Tweedle Dee Dumble Champ

[DucDone]

Hi. I have been building a Dumble Tweedle Dee Champ amp. Now finished it makes no sound, except scratch sounds on the preamp/PT tubes, and a very low noise when touching the jack tip.
I get voltage on all parts that should have and I have changed the filter caps, many of the resistors, looked closely on the input jacks and changed the tubes.

The OT wires I have connected the 0v to the 6v6 tube and the 8k to the rectifier. I have connected the 5v and 0v to the rectifier.

This looks like a straight forward build, so I am a bit puzzled?
Any immediate ideas on what to look for next?

 

[D'tar]

Now finished it makes no sound, except scratch sounds on the preamp/PT tubes, and a very low noise when touching the jack tip.

This is good sign

Any immediate ideas on what to look for next?

Yes! pictures of your input jack wiring please!

Edit: May as well give those voltage readings also.

 

[Wally]

DucDone, here is one of the oldest tests for any audio amplifier. Test plate voltages staring with the output..lthat 6V6. You should hear a pop through the speaker when you make contact for the test. If not, then the output section is not processing signal. If you hear a pop, move to the driver plate....the pop should be slightly louder. Same ting here....the lack of a pop 8ndicates a failure in that area. If there is a pop, then test the input preamp stage. This should be the loudest pop.
Makeup a voltage chart and share that.

 

[rangercaster]

DucDone, here is one of the oldest tests for any audio amplifier. Test plate voltages staring with the output..lthat 6V6. You should hear a pop through the speaker when you make contact for the test. If not, then the output section is not processing signal. If you hear a pop, move to the driver plate....the pop should be slightly louder. Same ting here....the lack of a pop 8ndicates a failure in that area. If there is a pop, then test the input preamp stage. This should be the loudest pop.
Makeup a voltage chart and share that.

Listen to Wally...

If he doesn't know the answer, he will admit it ...

In most circumstances, he knows...

 

[DucDone]

V1:246v pin 1, pin6 359v, pin8 283v.
V2: plate 406v, grids: 390 & 240v.
B1: 405v.

 

[Wally]

DucDone, what about the Pops! ? Did you hear anything when taking these voltages? The voltages are not good, ime. There is no way you should have 283vdc on a cathode of V1. What about the pin 3 cathode? The plate voltages on V1 are way high. You have some basic problems here.
Power tube ‘grids’....there are two there. I will assume that there is 390vdc on pin 4 which is the screen grid. The control grid, pin 5, should not be seeing that voltage you give us.
Is there a schematic for this build? In looking for some kind info I found this thread on a build. He gives some voltages that are more in line with what one would need to see. Note the two voltages in the 180VDC range and the 1.51vdc.....rose are the plates and the cathodes for V1. The 381vdc, 336vdc, and 22.9vdc are the plate, screen grid and cathode on the 6V6.
https://ampgarage.com/forum/viewtopic.php?t=25885

you need to check your power rail....why is it not dropping voltages for that V1? You need to understand why the cathodes of V1 are showing such a high voltage. What is the 240vdc on a grid of the power tube? Is that pin 5? If so, that coupling cap is not doing its job???? What is the cathode voltage on pin 8 of the 6V6?

Fwiw, a voltage chart is someht8ng each of us should know how to make. It is a simple th8ng, and its simplicity helps us to quickly and easily understand and relate to the voltage info.

Ex: Using that Amp Garage amp
Tube Pins. 1. 2. 3. 4. 5. 6. 7. 8. 9
12AX7s. 187. —- 1.51 Heaters. 183. - 1.51. Heater

6V6. - - 381. 336. 22.9. - - 22.9

if one does not want to make a chart, then
12AX7
P1- 187, P3-1.51, P4/5-3.15, P6-183, P8-1.51, P9-3.15

or...do what the poster at the Amp Garage did, which assumes some tech understanding without going into direct identification.

 

[radiocaster]

V1:246v pin 1, pin6 359v, pin8 283v.
V2: plate 406v, grids: 390 & 240v.
B1: 405v.

Way too much. You should check the resistors in the power circuit. You might need to put ones with higher resistance. What wattage are they?

Possibly you blew the 12AX7 as well. Quite a few 6V6s would not be able to withstand that either.

Or maybe your transformer just puts out too much juice.

 

[D'tar]

Imo... you have work to do before firing the circuit up again. Your voltages if accurate are way out of line. Check the schematic and ohm your cathodes to ground. You should be able to know what readings to expect. Nfb will throw off some readings. I recommend disconnecting nfb until all else is right.

 

[DucDone]

Hi guys, solved the problem, In layout the cathode for the power tube doesn't show a ground. Put it in, and there it was. Thanks a lot for great help.

 

[D'tar]

That's the DUmble super secret virtual cathode connection. There's virtually no connection! LOL..

Glad you got er goin!

 

[Wally]

DucDone, that would have been quickly revealed with a complete voltage check/chart. Kudos on finally finding it. What led you to that cathode?

 

[radiocaster]

DucDone, that would have been quickly revealed with a complete voltage check/chart. Kudos on finally finding it. What led you to that cathode?

Maybe D'tar's post?

 

[Wally]

Maybe D'tar's post?

yes, D’tar and I had been suggesting a full voltage chart/check from the beginning....posts,2 & 3. My post #6 was the first to note that one would need to know that cathode voltage at pin 8 of the power tube. That voltage had not been read up until that point. My question in post #11 was an enquiring into whether or not a voltage test revealed the lack of a grounding of that circuit or whether the problem was found by eye??? The point of my question in post #11 was that the problem would have been found at the first application of voltage to the circuit if a voltage check/chart had been done at that time. Such a check, with or without making a written chart, is imho a necessity.

 

[Dan_Pomykalski]

Hi. I have been building a Dumble Tweedle Dee Champ amp. Now finished it makes no sound, except scratch sounds on the preamp/PT tubes, and a very low noise when touching the jack tip.
I get voltage on all parts that should have and I have changed the filter caps, many of the resistors, looked closely on the input jacks and changed the tubes.

The OT wires I have connected the 0v to the 6v6 tube and the 8k to the rectifier. I have connected the 5v and 0v to the rectifier.

This looks like a straight forward build, so I am a bit puzzled?
Any immediate ideas on what to look for next?

Looking at just the layout, how is this different than a Fender Champ?

 

[D'tar]

Minor.....

NFB&Filtering

 

[Peegoo]

Glad you found the issue.

That amp would be much safer if the hot lead from the AC mains goes through the fuse first before it goes to the switch. The reason is if the switch fails in a dead short to chassis, the fuse cannot prevent the amp from catching fire.

 

[DucDone]

https://www.tdpri.com/threads/dumble-tweedle-dee-mods.771618/