Trainwreck express need help

[fugezii]

use 240v and measure the following values. Can someone tell me where the problem is? I don't know if it is normal.

[frankdrebin]

What about pins 3,6,8?

[pompeiisneaks]

that's very little data to go on to help 'find what's wrong'.

You are missing all the voltages for the preamp tubes except the anode of the first stage? Why? Where are the cathodes of both triodes and the anode of the second?

What actually is wrong? Description of what isn't working, and what you've tried to troubleshoot it may help as well. Have you tried chopsticking the amp to see if it changes things makes them better/worse etc?

High quality well lit photo's of the chassis may help as well.

~Phil

[wpaulvogel]

Really besides a lot of missing information, the power tubes are out of balance. V4 is weak compared to V5.

[fugezii]

Sorry, guys
I added the measurement,
The installation process was smooth, and he was able to start up normally a few days ago, but with noise. I tried to adjust by various methods. But after the adjustment, it can no longer continue to work, no sound, I don't know which part of the problem.

[martin manning]

Voltages don't look bad in general, but the idle current is way too high for 6V6's - 18W and 20.5W dissipation in 12W tubes :^0

As mentioned above, the output tubes are not well matched, but that won't stop it from making sound.

Don't rely on pin 5 voltage to set bias. Calculate dissipation as Pin 3 voltage x Pin 8 voltage. For V5, right now you have Pa = 427 x 0.0481 = 20.5W. Reduce Pin 5 voltage (make it more negative) to get dissipation under 9W. The Pin 3 voltage will increase when you do that, and you may have to reduce R29 to get more negative voltage.

The "no sound" problem is likely somewhere else, possibly a bad solder joint or accidental grounding of the signal.

[fugezii]

Voltages don't look bad in general, but the idle current is way too high for 6V6's - 18W and 20.5W dissipation in 12W tubes :^0

As mentioned above, the output tubes are not well matched, but that won't stop it from making sound.

Don't rely on pin 5 voltage to set bias. Calculate dissipation as Pin 3 voltage x Pin 8 voltage. For V5, right now you have Pa = 427 x 0.0481 = 20.5W. Reduce Pin 5 voltage (make it more negative) to get dissipation under 9W. The Pin 3 voltage will increase when you do that, and you may have to reduce R29 to get more negative voltage.

The "no sound" problem is likely somewhere else, possibly a bad solder joint or accidental grounding of the signal.

Thanks, man!

This is very helpful.
It is true that the volume potentiometer is grounded incorrectly.

How can I lower the voltage on pin 3. Can I replace 220k with 150k?

This is my first attempt to make a tube amp. I don't have much electronic knowledge.

Thanks again for your help

[RockinRocket]

The yellow Mallory cap is in the wrong spot.

Needs to couple v1 to v2. You have it placed between V1/A V2/B plates.

Check the schematic and go over the whole amp.

[fugezii]

The yellow Mallory cap is in the wrong spot.

Needs to couple v1 to v2. You have it placed between V1/A V2/B plates.

Check the schematic and go over the whole amp.

tanks man！
I will recheck all wiring.
It was originally soldered in the correct position, and I made a mistake when I changed it!

[martin manning]

How can I lower the voltage on pin 3. Can I replace 220k with 150k?

You want to lower the voltage on output tube pin 5's (make it more negative) to reduce the idle current. If you don't have enough range on the bias pot, then reduce R29 in the schematic, as mentioned above. If you have a 220k there now, replace it with a 150k and see if that works.

[fugezii]

How can I lower the voltage on pin 3. Can I replace 220k with 150k?

You want to lower the voltage on output tube pin 5's (make it more negative) to reduce the idle current. If you don't have enough range on the bias pot, then reduce R29 in the schematic, as mentioned above. If you have a 220k there now, replace it with a 150k and see if that works.

Thank you for your patience and guidance.
I replaced 220K on R29 with 150k today, but there was a whistle after the power was turned on. I replaced it back. Then I tried to replace the old RIFA and ROE capacitors and adjust the bias resistance, which worked well. The 6V6 on V5 is no longer overheated, no longer a bright red color! Then I did my measurements, which seemed normal, but there was still too much noise bothering me.

[martin manning]

Those voltages look better, but the dissipation is still too high: 0.0392 x 400 = 15.7W. You need to get that down to about 9W by making the bias voltage on Pin 5 more negative.
I don't understand how the plate voltage (Pin 3's) has dropped since last time, and even more since the time before that. Did something else change? Maybe the AC line voltage is lower?
The whistle you heard may be an indication that you have the output transformer plate leads reversed. I would try swapping them and see what happens.

[fugezii]

Those voltages look better, but the dissipation is still too high: 0.0392 x 400 = 15.7W. You need to get that down to about 9W by making the bias voltage on Pin 5 more negative.
I don't understand how the plate voltage (Pin 3's) has dropped since last time, and even more since the time before that. Did something else change? Maybe the AC line voltage is lower?
The whistle you heard may be an indication that you have the output transformer plate leads reversed. I would try swapping them and see what happens.

I adjusted the transformer input wiring from 220v to 240v. And adjust the bias potentiometer to the limit, the voltage of pin 5 is still not low enough, I will try to install 200k on r29 later, and then detect the voltage. The whistle is caused by the inversion of the output transformer. After the voltage is "normal", I will order a better set of tubes to try to eliminate the noise. Thanks again.

[martin manning]

You need to make R29 smaller to get more negative voltage at the bias pot.

[fugezii]

You need to make R29 smaller to get more negative voltage at the bias pot.

I got this!
I changed the R29 to 150k and adjusted the bias potentiometer. It is now down to 9W (0.0214*410=8.774; 0.0186*410=7.626), which is the latest reading. I added shielded wire and 820R to V1 pin 2, everything is so beautiful! The noise is in a reasonable range, thanks to all those who have helped and guided me! You guys so cool!