66 Vibrolux Issues

[fiftynine]

I have a 66 AA864 Vibrolux Reverb (GZ34) but can't find a schematic. I've been working to the AA964 schematic (also GZ34), and it's just been pointed out to me that that's the only schematic saying 315vAC, the rest say higher. That makes sense as the Mojotone replacement tranny chucks out 355. Incidentally, my tranny didn't come with a heater centre tap. Strange as most I've seen have, as does the schematic.

But, I did the filter caps to the AA964 schematic (16uf across the board like a Deluxe Reverb) and not with the larger cap and resistor combinations for the first stage like later Vibroluxes and bigger Blackfaces.

Is the five 16uf setup sufficient for my amp? Why did it change?

[VMS]

Go with AA964. According to this thread, bias circuit may have different value resistors but otherwise they are the same:

http://music-electronics-forum.com/t2563/#post20127

[VMS]

Are you sure about the heater center tap?

Specs show a GREEN/yellow CT:

http://www.mojotone.com/core/media/media.nl?id=12526&c=923962&h=1cee15546bae8ac95116&_xt=.pdf

...but if it is missing then make it with 100R resistors.

[fiftynine]

AA964 it is then.

Definately no heater CT so the 100's are in. Quiet as a mouse.

[eleventeen]

Those are among my all-time favorite amps. I'm not incredibly fond of 10" speakers in general, but a Vibrolux is almost the perfect package. I had a brown Vibroverb which I sold to Mr. Groove, Austin Pittman. Fender did not make a 35-watt amp driving a single 12" speaker for some reason. They shoulda!

[fiftynine]

Oh yeah, no 2 x 6l6 1 x 12" in the BF line up. Well I never.

A quick question, if I've got 650mV at the pots side of the 0.1uf 200v cap (the last blue molded before the PI), does it need replacing? All other blue moldeds read very few millivolts.

Cheers.

[sluckey]

A quick question, if I've got 650mV at the pots side of the 0.1uf 200v cap (the last blue molded before the PI), does it need replacing?

No. If you look at the schematic you'll see dc voltage on both sides of that cap.

[fiftynine]

Ok.

Can anyone hazard a guess as to why my vibrato intensity is a bit shallow? Are there any specific components that drift and would do that? I didn't want to go unsoldering caps for originality sake.

All electrolytics done by the way.

[tubeswell]

Ok.

Can anyone hazard a guess as to why my vibrato intensity is a bit shallow? Are there any specific components that drift and would do that?

The trem is bias-vary in the aa964. As the bias gets hotter the trem intensity decreases. If you make the bias adjustable (always a good idea), you will be able to cool it down, and get more slam in the trem.

[fiftynine]

Tubeswell, it's the opto-isolator trem as in AA964. I thought it was only the Princeton that got the bias-vary in the Blackface line up?

[sluckey]

Can anyone hazard a guess as to why my vibrato intensity is a bit shallow? Are there any specific components that drift and would do that?

de roach

[fiftynine]

Yup. Ta.

Can anyone tell me why my 2 x Jensen C10Q's read 6.3 and 6.2 ohms on their own and only 3.12 ohms hooked up in parallel? I have the original Jensen C12N's just been re-coned and ready to go in. They measure 5.1 and 5.4 ohms, 2.6 hooked up.

Is this right? Is it bad for my output tranny? For performance, tone and volume etc?

[firemedic]

That sounds about right. An 8ohm speaker will read somewhat less than 8 on a VOM. 2 8ohm speakers in parallel will read less than 4 ohms.

[sluckey]

http://en.wikiversity.org/wiki/Resistors_in_Parallel

[fiftynine]

Sluckey, thanks I did the maths before I posted. I hope I don't come across as a non-tryer. It's the low DC resistance, especially of the vintage speakers that concerns me. I've measured speakers before and never got quite that low for an 8 ohmer.

I know the resistance in operation is different but 2.6 ohms hooked up is pushing it for me.