Filament wiring question

[Magnetmaz]

I've looked at about a hundred schematics for tube guitar amps today and i can't seem to find one that illustrates just how to wire the tube heaters. All of the schematics show an output off the power tranny that runs to the power lamp, then to the tube filaments but doesn't actually picture it.

Can someone please help me out with this one? How exactly do i wire this?

Here is the original schematic. Note the upper left hand corner where it says "to all 6.3 volt heaters" but then leaves off which pins and in which order....etc. If someone could possibly photoshop some green wires over the diagram to show me how it would be wired that would rock.

http://www.ampwares.com/ffg/schem/princeton_reverb_aa1164_layout.gif

I'm a total tube newbie here.

Thanks

 

[SY]

No Photoshop here (sob!), but it's so easy, you don't need it. All the filaments are wired in parallel. That's it.

 

[dhaen]

SY, you forgot to mention that the wire pair should be tightly twisted together, and it's best to "daisychain".

 

[Magnetmaz]

i went and looked up the pin specs on the 6v6 and the 12ax7,...

and i think i can visualize how to daisy chain these up .....


is there any sort of polarity to the tube filaments?

 

[SY]

Excellent point, John.

If you've got 12AX7s in there, you want to wire them as 6.3V tubes, i.e., one connection to pin 9, the other to pins 4 and 5 (4 and 5 tied together). There's no polarity to filaments- life is sometimes easy.

 

[SHiFTY]

12AX7 - 12.6V filament with a centre tap (actually two 6.3V tubes joined in the middle)
6V6 - 6.3V filament

Run them in parallel if you have a 6.3VAC transformer. I always think of them like really crappy flashlight bulbs.

5U4 - 5V filament (needs a separate winding on the trannie)

They usually leave the filaments off the wiring diagrams to make the diagram less complicated, which is a good thing

And yes it is a good idea to use reasonably heavy stranded wire neatly twisted, and you can daisychain one valve to the next. They have to carry a fair amount of current, so make sure to use a thick enough wire.

BTW that is a very confusing wiring diagram- make sure you double and triple check it with the actual schematic diagram.

 

[Magnetmaz]

aw crap....i look for another 15 minutes and find this :
http://www.hoffmanamps.com/images/heater.gif

guess i posted too soon

Incidentally, the 5U4 is being used as a rectifer, and the 4 other leads besides the 2 green ones that go to the heaters all go through the 5U4.

Another question....

to the left of the turret board is an old school fender type Cap... it looks like this : http://shop.store.yahoo.com/torresengineering/cantypfilcap.html

here is the original schematic
http://www.kbapps.com/audio/schematics/tubeamps/fender/princetonreverbaa1164.html


any idea if i can just use a few 20 mfd caps instead of this $40 antique?

 

[dhaen]

There should be no problem using individual caps.
Personally, I'd go with the original if finances allowed.

 

[SHiFTY]

Yeah you can just use any old caps - provided they are of a high enough voltage rating. You should keep to the same uF values though.

I built a little 4W 12AX7/EL84 guitar amp just using el cheapo parts from an old tube tape deck, sounds pretty good. However I want more gain for more distortion!

PP 6V6 should have a lot of power esp. overdriven- hope you have a big funky speaker for it (hopefully a 12 or 15")

Its pretty cool when you first fire it up, that first jam is very enjoyable

 

[GRollins]

There was a question back up there somewhere about heater polarity. There isn't any. If you're using AC to run the filaments, it's a moot point. If you're running DC (most guitar amps don't--they use AC), then you can run them either way you want.
If you really, really want to get strung out, you can run DC filaments and reverse the polarity at intervals. Why? Because at the positive end, there's more potential and more electrons are boiled off (think of a long resistor, with the voltage dropping steadily along its length). Over time, the filament will age unequally from one end to the other. Note that not even the highest of the high end stereo companies worry about this. It's not worth losing sleep about.
Unless you want to start a high end guitar amp company and blow Mesa into the weeds...

Grey

Edit: Individual caps are fine.

 

[fdegrove]

HEATERS

Hi,

You can even run them from a negative voltage supply.

This can be useful at times where running them positive may just surpass heater to cathode insulation.

Going for a negative supply here will negate the need to lift the heaters.

Cheers,

 

[dhaen]

Frank,

I'm probably being "thick" here, but I don't understand your post.

Going for a negative supply here will negate the need to lift the heaters

Makes no sense to me.

Please explain to a simpleton..

 

[fdegrove]

WRONG FISH

Hi,

LOL.

Damm...I was just making sure Grey was alert and now I got you
in my nets...

While of course the first claim is valid...it doesn't help the heater to cathode insulation one bit.

Well...at least you're awake.

Cheers,

P.S.Noticed how the entire forum comes alive all of a sudden. ?

 

[Magnetmaz]

alright...another question.

I notice this amp predates the installation of a "standby" switch to turn on the heaters before you start wailing away..... i dont want to prematurely age my tubes, ....so....

any idea where in the schematic i should put an SPST?

 

[Joel]

I notice this amp predates the installation of a "standby" switch to turn on the heaters before you start wailing away..... i dont want to prematurely age my tubes, ....so....

Have you ever seen a hi-fi with a "standby" switch. This is another Fender marketing gimmick.

 

[dhaen]

Have you ever seen a hi-fi with a "standby" switch. This is another Fender marketing gimmick.

Joel, whether a "gimmick" or not on HiFi, it's not on instrument amplifiers. It's a quick way to come alive.

 

[Magnetmaz]

Well, its not just fender....its just about every other tube guitar amp built since 1967.

I've read alot of articles in the last couple days about how pushing a signal before your tubes have their 20 seconds of warmup time will lead to "plate stripping" or something where the tubes become less effective over time...

and i'm not questioning your call......i'm just curious why it seems so widespread.

 

[Joel]

Well, its not just fender....its just about every other tube guitar amp built since 1967.

Sure. And most also have black "tolex" coverings too. It's called "keeping up with the Jones's" in our country.

I've read alot of articles in the last couple days about how pushing a signal before your tubes have their 20 seconds of warmup time will lead to "plate stripping" or something where the tubes become less effective over time...

You can read a lot of articles full of *bs* directed at musicians. They are mostly full of half-truths, blatant inaccuracies, and groundless mythology. See "A Desktop Reference To Hip Vintage Amps" by Weber for a blaring example. This is now considered a bible amongst guitarists.

I have a 1937 Gibson EH-150, with nearly 400V on the output tube plates. It has all of its original tubes.

 

[Magnetmaz]

ideally, rather than tolex (which i hear is environmentally unsound) what would i use as a cover instead? Or should i just stain and poly the bare wood?

 

[dhaen]

Magnetmaz,

There is some disgreement as to whether the "cathode stripping" phenomenon exists or not, and under what conditions it (might) occur.

For an instrument amplifier, I would fit a standby switch anyway, because it allows "instant on". Whether you sequence the switches every time is up to you.

Cheers,