Help With Voltages On A Mission 5e3

[Gerard]

Hi, I just put together my mission 5e3 kit. This is my first build, and thought everything was going well. I turned in on and then turned the stand by on, everything seemed to be ok. I pluged my guitar into the normal #1 and was greeted with a nice buttery tube sound when , the volume and tone control worked fine. Then I pluged my guitar into the bright #1 and had slight volumn to #1 volumn position and then after that a the amp would cut out and there would be a somewhat loud buzzing, if the voulme was turned above #1.So I shut the amp off and reinspected all of my wiring, I did not find anything, so I turned the amp on again and pluged my guitar in the normal channel, it played for a short while and then nothing, no output at all. I need some help. Here are the voltages at the tube sockets. It looks like they are all high, except
the 6.3v filaments. Please keep your awnsers basic, this is my first build. The 5y3GT TUBE pin#2 5.3v ,pin#8 .5V, pin#4 339v, pin #6 339v. 6V6-valve #4,pin#3 446v, pin#4 420v, pin#8 71v the filaments have no d/c volts at them, only 3.3v a/c at pins #2 and #8. 6V6-valve #3, pin#3 447, pin #4 421v, pin#8 71v. 12AX7 valve #2, pin #1 203v pin#3 1.5v, pin#6 246v, pin#8 62v. 12AY7 valve #1, pin #1 157v, pin#3 2.43v pin#6 157. The 22uf 500v cap voltages are 447v, 421v and 308v respectivly. Thanks, Gerard.

[petemoore]

The 5y3GT TUBE
pin#2 5.3v ,
pin#8 .5V,
pin#4 339v,
pin #6 339v.
6V6-valve #4,
pin#3 446v,
pin#4 420v,
pin#8 71v
..the filaments have no d/c volts at them, only 3.3v a/c at pins #2 and #8.
6V6-valve #3,
pin#3 447,
pin #4 421v,
pin#8 71v.
12AX7 valve #2
, pin #1 203v
pin#3 1.5v,
pin#6 246v,
pin#8 62v.
12AY7 valve #1,
pin #1 157v,
pin#3 2.43v
pin#6 157.
The 22uf 500v cap voltages are 447v, 421v and 308v respectivly.
I'm not the one for pin voltages, but mostly they look pretty good to me [didn't say much], I find they're alot easier to read when stacked.
Not sure where a voltage chart for 5e3 references would be, where I'd look to look smart on it though.
Because of the fading described, I suspect heaters, and 3.3vac...they should be at 6.3vac? ..the filaments have no d/c volts at them, only 3.3v a/c at pins #2 and #8.
this shows pins 2 and 7 connecting the heater filament?
http://tdsl.duncanamps.com/show.php?des=6V6GTA

[MWJB]

As Petemoore says pins 2&7 of the 6V6s are the heaters not pins 2&8. But 3.3VAC to ground from either side of the heaters to ground looks good, really it's best to measure heater AC from pin 2 to pin 7 if wired as a twisted pair, rather than reading to gound.

Voltages generally look high to me if using 6V6s, 71v at pin 8 of the 6V6s is 3 times what I would expect, double check cathode resistor value, good connection to ground & cathode voltage? With a stock 250ohm cathode resistor you want less than 385v at the 6V6 plates.

[Gerard]

Possible No Heat

Thanks Pete and MWJB for your quick responses. After looking at the tubes I said pins 2 and 8, I ment 2 and 7.. The heaters are wired to pins 2 and 7.I measured all the heater voltages at pins 2 and 7 of the 6v6 tubes and pins 9,4 and 5 of the 12x7 and 12ay7. All of the voltage from pin to pin on the respective tubes and all measures 6.71 volts a/c. The amp has no sound output at all, not even a hum.It looks to me that the tube heaters are not doing their job, the tubes do glow though, but the don't feel very warm compaired to my other tube amp, and the P/T feels cold. I have gone through my wiring many times and compaired it to the layout provided. I used the Bruce's web site with the pictures during the assembly.It seems to me that all the voltages are hi compaired to the schematics supplied with the kit.I am not ready to send it back to Mission Amps for a fix yet!!

[MWJB]

Well if you have 6.71VAC at pins 2 & 7 of the 6V6s and at 4, 5 & 9 of the 12A# tubes, that looks pretty good, especially if the tubes are glowing (yellow points of light). How hot they get is more dependent on how much current the plates draw, rather than heater voltage alone.

So far, that 71v at the 6V6 cathodes is the most suspicious reading that you have, check this out first.

Yes, your voltages are high, you could have:

The wrong PT primaries wired up - select the next value up from your actual wall voltage (i.e. if you have 118VAC at the AC cord use 120VAC primaries, 121VAC from the wall use 125VAC primaries, etc.)

or...

High B+ voltages because of a miswired/poorly grounded/wrong value cathode resistor at pin 8 of the 6V6s. 71v developed accross a 250ohm resistor equates to >130mA of current per tube, either this is wrong or your tubes are dead (get a new pair anyway). 20-24v at pin 8 is more usual.

Just noticed ".5v" at pin 8 of the rectifier, this dc voltage should be the same as at the first filter cap as they are connected. Surely, this ".5v" is a typo?

[Gerard]

Sound With Low Volume

Thanks MWJB for steering me in the right direction. In the wiring layout supplied with my Mission amp, it showed to wire the 2 100 ohm
resistors from the 2 & 7 pins of V4 6V6 to the + side of the 22uf 100v cap. After further inspection of other 5e3 chassis pictures,It looked to me that the 100 ohm resistors should be wired from pin 7 to pin 8 and from pin 2 to pin 8 of the V4 tube, so that is the way they are wired now. Some of Bruces pictures were a little blury on how the resistors were wires in so I followed the wiring layout. That being said ,I now have all the correct voltages at all the points in the amp according to the schematics that Bruce supplied. Thanks again for helping me out, I'm really learning here. Now for the next problem. I have volume at both volume knobs but it does not seem to increase at all after the #3 setting The tone knob seems to work but when it is turned up to 12 with the bright channel on, the sound totally cuts off untill you turn the tone knob back below 12. Remember that I had much higher voltage running through all circuits before I rewired the 100 ohm resistors. I don't know if the high voltage caused ant other problems?, but atleast I have some sound now. Could the problem be with the preamp tubes or the volume pots? Is there any way I could check for voltages or resistence in these circuits that could lead to a faulty part ? Thanks again, Gerard.

[Gerard]

Screaching Noise From My 12ay7 Tube

After reading some threads I deceided to check the voltages at the 12ay7 tube, and when I probed pin #7 with the blue wire I notice that the tube would let out a faint screech which would coinside with the the turing of the bright channel volume and tone control, The tube screaching would increase in frequency as the tone pot was turned up?Thanks again , Gerard

[MWJB]

Volume levelling out after "3" - that could be normal & is often the case, turning up just increases overdrive & compression. Notice that the volumes are wired differently to most amps, this means they ramp up quick, if you can't live with it Bruce does a Vol/Tone kit that calms things down.

Sound cutting out with tone flat out smacks of a layout problem, shorten your grid wires to all tubes, look at your lead dress & compare carefully to Bruce's photos & other 5E3s.

Noise when probing a tube grid (pins 2 & 7 of 12A#7) is normal. You're normally just checking for dc at cathodes (3 & 8) & plates (1 & 6).

[Gerard]

Lead Dress

Thanks MWJB, could you explain to me what a lead dress is and If the third leg of the normal channel volume pot should be grounded to chassis ground or the input jack, Thanks, Gerard

[Bruce / Mission Amps]

Thanks MWJB, could you explain to me what a lead dress is and If the third leg of the normal channel volume pot should be grounded to chassis ground or the input jack, Thanks, Gerard

Lead dress just means to make sure the wires are only as long as really needed and not flying all over the place in a sloppy way.
The third leg of the vol pots (grounding lug) are connected together with a jumper wire and then grounded at the input jack's ground lug.
The input jacks are always grounded... remember the big star washers under the jacks? They dig into the brass plate for an excellent ground point.
They volume pots can be grounded at the brass plate if you wish but it is easy to run a single wire over to the grounded lug on the jack.

[Bruce / Mission Amps]

After reading some threads I deceided to check the voltages at the 12ay7 tube, and when I probed pin #7 with the blue wire I notice that the tube would let out a faint screech which would coinside with the the turing of the bright channel volume and tone control, The tube screaching would increase in frequency as the tone pot was turned up?Thanks again , Gerard

If you don't have a guitar cable plugged in and it screeches, I'm betting you have the input jacks wired wrong.