Philips 6411 PA tubeamp ground points

[kagliostro]

EDIT: old and new threads merged. New thread starts here, post #8. -PRR
Yesterday at a Flea Market I got a Philips EL6411/01 PA amp

(and 1 el81 tube) for € 25,00

the schematic shows 2 x ef40 + 2 x ecc40 + 4 x el81 tubes

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but inside the amp the chassis is labeled for 2 x el86 instead of 2 x ef40

I've read that electrically the ef86 is the same of ef40

don't know if the ef40 is more or less prone to be microphonic than ef86

here there are some infos that suggests ef40 in a good substitute for ef86 (may be better ???)

http://www.r-type.org/pdfs/ef40.pdf

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I've read the ecc40 (CV3884) tube is between an ecc82 and an ecc83

there is a right new tube substitute for it ??

http://www.r-type.org/pdfs/ecc40.pdf

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if I connect the speaker between the 10v and the 25v pins, can I use an 8ohm speaker ???

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as you can see the amp has two input tubes and I would like to have councils about to guitarize it

may be two different arrangements for two different inputs ?

may be to use one ef86 as V1 and the other as V2  ???

Thanks for any council about

Kagliostro

http://frank.pocnet.net/instruments/Philips/EL6411/EL6411.pdf

I'll prefer to avoid new holes in front - Sure I can use the little switch and the hole of the knob  of the ef86 bypass pot for other use

[tonewood]

Hi Kagliostro

Sorry I have more questions than answers but it sure looks cool & would be worth putting some effort into.
I couldn't get to the el6411.pdf file you posted.
I'm sort of afraid of contact bias like on the ef 40s simply because I don't understand how it works. Can you explain? If it were switched to cathode bias, could it sound exactly the same as the contact biased version?

thanks

[DummyLoad]

that is a cool find. 

should make a fine guitar amp as-is. love the switched "speech & music" filter. you could connect the two inputs to an A-B switch to select between input channels. if needed trim R24 to burn off gain so as to not overdrive the last gain stage and DC coupled concertina if your concertina goes in doubling. i'd replace the OA55 diode with a 1N4005-7. a cap job is likely to be a must. if it's too bass heavy, replace 68nF coupling caps coupling caps w. 22-47nF.

ECC40 uses an 8pin rimlock socket. here in the states they are rare and difficult to outside of the ebay market. don't know of other rimlock tubes with similar characteristics as i'm not too familiar with euro tubes.

just run two 8 ohm in series and use the 16ohm tap, or tie two 8 ohm in parallel and use the 3 ohm tap. it's a 40 watt amp, so you'll probably want to use 2 speakers.

EL81 is an interesting tube. data-sheets show TV horz. deflection and A.F. output service. conditions show an A.F. output of 20W for two tubes P-P at a paltry 200V B+.

just a thought, but before you fire it up, look for crumbled insulation on the plate cap wires - especially where they exit the chassis.

some pics of the guts would be cool!

--DL

[Frankenamp]

http://frank.pocnet.net/instruments/Philips/EL6411/EL6411.pdf

I can understand not wanting to make more holes in the chassis- beautiful metalwerk! Frank has quite a bit of info on his site.

[kagliostro]

Tonewood

I couldn't get to the el6411.pdf file you posted

Sorry there was something wrong into the link - try it now

I'm sort of afraid of contact bias like on the ef 40s simply because I don't understand how it works. Can you explain? If it were switched to cathode bias, could it sound exactly the same as the contact biased version?

Not able to understand well the question (and probably don't know the answer) hope someone can give help

DummyLoad

i'd replace the OA55 diode with a 1N4005-7 -  a cap job is likely to be a must - just a thought, but before you fire it up, look for crumbled insulation on the plate cap wires - especially where they exit the chassis

I agree

if it's too bass heavy, replace 68nF coupling caps coupling caps w. 22-47nF

if needed trim R24 to burn off gain so as to not overdrive the last gain stage and DC coupled concertina if your concertina goes in doubling

precious councils

ECC40 uses an 8pin rimlock socket. here in the states they are rare and difficult to outside of the ebay market. don't know of other rimlock tubes with similar characteristics as i'm not too familiar with euro tubes

May be I can find ecc40 at flea market (yesterday I got 4 x el81 NOS NIB tubes) but I was thinking to noval socket tubes like 12a*7 as to substitute (may be a 12au7 is fine ??)

just run two 8 ohm in series and use the 16ohm tap, or tie two 8 ohm in parallel and use the 3 ohm tap. it's a 40 watt amp, so you'll probably want to use 2 speakers.

yes I can do, but I was interested to know which will be the supposed impedance connecting to the 10v & 25v pins - also would like to have a math lesson about if someone has a few time to spend for that

some pics of the guts would be cool!

The photo I posted is from the web (soon I'll post someone of mine) - my unit is in near good conditions but not perfect, the plastic front panel is a bit ruined, but I think I can remediate (also there were some mods on the back of the amp for connections) - in my mind it will be nice to have the metal colored in different way than the plastic front panel, something like this Honda, the front panel of the color of the tank and the metal the same color of frame and fenders - the photo isn't so good but hope you understand

I think I must guitarize V1 circuit, as is the gain is too much (5.5 mv) don't you think ?

you could connect the two inputs to an A-B switch to select between input channels

do you mean to maintain two identical input (V1) circuits or to arrange it in different way ?

what about a switchable paralleled pentode input ?

Thanks

Kagliostro


p.s.: Frankenamp - you wrote the same time I was witing

Frank has quite a bit of info on his site

thanks I had the link but there was something wrong on the link I posted
 

[birt]

just to show what you can do with these old gray painted metal chassis:

[PRR]

> if I connect the speaker between the 10v and the 25v pins, can I use an 8ohm speaker ???

Yes.

> to guitarize it

Just plug and play.

It will be hot, easy to overload. Even when gain is turned down, the input grid may overload because there is "no" bias on the input tube. Try 1K cathode resistor on first tube.

Set up the other input as Pentode (right now it is triode-wired) and put a Fender Black-face tone-stack and volume control between plate and R14 270K mix-resistor. Try 100K plate resistor, 470K + 0.1uFd screen network, 2.2K cathode resistor with 0/0.68u/10u cap.

[kjulhansen]

Yesterday at a Flea Market I got a Philips EL6411/01 PA amp

(and 1 el81 tube) for € 25,00

the schematic shows 2 x ef40 + 2 x ecc40 + 4 x el81 tubes

---

but inside the amp the chassis is labeled for 2 x el86 instead of 2 x ef40

I've read that electrically the ef86 is the same of ef40




Kagliostro

Hi Kagliostro

I know this thread is 10 years old....but one question concerning the Philips EL6411. 

I recieved a 1956 Philips EL6411 sample for repair....just to help a friend. Unfortunately this Philips PA amplifier has been soldered several times, and many ground connections changed...this is easy to detect and see because of many scratches inside the chassis. A lots of things is changed...silicon instead of selen rectifiers and so on

A few bottom view pictures of another similar Philips EL6411 tubeamplifier would be a great help to bring the tubeamp back to factory standard.

Some of the wiring is obvious but the input groundpoints creates noise and hum on the output temninal in the area of approx 150mVAC

I have made several DIY tubeamplifiers, but I need a little help on this one

Thanks in advance

Rgds Kim

[kjulhansen]

https://el34world.com/Forum/index.php?action=post;quote=108396;topic=11703.0

Hi

In the old thread above I have asked for a few bottom view jpg´s concerning the Philips EL6411 PA tubeamp. 

I recieved a 1956 Philips EL6411 sample for repair....just to help a friend. Unfortunately this Philips PA amplifier has been soldered several times, and many ground connections changed...this is easy to detect and see because of many scratches inside the chassis. A lots of things is changed...silicon instead of selen rectifiers and so on

A few bottom view pictures of another similar Philips EL6411 tubeamplifier would be a great help to bring the tubeamp back to factory standard.

Some of the wiring is obvious but the input groundpoints creates noise and hum on the output temninal in the area of approx 150mVAC

I have made several DIY tubeamplifiers, but I need a little help on this one

I should have waited for a reply in the old thread, but this might be the way forward.......

Thanks in advance

Rgds Kim

[kagliostro]

OK, I'll try to help you, only you must have a bit of patience because at the moment I haven't photo of the amp

Ciao

Franco

[kagliostro]

Here I'm

this are photo that I have in my archive, not photo of my amp

Hope they can be useful for you





























Franco

[kjulhansen]

Here I'm

this are photo that I have in my archive, not photo of my amp

Hope they can be useful for you


Franco

Hi kagliostro

Thankyou for the jpg´s ....you have been most helpful :-)

Some of the foto´s will help me to bring the old tubeamp back in shape

The best regards

Kim DK