Eico 377 build

[xtian]

Got an Eico 377 tone generator, going to convert to a 3-5 watt SE, Fender style.

Eico 377 photos and schematic

This Eico has a cool variable capacitor, with about 200pF combined capacitance. Where would be the most effective tone shaping application in a Champ circuit?

[xtian]

Wired up as 5c1 with 6K6 power tube, 6x5 rectifier, original choke and filter caps, 6sj7 preamp. Just waiting for OT from Magnetic Components. Vari-cap wired to volume pot.

Any bets on whether this hot mess works first time? I'm giving 4:1 against.

[Reeltarded]

Can you test it with itself? hah

I like that thing!

[xtian]

Worked first time. Just needed a 1K cathode resistor for the 6V6; still runs cool at 330 on the plate and 23mA, but that's a happy compromise, 'cause I can drop a 6K6 in and it runs a little hot. Both sound fine, 6V6 a little louder, which is great. Perfect volume cranked for office rockin'. Variable bright cap is awesome!

[dorrisant]

Nice! Love to see people recycling.

Tony

[LeftyStrat]

You have to leave that variable capacitor on there. Bonus points for incorporating it into the circuit.

[surfsup]

xtian that is nice. Mine came out nicely too. I upgraded the banana clips and did a few mods. It produces a fairly nice signal...not awesome but more convenient than firing up the PC and dealing with MHz noise...

[xtian]

Ah, so you kept yours as a signal generator. Cool. I thought a standalone signal generator would be superfluous because of the tone generator on my iPhone. Wrong! The iPhone generates a decent sine wave, but square and triangle waves are rude approximations.

[Reeltarded]

That triangle is a bitch. Funny.

Consider metered output recordings that you can make yourself or even look for mix magazine's test tones online. They used to send them out with subscriptions. Whole battery of tones, sweeps, and bursts at known levels. Even has time code for when you are in a pinch..

Oh wait. We will never be in that pinch again.

[Blackburn]

Sweet! Love seeing this old stuff given new life.

I'll be doing something very similar with an old microphone amp, using all the stock tubes that came with it, well, maybe a nicer pair of 6V6s, but two input 6AV6 tubes and a 6AX5GT rectifier tube. Same trannies, too.

[xtian]

Here is Monkeymatic Eico 377 #2.

I lowered the heater voltage from 7.3vac to 6.3vac by installing 1R||1R in series with each heater leg.

The amp is sounding good. Gets a nice crunch distortion when dimed. But I'm getting only 1 watt clean output.

The 6SJ7 preamp seems to be functioning well. On the scope, I have 1v p-p input, and 80v p-p output.

This signal goes to the volume pot, then to the 6V6GT input grid, and at this pin (5) the signal only gets to about 40v p-p, with the top of the wave clipped. Typical? The amp's output waveform looks OK, though a bit asymetrical, before clipping.

I have only 272v on my 6V6 plate, which will limit my power. But I expect more than 1 watt. Could the low screen (220v) be limiting the power?

[gui_tarzan]

Hey, I've got one like that too. I've already gutted mine in hopes of turning it into an amp one of these days.

[xtian]

Well, no luck changing the screen supply. Tried a few options, the most drastic being the 5e1 style (no screen resistor). Got no significant change in volume nor tone.

I guess then, the output is limited by the power supply?

[jjman]

I'm confused how the output of the preamp could be 80v p-p whereas the grid of the 6v6 is clipping at 40v p-p. Aren't they at the same (ac) point in the circuit? Maybe you measured the preamp with the 6v6 removed? I did that once and the preamp output signal was huge. I believe the difference is the miller "load."

[martin manning]

Consider biasing the 6V6 up around 100%.