Jump to content
Gibson Brands Forums
Sign in to follow this  
TWANG

My EL34

Recommended Posts

Still giving me a hassle.

'Course I've been working on that Supro... which is just noisy but otherwise great.

 

My tubes wont lite up.

 

Now.. maybe they shouldn't.

 

I have it on the lightbulb tester.. because it had NO signal.

 

I went over the thing from input jack all the way through the preamp section..

 

I even reflowed solder to every single joint on the board, plus pots, and jacks.

 

the bulb lights.. dims. stays kinda bright.

tubes wont light.

and no pop off pin 6 preamp which is what I look for first when testing.

 

I had a stock ot and it worked fine.

 

now I have the mps020 which is 3K instead of 5K but I don't think that should be any cause of the current problem.

 

 

IF the solder joints are all good.

IF the ohms I'm reading (.3 max) at any point to point test.

IF the components are all in the right place and fine.

(they all test good)

 

 

THEN

 

How can I not have a signal?

 

If the tubes don't have enough juice to light up with the bulb in.. then why wont the lightbulb dim more?

 

Dont say swap tubes. no way I'm risking new tubes in there right now.

I should be able to get something going even if one of these tubes has bad mojo.. at least, I should get some problem that indicates a dead tube.

 

I'm gonna fire it once with no light bulb, just to see if the tubes get a little warm.

Share this post


Link to post
Share on other sites
Still giving me a hassle.

'Course I've been working on that Supro... which is just noisy but otherwise great.

 

My tubes wont lite up.

 

Now.. maybe they shouldn't.

 

Whether its a 6 volt or 12 volt heater' date=' you should see some red inside the

cathode..that is the filament heating up.

 

I have it on the lightbulb tester.. because it had NO signal.

 

I went over the thing from input jack all the way through the preamp section..

 

I even reflowed solder to every single joint on the board, plus pots, and jacks.

 

Now why would you do that..if the heaters don't light?

 

the bulb lights.. dims. stays kinda bright.

tubes wont light.

 

What kind of amp is it?

Did you check the power transformer winding? is there some kind of

power dropping resistor in series with the winding?

 

 

and no pop off pin 6 preamp which is what I look for first when testing.

 

I had a stock ot and it worked fine.

 

now I have the mps020 which is 3K instead of 5K but I don't think that should be any cause of the current problem.

 

IF the solder joints are all good.

IF the ohms I'm reading (.3 max) at any point to point test.

IF the components are all in the right place and fine.

(they all test good)

 

 

THEN

 

How can I not have a signal?

 

 

many reasons..you could have a shorted bypass cap or open coupling cap..that's one reason.

 

If the tubes don't have enough juice to light up with the bulb in.. then why wont the lightbulb dim more?

 

Are you using a 6 volt or 12 volt automotive bulb? It could be that the current available in the winding

is just enough to light the bulb but not enough to light all 6 or howmany tubes there are in the

amp?

 

 

Dont say swap tubes. no way I'm risking new tubes in there right now.

I should be able to get something going even if one of these tubes has bad mojo.. at least, I should get some problem that indicates a dead tube.

 

I'm gonna fire it once with no light bulb, just to see if the tubes get a little warm.

 

 

I would be testing the voltage on the 12 volt and 6volt winding with the tubes in place.

if you have less than 6.3volts ac, you need to trace back to the filament winding of the transformer.

I don't know what model of amp you have so therefore I don't have a schematic as handy reference,

but the symptom you are experiencing intrigues me.

Share this post


Link to post
Share on other sites

I went over the solder joints, etc. as a matter of course.

When there was no signal after changing the OT, I figured check to make sure you didn't bump something.

I don't really remember the sequence.

 

Stock vj PT.

I think I had a test paper on that.. something with a 9V battery and an led .. I'll check the pt or just swap in a different one.

 

all components test ok. but I suppose a meter doesn't always tell the tale.

 

 

It's my own turret board EL34.. you can see the specifics in an earlier thread in here.

 

I'm in a mess with the supro.

I'm in a mess with the EL34.

and I just made a tweed tone control that does nothing in an EL84 which baffles me no end since it's such a simple thing to start with but I know there's a cap in there that must be shot or I got a bad pot, since there's really nothing to look at otherwise.

 

 

here's the story on the EL34

http://forums.epiphone.com/default.aspx?g=posts&t=12394

gets interesting around post no. 32

Share this post


Link to post
Share on other sites
I went over the solder joints' date=' etc. as a matter of course.

When there was no signal after changing the OT, I figured check to make sure you didn't bump something.

I don't really remember the sequence.

 

Stock vj PT.

I think I had a test paper on that.. something with a 9V battery and an led .. I'll check the pt or just swap in a different one.

 

all components test ok. but I suppose a meter doesn't always tell the tale.

 

 

It's my own turret board EL34.. you can see the specifics in an earlier thread in here.

 

I'm in a mess with the supro.

I'm in a mess with the EL34.

and I just made a tweed tone control that does nothing in an EL84 which baffles me no end since it's such a simple thing to start with but I know there's a cap in there that must be shot or I got a bad pot, since there's really nothing to look at otherwise.

 

 

here's the story on the EL34

http://forums.epiphone.com/default.aspx?g=posts&t=12394

gets interesting around post no. 32

[/quote']

 

 

Long story there Twang. Didn't realize you had changed out o/p transformer. From the sounds

of it, it seemed to work (somewhat) with the original o/p transformer you had in there.

 

Bring us up to speed on what exactly is happening now.

What's the story with the filaments (heater) not coming on? Is that a new recent

symptom and is it on the El84 or this other amp you are working on?

Share this post


Link to post
Share on other sites

I have three amp probs.

 

and this is it.. from now on. ONE amp at a time, period.

 

 

An inexplicable refusal of at simple tweed tone to work.

I redid it three times. I've made at least fifteen of these.

It does nothing. Just laughs at me.

 

 

then there's the supro which started eating preamp tubes right when I was ready to ship it out.. I was moving wires etc., to reduce noise, so somehow it looks like I shorted something or fried something or whatever.

 

And the EL34.

I'm going to go out now and try one more light bulb test.

and do some checking on the actual parts and connections..

 

the main thing about that was the loss of any signal coming in. no pop on pin6..

and all I did was swap the OT .. so far as I am aware anyway.

 

right now I'm gonna put the el84 with the stubborn tone pot in a cab. and forget it for the time being.

 

the supro will get some attention first though

Share this post


Link to post
Share on other sites

supro

40 watt bulb inline with power

 

probe to grnd and other to test points.

 

R10 and on.. 245... 218 215 212 at pin.

ax7 3 .49?

4/5 6.2

6 157

8 1.1

 

el84

3 6.2

6 6.18

7 215

9 212

 

preamp tube is a svetlana I know is weak.. but it's lighting.

Share this post


Link to post
Share on other sites

fixed the tone pot hassle on the el84.

removed all and replaced the two pots..

must have been the volume pot all along since because it worked as volume, I never replaced it until now.

and now it works perfectly.

 

I have such good luck. *L*

Share this post


Link to post
Share on other sites
fixed the tone pot hassle on the el84.

removed all and replaced the two pots..

must have been the volume pot all along since because it worked as volume' date=' I never replaced it until now.

and now it works perfectly.

 

I have such good luck. *L*[/quote']

 

 

So it was a crappy volume pot that cut out the signal???...happens on guitars a lot,

so I'm not surprised. Curious though..why not get yourself a battery operated

1khz tone generator test probe and inject the signal at the control grids through

the various stages of the amp(s). Wouldn't this be an easier way to troubleshoot

than all the messing around measuring voltages, resoldering etc?

 

here's a schematic of one you can build yourself very easily.

 

http://www.circuit-projects.com/test-equipment/signal-injector-and-tracer-circuit.html

 

Just remember to make sure that no high voltage dc gets into it. The 1nf cap (1000pf)

on the probe output needs to be a 400v cap to block any high dc voltages

found in tube circuits.

Share this post


Link to post
Share on other sites

You know I tried that with a cd player.

and it went pretty well until I accidentally hit the wrong point. and fried the cd player!

So I'll be checking that out for sure.

 

I can't number the times I would have loved to be able to probe through the amp and find where the dang signal was dieing off.

 

I still can't believe that it was just that stupid pot.

But I swapped everything but the pot, twice, so that had to be it.

Share this post


Link to post
Share on other sites
You know I tried that with a cd player.

and it went pretty well until I accidentally hit the wrong point. and fried the cd player!

So I'll be checking that out for sure.

 

I can't number the times I would have loved to be able to probe through the amp and find where the dang signal was dieing off.

 

I still can't believe that it was just that stupid pot.

But I swapped everything but the pot' date=' twice, so that had to be it.

[/quote']

 

Sometimes it can be the simplest problem and we tend to look for something more

complicated.

 

BTW..it would be easier to understand what you are doing when you use tube terms

such as cathode, control grid, screen grid and plate when referring to tube pins.

 

there are so many variations of tube bases that it's hard sometimes to visualize

what you are describing.

 

I tossed out my old RCA /GE tube manuals years ago, when they replaced the tube

testers in corner stores with lottery terminals.

Share this post


Link to post
Share on other sites

The way I learned wasn't really a kosher education just hit and miss.

I can screw up the terminology, but I can still count when it comes to the pins.

 

 

the el84 amp is now working fine.

 

the supro is funky still.

 

and dig this on the el34

 

I get tubes glowing now.. I get ok voltages except..

0 on my heaters.

 

I tried this every way I could think of.

each heater pin to grnd.

to each other.

I get 0.

 

the tubes light but how can that be?

 

from R10 to the pin. I get 334 dropping to 314. perfectly acceptable to me.

the 12ax7 is odd

pin 1 220

3 1.6

4/5 0

6 213

7 .1

8 1.5

9 0

 

I tested them all. *L*

 

on the el34 I get

1/8 1.8

3 325

4 315

5 16

 

 

I don't have a clue on that mess of numbers.

 

 

I was really careful.. and I was sure I had found the problem with no signal.. pin 3/4 had a tiny wire touching between them.

I tested every wire for ohms.. all is well.. all components I can test out read fine.

used 40W bulb inline with power..

first with no tubes..then with.. then I took out the bulb.

 

no heaters .. ? but tubes light .. ?

Share this post


Link to post
Share on other sites
The way I learned wasn't really a kosher education just hit and miss.

I can screw up the terminology' date=' but I can still count when it comes to the pins.

 

 

I get tubes glowing now.. I get ok voltages except..

0 on my heaters.

 

I tried this every way I could think of.

each heater pin to grnd.

to each other.

I get 0.

 

the tubes light but how can that be?

 

 

heater voltage is usually 12.6v or (6.3) A/C, so you have to measure across the heater

pins on a vom with an a/c setting. You won't read anything on a DC setting.

since the heater winding is generally isolated from the chassis ground.

 

http://en.wikipedia.org/wiki/12AX7

 

]from R10 to the pin. I get 334 dropping to 314. perfectly acceptable to me.

the 12ax7 is odd

 

pin 1 220 (plate triode #1)

3 1.6 (cathode #1)

4/5 0 (heater voltages for both triode (heater is center tapped)

6 213 (plate of triode #2)

7 .1 (grid #2)

8 1.5 (cathode #2)

9 0 (center tap of a/c heater)

 

http://www.duncanamps.com/tdsl/show.php?des=EL34

on the el34 I get

 

1/8 1.8 (cathode and suppressor grid tied together inside tube) NORMAL

3 325 (plate of power pentode)

4 315 (screen grid)

5 16 (control grid) (this should be a dc bias and an a/c signal riding on

top of this bias from the preamp/driver section)

 

I don't have a clue on that mess of numbers.

 

 

look normal from what I can tell

 

.

 

 

I was really careful.. and I was sure I had found the problem with no signal.. pin 3/4 had a tiny wire touching between them.

 

Usually the supressor grid (normally at some cathode potential) and the heater(4) are not connected.

 

I tested every wire for ohms.. all is well.. all components I can test out read fine.

used 40W bulb inline with power..

first with no tubes..then with.. then I took out the bulb.

 

no heaters .. ? but tubes light .. ?

 

Well, everything looks copacetic. Heater voltages have to be measured on an meter scale that reads

a/c and not DC since the heater comes off a stepped down power transformer winding (6.3 or 12.6vac)

and at 60hz.

Share this post


Link to post
Share on other sites

I got it figured out. Usually the auto ranging just switches over..

but this time I pressed the button.. 6.5 heaters.

 

still no dang signal.

and really I thoroughly tested from input on.. even replaced the volume pot..

all it has is vol standby rear fuse and input jack.

 

everything is good but I can't find a signal.

 

I gotta find that batt. op. sig. gen.. was that you or strumbone that posted that..

I think I added it to faves..

 

but that's all I can think of now that I know everything I'll figure out by eye or meter is known.. I need to put some signal in there.

Share this post


Link to post
Share on other sites

well. turned all the way up you can hear the guitar very softly.

so. time to build that signal injector.

madkatb also had a design for an old pc powered speaker conversion so I guess I'll build both.

Share this post


Link to post
Share on other sites
well. turned all the way up you can hear the guitar very softly.

so. time to build that signal injector.

madkatb also had a design for an old pc powered speaker conversion so I guess I'll build both.

 

 

Dont keep us in suspense Twang..what "possessed" amp are you working on now?

 

here's another one that runs off a 1.5 volt penlite battery..you can use an aluminum

cohiba cigar tube to stuff in the circuit. In case you can't find a cigar tube, you could

use a plastic water pipe to keep the circuit inside.

 

http://www.redcircuits.com/Page59.htm

Share this post


Link to post
Share on other sites

the el34

it's insane.

 

I put in all new front end.

still no signal.

if you max the amp vol. you can just hear some guitar through it.

somewhere in there, the signal is simply dieing.. running to ground.. ??

it all checks/tests fine!

 

I'm talking magnifying glass.. reflowed solder. *sucked it out and replaced all the solder* *boy are my lips chapped!*

new caps all through, new wires.. new pot.. all Res. test fine..

 

I don't see how it could be anywhere but the front end.. but I don't see anything I missed in the front end.

test voltages are ok.

 

Though I wish I had a range of voltages for the el34 tube. like.. max good and min. good.

with the el84 I adjust between 300 to 320.

 

Also, I'm not sure how to use those tone generators.

hook on probe to star ground and then walk the hot probe through the amp?

 

I'll have to order parts for either of those gizmos, maybe I'll just buy one premade and save some time.

 

man this is frustrating.

and I did this last year on an amp, too. but I didn't save my notes.

Share this post


Link to post
Share on other sites
the el34

and I did this last year on an amp' date=' too. but I didn't save my notes.

[/quote']

If you posted here at Epi, maybe some of your 'notes' will be there.

Sheila

Share this post


Link to post
Share on other sites
the el34

it's insane.

 

I put in all new front end.

still no signal.

if you max the amp vol. you can just hear some guitar through it.

somewhere in there' date=' the signal is simply dieing.. running to ground.. ??

it all checks/tests fine!

 

I'm talking magnifying glass.. reflowed solder. *sucked it out and replaced all the solder* *boy are my lips chapped!*

new caps all through, new wires.. new pot.. all Res. test fine..

 

[/quote']

 

time to run to the priest and get some holy water and sprinkle it all around the

amp..but not on it of course! :-k

 

I don't see how it could be anywhere but the front end.. but I don't see anything I missed in the front end.

test voltages are ok.

 

Though I wish I had a range of voltages for the el34 tube. like.. max good and min. good.

with the el84 I adjust between 300 to 320.

 

Also, I'm not sure how to use those tone generators.

hook on probe to star ground and then walk the hot probe through the amp?

 

 

Grnd the grd probe to the chassis and use the test lead to touch the control grid

of each preamp tube to inject the signal. The tube should already have a negative

dc bias on the control grid, so if the plate has a good load resistor, you should hear

something. You probaby won't hear much at the control grid of the EL34, since

it takes a fair amount of amplitude "swing" on the signal to get it to conduct...

but..you can work your way back from the input of the driver tube towards the

front end stage.

 

If you had a scope, even a cheap one, you could place the probe between

the plate resistor and the plate of the tube to see what kind of signal and

amplification the tube is providing, but without that, you have to rely on

audible.

 

I'll have to order parts for either of those gizmos, maybe I'll just buy one premade and save some time.

 

 

You can, but these components are almost what I call junk drawer parts (cheap)

...for this non critical circuit you can sub a 2N3904 (NPN) transistor

for the BC547 and a 2N3906 (PNP) for the BC557. If you haven't worked with transistors before,

be careful as the lead configuration can vary on those tiny plastic TO92 cases...

here's a bit more explanation on transistors..

http://www.kpsec.freeuk.com/components/tran.htm

Share this post


Link to post
Share on other sites

You sure have more than your share of catastrophic issues with your builds! I'd say that, more than likely, you're just not paying full attention at all times, and frequently miss one critical element along the way that stops you cold.

 

I can say for myself that when I did my el34 vjr conversion, I forgot to run the wire that connect R1, 8, and 9, and C3 and 4, so I too, had zero output when I first fired up. It didn't take long to figure it out, but it certainly COULD have. It wasn't all that obvious unless you were looking right at it.

 

I suspect that your issue is going to be something similar. Either you've forgotten a jumper wire like that on top the board, or one underneath. That's my guess.

Share this post


Link to post
Share on other sites
You sure have more than your share of catastrophic issues with your builds! I'd say that' date=' more than likely, you're just not paying full attention at all times, and frequently miss one critical element along the way that stops you cold.

 

I can say for myself that when I did my el34 vjr conversion, I forgot to run the wire that connect R1, 8, and 9, and C3 and 4, so I too, had zero output when I first fired up. It didn't take long to figure it out, but it certainly COULD have. It wasn't all that obvious unless you were looking right at it.

 

I suspect that your issue is going to be something similar. Either you've forgotten a jumper wire like that on top the board, or one underneath. That's my guess. [/quote']

 

Good call! A picture is worth 1000 words right? Post some good pics on Sewatt and someone will spot the problem I betcha!

Share this post


Link to post
Share on other sites

Lately you are right.

but I'd say catastrophic is over the top.

They always work in the end, that is, so just frustrating.

 

Typically, I do find a mistake, something overlooked. Esp. lately since I stupidly took on three builds at once.

 

Let me put it this way, I also made three other amps while doing the supro.

swapped a 6V6 back to an EL84.. and built two marshall modded amps.

All fine.

 

But, the supro was my first point to point.. and the el34.. I must have done something wrong!

 

I actually had the supro done and so quiet it amazed me.. sounded great. until you got the tone to max. then it totally sucked.

I'm still trying to figure out what goes on in that front end to make the wierdness.

 

My cameras on off button broke inside the camera.. so phone pics would be all I've got.

 

But I'll take 'em. top and bottom.

I know. it's probably right under my nose, and something I'm just NOT seeing .. wouldn't be the first time, but this is the longest time!

 

thanks. I'll get back to ya.

Share this post


Link to post
Share on other sites

You know Twang tube amps are almost living things! I know it sounds weird, but things like parasitic oscillation and simple cable dress and routing can make an enormous difference in some designs. Stick with it you'll get it right!

Share this post


Link to post
Share on other sites

I had three marshallized.. all identical.

but one.. made noise acted up drove me nuts..

and finally, I just, as suggested to me, moved some controls. and it stopped.

I swear they were identical. but that one amp just said. I don't want to be identical.

 

The supro got dead quiet .. and now it's just a noise machine.

 

I took the day off. First in a long time, even for sunday.

For one thing, I cut my fret hand index finger tip stripping wire and I NEVER hurt my fingers working.

sometime you have to step back.

 

I'll get a signal into the EL34 on monday and see what's going on. I hope.

Share this post


Link to post
Share on other sites

phone pics but pics.

I can't see anything. I can't find a test it wont pass.

There's extra wire and a couple of funky things.. but that's ok until last go through.

*like the non sheilded wire to the pot, etc.*

 

 

EL34FIX1.jpg

 

EL34FIX2.jpg

 

EL34FIX3.jpg

Share this post


Link to post
Share on other sites
phone pics but pics.

I can't see anything. I can't find a test it wont pass.

There's extra wire and a couple of funky things.. but that's ok until last go through.

*like the non sheilded wire to the pot' date=' etc.* [/quote']

 

That point to point wiring layout can certainly get messy.

 

It's hard to tell from the pictures with basically a "rats nest" of components soldered in random orientations.

Sometimes it's just a matter of an extra wire strap to b+ or ground that is missing.

 

Can you draw the preamp schematic for us free hand or take a pic of the one you were using?

So we have a better idea of what you were doing.

 

Ok here's another question to throw out at you. Do you have the control grid bias resistors for the preamp

wired in properly. Do you have the cathode bypass electrolytic soldered in? This is necesary for a/c signals.

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
Sign in to follow this  

×
×
  • Create New...