EL95 Guitar amp

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EL95 Guitar amp

Postby Prometevs » Sun Oct 18, 2009 11:39 am

A friend of mine wanted a small Guitar amp. A small box with a 4" element. I have some parts from an old radio that I wan't to use in order to make it as cheap as possible. The parts I have is based on one EL95 Tube.

Any suggestion?
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Postby EWBrown » Sun Oct 18, 2009 2:49 pm

If your old radio "parts donor" is one of the 50s or early 60s vintage German-made Telefunkens or Grundigs (these often used SEP EL95s), then you have most every major component you will need, including the power and output transformers. Some later models used SEP EL84s, for increased output power.

I've seen the carcasses of these radios sell for very low cost, or sometimes even for free, the original owner usually has stripped out the tubes, and then junked the remains.

A 12AX7 / ECC83 for the input stages, and EL95 output (these like to work into 11K primary OPTs, the telefunken OPTs are generally 11K:4 ohms, or 12K:4 ohms.

Should be good for 2-3 watts output in pentode mode. Which would make a nice small practice amp, with a 4 inch speaker.

Tang Band (from Taiwan) makes some nice 4 inch, 4 ohm relatively high-efficiency speakers for not too much expense. Parts Express and others sell this product line). This combination definitely won't be able to compete with a Marshall cranked all the way up to "11"... ;-)

HTH

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Postby Geek » Sun Oct 18, 2009 4:51 pm

Hi,

I've played with 4" speakers in depth, you will, IMO, want to really, really consider at least 6", like this:
https://taweber.powweb.com/weber/csig6.htm
or
https://taweber.powweb.com/weber/asig6.htm

But if you need a 4", the ones scavenged from Philips radios (the octagonal ones) were about the best sounding.

Cheers!
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Postby Prometevs » Sun Oct 18, 2009 11:18 pm

EWBrown wrote:If your old radio "parts donor" is one of the 50s or early 60s vintage German-made Telefunkens or Grundigs (these often used SEP EL95s), then you have most every major component you will need, including the power and output transformers. Some later models used SEP EL84s, for increased output power.

I've seen the carcasses of these radios sell for very low cost, or sometimes even for free, the original owner usually has stripped out the tubes, and then junked the remains.

A 12AX7 / ECC83 for the input stages, and EL95 output (these like to work into 11K primary OPTs, the telefunken OPTs are generally 11K:4 ohms, or 12K:4 ohms.

Should be good for 2-3 watts output in pentode mode. Which would make a nice small practice amp, with a 4 inch speaker.

Tang Band (from Taiwan) makes some nice 4 inch, 4 ohm relatively high-efficiency speakers for not too much expense. Parts Express and others sell this product line). This combination definitely won't be able to compete with a Marshall cranked all the way up to "11"... ;-)

HTH

/ed B


This one is actually a Centrum (Sweden) but it with all the transformers and ECC83 at the input. I will not even try to compete with the Marshall :)

Do you have any suggestion on a schematic I can use. I don't know much about guitar amps.
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Postby ChrisAlbertson » Mon Oct 19, 2009 11:56 am

Do you have any suggestion on a schematic I can use. I don't know much about guitar amps.


The hardest part will be "voicing" the amp. Guitar amps are not at all like hifi amps. Hifi amps needs to cleaning reproduce their input but guitar amps color or even distort the sound. At the very least any guitar amp will shape the frequency response

If you want to buil;d from a known good sounding schematic then you will have to buy parts to match. If you want to use the parts on-hand then you will have to design your own schematic. or at least be wiling to do a lot of "cut and try" experiments after you get the amp to work in order to get the values of resistors and caps "right" for the tone you are looking for.

The speaker is an important part of the guitar sound. Guitar speakers are NOT "hifi". They typically don't reproduce lows below 80Hz or highs above 8KHz. You want a "real" guitar speaker not a hifi speaker if you can. The smallest will be 6" but you get better quality as they get larger.
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Postby Prometevs » Mon Oct 19, 2009 10:57 pm

ChrisAlbertson wrote:
The hardest part will be "voicing" the amp. Guitar amps are not at all like hifi amps. Hifi amps needs to cleaning reproduce their input but guitar amps color or even distort the sound. At the very least any guitar amp will shape the frequency response

If you want to buil;d from a known good sounding schematic then you will have to buy parts to match. If you want to use the parts on-hand then you will have to design your own schematic. or at least be wiling to do a lot of "cut and try" experiments after you get the amp to work in order to get the values of resistors and caps "right" for the tone you are looking for.

The speaker is an important part of the guitar sound. Guitar speakers are NOT "hifi". They typically don't reproduce lows below 80Hz or highs above 8KHz. You want a "real" guitar speaker not a hifi speaker if you can. The smallest will be 6" but you get better quality as they get larger.


(lol) I think this project is going to be fun.

What you mean is that I can use any amplifier schematic and then start testing, changing components until I'm satisfied. Is there any guidelines I can use for this?
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Postby Prometevs » Tue Oct 20, 2009 12:09 pm

Something like this for the amplification?

Image
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Postby ChrisAlbertson » Tue Oct 20, 2009 1:55 pm

Prometevs wrote:
ChrisAlbertson wrote:

What you mean is that I can use any amplifier schematic and then start testing, changing components until I'm satisfied. Is there any guidelines I can use for this?


Yes. Notice the hand drawn amp schematic that was posted. I think this was intended for HiFi. A guitar amp will try and boost the mid range and kill the highs and the lows. Choose a coupling cap that limits bass to 80Hz, same with cathode bypass caps no need for the amp to have gain in the low bass. and no need for highs past 8Hz

Also the schematic has only one triode gain stage. that is not nearly enough. You need at least two of those. Two 12AX7 stages will still give a mostly clean sound. You need at least one more (three total) to get into some seroius overdrive distortion.

A gutar amp with all that gain is prone to oscilation too. Limiting the baandwidth helps and also notice they use a longer multi-section power supply filter, one section per apir of triode gain stages. Guitar amps tend to be about twice as complex as hifi amps because of the complex preamps.

Between each stage you can play with coupling cap, cathode bypass, grid stop and miller capastance. to shape the tone. It is best to copy a know good sounding desing.

What I'd suggest is building your desiged output section with the power tube and OPT you have the them copying a preamp from the "building blocks" section of the ax84.com web site.



Youmight want a Fender/marshal style tone stack
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Postby EWBrown » Tue Oct 20, 2009 3:54 pm

A guitar amp will need more overall gain than a "hi fi" amp, so you'll want to use the other half of the 12AX7 as an initial gain stage to boost up the pickup's miniscule voltage to something that the rest of the amp can work with.

Angela Electronics has a single ended 6V6 giutar amp, you could adapt to the EL95 design.

http://angela.com/simple6v6guitaramplifierproject.aspx

Image


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Postby Prometevs » Wed Oct 21, 2009 1:45 pm

Thank you all. The Angela Electronics amplifier look very nice. Maybe I should use a 6AQ5 that I have instead.
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Postby EWBrown » Thu Oct 22, 2009 8:37 am

6AQ5 is close enough in operating characteristics to a 6V6, but it has somewhat lower plate (10W vs 12W) dissipation ratings. The 6V6 is pushed pretty hard in the Princeton, so you would have to lower the B+ to around 275V, in order to prevent premature 6AQ5 failures. Just use a higher DCR choke, this isn't overly critical as to inductance value, as long as it is 5H or greater.

The 6AQ5 (6005) should deliver about 2X the power output of the EL95.

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Postby soundbrigade » Thu Oct 22, 2009 9:38 am

About speakers, I have an old Philips thing salvaged from an old organ. It is I guess 8" AD4000 speaker and is really vintage looking.
I slightly recall that we are both from Sweden so if you like, you can drop in and collect it.
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Postby Prometevs » Thu Oct 22, 2009 10:21 am

soundbrigade wrote:About speakers, I have an old Philips thing salvaged from an old organ. It is I guess 8" AD4000 speaker and is really vintage looking.
I slightly recall that we are both from Sweden so if you like, you can drop in and collect it.


Well, I should like that :) However, even though I travel a lot I'm rarely in your whereabouts. Do you think that your speaker can suit my amp-project? My idea is to make a small combo so I need a speaker.
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Postby soundbrigade » Thu Oct 22, 2009 11:20 am

Magnus

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Postby Prometevs » Sat Oct 24, 2009 11:23 am

I've been out running and meanwhile designing the amp. Then I went to the lumber yard and bought a oak board. I will have the sides, top and bottom made from oak, oiled.

Right now I'm wondering about how to make the enclosing to the amplifier. Just bend some steel sheet or buy something. I think I will cover the loudspeaker with some fabric. For the input and the regulators I think I will use a stainless steel sheet.

And Soundbrigade! Yes I'm interested in your speakers. How do we solve it?
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