Filmosound model 202 conversion help needed

[Steven England]

Hi, I am bought a filmosound model 202 projector from around 1954 Vintage Bell & Howell 202 Tube Amplifier & Transformer | eBay (this is the same as mine, and wanted to know if it is possible to convert it into a guitar amp. I am a complete novice and will need to start from the absolute beginning but I am determined so if you have any advice I am keen to get going.
I know that the projector is in excellent condition (it came from a museum quality collection at auction, but I don't know if the amp is working or even where to start. I took out the amp and the transformer and then realized that I needed to power the amp up and wasn't sure if I needed the projector to do this, so I plugged it all back together and turned on the projector (which all runs just fine, but it didn't look like the amp had any power. I am not sure where to go from here and wondered if anyone had ever converted a model 202 specifically, or if anyone has the patience to help out a complete novice (I will put in the work and follow directions well). I am reading some basic tube electronics stuff as we speak. Thanks and I hope somebody can help. Steve.
If I can get some help I am planning to video the conversion from a complete beginners point of view (let's face it, complete beginner's point of view is all I have, but I thought it would be useful for all us first timers).
Thanks again, Steve.

[SpareRibs]

Hello,
I have done two conversions myself without much electrical knowledge, Have you got a treat in store for you! The very first thing you need to do is to get a (schematic diagram). That could be a major undertaking in itself. I doubt anyone could help you much without that at this point. Google it and it may come up. There are no shortcuts. This is going to be very difficult, but well worth it in the end
I have done a Magnavox phonograph and a Newcomb PA conversion. The more you find out things it seems the faster you start understanding until the whole thing starts to make sense. Anyway I will leave you to ponder that!

[olddawg]

You should measure the PT secondary voltages and list the tube complement. Then look at schematics of common guitar amplifiers that use similar specs. Then you can completely gut the thing and start over using just the chassis and transformers. I would suggest replacing the tube sockets with new ceramics. It isn't difficult to build up a new turret/eyelet board from new parts. If it is using wierd tubes change to more common types like 12ax7s. If you need slightly more B+ you can use an SS rectifier. If you need more filament current you can change the pilot lamp arrangement if it is on the filament line. If you take this approach you do not need the original schematic and will save a lot of time and grief by building an actual guitar amp rather than forcing a film projector amp to be one. Especially one wired point to point.

[Steven England]

Vintage Bell & Howell, CIRCA 1952,Model 202, Record & Play Magnetic and Optical Sound Play, Tube Amplifier with Transformer
Tube Complement 6AQ5 x 2, 12AX7 x 2, 5869 x 2, 5Y3-GT
16 ohm speaker output, Non sync input, Microphone input,Volume & Tone Control
Photos are shown at Vintage Bell & Howell 202 Tube Amplifier & Transformer | eBay
I have found the schematic, now I need to figure out what it all means! steep learning curve I think.
Can anybody give me a quick way to get it hooked up and see if it has life in it or not?
Thanks, Steve.

[olddawg]

Vintage Bell & Howell, CIRCA 1952,Model 202, Record & Play Magnetic and Optical Sound Play, Tube Amplifier with Transformer
Tube Complement 6AQ5 x 2, 12AX7 x 2, 5869 x 2, 5Y3-GT
16 ohm speaker output, Non sync input, Microphone input,Volume & Tone Control
Photos are shown at Vintage Bell & Howell 202 Tube Amplifier & Transformer | eBay
I have found the schematic, now I need to figure out what it all means! steep learning curve I think.
Can anybody give me a quick way to get it hooked up and see if it has life in it or not?
Thanks, Steve.

I can't think of a guitar amp that uses 6AQ5s. I here they are like miniature 6V6s and a pair is good for about 10 watts. Unfortunately I don't think you can just wire up a standard layout/schematic from a known guitar amp to these tubes. I'm sure there is someone on this board with mote experience who could make a suggestion on what to build.

[SpareRibs]

Hello,
Post the schematic. The similar tube 6BQ5 is an EL84. That is in a lot of tube amp configurations. Now go to Google and look for how to read schematics. The amp is in 3 sections. Preamp,Power,and output. Copy the schematic so you can use a few copies to write on. Divide the schematic into the three sections and look at them like that,with that method it will not be so overwhelming. Don't get in a rush, try to digest the information you have so far.
In order to turn it on you may have to look for a blown fuse,also the amp may not come on until the projector is loaded. at any rate I will leave you with that for now.(Google-Converting An Existing Amp Chassis For Guitar Use)

[olddawg]

Hello,
Post the schematic. The similar tube 6BQ5 is an EL84. That is in a lot of tube amp configurations. Now go to Google and look for how to read schematics. The amp is in 3 sections. Preamp,Power,and output. Copy the schematic so you can use a few copies to write on. Divide the schematic into the three sections and look at them like that,with that method it will not be so overwhelming. Don't get in a rush, try to digest the information you have so far.
In order to turn it on you may have to look for a blown fuse,also the amp may not come on until the projector is loaded. at any rate I will leave you with that for now.(Google-Converting An Existing Amp Chassis For Guitar Use)

If a 6AQ5 and a 6BQ5 were similar I would recommend just building an 18 watt Marshall clone or a Vox AC15. But they are not. You can't just plug 6BQ5s into this amp. There are lots of considerations. The B+ will be lower for starters. I guess you could use the preamp of either of those and adapt it to the existing 6AQ5 PI, power amp, and power supply. The good news is NOS 6AQ5s are dirt cheap so if you redplate a few there's plenty more around. They won't be modern replacements. The the tube has not been manufactured for many years.

[Steven England]

thanks guys, I really appreciate the help. It is late now so I will post the schematic in the morning (GMT -8hrs here), I'm off to do some bedtime reading on how to read schematics. Thank for your time and assistance. Best wishes, Steven

[Steven England]

Hi, here are the schematics for the Amplifier and the projector circuits.


The first thing I want to do (but please tell me if I am starting from the wrong point) is to check if the amp is working at all, and if not how to figure out what is working and what is not. The projector came from a very well kept collection that was in excellent condition so I would be surprised if it were not fully functioning when I got it, but I really don't know other than the projector powers up and runs, but I don't have any 16mm film to test it with.
Thanks again for the help, I am reading right now but don't want to break anything due to my lack of knowledge.
Cheers, Steve.

[olddawg]

You know....if you do have the whole system, you might consider selling it as what it is and getting something else. It isn't a really good candidate for conversion IMHO. An old PA or phonograph is better. Also, be aware that there are some pretty decent 20 watt tube amps out there new in the $300 range.

[SpareRibs]

Hello,
I just looked at the schematic, I couldn't download it from the forum so I found it online. There are two input jacks on the projector. One is for a microphone and I am not sure what the other one is. At any rate you can plug your guitar into one of those. The on off switch is on the volume control, just turn it on. Be sure you have a speaker connected. The output for the speakers are 8 and 16 OHM. An 8-ohm stereo speaker will work just to try it out.
There is probably going to be a lot of stuff to remove to just have a guitar amp, but as you go along you will be able to sort it out. Also go to the search function and search
Bell and Howell 202 amp conversions, Some people are doing it and will be able to give you a
lot of information, as they are actually doing it.

[paggerman]

Vintage Bell & Howell, CIRCA 1952,Model 202, Record & Play Magnetic and Optical Sound Play, Tube Amplifier with Transformer
Tube Complement 6AQ5 x 2, 12AX7 x 2, 5869 x 2, 5Y3-GT
16 ohm speaker output, Non sync input, Microphone input,Volume & Tone Control
Photos are shown at Vintage Bell & Howell 202 Tube Amplifier & Transformer | eBay
I have found the schematic, now I need to figure out what it all means! steep learning curve I think.
Can anybody give me a quick way to get it hooked up and see if it has life in it or not?
Thanks, Steve.

Wow. I'd love to have a crack at this one! The 6AQ5 is electrically similar to the 6V6 but in a 7 pin miniature envelope. Someone else on this board rates the 6AQ5 as a favourite non-mainstream guitar amp valve. I have used a 6aq5 in a radio conversion - it was in there when I got the radio. I also used the Russian EF86 equivalent and a 6AT6. I love the sound of this little amp and it's plenty loud enough so that wife and child can hear me when they are in the car on the drive.

My advice to you is to gut all the electronics. Old components with straying values and leaky caps designed to amplify cleanly is not going to make a good guitar amp. My first amp build - with no previous knowledge - was the Lamington at Valve Heaven - Home. The good news is that you have the transformers, so you don't need to mess with the quadrupler. Look at lots of schematics and learn the common themes. The Marshall 18w is a good reference. Also try the PP schematic at Amp Maker: Guitar amp kits and parts. You'll see common themes - learn and understand these. Some purists will say that for different secondary voltages you will need to adjust bias etc. you could. Or you could build your first amp, possibly burn out the valves and put it down to experience. However, with your Filmosound you have a PT that was built for those valves so you should be OK. For the output stage (the 2x 6aq5) find any guitar amp with 2x 6v6 as an output ( there are hundreds) and copy the design. Remember that the pin numbering is totally different - so get the data sheets from TDSL and compare/contrast. Read Merlin's web pages - then buy his books. I think the consensus is that there no better texts for noobs.

What you will end up with is a unique amplifier that will be hugely satisfying to play and that you can use to tweak as much as you like as you learn more about what's going on inside.

However. Word of caution. These things can go ZAP in a lethal way. Even days after being switched off Learn how to test for voltage on the filter capacitors. Learn how to discharge them. Test for voltage afterwards. I have never had to poke around inside a 'live' amp and don't really want to - huge caution required.

Quick test for viability - remove all valves. Set your DMC to 1000VAC. Clip the black lead to the chassis. Put one hand in a pocket. Turn on. Use the red lead to test voltages off the PT. anything? No? Try the fuse. Still nothing? Unplug from mains. Work out how the PT is constructed. Icahn see that someone has posted a schematic but the iPad I am using doesn't work so well with pictures on this board. Check for continuity on each of the windings. Expect a resistance of up to 1000R. If you transformer is good you are well on your way to a fantastic alternative to learning how to play guitar properly.

One final tip - there is a heap of information on the Internet, not least here. Try searching for your answer before asking. You will learn lots of other stuff on the way.


Those 5879 pentodes are probably overkill for what you need. However, the sockets offer scope to change the design to something more conventional. You could replace the 6AQ5 output stage with an EL84 output stage. Or you could go weirder and use them as a gain stage with Merlin's morph control. Pentode gain stages sound lovely.

Google searches:

Merlin valve wizard
Duncan TDSL
Schematic heaven
Valve heaven lamington
Ozvalveamps
Ampmaker
Aiken amplification (tech info)
Ax84.com
18watt.com
Tube depot has some easy to read schematics with useful info.