New amp project... 18 watt marshall clone

[rstites]

Re: New amp project... 18 watt marshall clone

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If you run a SS rectifier, you'll need a way to throw away quite a few volts... You may want to get the heyboer output, and get a hammond power transformer that's the proper voltage once you've rectified it. a 290-0-290 transformer will put out roughly 406v with solid state, and 327v with a 5Y3GT. I don't know what the voltage loss is with the EZ81 rectifier tube, which is what all the 18 watts have... but I'm sure it's as bad or worse than the 5Y3GT. This is why I like building amps with octal rectifiers when I have room - you can swap out the rectifiers and change the voltage easily. It's like a variac that's safe!

Pete

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Thanks for the info. I knew there was a loss using a tube rectifier, but I was not aware that it was that extreme. In fact, that gives me one other thing I should look at on my P1X. I'm using a Champ power transformer rather than the Hammond one specified in the project, so I should probably check how much voltage my tubes are seeing and whether it's too high to make them happy...I'm pretty sure that this is a higher voltage transformer than the one spec'ed in the original project. In addition, I used a couple of slightly different value components so I could get it up and running.

Ross

[rstites]

Re: New amp project... 18 watt marshall clone

An update...

I got back in town and finally got a chance to mess with the amp tonight (P1X). I put a shielded cable from the input to the first triode and it took all the oscillation out. Right now the amp sounds pretty good and can get an amazing amount of crunch for just two gain stages followed by a full tone stack. It's late, so I'm shutting down for tonight. I'm anxious to try it tomorrow through a 12" speaker and with a boost. It might get into hard rock territory with those and I'm hoping the bigger speaker will help the bass response. Right now I'm testing through an 8" champ speaker.

Pete, have you looked at the November Project on the AX84 site? I just noticed it for the first time and thought some elements of it might be interesting combined with the 18 W Marshall, or for someone looking to move away from the 18 W a bit. In fact, the November looks very much like the 18 W TMB preamp except that the two channels are set up like a Superlead. Interestingly, they have the November set up for a choice of fixed or cathode bias via a switch.

On the power transformer, I'm assuming something like a 220-0-220 would be fine for a solid state rectifier. That should give me about 310 V off the rectifier. My understanding is that I really should stay at 300 V, or less, on G2. Does that all seem correct?

Ross

[Twisteramps]

Re: New amp project... 18 watt marshall clone

Good deal Ross! That shielded cable is a lifesaver. [img]/images/graemlins/smile.gif[/img] I really like running low wattage amps into a sealed 4x12... you should really give that a shot.

300v or so is good on an EL84. Some guys really push the voltage on them (Dr.Z among others) but I tend to like power tubes with less volts on them than more, especially on lower wattage amps where you're wanting that 'browner' sound anyways.

A friend of mine just built a November and can't get it to work... I may offer to troubleshoot it just to fix it and hear what one sounds like. Check out my other thread here for news about my first 18watt build.

Pete