first build trouble... help please?

[smolder]

My first build (yea... probably should have been a kit)... have learned a ton... but am stuck.

The chassis and transformers came to me build... but sloppy and not my thing so I decided to start from scratch with a new board and new tube sockets.

Its a clone of a spitfire but with 6V6's. I did mod some components to accommodate the 6V6's. I also mounted the board 180 degrees from what makes sense... but will fix that later. And the line out has been disconnected for trouble shooting.

I have 5 volts on pin 4/5 of the 6V6. It powers up and all tubes light... but I get no sound. I have swapped out all tubes for known working ones. And have been over the schematic and layout a dozen times. Not sure what to do next. Any help (and critique) would be very much appreciated.

top layouts





main board






Chassis wiring





thanks for any insights in advance...

Mark

[cminor9]

Do you get any sound at all? What happens when you twist the knobs? What are the voltages on the + side of each filter cap? What are the DC voltages on the tubes plates? You might also want to explain what exactly you did to accommodate the 6V6 power section.

You say you have been over the board and layout a dozen times. Sometimes I find that I focus on the board and not as much on the other stuff like the tube sockets, vols/tone controls, etc. Did you go over all the connections to the non-board stuff?

Your board looks nice and neatly laid out, and it looks like you have stuff in the right places (can't see all of the values on the components though.)

Some recommendations:
* Twist the heater wires on the tubes, as this will cancel the 120hz hum. Give it a good tight twist so that the two wires intersect at roughly 90 degree angles. Putting one end of a pair of wires in a vise and the other in a drill chuck works well.
* In fact, twist any wires with 120hz AC on them, such as mains wires. I like to use a cable tie to keep em together, too.
* Then, mount the board and run the wires from the board to the various components. Try to keep the wires running to the grids of the tubes away from the wires running to the plates as much as possible, and where they do cross do it at right angles. Also, don't make the wires too long. Right now, you have a very "loose" build, if that makes sense. This won't cause the amp to not work, but will cause it to make noises you don't want it to make.

The general idea is that you don't want wires just running helter skelter, since wires carrying AC can cause hum and/or induce AC into other wires.

My recommendations won't directly fix the problem at hand, but might help ensure that when you do get this thing up and running your excitement won't be met with a loud hummmmmmmm. Plus, in the process of doing this you might uncover a bug.

In general, I like to keep a printed copy or two of the layout on my bench. I check EACH connection and mark it off. Do this a few times. I usually find something wrong this way.


Sorry if I am rambling...I am very tired from staying up till 3am last night working on my own matchless spitfire clone (funny co-incidence!) I'm building it into a tiny hammond reverb amp chassis.

Anyhow, post more details about the voltages and other info I asked for and I'll try to help.

[smolder]

Do you get any sound at all? What happens when you twist the knobs? What are the voltages on the + side of each filter cap? What are the DC voltages on the tubes plates? You might also want to explain what exactly you did to accommodate the 6V6 power section.

You say you have been over the board and layout a dozen times. Sometimes I find that I focus on the board and not as much on the other stuff like the tube sockets, vols/tone controls, etc. Did you go over all the connections to the non-board stuff?

Your board looks nice and neatly laid out, and it looks like you have stuff in the right places (can't see all of the values on the components though.)

Some recommendations:
* Twist the heater wires on the tubes, as this will cancel the 120hz hum. Give it a good tight twist so that the two wires intersect at roughly 90 degree angles. Putting one end of a pair of wires in a vise and the other in a drill chuck works well.
* In fact, twist any wires with 120hz AC on them, such as mains wires. I like to use a cable tie to keep em together, too.
* Then, mount the board and run the wires from the board to the various components. Try to keep the wires running to the grids of the tubes away from the wires running to the plates as much as possible, and where they do cross do it at right angles. Also, don't make the wires too long. Right now, you have a very "loose" build, if that makes sense. This won't cause the amp to not work, but will cause it to make noises you don't want it to make.

The general idea is that you don't want wires just running helter skelter, since wires carrying AC can cause hum and/or induce AC into other wires.

My recommendations won't directly fix the problem at hand, but might help ensure that when you do get this thing up and running your excitement won't be met with a loud hummmmmmmm. Plus, in the process of doing this you might uncover a bug.

In general, I like to keep a printed copy or two of the layout on my bench. I check EACH connection and mark it off. Do this a few times. I usually find something wrong this way.


Sorry if I am rambling...I am very tired from staying up till 3am last night working on my own matchless spitfire clone (funny co-incidence!) I'm building it into a tiny hammond reverb amp chassis.

Anyhow, post more details about the voltages and other info I asked for and I'll try to help.

Awesome... thanks Cminor9.

Funny... I have an organ amp (not a hammond) sitting here as a future project. Not sure what I will do with these big transformers... its a 6L6 set up.

OK... found a couple of minor issues and fixed them. Now I have hum... when the power comes on, but no sound. The whole thing is set up poorly frankly and will likely give me some hum. But I can re-thing the over all layout later.

I like the idea of marking off the layout and schematic as I go. I'll do that in the morning. appreciate the time you took.

Mark

[cminor9]

Funny... I have an organ amp (not a hammond) sitting here as a future project. Not sure what I will do with these big transformers... its a 6L6 set up.
Mark

I wish I had an organ chassis with the iron sitting around like that. Oh, the possibilities! Tweed Super 5F4! Well, that's what I have been drooling over.

[smolder]

I wish I had an organ chassis with the iron sitting around like that. Oh, the possibilities! Tweed Super 5F4! Well, that's what I have been drooling over.

I think I paid 120 on the bay for it. There were a bunch of hammonds there last week. a guy in minnesota breaks em down, removes the tubes and sells them. Do a search under electric guitar amplifiers for 'project'.

[olddawg]

I wish I had an organ chassis with the iron sitting around like that. Oh, the possibilities! Tweed Super 5F4! Well, that's what I have been drooling over.

Or something like this: http://cgi.ebay.com/VINTAGE-RAULAND-...d=p3286.c0.m14

[loudthud]

I have 5 volts on pin 4/5 of the 6V6. It powers up and all tubes light... but I get no sound.

That ain't right. You should have something around 340V on pin 4 and 0V on pin 5 of the 6V6s.

What's the value of the big 10W resistor? For 6V6s it should be something between 250 and 330 ohms. The cap connected across it should be 25uF, you have 0.22uF, but you can leave it until we get a sound to come out.

Here's a schematic I found. http://schematicheaven.com/newamps/m...s_spitfire.pdf

I don't see a choke. Did you leave it off?

How do your voltages compare to those on the schematic?

[smolder]

That ain't right. You should have something around 340V on pin 4 and 0V on pin 5 of the 6V6s.

What's the value of the big 10W resistor? For 6V6s it should be something between 250 and 330 ohms. The cap connected across it should be 25uF, you have 0.22uF, but you can leave it until we get a sound to come out.

Here's a schematic I found. http://schematicheaven.com/newamps/m...s_spitfire.pdf

I don't see a choke. Did you leave it off?

How do your voltages compare to those on the schematic?

Thanks Loudthud...

I reworked the components you mentioned... including the 25uF (though I am using a 20uF)... but will have to replace that 10w... right now it is 100 ohms. I think I have a larger one in that range.

That is the schematic set I have been working from.

I am using a large resistor for a choke for the moment. 1k 5w.

All of my vdc is higher... in the 380 range instead of 350. I am 'guessing' that might be the transformer I am using.

Here are this morning's readings on the preamp section:

V1 V2
1 375 380 vdc
2 2.1 1.9 mV AC
3 1.5 5.7 mV AC
4 3.5 v 3.55 v AC
5 3.51 v 3.55 v AC
6 374 379 vdc
7 1.8 91 mV AC
8 1.5 5.8 mV AC
9 3.55 3.51 VAC

[loudthud]

Hard to make sense out of your readings. I'm looking for DC volts measured to ground. The software for this forum doesn't like tables padded with spaces so unless you want to learn HTML or whatever it is, just put one tube pin per line. The resistor in place of the choke should get the amp going but the 6V6s will be running way too hot because of the low cathode resistor. You need something there between 250 and 1K at about 5 watts so we can find the problem and once we can get a signal through the amp, we can fine tune it. We'll just ignore the heater wiring as long as the tubes are glowing.

It looks like the 47K resistor in the V2 circuit isn't connected to ground. If this is the case you'll measure something like +5Vdc on both ends of the 47K with a tube plugged in.
　
V1
1 375 Vdc
2 2.1................should be very close to zero volts DC
3 1.5 Vdc
4 heater
5 heater
6 374 Vdc
7 1.8...............should be very close to zero volts DC
8 1.5 Vdc
9 heater
　
V2
1 380 vdc...............too high should be around 250Vdc
2 You won't get a valid reading
3 5.7 mV AC.............should get around +60 Vdc
4 heater
5 heater
6 379 vdc...............too high should be around 250Vdc
7 You won't get a valid reading
8 5.8 mV AC.............should get around +60 Vdc
9 heater

V3/V4 6V6
1 no connecton
2 heater
3 380 Vdc
4 380 Vdc maybe a little less than pin 3
5 0 Vdc
6 no connection
7 heater
8 +25 Vdc {depends on the cathode resistor}

V5 5AR4 or 5Y3 Use extra caution! Don't worry about this tube. It seems to be working because there is +380V in the amp.
1
2 about +400 Vdc
3
4 about 300 VAC
5
6 about 300 VAC
7
8 about +400 Vdc

Edit: I can see in your pics where the 47K is connected to the 220K resistors that go to the 6V6 pin 5 through the 1.5K and to the ground end of the 10W resistor but not to any other ground. Check your ground wiring for missing wires.

[smolder]

Awesome stuff loudthud... very helpful

stupid questions though... which is the cathode resistor? Is that the 10 watt cement one I have?

Thanks!

[loudthud]

stupid questions though... which is the cathode resistor? Is that the 10 watt cement one I have?

Yes, that's the cathode resistor for the 6V6s connected to their pin 8. V1s cathode resistor is the 1.5K and the cathode resistor for V2 is the 1.2K. The 47K is in the cathode circuit of V2 but it's called the "Tail" resistor.

[smolder]

The resistor in place of the choke should get the amp going but the 6V6s will be running way too hot because of the low cathode resistor. You need something there between 250 and 1K at about 5 watts so we can find the problem and once we can get a signal through the amp, we can fine tune it. We'll just ignore the heater wiring as long as the tubes are glowing.

Curious... I put a 256 ohm 5 watt in the place of the 100 ohm 10 watt. The vdc for the 6L6's went from 384 to 400 on pins 3 and 4. I think that is in the wrong direction, no?

[loudthud]

I was confused. Not sure why but don't worry just yet.

Did you see my edit at the end of post #9? Have the voltages on V2 pins 1 and 6 come down to about 250 volts?

Post the DC voltage you have now on V1...V4.

[smolder]

I did put a ground in for the 47k resistor. AND as I said... I put a 256 ohm resistor in place of the 100.

Reading now...

V1
1 391 vdc
2 0
3 0
4 3.57 v
5 same as 4
6 392 vdc
7 231 v
8 0
9 3.6 v

V2
1 396 vdc
2 .007 vdc
3 .001 vdc
4 3.6 v
5 same as 4
6 396 vdc
7 2.5 v
8 .9 vdc
9 3.6 v

V3 (power)
1 -
2 3.55v
3 402.6 vdc
4 402.8 vdc
5 .003
6 -
7 3.6 v
8 0

V4
1 -
2 3.56 v
3 402.9 vdc
4 402.9 vdc
5 .004 vdc
6 -
7 3.6 v
8 0

[loudthud]

Did you have tubes installed when you took those readings? Are the two preamp tubes 12AX7s?

What voltage readings on V1 are telling me:

Pins 2 and 7 should be connected together and both should be zero volts. What's going on here?

Pins 3 and 8 should be connected together and read about +1.5V, but both are reading zero volts. Was a good tube plugged in? The zero volt reading means either 1) they are connected directly to ground or 2) if they are connected to the 1.5K resistor, no current is flowing (as if no tube was plugged in). If a good tube was plugged in, they would read something like +3 or so volts if there was no current path to ground.

Pins 1 and 6 are reading what looks like unloaded B+. This is consistent with no tube plugged in or no current flowing.


What voltage readings on V2 are telling me:

Was a tube plugged in when you took the readings?

Pins 1 and 6 are reading what looks like unloaded B+. This is consistent with no tube plugged in or no current flowing.

Pins 3 and 8 are supposed to be connected together and should give the same reading. The resistors in your picture look like different values than the schematic. It looks like 1.5K and 24K. The amp should still produce sound with these values.

Pins 2 and 7 won't give meaningful readings when a tube is plugged in but both should read zero volts with no tube.


Please verify the following resistances to ground. Power off. Line cord unplugged. Caps discharged. If you don't know how to safely discharge the caps, search or ask for instructions.

V1 Pin 3 and/or 8... 1.5K Your meter may act strange because of the capacitor in the circuit.
V1 Pin 2 and/or 7... 68K
V2 Pin 3 and/or 8... 25.5K...48.5K if you have resistors like the schematic
V2 Pin 2 and/or 7... Something over 1 Meg.
V3/V4 pin 8... 256 ohms. Your meter may act strange because of the capacitor in the circuit.