5F2a, built and at the starting gate

[dig22]

bad pilot lamp holder

[JHow]

bad pilot lamp holder

I understood that the part was bad, but bad in what way?

Shorted? Open? Bent? Broken?

I am curious because I have a tendency to buy the cheapest thing out there.

"I'm not gonna pay a lot for this muffler!"

[dig22]

bad pilot lamp holder?

I don't know what was wrong with it. The continuity seemed to work when tested. But the part didn't work in amp after hooking it up and re-hooking 5 times. The new part worked immediately.

[dig22]

Voltage joy

Not sure my voltage readings are correct, but I'm just so happy there's any voltage there at all.

might be premature, listing my voltages below, as I know there is short to ground from 12ax7 pin 7. I think I over soldered at the pot. I'll fix that tomorrow.
Does this short to ground effect other voltages?

5Y3:

across pins 2 & 8: 438 Vac
across pins 4 & 6: 637 Vac

B+ hovers around: 437 - 438

6V6
pin 2: 3.28
pin 3: 426
pin 5: 40
pin 7: 3.27
pin 8: 53


12AX7
Pin 1: 219
Pin 2: 72.4
Pin 3: 426
Pins 4/5: 3.28
pin 6: 212
pin 7: 0 (shorted to ground)
pin 8: 1.87
pin 9 3.27

The amp squeals when tone pot is cranked, but that's shorted. I'll attack that tomorrow.
Am I on track?

And thanks to all. I've learned quite a bit in this forum.

[tubeswell]

I know there is short to ground from 12ax7 pin 7. I think I over soldered at the pot. I'll fix that tomorrow.
Does this short to ground effect other voltages?

No - shorting the grid to ground (if indeed it is actually shorted to ground) won't affect other voltages, it just means no signal will get through the amp between the input and the speaker

5Y3:

across pins 2 & 8: 438 Vac
across pins 4 & 6: 637 Vac

B+ hovers around: 437 - 438

So that B+ is with all the tubes installed?

6V6
pin 2: 3.28
pin 3: 426
pin 5: 40
pin 7: 3.27
pin 8: 53

Pin 5 looks wrong - that is the grid pin, and the grid should be at 0 in a cathode-biased stage. Re-check your wiring

What is the voltage at Pin 4 (out of curiosity)? (The screen)

12AX7
Pin 1: 219
Pin 2: 72.4
Pin 3: 426
Pins 4/5: 3.28
pin 6: 212
pin 7: 0 (shorted to ground)
pin 8: 1.87
pin 9 3.27

So these are idle DC voltages?

Pin 2 is a grid and shouldn't have any voltage on it
Pin 3 is way wrong - that is a cathode and should only be at ~1-2V

Re-check your wiring, (or your pin numbering)

FYI - dual triode 9-pin miniature tube pin configuration

1= plate 1
2 = grid 1
3 = cathode 1
4 = filament
5 = filament
6 = plate 2
7 = grid 2
8 = cathode 2
9 = filament

Got any pics of your build you can upload?

[dig22]

Tubes in meter on

Hey Tubeswell. Thanks again for new info. I fixed the short from grid to Vol. pot

Here's a link to amp pics if you want to see more detail. Click on any image to enlarge or shrink:

http://imageevent.com/dig22/dig22ff2amay292010

RE: input jacks. For #1 input, should it be wired exactly like the layout in Weber 5f2a or is there another way?

I swapped tubes today and I'm thinking I might need a new meter.
but here's what I have with tubes in:

5y3 Unitron (is this a decent tube or should I swap it out?)
Hi v: 633 Vac
5v: 5.25
6v: 6.58

Tungsol 6v6 GT
pins 2&7: 6.55 Vac
pin 3: 431 Vdc
pin 4: 418 Vdc
pin 5: 312 Vdc
pin 8: 74 Vdc

Ge 12ax7
pin 1 /plate: 178 Vdc
pin 2 / grid: .47 Vdc
pin3 / cathode: 236 Vdc
pin 4&5 &9: fil 6.5 Vac
pin 6 /plate 2: 242 Vdc
pin 7/ grid 2: 0
pin 8 / cathode2: 1.29 Vdc

I measued in the morning and in the afternoon and some voltages stayed the same, some varied.

I couldn't resist and plugged in guitar. Eureka there was sound. It's really really low and distorted, but at least something coming from the speaker so I am hopeful.

Thanks again to all for support.

[Bruce / Mission Amps]

5y3 Unitron (is this a decent tube or should I swap it out?)
Hi v: 633 Vac
5v: 5.25
6v: 6.58

Tungsol 6v6 GT
pins 2&7: 6.55 Vac
pin 3: 431 Vdc
pin 4: 418 Vdc
pin 5: 312 Vdc
pin 8: 74 Vdc

Ge 12ax7
pin 1 /plate: 178 Vdc
pin 2 / grid: .47 Vdc
pin3 / cathode: 236 Vdc
pin 4&5 &9: fil 6.5 Vac
pin 6 /plate 2: 242 Vdc
pin 7/ grid 2: 0
pin 8 / cathode2: 1.29 Vdc

Wow, what a mess.
To be honest, your rectifier measurements are almost meaningless to me.

Lug 8 of your 6V6 should be closer to 15vdc-18v... not 74vdc!... either the 2 watt resistor is blown open, you don't have the biasing resistor grounded right or it is not connected or soldered to lug 8 right.

Unless you have a bad 12AX7 tube there should be zero volts on lugs 2 and 7.
Lug 3 of the 12AX7 socket should be very similar to lug 8... so lug 3 can't be connected to or grounded through a biasing resistor that's grounded either.
Also, I didn't read that the chassis was painted... another potential problem that could or will pop up.

[JHow]

I swapped tubes today and I'm thinking I might need a new meter.

Probably not, unless its like a Fluke or somesuch, in which case I'll take it off your hands for a small disposal fee.

Seriously, be mindful of the settings you use: AC for AC and DC for DC, for example. Make sure your battery is fresh.

RE: input jacks. For #1 input, should it be wired exactly like the layout in Weber 5f2a or is there another way?

Sorry, I don't know what the weber layout is, but it looks like you have the fender style jack wiring, judging from the pictures. I think, however, the blue wire from the shunt on jack #1 should go the ground side, not the tip side of the jack. I would double-check that,since it is hard to tell in photo.

FWIW, since the amp isn't running exactly, we haven't talked about hum issues yet, but an alternative way to do the hi-lo jacks is shown here:

Common hookup info

Essentially move the 75K/68K res directly to the jacks and use shielded wire to the grid.

5y3 Unitron (is this a decent tube or should I swap it out?)

A workin' rectifier is a good rectifier.

I measued in the morning and in the afternoon and some voltages stayed the same, some varied.

Yes, this happens to me too, after those Memorial Day margaritas.

As Bruce noted, these voltages are off. Ignoring the rectifier for a minute, what is your voltage from the junction of the 16u cap and the 10K power resistor to ground? Are you in the neighborhood of 370-400VDC (direct current)?

Also, on your board I didn't see a connection between the first two filter caps, is that under the board?

FWIW, here are some voltages from my working 5F2a. You should be looking for the same relative values (that is, you don't need exactly what I have, but something close).

I list the pin and the function of each pin, which I think is a big help for you to think about when diagnosing problems. 312 volts on "pin 5" is arbitrary, but if you say you have 312 volts on the 6v6 grid, then right away you know you have problem. (I'd be checking the black wire that is supposed to go to the junction of the 220kR and the .02u cap).

Example working voltages (VDC measured to ground):

6v6
pin 3 plate 356V
pin 4 screen 315V
pin 5 grid 0 (practically zero)
pin 8 cathode 19.5V

12ax7 (dual triode)
pin 1 plate 162V
pin 2 grid 0 (zero)
pin 3 cathode 1.4V
pin 6 plate 166V
pin 7 grid 0 (zero)
pin 8 cathode 1.45V

For the heaters, measure VAC across:

12ax7 across pin 5,4 to pin 9 (should be around 6.3V)
6V6 across pin 2 to pin 7 (should be around 6.3V)

Anyplace you deviate substantially from this, find out why, and you will likely very soon have a live amp.

[dig22]

Look on the bright side Bruce...

could be raining...

when you say mess, I hope you mean voltages and painted chasis! BTW that chassis is what started me on this build. I looked at an old surge suppressor and thought, "wow, good chassis for a 5f2a." Dumb idea! Much more work that I imagined and I'll probably end up buying a new chassis anyway.

I'll wait to hear Tubeswell's suggestion and go at it again.

In the meantime, how do I check a resistor's integrity? (almost sounds like a joke)

-d22

[dig22]

Thanks JHow

Re: jacks: I'm re-doing. That's why no pics.

FWIW, since the amp isn't running exactly, we haven't talked about hum issues yet,

No hum issues yet. just a bit of squeal.

Essentially move the 75K/68K res directly to the jacks and use shielded wire to the grid.

The wire from vol pot to grid is shielded.

As Bruce noted, these voltages are off. Ignoring the rectifier for a minute, what is your voltage from the junction of the 16u cap and the 10K power resistor to ground? Are you in the neighborhood of 370-400VDC (direct current)?

Will check and report back.

Also, on your board I didn't see a connection between the first two filter caps, is that under the board?

yes.

find out why, and you will likely very soon have a live amp.

I hope you're right.

[Bruce / Mission Amps]

could be raining...

when you say mess, I hope you mean voltages and painted chasis! BTW that chassis is what started me on this build. I looked at an old surge suppressor and thought, "wow, good chassis for a 5f2a." Dumb idea! Much more work that I imagined and I'll probably end up buying a new chassis anyway.

I'll wait to hear Tubeswell's suggestion and go at it again.

In the meantime, how do I check a resistor's integrity? (almost sounds like a joke)

-d22

Ha ha... Yes, I meant the voltages are a mess.... the paint can make it hard to get a proper grounding scheme to work.
Shut it off, drain the B+ from the filter caps and use your DVMM to measure DC resistance across the resistor leads.
The 178v plate voltage on lug 1 is OK but the cathode can not be 236v... unless the wire is actually connected to the junction of the two 100K plate load resistors somehow or the leads are backwards etc etc etc.
And, it is hard to see how there would only be a 58v difference between the plate and cathode even though backwards.

[tubeswell]

here's what I have with tubes in:

5y3 Unitron (is this a decent tube or should I swap it out?)
Hi v: 633 Vac
5v: 5.25
6v: 6.58

I think these are normal enough to be 'normal' - so far so good

Tungsol 6v6 GT
pins 2&7: 6.55 Vac
pin 3: 431 Vdc
pin 4: 418 Vdc
pin 5: 312 Vdc
pin 8: 74 Vdc

Pin 3 (the plate) and Pin 4 (the screen) look normalish, but Pin 5 (the grid) is way too high - should be about 0 - not sure how you have that connected - I'd recheck the wiring on the back of your board - it should be going to the junction of the 220k grid leak resistor for the 6V6 and the .02uF coupling cap.


Pin 8 (the cathode) is way too high - should be about 20 or so - Bruce knows what he is talking about much more than I. You must have the wrong resistor hooked up as the cathode resistor. It should be about 470R to 500R (that is "R", and not "k". R = Ohms k = kiloOhms)

Ge 12ax7
pin 1 /plate: 178 Vdc
pin 2 / grid: .47 Vdc
pin3 / cathode: 236 Vdc
pin 4&5 &9: fil 6.5 Vac
pin 6 /plate 2: 242 Vdc
pin 7/ grid 2: 0
pin 8 / cathode2: 1.29 Vdc

Pin 3 (cathode for 1st triode) is the brown wire going to your 1500R/25uF Rc combination at the right-hand end of your board. Are you sure that is 236V? If it is, then you must have a wrong supply wire connected up at the back of the board somewhere. It should only be about 1-2V

Pin 2 (grid for 1st triode) shouldn't have anything on it either, so I would double and triple check the wiring with your Rmeter to see that it corresponds to the layout diagram and that you haven't got continuity between the grid and (say) one of the plate supply resistors (maybe incorrectly via the back of the board?)

Are you using the 5F2A layout diagram?

[dig22]

swapped resistor, new voltages, ain't she sweet ...

Howdy All,
Well this Memorial Day will certainly be memorable.

I did, indeed, use a 470K resistor instead of R470. Oops. A few bad solder joints corrected and damn if the mess on my bench doesn't sound like an amp (even with the lousy test speaker). Quiet as can be but for a little intermittent scratch in the pots in various spots. I think the pots are bad. I've taken them apart and re-soldered them 10 times.

Here are the voltages, not perfect, but getting closer:

6v6

pin 3: 337 VDC
pin 4: 298
pin 5: 6.5
pin 8: 20.6

12ax7

pin 1: 153
pin 2: .29
pin 3: 1.5
pin 6: 184.5
pin 7: .1
pin 8: .95

I'll list the caps below and I'd appreciate someone tell me the common reference name for each (if there is one).
1st cap 16@450 346 Vdc
2nd cap 16@450 348 Vdc
3rd cap 8@450 299 Vdc
4th cap 8@450 260 Vdc

1st 25@50 20.6 Vdc
1st .02 185 Vdc
2nd .02 153 Vdc
2nd 25@50 1.7 Vdc

I tried some various tubes and that changes voltages a bit here and there but I went back to same I started with for continuity.

Anything else I can check or try for getting the voltages more spot on?

Re: input jack 1:
Am I reading the construction wrong or the layout or both? I tried fender and Weber ways and neither worked.
Fender:
a. sleeve to ground
b. 1 meg resistor across the sleeve and tip
Weber:
a. sleeve to ground
b. 1 meg resistor across the sleeve and tip
c. connection between sleeve and switch.
Here's what does work:
a. sleeve to ground
b. 1 meg resistor across the switch and tip


And that's it for today. Onward to the B-B-Q.
I'll keep thanking you all because I can't do it enough. I'm having a grand time of it - D22

[JHow]

Actually, those voltages now look pretty good. Not sure you need to dial in any further.

Regarding jack, way at the top of the thread Bruce posted the weber scheme. Jack #1 has 1Meg R across the tip and ground/sleeve, and has a connection from ground to the switch/shunt. You can actually bend the lead on a 1 meg and make that switch/shunt connection with the end of the resistor. The switch connection isn't crucial, except that it shorts out the tip (input) when a cord isn't plugged in, preventing hum when changing cords. The layout as shown above is for the standard switchcraft #12a type.

[Bruce / Mission Amps]

Cool, now you are making some progress.
I knew there was something wrong with that power tube biasing resistor and some kind of wiring error on the preamp tube socket.

Oh, and, Pin 5 of the 6V6 should be ZERO volts.
There should be nothing there because it is grounded by the 220K grid load resistor and the amp is cathode biased, which means the bias is on the cathode, not the grid.
If your DVMM has survived this far, this could be caused by a bad power tube or a leaking coupling cap from the #6 plate lug of the preamp tube.