BALMORAL ELECTRIC: Set of tone benders

Just to offset the amplifier posts for the pedal folks - here’s a set of three tone benders that I just finished   

PROJECTOR: Bell & Howell Gaumont, Model 601

I know, I know—this is starting to drift even further from pedal circuits with each post, but stick with me for a moment.

These old Bell and Howell projector amps have quite the following, so I’ve been keeping an eye out for one for a while. The catch is, they don’t pop up on the secondhand market very often—at least not the older valve-based models.

So when this one showed up on Marketplace at a reasonable price, I couldn't resist. It came from an older couple on the Sunshine Coast, which is about an hour from my place (Queensland, Australia). According to them, the amp originally belonged to a great uncle who bought it new in the early '50s. It had been in storage for about 20 years, and no one in the family was interested in keeping it. Apparently, it was still working when it was put away.

Basically the amplifier is hidden away under the projector (which is built like a tank by the way).   

BELL & HOWELL GAUMONT, MODEL 601 (FILMOSOUND 179)

These amps are often called "Bernie" amps, named after a guy in Canada who’s believed to have been one of the first to modify them for guitar use. Bernie himself is something of a mystery—nobody seems to have ever met him or been able to track him down, and almost every amp he worked on has its own unique character.

Beyond their vintage charm and distinctive components, these amps are known for their unusual tone control. The tone circuit varies between different models, but this particular one is wired into the negative feedback loop and the cathode of one of the valves. When you adjust the tone knob, it feels like a lot of subtle things are happening at once.

The amp itself has;

• 2 x 6V6GT  cathode biased, push pull, power amplifier
• 1 x 6SL7GT (ECC35) dual triode for the phase inverter
• 1 x 6J7GT (EF37A) pentode for the preamp
• 1 x 5Z4 full-wave rectifier (Model 179 lists a 5Y3GT on the schematic).  

No little mini 9 pin bases here - all octal bases.  There's an additional 6V6GT as part of the projector system, and some other random valve that has no place on a guitar amplifier.

I really like the little grill cloth protector panel. 

This is actually the back, despite looking a bit like a speaker grill.

Unfortunately the rubber had hardened and has become so fragile that the leads can't be used.  I am saving the metal connectors, as they still seem good.  The cable is so bad, I can't even strip the outer layer to save the wires inside.  It's all gone.

The projector and speaker both came in really well made canvas cases.  Given that these were made in the late forties, perhaps someone with a bit of experience making kit for the military put these together?  The leather carry handle poked out the top - there's nothing left of it, apart from the wire frame.  Surprisingly the leather around the base is still in great shape.

While it doesn't have a label, these are usually marked as B.A.F.  Type T60 (British Audio Film Limited) and the general consensus is that they were made by Goodmans, and is similar if not the same as the Audiom series.   I have another Ampro projector speaker cab with a Goodmans in it that sounds great.  This one is not as nice as the Ampro, but it’s still pretty good (the Ampro has a physically larger cab, and a different model speaker) I was happy to see this speaker in such good condition.

And thanks for checking the speaker GB - in April 1949...  

And if you've seen photos of the projector and wondering how difficult it is to get the amp out - it's not.  It drops out the base after removing four screws.

These amps are notoriously tricky to work on—there seems to be two main schools of thought: strip the circuit out and start from scratch, or, leave them almost untouched and run with it as is.

Since this one’s from the late '40s, I’m not too confident about the state of the capacitors.  That said, there are people who using this model of a similar vintage without mods or repairs, so it’s not entirely out of the question. Maybe there’s hope!

BELL & HOWELL, MODEL 179 SCHEMATIC

Just looking at this schematic makes my head hurt, as for me it's just not laid out in a logical manner.

From the Hammond 1750 output transformer series, this is listed as a drop-in replacement for a Fender Vibrolux Tweed, 5F11  -  they're supposed to look similar to the original Fender transformer where possible.  That being said - this sticks out like dog’s balls when mounted on a crusty old amp. 

Materials etc are also supposed to be similar to get as close as they can (within reason I suppose).

It was a bargain, at $76 +GST (Australian dollars) from Mouser, including free delivery.  Like all things Hammond, it feels well made.  

• 8,000 ohms plate to plate
• 16, 8 & 4ohm secondary windings (these options would not have been on the original)
• rated at 15w
• bobbin wound

Turn Ratios

4 ohm turn ratio     44.77  (2004.35)

8 ohm turn ratio     31.58  (997.29)

16 ohm turn ratio   22.38  (500.86)

Frequency response

75hz to 15khz  

Inductance

19.66H

HAMMOND 1751M OUTPUT TRANSFORMER DATASHEET

THIRD MAN: Fuzz A Tron

 If you're in the USA, for $75 you may as well buy the kit.   

THIRD MAN FUZZ A TRON VERO LAYOUT

Spoiler alert - it's a modded Fuzzrite.  330k resistors instead of 470k, and it's missing a resistor that formed a high-pass filter on the output of Q2.

VALVE DATASHEET: 6V4 Full Wave Rectifier

 

6V4 / EZ80 FULL WAVE RECTIFIER DATASHEET