My EL34

[TWANG]

I used http://turretboards.com/layouts_schematics/vjr/vjr_layout_main_marshallized_octal.pdf

turretboards.com layouts.. vjr. marshallized octal

 

but I did swap some values as per M Theorys amp.

The wiring seems to me to be perfect. I've been over it too many times for any obvious error.. so it has to be something that is, sort of,

able to hide.

 

I followed all solder joint testing.. component testing to the max, and repeated, and even replaced.

Still it eludes me completely.

 

When it was running I thought all I had to do was choose control options and clean up/shorten the wiring.

 

You can see the things that would be improved at final build.

that floating orange cap..

the too long wires and too vibration prone setup of the cement blocks..

the long red unshielded wire to the vol. pot...

the plain wire replacing R10, instead of covered wire..

Some degree of anal interfernce with the front star grounds looks..

etc..

 

In short it should have been all cosmetic for the most part with some incidental performance improvement.

Instead it's been a month of sitting here feeling stupid.

[carverman]

but I did swap some values as per M Theorys amp.

The wiring seems to me to be perfect.

 

How can it be "perfect"' date=' if you are saying you have no gain in the preamp?

How come the picture of the amp looks so much neater than yours?

 

What is the preamp tube? Do you have a schematic for it or are you just building it from the

pictorial (kit?) provided?

 

I've been over it too many times for any obvious error.. so it has to be something that is, sort of,

able to hide.

 

I followed all solder joint testing.. component testing to the max, and repeated, and even replaced.

Still it eludes me completely.

 

You are sure you have the correct components, resistor values and the tube is

biased correctly. What are you using fixed divider input bias and cathode bias?

 

 

When it was running I thought all I had to do was choose control options and clean up/shorten the wiring.

 

So you had it running at one point then you started to mess around with it?

 

You can see the things that would be improved at final build.

that floating orange cap..

the too long wires and too vibration prone setup of the cement blocks..

the long red unshielded wire to the vol. pot...

the plain wire replacing R10, instead of covered wire..

Some degree of anal interfernce with the front star grounds looks..

etc..

 

In short it should have been all cosmetic for the most part with some incidental performance improvement.

Instead it's been a month of sitting here feeling stupid.

 

 

Where is the schematic for this thing?

[TWANG]

It's a valve junior with an el34 the schematic is everywhere.

 

The component value changes were made according to M Theorys build.

The signal is lost.. which happened when I didn't touch anything not involved in the OT swap...

so must have already been a mistake? or a bad job of -- something I can't find.

 

 

"seems to me to be perfect" shouldn't need explanation. How can you focus on 'perfect' when it's preceeded by 'seems'?

 

I always work from a layout pinned over my bench and a schematic, when I have one, in my folder drawer.

 

I'm happy with my degree of neatness!

 

If the bias were off, it wouldn't be off by enough to kill the signal in the preamp stage, would it?

 

 

Some ****** thing is going on.. and of course I'm the ****** that did it.

so now we've established that, .. I wonder what could be wrong in there.

 

Had to refret a guitar and finish some guards today so.. didn't get to this at all.

 

 

Thanks!

I really appreciate anyone willing to take some time with my amateur/hobby problems.

 

 

TWANG

[carverman]

It's a valve junior with an el34 the schematic is everywhere.

 

The component value changes were made according to M Theorys build.

The signal is lost.. which happened when I didn't touch anything not involved in the OT swap...

so must have already been a mistake? or a bad job of -- something I can't find.

 

You need to establish which preamp section is (not) working.

 

Is it v1A or V1B? Assuming correct components and necessary jumpers installed...take a

signal generator and inject a signal at the wiper of the volume control. That will take you

directly to the second stage. It would be nice if you had some kind of signal tracer' date=' but

obviously you don't and when trouble shooting amps, you need something more than an

led or lightbulb.

 

Here's some ideas to explore:

 

Do you have a shielded wire with the shield connected to the volume control and the circuit

board?

 

Are the cathode bypass caps (22 uf) for both preamp stages installed observing

correct polarity at the cathode connections?

 

 

If the bias were off, it wouldn't be off by enough to kill the signal in the preamp stage, would it?

 

It might. It depends on how much it's off. Usually its a negative dc level of a volt or less.

 

 

Some ****** thing is going on.. and of course I'm the ****** that did it.

so now we've established that, .. I wonder what could be wrong in there.

 

Well it's not rocket science, but in order for a tube to conduct and amplify the signal

present at the control grid, you need a negative bias on the control grid, a plate voltage

present at one side of a plate load resistor and a connection of the cathode to ground,

via a cathode bias resistor. The a/c signal bypass cap (cathode) just allows the ac signal to flow from

ground to the plate through the tube without being attenuated by the dc potential cathode resistor.

 

So:

 

if the ground connection is missing from the power supply ground plane, then nothing is

going to happen in that stage.

 

I don't know how you wired it up, so I can't help you there,

but it helps to follow a schematic and understand what the component or wire

jumper is doing in that stage. Otherwise, if you are just doing connections without an

understanding of the circuit, steps could be missed.

 

I think that you need to double check all the connections to the tube sockets again

following the schematic and check off each point connection to make sure both ends

are connected to something.

 

That ground needs to be connected to

the ground of the power supply filter cap at B3 which goes through a 10k voltage

dropping resistor before it goes to the plate of both preamp stages.

 

 

Without a signal generator/scope it's a lot harder, but should still be achievable.

[Strumbone]

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.

 

 

That would be carverman in the post up above. Heck, before I cleaned out the attic, I had a signal generator and a 20Mhz "O" scope from my Navy days...sigh.

[TWANG]

currently that's an unsheided wire as I noted.. the red one.. I took out the original sheilded one just to see if IT was a problem.

no difference.

 

and yes I gotta get a signal in there and see where it's stopping.

 

all the parts are ground correct and value correct.

 

I'll get in there though.. and double triple quadruple check.. again!

[TWANG]

my pc speakers which I pulled out of storage had no wall warts..

DER KOMMANDANT

decided to neaten the storage area and the pc speaks were not labelled for which wall wart they needed.

 

soooo.

 

off to the junky store to pic up some used ones so I can get a signal through there.

[TWANG]

ok. now have portable cd player and set of cheapo pc speakers.

 

 

so now I have to test myself on knowing how the dang preamp works

and hope I don't fry the cd player or speakers too soon.

 

I have a supro build with some noise in it, too.. so this should help with both amps.

 

and carver is right .. no layouts here. gotta use the schematic for this.

 

so.. off I go for the final push.

 

(dang those supro vjs sound cool)

[TWANG]

hey what happened to the instructions on how to build the pc speakers.. cap on probe, etc..

can't seem to find the thread.

[deflepfan]

hey what happened to the instructions on how to build the pc speakers.. cap on probe' date=' etc..

can't seem to find the thread.

[/quote']

Was it a victim of TGC (The Great Crash)?

Sheila

[TWANG]

can I

 

hook up a cd player to a couple of probes..

clip phones ground probe to star ground on amp..

turn on amp..

play cd

 

place hot probe off cd phones output to..

input jack tip..should get music!

 

then r2 at pin 2

so right there I would be testing signal clarity for the jack.. and r2 to the pin.

so if I had a really bad R2. I should hear it..

 

 

would I then ignore R1. the pull down resistor..

that would be the 470K on the supro vj..

that is. I wouldnt' run the hot cd signal to the ground side..and I've already tested to the pin.

 

so

 

I would connect the signal to R3/C1

plate resistor and coupling cap..

where they connect.. and lead to v1a

 

and then R4/C2

to check v1b..

 

then the vol pot in and out..

 

how about R9/C3 R8/C4 ?

 

 

I'm just not sure of what all would be safe..

[carverman]

can I

 

hook up a cd player to a couple of probes..

clip phones ground probe to star ground on amp..

turn on amp..

play cd

 

place hot probe off cd phones output to..

input jack tip..should get music!

 

then r2 at pin 2

so right there I would be testing signal clarity for the jack.. and r2 to the pin.

so if I had a really bad R2. I should hear it..

 

 

would I then ignore R1. the pull down resistor..

that would be the 470K on the supro vj..

that is. I wouldnt' run the hot cd signal to the ground side..and I've already tested to the pin.

 

so

 

I would connect the signal to R3/C1

plate resistor and coupling cap..

where they connect.. and lead to v1a

 

and then R4/C2

to check v1b..

 

then the vol pot in and out..

 

how about R9/C3 R8/C4 ?

 

 

I'm just not sure of what all would be safe..

 

 

Inject the a/c signal througha coupling cap (.01 uf) to the control Grid of a tube if you want to

test for conduction (amplification) of the tube. Check your schematic and figure out where that

is on each tube base.

[TWANG]

I got back in it tonight but to no avail.

took the board completely out..

not a thing could I find that didn't seem right on the money.

I replaced a couple of oxide resistors just for the halibut..

I replaced the rat shack non polarized, same reason.

 

So.. time to build the signal generator.

 

but I think I'll use an old cd player first and

 

Inject the a/c signal througha coupling cap (.01 uf) to the control Grid of a tube if you want to

test for conduction (amplification) of the tube. Check your schematic and figure out where that

is on each tube base.

[carverman]

I got back in it tonight but to no avail.

took the board completely out..

not a thing could I find that didn't seem right on the money.

I replaced a couple of oxide resistors just for the halibut..I replaced the rat shack non polarized' date=' same reason.

[/quote']

What are oxide? Cracked carbon composition, metal film, or something else?

Did you measure your resistors to see if the value is correct?

 

but I think I'll use an old cd player first and

Inject the a/c signal througha coupling cap (.01 uf) to the control Grid of a tube if you want to

test for conduction (amplification) of the tube. Check your schematic and figure out where that

is on each tube base.

 

Well don't keep us in suspense for all these weeks...we could have sent Apollo 13 to the

moon and back by now..except for a small.."Huston! I think we got a problem!

which we will change to. "Forum"...I have a problem! and I've double and triple checked

everything..now can we collectively troubleshoot for me?

 

Duct tape..that otta do it..they used it on Apollo 13 when the square tubing of the

command module air system didn't fit the round holes of the carbon dioxide scrubbers.

NASA engineered of course..square pegs can fit into round holes...

 

CD player will work, but put it through some kind of volume pot first, if you hit a 12ax7

preamp with too big a signal you will get distortion. Its a crude way of doing it, but

you may be able to establish something..and the saga of the mysterious "why is it

not working?" problem continues....

 

BTW..if you are going to inject a very low signal and I do mean very low..a few millivolts

into the grid of the preamp tube...you will need something to see the results of any

tube amplification at the plate of the tube..how are you planning to take off the

signal without a signal "tracer"?

[TWANG]

metal oxide.. new one one you?

everything was tested, and more than once.

bare wires were tested.

 

Yes, I do come in here for the collective experience of those willing to add to the learning experience.

That's a big part of the point of calling it the human race, sez me!

 

I'm going to try the cd player because I have to order stuff to get a signal injector built.

 

I don't know what

 

how are you planning to take off the

signal without a signal "tracer"?

 

that means. Having never done this before.

Thanks for the help!

[carverman]

metal oxide.. new one one you?

Yes.

 

Yes' date=' I do come in here for the collective experience of those willing to add to the learning experience.

That's a big part of the point of calling it the human race, sez me! [/quote']

it's more like the rat race these days...

 

I'm going to try the cd player because I have to order stuff to get a signal injector built.

I don't know what that means. Having never done this before.

 

Signal in (grid of tube..then something magical happens...tube conducts..signal appears amplified

at the plate load resistor..if the tube is working that is.

 

If you don't have a signal tracer..take a .01 400v cap and maybe 1 megohm resistor in series and connect it to a jack cord to another amp you have kicking around...turn the volume down at first. make sure you have an ac signal only

and not dc potential which can be quite high. The coupling cap will ensure that only ac amplified

signal from the tube is passed and block the dc potential at the plate resistor..comprehende?

 

So lets say the tube has a gain of 100...and you inject a 10 mv signal.

That should be 100 x 10 = 1000mv at the plate resistor.

If the tube is not conducting, then something is not connected..either the cathode, cathode resistor,

cathode bypass cap or the plate resistor. If these are connected and the B+ is there

it should work, provided the heater warmed up.

[TWANG]

I still consider myself new to this in many ways. Though I've been at it a fairly long time.

 

I've been corrected about Resistors a few times.. like using higher wattage than would ever be needed.. or putting R in places where a different type

would be better.. I understand Metal Oxide can be noisy in some spots.

I haven't printed out the info I've collected.

 

What I do is keep to bulletin boards near my bench..

One in front of me. layout or schematic..

and one off to the side, much bigger, with anything I forget more than once... a general reference board with diagrams, illustrations, pictured, information, charts, etc.

 

I'm redoing that board now as some things I have actually learned and don't need reminders, and some things, like where to put which type of resistor, will go up in it's place.

 

I do not, still!, have a full understanding of how the juice passes through the front end, IOW how it 'works' through the tube.

 

So.. sorry to blather on, but maybe that will help people to realize why sometimes I get stumped.

It's very hard to make an education, as opposed to being taught.

 

I will have to read your post again. apply serious thinkitude. and see then if I understand it.

 

Here's what I'm guessing as I read it now.

 

.01uF cap 1M R in series.

 

but connected how?

to where?

input of other amp?

output of other amp?

 

 

I'm guessing that you mean.. connect a cord to the input of another amp. volume down. turned on.

the free end of the cord will be a tip with the components added to it.. the ground being perhaps alligator clipped to ground in the

amp I'm testing.

 

??

 

So my first question is.. will my meter then show no dcV if I test at the free end of the cord.. and just show acV?

in which case I'd be ready to test the problem amp.

 

So. I'd then measure mv at the cord.. and touch tip to plate Res. of problem amp..

If it isnt' conduction then I have to look at

 

cathode, cathode resistor,

cathode bypass cap or the plate resistor

 

I feel they ARE connected, I feel the B+ is there. it tests there on the meter..

 

so the question next is..

the heaters read 6.5.. very good given 6.3 is supposedly perfect.

but does that tell me the heater warmed up?

 

IOW that should indicate the heaters are getting V's.. and if the tube works in another amp so we assume it's a good tube..

 

 

There's an old timer here in town, retired.. I think I'll pop over there and see if he'll give me a laugh..

also I'll post some pics with the new camera.

 

But you gotta stop making fun of my mess. *G* Man I can't keep it neat AND go over and over and over it changing things.

 

thanks again.

TWANG

[m-theory]

I can't keep it neat AND go over and over and over it changing things.

Maybe that's cause enough to completely disassemble the board and start over from scratch. Sometimes, as much as it sucks to do something that drastic, that turns out to be the best path to take. Obviously, SOMETHING on that board isn't right, or you'd have it working by now, right? So, if the board's a mess right now anyway, what have you really got to lose by taking it all apart and starting over, other than a couple hours of your time, which will probably be spent just debugging the mess anyway.

 

I have found, without any deviation whatsoever, that whenever I'm sloppy in any way in my electronics work, it comes back to bite me in the *** somehow, someway, at some point. I ALWAYS end up rebuilding the sloppy section and it ALWAYS pans out better for me.

[TWANG]

I don't see any other path.

I do generally build a bit sloppy as far as wire length or lead length then when it's done being tweaked.. neaten it all up.

Might as well just do it, after all, it will give me a chance to really double check every bit.

 

 

I took my recent marshall build.. which is inexplicably making noise.. to the local retired guy..

He's pretty cool.. you should see his leftover components, etc.. boxes and boxes of tubes.. NOS.. RCA mostly..

carbon comp resistors. I checked and he's got the Mojo R4s..

tons of stuff.

I told him I'd come buy and buy parts off him from now on instead of online.. besides it's way great to be able to talk to someone who's done all this

for years.

 

Anyway.. He showed me a way to test for noise I hadn't run into before..

and he said the amp .. not the el34, the marshall.. just has a mistake and I have to find it.

He kinda grinned about it, and you know. I wasn't offended. sure He's laughing at me a little bit. but

I think that grin is also from someone who's hit a wall of similar type.

 

so. Off I go on that amp to try the new test.

and then I tear the el34 to bits.. AFTER I get the parts from him to make carvermans test tools!

He's got everything down there I think.. old stuff from sprague and transistors and. on and on.

[carverman]

I do not' date=' still!, have a full understanding of how the juice passes through the front end, IOW how it 'works' through the tube. [/quote']

 

Ok here's a quick 101 on tube theory TWANG. Yer gots yer plate with a very positive

high dc potential on it.(.the anode actually), then you gots yer cathode which is biased

to ground and is the source of millions of these little guys called electrons, which like

to flow from negative to positive..if left unimpeded by something called a control grid

which acts sorta like a gate.

 

If you bias this gate (grid) with a negative voltage (it's like closing

the gate shut so that very few of these electron suckers get to the plate. If you make

the grid (or gate) less negative than its normal no signal bias, (ie: more positive),

then more of these little electron suckers rush over to the plate (from the electron rich

coating on the cathode) to complete the circuit back to the power supply.

 

The a/c signal (the signal from a guitar or signal generator) modulates the grid bias making it less negative and

depending on the transconductance (gain) of the tube and the biasing resistors, and the

plate resistor which allows the tube to work..then a miracle happens and a larger signal

than what you put in should be present at the plate end of the load resistor.

 

 

Here's what I'm guessing as I read it now.

.01uF cap 1M R in series.

but connected how?

to where?

inpt of other amp?

 

 

I'm guessing that you mean.. connect a cord to the input of another amp. volume down. turned on.

the free end of the cord will be a tip with the components added to it.. the ground being perhaps alligator clipped to ground in the

amp I'm testing.

 

YES

Well essentially you are taking the signal out of the preamp stage and a/c coupling it and to eliminate overloading

the input stage of your amp, you should use some kind of voltage divider ..like a 1 meg resistor in series with the

tip of the guitar cord..but at the end of the cord you are using for testing. The other end is just a 1/4 phono jack

that you plug into a guitar amp input. It's a crude way of testing for signal, but if the tube is amplifying, you should

hear your CD signal passing through the pream stage (under test) and into the working guitar amp.

 

Since you don't know which stage is NOT working on this amp, you can't depend on the o/p tube to do the job

unless you know for sure it is working.

 

 

So my first question is.. will my meter then show no dcV if I test at the free end of the cord.. and just show acV?

in which case I'd be ready to test the problem amp.

 

IF you a/c couple at the plate resistor, the cap should not show any dc voltage on the end of the cap that

goes to the 1 meg resistor and cord. As far as ac volts. ,most ac meters may have trouble reading audio signals

but there should be some deviation on the ac scale.

 

So. I'd then measure mv at the cord.. and touch tip to plate Res. of problem amp..

If it isnt' conduction then I have to look at

 

cathode, cathode resistor,

cathode bypass cap or the plate resistor

 

Yes, but don't forget the grid bias resistors as well.

 

I feel they ARE connected, I feel the B+ is there. it tests there on the meter..

Then there is no reason why the tube shouldn't work..as long as you have the connections

with the correct resistors connected to the elements of the tube. it has to work...unless you

have a dud tube and that is unlikely.

 

so the question next is..

the heaters read 6.5.. very good given 6.3 is supposedly perfect.

but does that tell me the heater warmed up?

 

It depends on how the heaters are wired... in parallel (need the heater center tap wired to gnd), or in series (12.6)

I presume from what you tell me that the heaters are wired in parallel? In that case pin 9 should go

to ground as it divides the heaters in parallel. Of course the heater current will be higher (300ma).

 

 

But you gotta stop making fun of my mess. *G* Man I can't keep it neat AND go over and over and over it changing things.

 

thanks again.

TWANG

 

Did I make fun of your mess? Sorry about that..I just mentioned "rats nest" a few posts back. Ok, I won't

do that anymore.

 

Did you mean *C* man? I never worked for the govamint..so I'm not a "G" man unless you meant someone

else on this forum.

ok, do the best you can to get it working.

[TWANG]

Carver I'll read your post later. I'm busy right now.

BUT

 

 

I wanted to tell a quick story here.

 

My supro build was noisy and wouldn't quit no matter what.

I tried and tried and finally built a new board and made a marshallized jv.

 

SAME noise!

 

spent lots more time. no results.

 

Went down today to a guy who's retired repairman..

he suggest..

put a R over any grid R and see if that tells you..

 

so I put a 10K over R5.. just holding it with needle nose over the R while amp live.

noise stopped!

Replaced R5. which was testing good everytime..

noise gone!

 

BUT then I discovered..

the amp was a bit wobbly on the bench. so I went to straighten it out..

when twist pressure. very slight. applied to amp.

noise came back..

So there is one more thing wrong..

 

somehow the pressure of twisting the chassis or the board made it show up.

 

I'm convinced now that I'm finally onto this amps problem.

It sounds good.. so long as you don't twist the chassis. Of course, I'll fix that, but boy I feel much better!

 

and The *G* was old school pc shorthand for *grin*.

 

and no offense taken, that's why the *G* was there..

 

Everyone's cool in my book!

[carverman]

So a "twist of fate" brought your old problem back?

You know, you could write a book on this little amp adventure.

Check all your ground connections.

[TWANG]

turns out I jumped the gun on that amp too.

I was out until three am .. second night in a row with that amp.

 

same noise.

 

the el34. I'm sure I'll find. it's happened to me before and it's a question of finding the spot..

 

but the above amp..

it's amazing.

Last night I swapped at least six components.

Yes. the testing was TOTAL.

I checked every wire for ohm.. all fine..I checked grounds.. all fine.

I put a wire to ground and then connected the other end to each ground point.

No change.

I pulled off all the controls, tone volume gain.. and replace the vol. pot twice.

no change.

 

There' s nothing left to do on that amp except tear it completely apart and start over.

which will be the second time!

 

I am plagued.

 

you can twist the amp all you want now it has no effect.

I think that there is something in there.. that was there from the start. that's what created the noise .

I think that I didn't cure the twist noise problem. I think I made it permanent.

 

I think I'll even replace the sockets this time.

 

 

The el34 for all it's hassle is, to me, still just a simple typical thing that can happen. somewhere it's grounding out or not passing the juice.

but this other amp.. it's cursed by demons.

[carverman]

turns out I jumped the gun on that amp too.

I was out until three am .. second night in a row with that amp.

 

 

There' s nothing left to do on that amp except tear it completely apart and start over.

which will be the second time!

 

I am plagued.

 

Sounds like you need to call one of those demon exorcizers. That amp is possessed!

If it gets to you' date=' next thing you know you will be levitating off your bed and talking

demon gibberish...

 

you can twist the amp all you want now it has no effect.

I think that there is something in there.. that was there from the start. that's what created the noise .

I think that I didn't cure the twist noise problem. I think I made it permanent.

 

You mean you finally broke it?

 

I think I'll even replace the sockets this time.

Why replace the sockets? That's troubleshoot ing using the shotgun approach.

Why not just get a shotgun and some buckshot?...

 

but this other amp.. it's cursed by demons.

 

 

Lyrics for Exorcising Demons :

 

I've been frustrated with this amp of mine,

And I've been stumped too long

Even though I've tried in many ways

To figure out where I went wrong

 

Don't seem to have time for anything else

Or all the dishes piled up in the sink

It just keeps coming back to haunt me

Sometimes I can even hear it taunt me

 

So leave me now demonic infiltrators and be gone

Leave my amp(s) alone tonight

Stop this electrical insanity once and for all

and please... just let me see the light!

[TWANG]

I tried chanting that nude in the forest and some really mean squirrels giggled at me mercilessly.

And to think I feed their city cousins all winter!

 

I emailed the guy waiting for this. it was supposed to be a fun build for me and a cheap amp for him..

I'm giving him all this suffering, a weber OT and a complete rebuild. for 60.00

I've never been so embarrassed.