Tube Amp Archive

You could start rectifing, levelling the filament supply with cap and measure it, it should be around 14V but usually is a bit less. To be perfectly supplied the filament of ECL84 should be in parallel with 6.3V but in series they will also work with small tolerance and you could give it a try, guit...

With your soundcard and a buffered voltage divider you can use this powerfull free software http://www.sillanumsoft.org/

I'm using it with the line in of my old Lexicon Alpha and it works very well.

Those are interesting IC. Unlucky the AMC3301 claim an input bias current between -40uA and -20uA, this makes this IC not suitable for signal triode and pentode current measurement. I was studying the AD8479 to make a continuous measurement of anode current but with this IC raising the shunt resisto...

What kind of hum do you have?

I've spent 5 month attempting anything possible and at last I discoverd that there was some strange unbalance in the heater and the humdinger, a trimmer between heater and a common voltage, solved at all!

I'm carrying on my humdinger evangelization opus

TUBEDUDE wrote: ↑Wed Jan 13, 2021 2:36 am You could reconfigure as an anode mixer.

This is a good idea, unless you have arranged the circuit in that way for some "sound" related reason, the anode mixer will be a better solution, I've successfully used with JFET transistors and I think that also with tubes will work.

Virtually the 470k resistors are high enough to isolate the two circuits from each other, but I think that the tonestack of the upper circuit will also act in the other channel, maybe just a little bit but can be subtle and annoying. The best solution is to buffer the upper channel. The only way to ...

Can you check the circuit voltages? The first sample sounds like a misbiased tube (or a broken one). It could also be a blocking resistor value mistake (the resistors that are in series with the grid). With tubes hi-gain design is really difficult to not get oscillation if all catode of the first tu...

Do you mean trimmers like those below? vintagetrimmer.png I would not recommend you to use those kind of trimmers, they usually collect powder and dirty and they easily broke. During my TV repair duty I've often substituted those kind of trimmers with the modern and closed ones, in old CRT TV. I've ...

...For power amplification you should consider the maximum power transfer to the load and in this case the two impedance should be matched, so an amplifier with an internal resistance of 100 ohm can deliver the maximum power to a 100 ohm load... The max power transfer theorem makes for very ineffic...

It seems as if the impedance are designed to loos power instead of building power. Just to point out, power can be generated, transferred, dissipated but not builded :D The amplification of an audio frequency signal can be divided in two main branch: 1) Level amplification: the voltage of the signa...

dragonbat13 wrote: ↑Tue Jan 05, 2021 3:03 pm

But then when I read about circuits the impedeances always seem to be backwards.

Sorry, I can't understand this sentence, can you be more specific?

Using snubbers is always an improvement because oscillation caused by solid state rectifier can add ghost notes and other noises that can be heard only in some situation and appears to be magical. I can recomend you to use transformer snubber rather than diode snubber because UF5408 almost solve rev...

Without a resistor in series they only shift the oscillation towards the audio frequencies, it's a common mistake on snubbers or an industrial cost savage.

If the amp has no problem don't touch them, if you hear some noise you can consider adding a 100ohm (or so) resistor in series with those caps.

Good afternoon and good new year to all! I'm gonna buy a PCB set for this amplifier from JLC, is any european guy interested in one set of this? JLC only print 5 items for each PCB so the other 4 are useless for me (at least in short period), if anyone needs a PCB I'll be glad to sell them without c...

For an EL34 HiFi amp I built time ago I've used this schematic: