problems with my amp...

[distorted_frequency]

I'm having problems with my build, the voltages on my power tubes isn't correct and channel 2 doesn't work. channel 1 works but its very quiet. i looked over the layout a 4 times and it seems OK. if needed i could post a pic of the amp.

i dont know how to attach the schematic, its a pdf.

thanks a ton

rob

[defaced]

Hit reply, and below the area where you make your post, there's a section titled "additional options". Hit the "manage attachments" and use that to upload your pdf.

[distorted_frequency]

cool thanks

[loudthud]

What voltages seem wrong? The layout is not as clear as it should be. One problem I see is the connection of R55 and R56. They should probably go to the terminal strip where they would connect to the 290V line.

Did you get the Hammond 260E to sub for the power transformer? I saw your post on some German Forum. How did you wire it up?

[distorted_frequency]

In the "instruction manual" it ses that I should be getting 35mv at R51 and R52, I get nothing, (I thing I may be measuring wrong). all other voltages are correct.

I fixed my problem with the channel 1 (bad solder joint) but i still get no sound from channel 2, I think I may have a faulty switch, I will replace it tomorrow and see.

This is my first amp build. I'm glad that I got the amp semi working without causing any parts to burn up, so I'll consider this a success thus far.

as for the transformer situation, I just used the transformer that came with the kit and got a separate step up transformer that plugs into the wall. I figured I'd be better off to build an amp first before I start changing stuff around.

[PRNDL]

I should be getting 35mv at R51 and R52, I get nothing, (I thing I may be measuring wrong). all other voltages are correct.

That's the bias for the output tubes. If the amp works, then you must be measuring wrong.

The most obvious is most meters need to be set to a low voltage scale. 35 mV on a 450V scale would show up as zero.

Once you get channel 2 working, you'll want to set the bias by changing VR9 while measuring the voltages at R52/2.

[distorted_frequency]

ok, i was measuring wrong, thats all good. i still cant get channel 2 working. i can hear it really really quiet when i switch to it but its a whisper when the volume is all the way up.

any tips for hunting down the problem? i looked at the schematic/layout for another hour and i still cant find an issue.

[PRNDL]

i still cant get channel 2 working. i can hear it really really quiet when i switch to it but its a whisper when the volume is all the way up.
any tips for hunting down the problem? i looked at the schematic/layout for another hour and i still cant find an issue.

The simplest tip is to listen for the loud clicks that occur when you touch the test probe (for your DMM) to measure voltages on the preamp tubes. You should hear them when measuring the anode (pins 1 and 6 on a 12AX7), cathode (pins 3 and 8) and grid (pins 2 and 7) voltages.

If you hear clicks, move backwards through the circuit until they disappear, which tells you where the problem is.

The most common scenario is to hear the clicks at the first preamp grid, which means the input jack is wired incorrectly (it happens all the time!).

Does that make sense?

[Enzo]

First thing I would check is the wiring on the channel switch. If you get it wrong, one of the channels would still work, but switch to the other and the two preamps get connected together and nothing to the power amp.

[distorted_frequency]

i still can't figure it out. i cant even see the signal path, theres too many things in parallel for me to systematically check back from the power amp.

there is one section of the amp that doesn't pop when i test it: C18, C19 , and C20. also should it pop when i check the tone controls? i ask because it doesn't.

i don't understand electronics enough to trouble shoot this thing, I'm ready to throw it in the trash! I quit.

[distorted_frequency]

ok, i think i can find out for sure if its my tone stack by jumpering over it. will this hurt the amp?

[distorted_frequency]

i definitely pin pointed my problem, V3 is the culprit, i hope i mesured the pins again and heres what i got:

1: 225v
2: 107v
3: 107v
4/5 and 8: 7v
6: 0, it should be 110 tho right?
7: 0

i measured all pins to ground except 4/5 to 8. is it a bad tube?

[Bruce / Mission Amps]

i definitely pin pointed my problem, V3 is the culprit, i hope i mesured the pins again and heres what i got:

1: 225v
2: 107v
3: 107v
4/5 and 8: 7v
6: 0, it should be 110 tho right?
7: 0

i measured all pins to ground except 4/5 to 8. is it a bad tube?

With a quick look, Pin 2 should have nearly zero volts, as pin 7.
Pins 4 and 5 should only have 3 or so volts of filament voltage on them and not tied to 8.

Pin 6 should be 110v and pin 8 should be 1 volt or so.
8 can't have 8 volts unless it is wired wrong or tied to the filament string through a DC source for hum control...

[distorted_frequency]

its wired the same as the schematic, what do i need to change? Also, some of the resistors(R12, R13, R14, R31) on the socket are not reading the same value as when I put them in they are less now, they all read about half of what they should. i got new parts so i will replace them.

[Paul P]

its wired the same as the schematic, what do i need to change? Also, some of the resistors(R12, R13, R14, R31) on the socket are not reading the same value as when I put them in they are less now, they all read about half of what they should. i got new parts so i will replace them.

Do you mean with the resistors installed in the circuit ? They could easily
read less than their value if there are other resistances in parallel to them.
This is normal. You have to unsolder and lift at least one lead to get a proper
reading.

Paul P