BF Super Reverb aa763 Normal Channel -- how to increase headroom?

[mort]

no scope yet. It's on the list for this year, along with a larger air compressor and scroll saw.
I do have a signal generator though.

[g1]

That's a standard totem-pole (series) cap arrangement in post #58.
Just a very non-standard way of drawing it .

[Malcolm Irving]

The cross purposes I was alluding to are your analysing a hypothetical amplifier with no volume control and TheTinMan analysing a real guitar amp with a volume control positioned after the first stage (or later). There can be no disagreement here because you are not discussing the same circuit. You are both right

Yes, fair enough. But the actual circuit that Mort is asking about only has one stage before the volume control, and I'm pretty sure that even a hum-bucker wouldn't cause break-up in that first stage.

[Dave H]

I'm pretty sure that even a hum-bucker wouldn't cause break-up in that first stage.

You are right of course. It would need an input of more than 1V peak. You'd most likely have to use a stomp box to boost the signal.

[Jammin'John]

Loud

I'm just getting a laugh about the idea that a Super Reverb isn't loud enough in a club nowadays.

JJ

[Leo_Gnardo]

I'm just getting a laugh about the idea that a Super Reverb isn't loud enough in a club nowadays. JJ

Indeed, club managers sometimes hassle my clients with 15W Blues Juniors or Deluxes. If they see you bring in a big amp start hassling even before you plug it in. They want bands to play at transistor radio volumes. Phooey what fun is that?

Breaking point is, if bartenders can't hear the orders, band's too loud. Up to that, anything goes. LG's rules.

[pdf64]

no scope yet...

If you've got a pc with soundcard, then see link in post #43 to use it as a scope.

[Jammin'John]

Hell,I've been putting less efficient speakers in my more powerful amps & more efficient ones in my less powerful amps.
I also have been using 5r4's to lower voltage to get a brown sound earlier on in my Tweed clones.

JJ

[Leo_Gnardo]

Hell,I've been putting less efficient speakers in my more powerful amps & more efficient ones in my less powerful amps.
I also have been using 5r4's to lower voltage to get a brown sound earlier on in my Tweed clones. JJ

Another cheap n dirty way of getting more oomph, cover more of the back of your open back amps with a sturdy board, leaving enough room for the tubes to breathe, and maybe small window so you can stow the cable & pedal. Won't make much diffo in high frequencies, but low & low mids will be noticeably improved.

[TheTinMan]

That's a standard totem-pole (series) cap arrangement in post #58.
Just a very non-standard way of drawing it .

Mort - my apologies. Those filter caps are drawn and built correctly. It's one of those cases where I've seen the same thing drawn the same way so many times that I didn't see your variation as being identical.

I've attached the AB763 Super Reverb snippet just to show you what I'm used to seeing. There's absolutely nothing wrong with the way you drew it - just different. And I was looking over the schematic looking for anything out of the ordinary which might be causing you difficulty.

Chip

[mort]

No apology necessary, Tinman. It's all good conversation.




Hey quick question to anyone, does an EF86 tube generate significantly more heat than say a 12ax7? I've put tube shields on all the 9 pin tubes and was just wondering about the 86 and if there's a reason not to put a tin can on it?

[Malcolm Irving]

No need for a can on the EF86, it has an internal screen that comes out on pin 2 (which should be grounded).
The cans for 12AX7 etc. provide screening and some physical protection, but are not good from the heat point of view - they reflect some heat back into the tube.

The EF86 generates less heat than a 12AX7.
EF86 heater power = 6.3 x 0.2 = 1.26 W
EF86 max. anode dissipation = 1 W
12AX7 heater power = 6.3 x 0.15 x 2 = 1.89 W
12AX7 max. anode dissipation = 1 x 2 = 2 W

[Lydian]

Ignoring any actual amp issue, I once contemplated adjusting the cathode bias of a pre-amp tube. In your case I would assume V1.

http://music-electronics-forum.com/t41452/

I just thought of something else.

Some 12ax7's are known for being a little louder, breaking up earlier, etc. you could put a RCA blackplate in V2 to let the vibrato channel break up earlier, or put a sylvania grey long plate in V1 which stay pretty firm. I noticed the reissue Mullards are pretty firm and clean too. I could probably go into details if needed on options. I've been tube crazy lately.

[CraigB]

Tin Man's thoughts certainly match my experiences with a Vibrolux Reverb build. The two gainstage preamp with the fender tonestack in the middle could not produce enough voltage to really push the power amp. The distortion or "lack of headroom" came from the preamp. I had no scope to determine this so I put a master volume after triode 2 and found that the distortion stayed even when the MV was turned down. I replaced the 22uf cathode caps on the first two triodes with 4.7 uf. That change cut the bass distortion at high volume settings without cutting the apparent bass music content.
Good luck with all these ideas!
Craig