Jalopy project: Cinetechnic projector > 18W

[andrew_k]

I lurk here most days and enjoy reading the posts (esp. 6BM8 experiments. Love those bottles!) but don't really have anything to add so I just sit back. However the current run of "jalopy" projects and conversions is right up my alley so I figured I'd share one I'm currently working on that I'm quite excited about.

This amp's former life was as the bottom half of a Cinetechnic "Debrie 16 Professional" 16mm projector belonging to the Dept. of Customs & Excise here in Australia. My girlfriend picked it up at a garage sale for $10 12 years ago and it sat in her parents shed until we bought a house together 6 months back and they demanded all her stuff get cleared out. I spotted it, and BAM -- mine! :tongue9:





...and best of all:


The plan is for twin channels.
First channel is EF86 (100k load, .1 screen bypass, 10uf cathode bypass) into a mid scoop. I never do much more than adjust the amount of mids so I figure on this I'll cut to the chase and just put in a mid-scoop.
Second channel, PI and PA are the HiWatt side of the "Marwatt" 18W variant from 18W.com. I've got a VVR kit from Dana Hall for this one and might make a switchable option of using the UL taps on the OT. Various primary impedances are available with this OT and I plan to go for ~10k:8ohm. 

Other than stripping all old components from the tagboard, wiring changes will be minimal. All heater, PT and OT wiring will remain intact. The amp was flooded with machine oil from the adjustable projector base, most of which I've now cleaned out. I also removed all nuts/bolts/washers for the valve sockets, panels and controls; gave them a scrub and soaked them in WD40 to get all the grease off.

before:


after:

The knob on the side panel is the VVR.
The single input feeds both channels via SPDT switches to allow either channel to be used or both in parallel.

restored valve sockets:

[LooseChange]

That's cool.  Did you get that meter to do anything?

[tubenit]

I like it!  What a cool project.

With respect, Tubenit

[HotBluePlates]

Astounding final result!! And you got some very nice tubes to go in your jalopy!

You could use the spike in front to impale a transitor Marshall mini-amp. 

[RicharD]

Schweet!

[Platefire]

Man! Thats some heavy looking cast steel housing. Looks military strong. Sure looks a lot better after you cleaned it up. Kool Deal. Plate

[andrew_k]

Did you get that meter to do anything?

Unfortunately not. It goes up to 120V AC and I had to wire the two 110V primaries in series as a closer match to our 240V mains.

Astounding final result!! And you got some very nice tubes to go in your jalopy!

Thanks, except it's all smoke and mirrors right now -- only the outside and top of the chassis is cleaned up. The amp isn't built yet.

[DummyLoad]

Astounding final result!! And you got some very nice tubes to go in your jalopy!

You could use the spike in front to impale a transitor Marshall mini-amp. 

 

[RicharD]

>Other than stripping all old components from the tagboard
Are you gonna try to reuse some of them old parts?  I would.  That thang reeks of Marshall.  (100K and 1K5 resistors, a couple of mustard caps....)  I smell magic.

Nice set of tubes.  Wicked cool chassis.  Transformers look really well built.  $10.00 amp if I ever saw one.   

[andrew_k]

Are you gonna try to reuse some of them old parts?  I would.  That thang reeks of Marshall.  (100K and 1K5 resistors, a couple of mustard caps....)  I smell magic.

Only the mustards. I have sozos to make up the rest. My last jalopy, a bakelite radio to hybrid brown/black vibrochamp won a video contest by tube depot and the prize was a voucher... lots of sozo's, solens and other "high grade" components I wouldn't normally go for. I'm using carbon film for all the resistors other than a wirewound 5W for the EL84 bias.

What kind of resistors are the white ones? They all had wax leaking out. The PA had a 25µF/25V bypass cap (wtf? on both counts!) and the bias resistor had burnt a decent hole through the tagboard backing.

[PRR]

>> Did you get that meter to do anything?

> Unfortunately not. It goes up to 120V AC

Probably not a 120V meter. Probably a 1mA (or less) meter, plus a resistor and a rectifier.

Trace back from the meter to see how they fed it.

Or disconnect it, connect to 9V battery through 220K resistor (0.04mA), and see where it reads. If it swings wrong way, reverse leads. If it reads low, reduce the resistor. You may need 10K to get 9/10th of full scale; that would be a 1mA meter movement.

Knowing the basic meter sensitivity, you can work out the circuit needed to read any higher current or voltage. For example a 1mA movement with a bridge rectifier and 5K or 8K series resistance will read about 8 Watts in 8 ohms: a rough "VU meter" scaled to the amp's power. Or 300K to the VVR B+ will read yoor actual supply voltage.

It is remotely possible it is a moving-vane meter and ONLY works on AC; but that's unlikely, specially in high-class gear.

[HotBluePlates]

What kind of resistors are the white ones? They all had wax leaking out.

I *think* those are british-style carbon comps. I've seen them inside of Vox and Hiwatt amps before. The "wax" probably isn't wax, maybe solder flux or maybe a wax end-cap. I don't remember seeing wax caps on the ones I've seen before... but I sure haven't seen everything.

[andrew_k]

Knowing the basic meter sensitivity, you can work out the circuit needed to read any higher current or voltage. For example a 1mA movement with a bridge rectifier and 5K or 8K series resistance will read about 8 Watts in 8 ohms: a rough "VU meter" scaled to the amp's power. Or 300K to the VVR B+ will read yoor actual supply voltage. 

Fantastic, thanks PRR! I was hoping you'd have something to say about making use of that meter.

I *think* those are british-style carbon comps.

Interesting, thanks. They're all in the bin now; I don't go for resistor mojo   

[Refugee]

I am going to have a go at getting you jealous with a picture of the 25W version when I have sorted out the fussy file extensions.

[kagliostro]

I've a name for your guitar amp

THE RHINOCEROS 

Nice amp, last month I can get one similar unit in very good shape for € 50.00

but it was a complete unit with the projector and I do not have the heart to dismantle

K

[Refugee]

It was in the early 1980s when I pulled about 10 of them out of a skip.
I did not dismantle a projector.
I have 4 of them left and I intend to set them up as a stereo system.
A vintage quadrophonic decoder is needed here.