodical approach. Where should I be looking next? Any sound, even a squeal or hum would be good, then I would know that the amp can actually produce some noise.

Thanx!

[RossH]

The OT common can just go to the jack and everything will still work. Although most often grounding the common will reduce some noise.

Other than that, if you have no noise, period, I would start with the obvious (making sure the output plates are connected to the OT and the center tap is connected to B+). If that's cool then start checking if you have DC voltage on the plates, cathodes, and grids of all the tubes. Post what you find. Make sure all that stuff is OK.

After getting that data we can move to the next step based on this information.

Ross

[PhatTele]

Success!!

I took it over to a friend of mine who is an amp tech and we went through it. Everything was wired correctly, but no voltage was getting into the preamp. We backtracked and found that one connection, for no obivous reason, was preventing current from passing through. We cleaned up the connection, resoldered it, and now it works like a champ (or an 18 Watt to be more precise )

We played through it, but it was late so I haven't really had a chance to put the amp through it's paces. Meanwhile, our initial impressions are that it sounds great. The Tremelo is huge and deep (look out Link Wray!). This is probably because I ended up having to use a 10K pot for the Intensity (s/b 1K) and a 3M pot for the speed (s/b 2M) which was all I had access to.

I'll be playing it through either a 1x12 closed back cab with a Weber California or a 2x12 closed back cab with two Weber Chicagos. It should sound great.

I need to figure out how to post some pictures of the chassis. I ended up using lug terminal strips fixed to an epoxy board instead of an eyelet board or a board with turret connectors. It may not be as aesthetically pleasing as other methods, but the terminal strips were really easy to work with and everything is exposed...making trouble shooting all that much easier.

Thanks for everybody's help!

[Jason]

Tele,

Have you checked all electrode voltages, wiring, and grounding? Also, before you power the amp up again, check the continuity of the PT, switch, fuse, and cord. Unplug the amp, flip the power switch to the "on" position, and check for continuity across the hot and neutral baldes of the AC cord plug. If you get continuity, then variac the amp by ramping up slowly to wall AC voltage--check all electrode voltages while performing this operation. The reason for the Variac is so that you don't inadvertantly fry anything if there is a problem with components, etc. It also helps to isolate you and your amp from the raw AC from the wall.

I am assuming that you have checked your tubes, speaker, cord, guitar, fuses, etc. If not, check this type of stuff before you plug the amp in.

If you are getting proper electrode voltages, but there is still no sound, check for parasitic oscillations and proper AC signals. Go through each stage from back to front and verify that there is AC signal [sine] reaching each stage. Once you get to where things get cattywhompus, you know which stage is giving the problem. Also, if you don't own a scope, you can still diagnose the whole amp using a similar method with a mulitmeter set to DC/AC volts--depending on where you are in the amp. Use DC volts and check each plate, grid, and cathode of each tube and listen for "pops". Prior to doing this though, you should have already checked all of your AC, power supply, and output voltages.

Hope this helped a bit. If you want more clarification, let me know.

Jason

Jason

[Plexi]

"""I ended up having to use a 10K pot for the Intensity (s/b 1K)"""

I can say for certian.. you will run into problems if you keep the 20k pot in there.. When you do get a chance to fire up the amp for testing..try the trem channel..and turn the intensity pot.. I think you'll see what i'm talking about. You'll have to put the 1k pot in.. you might get by with the 3 meg speed pot..i haven't tried that to see what differences are..
Richie

[Plexi]

should have typed 10k.. typing in the dark here..

[sws1]

What do you mean by "listen for pops"? Are you saying that when mentioning DC voltage against ground, you should here a pop? Including all tube pins?

[PhatTele]

When we did the trouble shooting, we checked the voltages as we went along. It turned out that no voltage was getting to the first preamp tube. That's when we started back tracking through the power section and into the preamp to find the problem. There was a solid connection that, physically, seemed fine, but for some reason was not passing current. All we did was desolder it and resolder it. Then, it worked fine. Go figure. The voltages all now seem appropriate given what's marked on the schematic.

Re: Tremolo - The tremolo is VERY intense using that pot combination, but it's still actually pretty cool. Even though it's usable and cool, I'm going to keep an eye out for the correct components and replace them at some point.

Meanwhile, I've discovered some weirdness going on with the Tone pot of the first channel. When it's turned all the way off, I get a horrible squeal. But, when it's on, it works fine. This is today's project.

[Graydon]

Meanwhile, I've discovered some weirdness going on with the Tone pot of the first channel. When it's turned all the way off, I get a horrible squeal. But, when it's on, it works fine. This is today's project.

I put a small resistor (~390ohm) in line with the tone pot between the bottom of the pot and the cap. It simulates the pot being not quite off. Seems to work fine and I don't detect that it affects tone at all. It does stop the squealing.

HTH

[PhatTele]

Graydon - That was it!! Thanx!!

I had a 470 ohm resister lying around which I wired in series with the cap going to the bottom of the Tone pot. The squeal is gone and the amp is ready for gigging. What was going on there?

[Jason]

What do you mean by "listen for pops"? Are you saying that when mentioning DC voltage against ground, you should here a pop? Including all tube pins?

Well, I should clarify a bit--check out Pittman 3.0 or 4.1. You set your meter to VDC and probe the P,G,K pins on the tubes inorder to disturb the signal--which will create a popping sound. If you get a pop, that stage is getting signal. If you get no pop, that stage is not getting signal.

Jason