The Amp Garage

Ponder the configuration of Dwell and Volume pots. Adjusting dwell changes volume, you have to compensate with volume pot. Reverb return level pot configured "backwards" as a reostat will interact with volume control. ok, this we can live with. On this last schem there's no dwell control at all, va...

Well, I'd say this one's a bit weird. btw, it's ECL86 not 83. Ponder the configuration of Dwell and Volume pots. Adjusting dwell changes volume, you have to compensate with volume pot. Reverb return level pot configured "backwards" as a reostat will interact with volume control. ok, this we can live...

ECL82 is my tube of choice for reverb drive. You can connect screen grid cap both ways, doesn't really matter. Screen grid resistor in this circuit seems rather too large, should be in the range 2-5 kohms. Also, put a 2.2nF/400V cap across transformer primary. The pentode in ECL82 should see 8k plat...

You can always connect caps in parallell. 22nF+10nF gives 32nF. Given that most caps are +/-10% tolerance on value you end up pretty close to nominal 33nF. Or, why not experiment with different cap technologies in parallell? For example: 22nF metalized poly 10nF metal foil poly 1nF ceramic for that ...

Well, there's no need reinventing the wheel

Have a look at the tables on pp. 2&3 in the EF86 datasheet for component values at different supply voltages etc. There's even a table for using EF86 in triode mode which is quite interesting to try.

Have fun

An interesting side effect I noticed a while back while adjusting the trimmer on one of my amps. I use the scope on the output method personally. As you increase the signal into the amps you will start to hear the the output transformer start to squeal at the signal generator frequency. The squeal ...

An interesting side effect I noticed a while back while adjusting the trimmer on one of my amps. I use the scope on the output method personally. As you increase the signal into the amps you will start to hear the the output transformer start to squeal at the signal generator frequency. The squeal ...

There are several opinions as to how the phase inverter symmetry should be adjusted. Adjusting for equal signal amplitude at the PI plates leaves two other stages of the power amp out of the chain i.e. power tubes and output transformer. Even if you have a "matched pair" of tubes they're usually mat...

Heater voltage should be referenced (conected) to some dc potential, either ground or a potential positive respective to cathode. This is recommended for 2 reasons: 1. If the heater suply is left unreferenced it will assume any arbitrary potential rel ground and cathodes which may or may not be high...

Not as an amp builder but as transmitter and ham radio builder, I would prefer lifting the center tap of the transformer from ground where possible. The problem with this approach is that you still have high voltage across the two outside leads of the transformer. Don't mislead yourself into thinki...

Being a friend of Bjorn Juhl, the amp's designer who is an electronics wizzard and a great guitar player in his own right I can vouch for the originality of his design. Mad Professor is not a cloned design although capable of "cloning many sounds".

Some amps with EL84 run them at plate voltages way above max specs. More often than not this condition is also accompanied by too low screengrid resistors and insufficient cooling. I would suggest checking screengrid resistors and replacing them with new ones in the range 470ohm to 1k. Installing a ...

If I wire a cap, or a cap and resistor in series, between the plate and the grid of a tube, that's called positive feedback, right? Wrong. That's negative feedback since the signals on plate and grid are in opposite phase. What does it do to the gain and the sound? What sound different when using p...

Hi guys, my 1st post here...been lurking for a while but had nothing constructive to contribute since I'm not building any TW or D-clones, prefer to go my own way :wink: There are several dual triodes with shield between the halves, these are mostly of russian origin, some are still in production. T...