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2xEL84 Amp Questions

3/3/2000 3:02 PM
Morris	2xEL84 Amp Questions I need advice on setting up the output section of a Class AB 2xEL84 amp. I'm using a Hammond 270FX PT (275-0-275, 150 ma) and a Magnequest 565 OT that has UL taps. Questions below: 1) Is this PT too stiff for this amp? I'd love to use a SS rectifier to save above chassis real estate, but a tube rectifier might be needed to drop some voltage. I have a Chinese 5AR4/GZ34 that I could use? What do you think? 2) Should I run this amp UL or in the traditional Vox/Matchless fashion? If I do run it UL, will I have to drop even more voltage to the OT as to not overload the screen grids? Should I use screen grid resistors in a UL setup? The UL hi-fi schematics I've seen leave them off. 3) It seems like a UL setup would require more PS filtering for the OT since the screen voltage is also derived from the OT. Would a CRC setup after the rectifier with the OT supply derived from the second capacitor be enough? 4) The preamp will be a 6SL7 setup Fender-style. I was also thinking about a second channel (non-switchable) with an EF86 front-end. What would you recommend for a splitter? I guess I could use the tried-and-true Vox/Matchless splitter, maybe with a 6SL7 instead of the 12AX7, but might a 12AT7 setup like a Blackface be better? I also have a 6SN7 here. What do you think? 5) What EL84's do you recommend? Thanks in advance for all of your help! Morris

3/3/2000 3:02 PM

Morris

2xEL84 Amp Questions

I need advice on setting up the output section of a Class AB 2xEL84 amp. I'm using a Hammond 270FX PT (275-0-275, 150 ma) and a Magnequest 565 OT that has UL taps. Questions below:

1) Is this PT too stiff for this amp? I'd love to use a SS rectifier to save above chassis real estate, but a tube rectifier might be needed to drop some voltage. I have a Chinese 5AR4/GZ34 that I could use? What do you think?

2) Should I run this amp UL or in the traditional Vox/Matchless fashion? If I do run it UL, will I have to drop even more voltage to the OT as to not overload the screen grids? Should I use screen grid resistors in a UL setup? The UL hi-fi schematics I've seen leave them off.

3) It seems like a UL setup would require more PS filtering for the OT since the screen voltage is also derived from the OT. Would a CRC setup after the rectifier with the OT supply derived from the second capacitor be enough?

4) The preamp will be a 6SL7 setup Fender-style. I was also thinking about a second channel (non-switchable) with an EF86 front-end. What would you recommend for a splitter? I guess I could use the tried-and-true Vox/Matchless splitter, maybe with a 6SL7 instead of the 12AX7, but might a 12AT7 setup like a Blackface be better? I also have a 6SN7 here. What do you think?

5) What EL84's do you recommend?

Thanks in advance for all of your help!

Morris

Replies:

Rebel420 Before we begin, you hsould jump on... -- 3/3/2000 3:25 PM
Lee M. Based on the voltage I got on my 27... -- 3/4/2000 12:33 AM