LinkBack URL
About LinkBacks
Reply With QuoteOh, stop blubbing.Does the pilot light come on? Do all of the tubes light up? Any sound at all from the speaker? (Humming, hissing, etc)
ok....so I've spent the last 3-4 hrs re-doing everything
I made sure all the nodes on the board is good, made sure every joint is solid, placed a layer of insulation under the board.... I've shortened all the wires and made it look neat....
All hopes are high, plugged it in and got nothing ......
I'm about to burst into tears......
Oh, stop blubbing.
"Enzo, I see that you replied parasitic oscillations. Is that a hypothesis? Or is that your amazing metal band I should check out?"
pilot light comes on
tubes all glow !
no sound at all
Do you have a voltmeter so we can check a few first order things, like determining if the tubes are biasing up?
Measure the DC voltage on the cathodes of both triodes and the power tube to see if there is anything working.
Not important yet, unless you accidentally grounded the signal path, but your shielded audio cable from the volume pot is grounded incorrectly for most current schemes.
Originally Posted by Bruce / Mission Amps
Yep, ok but which pin do I measure? and do i measure to ground?
Thx!
Has your voltmeter arrived yet? (as suggested in the telecaster forum, you need to provide all the idle voltages of the filter cap nodes, plates, screens, grids, and cathodes, and also check the DC connections with your R-meter for continuity)
Building a better world (one tube amp at a time)
Sorry to start with the obvious but have you verified the speaker is working?
"So, for my small experience in the trade I would think that killing customers is, at the very least, bad for business." -Chuck H
Disclaimer: "Take my advice; don't listen to me"-Neil Young. "I'll lie again and again and I'll keep lying; I promise"-Henry Rollins.
Ok I started taking voltages with the new meter
from left to right on the turret board
16uF cap : 357V
8uF cap : 184V
8 uF cap : 158V
25 uF cap : 7.55V
node between 1.5k and 22k resistor : 0.77V
0.022uF cap : 102.5V
0.022uF cap : 93.4V
25uF cap : 0.965 V
So seems like some are different to what weber suggests in the diagram
yes I did that too
Here are my findings
What (dropping) resistance have you got between the 16uF and the 8uF filter caps? The Fender 5F1 schematic says 10k (but you could easy halve that). The screen voltage could be a wee bit higher. (you want about 300V there) Or did you put the 22k in there by mistake? (instead of the 10k?)
Check that the dropping resistor connecting to this cap is 22k. (160ish is kinda low - You want about 250V there)
This is way too low. You should have about 18-19V. Check that you have a 470 Ohm cathode resistor in parallel with the 25uF cap.
This is too low as well. This should be about 1.5V. This may come right when you check/correct the the dropping resistors in the supply rail
THese are a bit on the low side, they want to be around 150V each. This should come up when you check/correct the dropping resistors in the supply rail
Again this is low. You want about 1.5V here (same at the other pre-amp cathode resistor)
Double-check that you have the correct supply resistors in the filter cap chain.
Double check that you have all the correct connections in the signal path - input to grid of V1, plate of V1 to coupling cap and then to input of Vol pot, wiper of vol pot to grid of V2, plate of v2 to coupling cap and then to grid of 6V6. test the connections for DC-continuity with your R-meter
Refer to the layout below
Last edited by tubeswell; 06-22-2012 at 09:24 AM.
Building a better world (one tube amp at a time)
Can you post some decent resolution gutshot pics of the chassis?
Building a better world (one tube amp at a time)
Sorry I dont know how to comment between a qoute so I will just bold them :P
ok I'll double check with that diagramWhat (dropping) resistance have you got between the 16uF and the 8uF filter caps? The Fender 5F1 schematic says 10k (but you could easy halve that). The screen voltage could be a wee bit higher. (you want about 300V there) Or did you put the 22k in there by mistake? (instead of the 10k?)
The resistor across there is 9.96k so I think its right
Check that the dropping resistor connecting to this cap is 22k. (160ish is kinda low - You want about 250V there)
That cap is 21.7k so I think its ok too
This is way too low. You should have about 18-19V. Check that you have a 470 Ohm cathode resistor in parallel with the 25uF cap.
the cathode resistor is 466 ohms
This is too low as well. This should be about 1.5V. This may come right when you check/correct the the dropping resistors in the supply rail
THese are a bit on the low side, they want to be around 150V each. This should come up when you check/correct the dropping resistors in the supply rail
Which one is the dropping resistor?
Again this is low. You want about 1.5V here (same at the other pre-amp cathode resistor)
Double-check that you have the correct supply resistors in the filter cap chain.
Double check that you have all the correct connections in the signal path - input to grid of V1, plate of V1 to coupling cap and then to input of Vol pot, wiper of vol pot to grid of V2, plate of v2 to coupling cap and then to grid of 6V6.
Refer to the layout below
The heater wire doesnt look the same in the layout....
If you're planing on building more amps... get use to it. ;-)
I see that you've probed some stuff in the preamp. Here's some thoughts about that. You state that you get noting, I take it you mean no sound what so ever, not even a hum. This would suggest gnarlys in later stages in the amplifier. (Possibly even the speaker connection.)
They said, son, your soldering is ground breaking.
The dropping resistors are the 10k and 22k resistors (if your's measure at 9.96k - that's close enough to 10k, and 21.7k is close-enough to 22k).
Check you have the correct value plate resistors for the 12AX7. They should be 100kOhm each. The 12AX7 stages both might be pulling too much current maybe (if the plate resistors are wrong), and this could pull the pre-amp supply down
Building a better world (one tube amp at a time)
Aren't the tubes glowing?
They said, son, your soldering is ground breaking.
yes they are
I've tried to make it as close as possible without losing focus
Hard to tell what's going on behind the board. Do some continuity checks with your r-meter. The following should all read 0
The 6V6 grid (pin 5) to the junction of the 220k and the 0.022uF.
The 12AX7 input grid (pin 2) connected to the junction of the 2 x 68k.
The 12AX7 2nd grid (pin 7) connected to the pot wiper (This is a shielded cable, but you may've inadvertently shorted the cable core to the cable shield at one of the cable ends)
The 12AX7 2nd cathode (pin 8) connected to the junction of the 22k and 1k5.
The 25uF, 470R, 220k junction connected to the ground side of the 10uF pre-amp filter cap.
The 1st two filter cap grounds (the 10uf and the 22uF) connected together.
Building a better world (one tube amp at a time)
I've checked all those connections are good !
Apart from the low voltages, I'm still wondering whether the shielded cable from Pin 7 of the 12AX7 to the vol pot is shorted to the cable shield. If Pin 7 to ground reads zero ohms with the pot maxed, I suspect it may be.
Regarding the low voltages, another possibility is that you may have a partially-shorted or improperly grounded filter cap (one of the 10uF caps). Have you got a spare 10uF or 22uF filter cap that you can tack in parallel with one of the 10uFs (one 10uF at a time) to see?
Did you check that the plate resistors for the 12AX7 (the ones going to the .022uF/plate socket pins (1 and 6) junctions) were 100k each?
The other things is - are you triply sure you have the 6V6 grid (Pin 5) going to the junction of the 220k/.022uF? (and not to the 220k/470R/25uF?), and are you positive you have the 220k/470R/25uF going to the 10uF pre-amp filter cap ground (and not to the 220k/.022uF junction)?
Building a better world (one tube amp at a time)
I will try to use a normal wire to see if it is the shield,
I dont have any spare caps because this is my first build
Those resistors are 101.9 and 108.1
When you measure the resistance between Pin 5 of the 6v6 to the 220k/.022uF junction, what reading does the R-meter give?
Building a better world (one tube amp at a time)
It gives 0.04
and I've tried a normal wire still no sound
When you put the R-meter between the 10uF pre-amp filter cap ground and the 470R/25uF/220k junction, what is the resistance reading?
Building a better world (one tube amp at a time)
0.8ohms for both 10uF caps
Put your meter on the 'VAC' setting and measure between pins 2 and 7 of the 6V6. What is the VAC reading?
Building a better world (one tube amp at a time)
0.542V Or do I need to plug it in and turn it on ?
oh its now 0....
stupid me, its 6.77
as the tubes warms up, its now 6.80
It should be 6.3VAC. The heater can't be working. In the pic of your wiring to the lamp holder, the way you have them wired suggests that there's no connection between the 2 lugs on either side of the lamp holder. Try soldering a bit of wire between those two outside lugs (with the lamp removed of course). (Don't change anything about the end lug at this stage)
The other thing is, have you grounded the PTs' heater winding centre tap? (does the heater winding even have a centre tap?)
Building a better world (one tube amp at a time)
nono I didnt turn on the amp before
now that its on, its now 6.82
Well then maybe its still gotta be something not right on the back of the board.
Is there any sound out of the speaker with the amp on (a faint hiss or hum?)
Building a better world (one tube amp at a time)
not really .... in that case.... I'll pull the board out again....
I'm just worried its the transformers
So what do I do after I pulled it out?
This was an earlier pic, I think he's reflowed since then....
http://a6.sphotos.ak.fbcdn.net/hphot...79728901_n.jpg
It's poss there's a wire been trapped and shorting? but it would have shown up by now, all I can think is there's a component fault somewhere.
There are currently 1 users browsing this thread. (0 members and 1 guests)
Posting Permissions
Bookmarks