Massie Model 1263

[Tiny_Daddy]

Anyone ever seen a schematic? Made in Los Angeles. GZ34, two 6V6, several 12AX7, Tremolo.

[HotBluePlates]

Never heard of it. But apparently the model name is "St George".

See if that schematic matches your circuit. Looks like whoever drew it had to make it themselves because they couldn't find one out there.

[Tiny_Daddy]

Wow, yes that's it! Except for the rectifier tube. But this amp does not have the original transformers so someone must have changed it. Now I can find out why the trem don't work without tracing the whole thing out. Thanks!

[DummyLoad]

somewhat interesting concertina and concertina driver arrangement.

trem osc. - R24 seems wrong. maybe should be 3K3?

--DL

[HotBluePlates]

trem osc. - R24 seems wrong. maybe should be 3K3?

V4A and B look to be grid-leak biased. I'm not sure it's a good idea for a trem oscillator, but it very likely works. The trem is only called on to output a signal as big as the incoming guitar signal.

The driver is direct-coupled to the concertina. It seems the voltage divider reduces drive somewhat, and also sets the grid bias of the concertina.

[PRR]

> R24 seems wrong. maybe should be 3K3?

R24 is a grid resistor. Certainly not K-size. 3meg fits the C-R-C-R-C-R sequence.

> grid-leak biased. I'm not sure it's a good idea

When running, all trems (nearly all 1-tube oscillators) run self-bias through grid rectification. You usually find a large negative grid voltage despite no DC path except to ground.

It is odd though. Especially using a whole 12AT7. We have enuff trouble with weak 12AX7s not tremming. Maybe it "had" to be zero-biased to start at all?

Does save an electrolytic.

> the voltage divider reduces drive somewhat, and also sets the grid bias of the concertina.

The optimum plate voltage on the gain stage may be 1/2 to 2/3 of supply. The optimum grid voltage on cathodyne is often 1/4 to 1/3 supply. No fit. However a 2:1 divider makes the DC voltages come out close. The AC/Audio is passed through C20 0.01u, unity-gain above 20Hz.

[Tiny_Daddy]

OK I start to think this circuit is someone's (failed) science project?
Had to swap the output tube plate leads in order to install the feedback resistor.
Then I compare the trem to Fender's trem circuit. Tried 12AX7, still nothing. Added a bypassed 1.5K cathode resistor. Oscillator slowly starts but dies when the speed is turned up. No wonder it's rigged so the oscillator runs all the time. Changed the plate resistor to 100k, no change but I left the 100K, can't hurt. Reduced C17 to .03uf and now it works over the entire range. But for a trem it doesn't have much depth. That's all she gets for now.

[DummyLoad]

R24 is a grid resistor. Certainly not K-size. 3meg fits the C-R-C-R-C-R sequence.

misread schema - thought it was cathode R. sorry.

The driver is direct-coupled to the concertina

yes, i know it is direct coupled - guesstimating that Va of the is about 1/2 B+ and split again w/ 2M2 divider -  if i'm even in the ballpark, DC bias is around 1/4 of B+ with that arrangement - so then with 200K Rl; Vo/Vo' swing would be ~1/4 of B+ - interesting way to direct couple. the GC driver sees a 4M4 load and seems to be optimized for gain - AV is around 75 or threabouts. optimum bias for concertina is around 1/4 B+ and this arrangement fits that RoT. that and along with significant gain from the GC driver make it interesting to me. the only drawback that stands out is that with a 4M4 load, f-3dB of the GC is around 50k - i guess that's acceptable for geetar amp?

--DL

[HotBluePlates]

the only drawback that stands out is that with a 4M4 load, f-3dB of the GC is around 50k - i guess that's acceptable for geetar amp?

On another forum, folks were offering comments about the best guitar cable out there. Anecdotal evidence was about the only proof offered, along with some misquoted and/or half-truth claims about low cable capacitance.

I tracked down the specs for Klotz, George L's, 2 versions of Mogami, and Monster Rock and Jazz cables. I also posted the total capacitance of a 15' cable for each type (the original post asked specifically for recommendations for the best 15' cable), including the input and Miller capacitance of the first gain stage, and calculated the f-3dB point. Input grid resistance was assumed to be 68k.

The lowest cap. cable of a 15' length had an f-3dB of ~5.5kHz (~11kHz if you assume 34k due to parallel input resistors); the highest capacitance cable was -3dB at ~2.4kHz.

So 50k doesn't seem too bad now, and likely high enough to avoid any problems related to the feedback loop.

[PRR]

> the GC driver sees a 4M4 load

2.2Meg above 20Hz... there is a cap across the top resistor.

> f-3dB of the GC is around 50k  - i guess that's acceptable for geetar amp?

Sure. Anyway there could be NFB around the whole thing. With heavy NFB it isn't unusual to be rolling-off the internal gain before 5KHz so that loop-gain gets to unity before the OT top-resonance phase-shift hits. Not an issue here since the loop-gain is not large.

[super&plexi]

Hi folks, long time lurker,...... 'bout time I shed the cape, and by the way, a sincere new year(s) ahead hope that all you wish & hope for comes to you.  ....now the important stuff! CONGRATS on finding a Massie. I had a couple (2 6v6, 3 12ax7, recto-not sure), in head form. Sold one, other stolen, but pound 4 pound little monsters, both of em!. Seemed to be deluxe(ish), but no board. Point to Point in the literal sense, not real pretty, but vol. on 10, tone on 11-1o'clock, and somewhere between Ted Nugent, & Roy Buchannon! Best I can remember  of aesthetics is 2 channel, (trem channel not working/or very weak on either) chrome front knob panel w/white markings, black smooth vinyl, or maybe paint on the cab, and silver grille cloth. On the small side of a boogie head. They both had large sprauge O.D.s throughout, & our repair guy at the time said he 'remembered'/'thought' that Massie was a fender amp guy back in the 'ol days. Our shop was in Huntington Beach CA., close to Fullerton,(FENDERTON), & quite a few St. George amps came through. We didn't archive the circuit, (I didn't think of theft), but they both seemed to possibly be hot rodded. One of 'em would drive a 100watt Marshall cab real nice, and of all the (low cost) amps that came through our shop, those little buggers, and a Supro "lightning" bolt represent the "ones that got away, or why the heck did I sell that" terms real nice. Pure fun to play. sorry I don't have comprehensive knowledge, but maybe this helps. Cheers.