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**hesamadman** · 08-05-2013, 04:04 PM

** correction.... the 100k next to the .1uf capacitor is fine

**ReadyTeddy** · 08-05-2013, 04:20 PM

Post a schematic. Buy or borrow an oscilloscope. The rest will be easy.

**hesamadman** · 08-05-2013, 05:02 PM

1st preamp tube-

pin 1- 260 vDC
pin 2-
pin 3-
pin 4 and 5- 2.7 vAC
pin 6- 220vDC
pin 7-
pin 8-
pin 9 around 2.7 ACROSS BOTH pin 9 AND pin 4/5 I GET ABOUT 5.9 vAC

2nd preamp tube-

pin 1- 170 vDC when my lead touches this I hear a noise in the amp.
pin 2-
pin 3- around 2-3 vDC
pin 4 and 5- 2.7 vAC
pin 6- 319vDC
pin 7-
pin 8-
pin 9 around 2.7 ACROSS BOTH pin 9 AND pin 4/5 I GET ABOUT 5.9 vAC

3rd preamp tube-

pin 1- 234 vDC when my lead touches this I hear a noise in the amp.
pin 2-
pin 3-
pin 4 and 5- 2.7 vAC
pin 6- 220 vDC
pin 7-
pin 8-
pin 9 around 2.7 ACROSS BOTH pin 9 AND pin 4/5 I GET ABOUT 5.9 vAC

**nickb** · 08-05-2013, 05:23 PM

Originally posted by hesamadman View Post

** correction.... the 100k next to the .1uf capacitor is fine

As a generalization, measuring component values in circuit fraught with difficulties. Only do it if you fully understand the effect the circuit might have on the measurement.

The most common reason for builds not working is a wiring problem so
(1) check, check and then ask a friend to check again.
(2) check the right components are in the right place.
(3) Measure the DC voltages on all the preamp tubes as follows:
pin 1 to ground,
pin 2 to pin 3
pin 3 to ground
pin 6 to ground,
pin 7 to pin 8
pin 8 to ground

**loudthud** · 08-05-2013, 05:30 PM

I'll bet the input jacks are not wired correctly.

**hesamadman** · 08-05-2013, 05:36 PM

guessing third preamp tube isnt getting what it needs?

1st preamp tube-

pin 1- 260 vDC
pin 2- ~0
pin 3- 2.9
pin 4 and 5- 2.7 vAC
pin 6- 220vDC
pin 7- ~0
pin 8- 2.04
pin 9 around 2.7 ACROSS BOTH pin 9 AND pin 4/5 I GET ABOUT 5.9 vAC

2nd preamp tube-

pin 1- 170 vDC when my lead touches this I hear a noise in the amp.
pin 2- ~0
pin 3- 1.6
pin 4 and 5- 2.7 vAC
pin 6- 319vDC
pin 7- 170
pin 8- 180
pin 9 around 2.7 ACROSS BOTH pin 9 AND pin 4/5 I GET ABOUT 5.9 vAC

3rd preamp tube-

pin 1- 234 vDC when my lead touches this I hear a noise in the amp.
pin 2- 12 is this low?
pin 3- 41
pin 4 and 5- 2.7 vAC
pin 6- 220 vDC
pin 7- 13
pin 8- 12
pin 9 around 2.7 ACROSS BOTH pin 9 AND pin 4/5 I GET ABOUT 5.9 vAC

**eschertron** · 08-05-2013, 05:37 PM

Originally posted by hesamadman View Post

pin 1- 170 vDC when my lead touches this I hear a noise in the amp.
pin 1- 234 vDC when my lead touches this I hear a noise in the amp.

You've demonstrated the basics of signal injection. the small level shift when probing the plate (pins 1 or 6 ) of your preamp tubes is amplified by the rest of the circuit and you hear a 'pop'. I'm surprised you don't get a pop (or a hummy noise) when probing pins 2 or 7. you can use this technique - with or without refining it by using a function generator or audio source - to find the places in the amp where signal SHOULD pass but DOESNT. Use the schematic for the amp, and understanding where the signal path is, you can backtrack from the output section toward the inputs, ensuring that the signal is heard before and after each component in the path. And yes, sometimes the signal is riding on high DC voltages, so protect your test gear (and your life!) with a properly-designed decoupling circuit.

As ReddyTeddy says, post a schematic of your build, and you will get some great help debugging your amp.

**eschertron** · 08-05-2013, 05:50 PM

Originally posted by hesamadman View Post

pin 4 and 5- 2.7 vAC
pin 9 around 2.7 ACROSS BOTH pin 9 AND pin 4/5 I GET ABOUT 5.9 vAC

For the heaters, it is not usually beneficial to measure their voltages with respect to ground. Verifying that you have 6.3vac (plus/minus a few 1/10 of a volt) from pin 9 to pins 4 and 5 (tied together) then you've checked the heaters out OK. So 5.9vac is in the ballpark.

Note that this is a generalized "first pass" check, some problems may require you to investigate further.

Also some of your readings give a number without ac or dc. Be clear about this when posting. And be aware of polarity on the dc readings. I would expect pins 3 and 8 of V1 to be a few volts NEGATIVE. If pin 3 is 2.09vdc positive with respect to ground, that would be a very bad thing.

**hesamadman** · 08-05-2013, 06:01 PM

Originally posted by eschertron View Post

For the heaters, it is not usually beneficial to measure their voltages with respect to ground. Verifying that you have 6.3vac (plus/minus a few 1/10 of a volt) from pin 9 to pins 4 and 5 (tied together) then you've checked the heaters out OK. So 5.9vac is in the ballpark.

Note that this is a generalized "first pass" check, some problems may require you to investigate further.

Also some of your readings give a number without ac or dc. Be clear about this when posting. And be aware of polarity on the dc readings. I would expect pins 3 and 8 of V1 to be a few volts NEGATIVE. If pin 3 is 2.09vdc positive with respect to ground, that would be a very bad thing.

This is a similar circuit. It only mentions one negative voltage and it is in the output section. Do i still need negative voltages in the pre? And as far as AC or DC...the only AC im getting is from heaters and the rest is DC. Is this correct?

**eschertron** · 08-05-2013, 06:13 PM

Originally posted by hesamadman View Post

[ATTACH=CONFIG]24558[/ATTACH]

This is a similar circuit. It only mentions one negative voltage and it is in the output section. Do i still need negative voltages in the pre? And as far as AC or DC...the only AC im getting is from heaters and the rest is DC. Is this correct?

Yes of course - brain fart on my part. Pin 3 of a preamp tube (the cathode) is pulled a few volts positive by the action of the tube, and so makes pin 2 (the grid) a few volts negative in relation to pin 3 (see nickb's comments about measuring).

Your build will most likely be close to the chart provided. Don't be concerned at this point with small deviations. Values that are severely out of whack should direct your attention to verifying part values and wiring in attached components.

As you troubleshoot with finer detail, you will want to see AC signals 'riding on' the DC in the circuit; so both AC and DC measurements, if your meter allows selecting for each, will come in handy at some point.

**nickb** · 08-05-2013, 06:20 PM

Originally posted by hesamadman View Post

guessing third preamp tube isnt getting what it needs?

3rd preamp tube-

pin 1- 234 vDC when my lead touches this I hear a noise in the amp.
pin 2- 12 is this low?
pin 3- 41
pin 4 and 5- 2.7 vAC
pin 6- 220 vDC
pin 7- 13
pin 8- 12
pin 9 around 2.7 ACROSS BOTH pin 9 AND pin 4/5 I GET ABOUT 5.9 vAC

Pin 8 is wrong
(1) check your measurement
(2) measure the voltage between pins 2 and 3, and pins 7 and 8. NOT pin 2 to ground and pin 7 to ground - doing so will give you incorrect readings.

As eshertron says, you discovered the crude signal injection test. You should also have pops when you touch the pins 1,2,6 and 7 of V1 assuming volume is turned up so that narrows it down a bit. Did you do steps 'check the wiring' and 'component placement'? I would concentrate on volume control/tone stack correctness.

**hesamadman** · 08-05-2013, 06:22 PM

it looks as if my pre amp tube #3 is pretty far off. I should have around 40 vdc on 2,7, and 8. DO you have any idea why I dont?

**hesamadman** · 08-05-2013, 06:30 PM

I dont get anything between 2 and 3 or 7 and 8

**eschertron** · 08-05-2013, 06:45 PM

Originally posted by hesamadman View Post

it looks as if my pre amp tube #3 is pretty far off. I should have around 40 vdc on 2,7, and 8. DO you have any idea why I dont?

There are a lot of components that set up that phase inverter circuit. Verify the values of all of them, check for bad solder joints, and with the power off and the tubes pulled you can take some continuity readings across various parts of that assembly. If you post a schematic with part numbers (the one I pulled up did not have components numbered, and so is just about useless for a discussion like this) it will become easy to discuss the specific values and voltages in your amp.

To eliminate 1 easy fix, swap tube 2 and 3 and verify that there is no change in the readings that you get.

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Please help. Troubleshoot first build?!?!?

Please help. Troubleshoot first build?!?!?

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