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Amp Build....Advice/Opinions

6/21/1999 12:58 PM
bobCT	Amp Build....Advice/Opinions So I starting on my first homebrew project...finally. I'm using an '80's Concert (Rivera designed) as the foundation. The amp will basically be a two channel Fender clone....one channel Fender Blackface, 2nd channel Torres Super Texan (I breadbroaded this circuit into another amp and it really suits my style of playing), reverb, vibrato, pt-to-pt wiring. Possible pentode/triode switch but otherwise pretty basic. Some questions: 1) I haven't decided whether I am going to use 6V6's or 6L6's in the final design. Is there an optimum B+ that will allow me to use either interchangeably (re-biased of course). 2) The Concert puts out 60 watts or so, way more than I need. Would going to a split load driver as opposed to a long-tailed driver subdue the amp somewhat? Is one design more "toneful" than the other? 3) The Concert OT has 4 and 8 ohm taps...a plus in my book. Will the OT work with 6V6's and 6L6's? 4) I know I convert the solid state rectifier to a tube rectifer. Will a tube rectifier support 6 12AX7's and 2 6V/6L6's? 5) Given a choice...what vibrato from which Fender amp would you use? I appreciate any opinions/advice/guidance. I am sure I'll have more questions as this project moves forward. Thanks. bobCT

6/21/1999 12:58 PM

bobCT

Amp Build....Advice/Opinions

So I starting on my first homebrew project...finally. I'm using an '80's Concert (Rivera designed) as the foundation. The amp will basically be a two channel Fender clone....one channel Fender Blackface, 2nd channel Torres Super Texan (I breadbroaded this circuit into another amp and it really suits my style of playing), reverb, vibrato, pt-to-pt wiring. Possible pentode/triode switch but otherwise pretty basic.

Some questions:

1) I haven't decided whether I am going to use 6V6's or 6L6's in the final design. Is there an optimum B+ that will allow me to use either interchangeably (re-biased of course).

2) The Concert puts out 60 watts or so, way more than I need. Would going to a split load driver as opposed to a long-tailed driver subdue the amp somewhat? Is one design more "toneful" than the other?

3) The Concert OT has 4 and 8 ohm taps...a plus in my book. Will the OT work with 6V6's and 6L6's?

4) I know I convert the solid state rectifier to a tube rectifer. Will a tube rectifier support 6 12AX7's and 2 6V/6L6's?

5) Given a choice...what vibrato from which Fender amp would you use?

I appreciate any opinions/advice/guidance. I am sure I'll have more questions as this project moves forward.

Thanks.

bobCT

6/21/1999 9:36 PM
MKB	Hello, Bob. I now have a Concert like yours, and maybe can help with a few of your questions. 1.)You may have to lower the voltage a little to run 6V6's, as the Concert has around 475V out of the rectifier. A bit hot for 6V6's, especially new ones. 3.)The output TX should work fine with either but you may have to switch output taps depending on the tube compliment. Maybe you could use four 6V6's to get approximately the same impedance as two 6L6's? 4.)I would guess that a 5AR4 or 5U4 should be able to handle these just fine. Also, your layout may be critical, as the eighties Concert is pretty cramped as it is- the power tubes are too close together IMHO. You shouldn't have too few preamp tube sockets however!;<)

6/21/1999 9:36 PM

MKB

Hello, Bob. I now have a Concert like yours, and maybe can help with a few of your questions.

1.)You may have to lower the voltage a little to run 6V6's, as the Concert has around 475V out of the rectifier. A bit hot for 6V6's, especially new ones.

3.)The output TX should work fine with either but you may have to switch output taps depending on the tube compliment. Maybe you could use four 6V6's to get approximately the same impedance as two 6L6's?

4.)I would guess that a 5AR4 or 5U4 should be able to handle these just fine.

Also, your layout may be critical, as the eighties Concert is pretty cramped as it is- the power tubes are too close together IMHO. You shouldn't have too few preamp tube sockets however!;<)

6/21/1999 10:26 PM
Steve F	Just .02 re: the output tube question - my 4 x 6V6 home brew uses a Bandmaster OT into a 4 ohm cabinet. It works well, I get about 50 watts. If I want to switch to 6L6's I can pull the 6V6's and put in two 6L6's - as pointed out you may need to re-bias, but the impedance is close. My personal observation is that the 4 6V6s sound a bit richer than a pair of 6L6's - or a pair of 6V6's for that matter - I have a half power switch that disconnects the cathodes of two of the tubes, and the tone suffers a little. Regards, SF

6/21/1999 10:26 PM

Steve F

Just .02 re: the output tube question - my 4 x 6V6 home

brew uses a Bandmaster OT into a 4 ohm cabinet. It works well, I get about 50 watts. If I want to switch to 6L6's I can pull the 6V6's and put in two 6L6's - as pointed out you may need to re-bias, but the impedance is close.

My personal observation is that the 4 6V6s sound a bit richer than a pair of 6L6's - or a pair of 6V6's for that

matter - I have a half power switch that disconnects the cathodes of two of the tubes, and the tone suffers a little.

Regards, SF

6/22/1999 1:12 PM
Michael Polutta	1. I have one of those Concerts too. I have approx. 500V on the plates. FAR too much for 6V6s. FAR too much. 475 is not much better. You'll definitely have to adjust the bias range as well. I would not make the transition to 6V6s with this amp without replacing the power xfmr. 2. Going to 6V6s will do more to change the tone than changing the phase inverter. It is true, though, that the cathodyne inverter gives less drive to the power tubes than the long-tailed pair. "Toneful" is way too subjective a term to even ask about. 3. Should work w/ 4 6V6s. Just 2 6V6s and you'll really need a higher P-P impedance for a good match. The 6V6 needs approx. double the P-P impedance of the 6L6. 4. The power xfmr has no 5V tap, so you're going to have to make some arrangements to power the tube rectifier filament. Good luck finding room on that chassis for another power xfmr - even a small one. 5. Which do YOU like? Further, how many triodes will you have available? If you don't have enough to do a "blonde-era" vibrato then the question is answered before you ask. I have dramatically rewired my Concert, originally purchased from Torres (never again - UNBELIEVABLY BAD construction!). The distortion channel looks like a Marshall circuit now (except for the lack of solid-state distortion devices!) with a cathode follower and the tone stack last in the chain before the master volume, and I've futzed with the cathode and interstage cap values a lot. The first stage only uses one triode instead of two in parallel. The clean channel's goofy bright switch is now wired like a blackface - with a dramatic improvement in the response (to my ears - not nearly so "honky"). The reverb drive circuit also now looks like a blackface. The phase splitter cap values have been massaged more to my liking. The "Gain" control is now a rotary switch that adds various capacitors in parallel with the treble cap in the distortion tone stack to thicken the sound - this is the ONLY thing remaining from Torres. Good luck, Michael

6/22/1999 1:12 PM

Michael Polutta

1. I have one of those Concerts too. I have approx. 500V on the plates. FAR too much for 6V6s. FAR too much. 475 is not much better. You'll definitely have to adjust the bias range as well. I would not make the transition to 6V6s with this amp without replacing the power xfmr.

2. Going to 6V6s will do more to change the tone than changing the phase inverter. It is true, though, that the cathodyne inverter gives less drive to the power tubes than the long-tailed pair. "Toneful" is way too subjective a term to even ask about.

3. Should work w/ 4 6V6s. Just 2 6V6s and you'll really need a higher P-P impedance for a good match. The 6V6 needs approx. double the P-P impedance of the 6L6.

4. The power xfmr has no 5V tap, so you're going to have to make some arrangements to power the tube rectifier filament. Good luck finding room on that chassis for another power xfmr - even a small one.

5. Which do YOU like? Further, how many triodes will you have available? If you don't have enough to do a "blonde-era" vibrato then the question is answered before you ask.

I have dramatically rewired my Concert, originally purchased from Torres (never again - UNBELIEVABLY BAD construction!). The distortion channel looks like a Marshall circuit now (except for the lack of solid-state distortion devices!) with a cathode follower and the tone stack last in the chain before the master volume, and I've futzed with the cathode and interstage cap values a lot. The first stage only uses one triode instead of two in parallel. The clean channel's goofy bright switch is now wired like a blackface - with a dramatic improvement in the response (to my ears - not nearly so "honky"). The reverb drive circuit also now looks like a blackface. The phase splitter cap values have been massaged more to my liking. The "Gain" control is now a rotary switch that adds various capacitors in parallel with the treble cap in the distortion tone stack to thicken the sound - this is the ONLY thing remaining from Torres.

Good luck,

Michael

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