Simple EL84

[Mas Penk]

Hi guys

Just wondering have you ever make this Amp....

http://www.diyparadise.com/simpleel84.html

I just wondering how it sounds...??

[Brett]

Originally posted by Mas Penk
Hi guys

Just wondering have you ever make this Amp....

http://www.diyparadise.com/simpleel84.html

I just wondering how it sounds...??

There is a similar design on the Triode site, but using a 6C4 fo the driver. When I built my ST35 clone I tried it for fun, but it sounded quite poor. For the couple of extra dollars to have 2 ECC99 (1 per channel) and a couple of transistors/FETS to make a CCS in the tail of the driver to make a differential stage, you'll get a much better sounding amp.

Alternatively, you could use a paraphase splitter like the Magnavox console amps. This can also sound very good, and doesn't require the CCS.

Also, the amp you linked is wired in UL, it's output impedance will be quite high which may create some frequency response errors

[andyjevans]

Why not use another ECC99 and have a gain stage into a concertina? The ECC99 is both a great gain stage - low anode impedence so you can have an unbypasased cathode resistor - and a great tube for a concertina. I don't have a circuit, but you could start with 22k anode resistor on the first valve and 22k on top and bottom of the concertina, and adjust the cathode resistor of the input tube to suit your needs. I'm about to try this very thing when I get some time. At the moment I'm using a 6EW7 - second section first, into the first section as a concertina. Sounds pretty nice, and very simple.

[Brett]

Originally posted by andyjevans
Why not use another ECC99 and have a gain stage into a concertina?

Speaking for myself, I've never heard a concertina I liked, with a diff always sounding better and having one less stage. When I played with the paraphase it surprised me how good it could sound too, but completely different to the diff.

[Mas Penk]

If i use EL84 as Driver will it sound better?
Because that site the author said that the amp will be more natural and live if we drive with EL84. It looks like he follows the Sakuma Amp which has implement "like drive like". Meaning if we like the sound of EL84 then use EL 84 to Drive EL84...

btw does anyone has schematic for Good & Simple EL84... ?
Does magnavox amp use same OP spec like i have 8K PP with UL 40%?

thanks

[fdegrove]

Hi,

When I played with the paraphase it surprised me how good it could sound too, but completely different to the diff.

Agreed...not too many people understand differential stages though.

I feel every tubelover owes it to himself to study phasesplitters and balanced circuits indepth...

Understanding AC behaviour versus DC behaviour does help alot, as does static versus dynamic behaviour....

Greetz to OZ,

[fdegrove]

Hi,

It looks like he follows the Sakuma Amp which has implement "like drive like". Meaning if we like the sound of EL84 then use EL 84 to Drive EL84...

Sorry to say so but too much salt is just that....

Cheers,

[Brett]

Originally posted by Mas Penk
If i use EL84 as Driver will it sound better?

I like the EL84 as a driver for larger powertubes, but I seriously doubt it's going to sound any better here.

Because that site the author said that the amp will be more natural and live if we drive with EL84. It looks like he follows the Sakuma Amp which has implement "like drive like". Meaning if we like the sound of EL84 then use EL 84 to Drive EL84...

Wrong. Sakuma-san's idea in using an 845 to drive an 845 is to have a driver that is able to swing the up to 140Vpeak that an 845 needs with as low a distortion as the 845 output tube, not because of the "sound" of the tube. Similarly with the 300B=>300B, though it's less of an issue with the 300B only needing 80V or so.

In the case with the EL84, you only need about 20V to drive the grids however you run them, and an ECC99 is more than up to the task. The ECC99 also hav less than half the input capacitance so it's easier for the previous stage to drive too (vi a vis the EL84 as a driver).

btw does anyone has schematic for Good & Simple EL84... ?
Does magnavox amp use same OP spec like i have 8K PP with UL 40%? [/B]

As I mention above, an EL84 UL amp with no NFB is going to have a very high output impedance and will affect the frequency response of the speaker markedly. So you either need to go triode and live with less power, or add some feedback which will mean more gain is required in the driver.

I'm not really fond of UL, preferring pentode esp if using NFB.

The Magnavox I mentioned is pentode with NFB.

Another simple design is the Acro or Dyna designs posted below. I'd use a 6SL7 in preference to the 12AX7 though.

[Brett]

The Acro

[Brett]

Originally posted by fdegrove
I feel every tubelover owes it to himself to study phasesplitters and balanced circuits indepth...

Understanding AC behaviour versus DC behaviour does help alot, as does static versus dynamic behaviour....

Hi Frank,
Can only saw I agree.

One pet hate of mine is the term phase-splitter, because it's not a splitter, but an inverter, and then you get all these idiotic posts from the cult of the SET types who think that it cuts the signal in half.

Cheers
Brett