Amp Projects

[Lectroid]

Over the past three years I've built three amps of increasing complexity, with the help of so many people. I thought I should show everyone how they turned out.  (If this is the wrong forum, please move, thanks)

My first, a Bell & Howell 179 conversion.  It's like a 5E3, except with a 6SJ7 Pentode in the first stage.  Very clear and solid and lower volumes, then breaks up into a nice Deluxe growl at higher settings.  Hammond organ 12" speaker.  I did the cabinet and tolex myself.

The second two are of my DR 1-channel AB763, no tremolo.  Cabinet is from Guitar Cabinets Direct, panel by Sandy Henry. and the speaker is a Jensen P12Q.  At 25 Watts, I thought it would be enough but this thing gets loud.  I may have to upsize it.

[CrocMule]

Nice work.  The tolex looks pro.

I wouldn't mind seeing a gut shot of the Bell & Howell...

I've built three amps of increasing complexity

And what's behind door #3?

[Lectroid]

@CrocMule,

Thank you.

Door #3 was a Princeton AA964 clone.  I swapped the Fender tremolo circuit for sluckey's Tremor-lator, which worked well.  Never got around to putting it in a cab--I use the chassis to play with circuit ideas. 

The B & H Deluxe clone was my very first and it was an ongoing mess for 18 months as I learned what I was doing, and how amps worked, etc.  I rebuilt some sections 2 or 3 times and it's still pretty ugly.  I do have 'Before' pics of the original projector amp.  Also, it was an *extremely* tight chassis so it was a real trial by fire.  I ended up just gutting the chassis.

As you can see, the level of packing in there was amazing, with those old-style components.  Note the actual metal rod that operated a leaf switch to change inputs when a microphone plug was inserted.  All of the circuitry for reading sound off the filmstrip wasn't needed anyway, so I started over as a point-to-point build.

Also, here's the schematic of what I ended up with (after much help from the denizens here).  If I get time today I'll get you a pic of the final circuit.

[CrocMule]

Holy cow, that's a tight chassis.  Working in that would make me feel claustrophobic.

Interesting circuit.  How do you like the 6SJ7 in V1?  That's probably covered in an earlier thread.  You got a link?

[Lectroid]

Try this: 

https://el34world.com/Forum/index.php?topic=26814.msg295241#msg295241
Or search on my user name and you might find some others.

I like the 6SJ7; I'm pretty happy with the sound for a first amp.  In the B&H, it was originally a 6J7 but that tube is very microphonic and several people advised a swap.  I ended up mounting the tube socket on thin grommets, sitting on the chassis, and I have two o-rings on the tube can to soak up any other vibrations.  It's pretty quiet.  I think I may revisit the Volume-Tone area someday but overall it's a good little amp.   (12-14W?)

Here's a B&H rebuild blog by Huw Price on guitar.com:
https://guitar.com/guides/diy-workshop/diy-workshop-bell-howell-filmosound-amp-conversion-part-two/

Too bad the old projectors are getting so hard to find.  I've looked at a lot of them and I think the 179 or 285 are the very best to convert.

[bmccowan]

Very nice. Funny, I have two Filmosound 179s I bought years ago after reading about Ry Cooder's work with them. Every time I opened one up, the clutter scared me and I put the base back on and started something else. The day after TG, I grew some stones and gutted one of them. Who and how were those built?! everything is just jammed in there. I worked out a schematic, pretty similar to yours, but borrowing more from the very early bassman and a PI from Valco. I am playing around with layout ideas now. Everything so close together calls for true point-to-point, eh?
I'm also changing V1 to a 6SJ7. A few early Fenders and many Gibsons and Valcos used that tube in V1. The EF86 and 5879 are not a lot different. I've built quite a few amps with pentodes in V1 and like it a lot, I've also put them in V2, driving them with a triode in V1; ala Matchless Clubman and Merlin recommendations - cleaner, smoother, louder, but nothing works better for bottleneck slide than a pentode in V1 IMO - pure juke joint.

[Lectroid]

@CrocMule,

Here's the interior shot you want of my build. 10"x7"x2"...tight.

@bmccowan,
Someone smarter than me said it would be Absolutely The Worst first project I could take on.  So I went ahead anyway, and proved him right.  But I learned a lot, so I guess it was worth it.  The density of the original layout still blows me away when I think about it, especially all those little metal plates in odd places to kill interference between close-packed sections.  And the whole thing had to sit inside a rumbling electrical machine and reproduce good sound.  Amazing.

I'm also having thoughts of revisiting the 179, cleaning up the layout, etc.  And maybe tweaking the circuit a little.  I had in mind to check out some of the early 50s amps to see how they used pentodes in V1.  Do you have a schematic you're willing to share?

[dtbradio]

I may have missed something in replies, but do you have any audio/video files of the amps in action? Would love to hear samples! I'm working on my very first tube guitar amp project, and enjoy comparing results with other's builds.

[bmccowan]

Sure Lectroid - I'll post what I intend for the one I just gutted, and a couple others, later today. For other amps - there are many. Fender only had a very few. Most early Gibson, and Valco (Supro, National, Oahu) amps used 6SJ7 in V1. Lots of schematics right here on Doug's schematic pages. Leon C has collected many such amps, is a great guitar player, and demos them on YouTube.

[dmp]

Hi LectroidI'm helping a friend with a filmosound 179 right now.Unless you already changed it, you might want to look at the tone stack before doing anything else. These have a cool James / Baxandell tone stack design - BUT the tone pot is a dual 3M that (I think) counter rotates bass and treble. If you try separate bass/treble pots you will have a huge range increase & improvement on the tone you can get.The V1 pentode stage is wired pretty standard - other than the high grid resistor (1M). The Vox amps used a variable switched set of capacitors after this stage to make a HPF (less bass).
You can be deliberate in what you want from the frequency filtering - ie. a HPF leaving V1 combined with the tone stack design. Check out the "tone stack simulator web"

What are the codes on your transformers? My buddy has a version with 606 (Schumacher) and it sounds fantastic.

[bmccowan]

dmp - are you sure that amp is a 179? I think that might be a different model: 385? No dual pot in either of the two 179s I have.

[Lectroid]

@dmp,

My B&H transformers both have a 138 code - Stancor.  Both PT and OT are over-powered for the amp IMO.  Lots of reliability built-in.

I agree with bmccowan that your chassis is likely a 385.  Do you have schematics?  The 385 definitely shows the dual tone pot.  The 179 has a rather different (but still interesting) tone circuit.  At the time I could not understand how it worked so I used a Deluxe 5E3 circuit.   I have a doc with most B&H tube model schematics.  If you PM me with your email, I'll copy you.

@dtbradio,
I don't have any samples right now, maybe I'll lay something down.  What are you working on for your first project?

[dmp]

Just checked, my mistake, it's a 385 that we are working on.

[bmccowan]

Lectroid - attached is the starting point schematic for my 179 "Schoolie" - fond memories from Jr High school of the AV department wheeling in a Filmosound to show us Reefer Madness, or the Horrors of Gonorrhea.
Also attached are a few Gibson Schematics with 6SJ7 in V1. Merlin has a good chapter on pentodes on his Valve Wizard site.

[Lectroid]

@bmccowan,

Many thanks for all this.  I worked as a student projectionist long ago at San Diego State.  One week I had to watch "Seal Island" three times--they didn't pay me enough to endure that.  But what amazingly complex and tightly-packed machines, back when American manufacturing was at its peak.

I can't read the 179 schematic--for some reason Autodesk is not letting me log in, maybe cause I'm on a Mac?  Is there any chance you might have a PDF or JPG?   No worries if not.

Thanks again

[bmccowan]

Trying a GIF - I usually mess this up

[sluckey]

I can't read the 179 schematic--for some reason Autodesk is not letting me log in, maybe cause I'm on a Mac?

It's not an Autodesk file. That file was created by a freeware program called ExpressSCH.

There is a free MAC program called JSchem that can also view those *.sch files.

Hoffman even has a forum dedicated to ExpressSCH and JSchem.

[Lectroid]

@bmccowan,
Got the GIF, it opened just fine, thanks.  If I may ask, why'd you used a paraphrase PI instead of a cathodyne?

@sluckey,
I try to learn 3 new things every day--it's not often I get them in one post!     On my machine SCH file were linked to Eagle CAD from Autodesk, a subscription service (well, used to be) which I avoid when I can.  Never knew about JSchem, just avoided SCH files.

But I downloaded JSchem and can now open SCH files. Never able to before so this is great.  Thanks again.

[bmccowan]

paraphrase PI instead of a cathodyne? No particular reason, other than I like early Valco amps and most use that type of PI. Other than that, its all sort of a long ongoing experiment for me: play it for a while, see how it sounds, change it up maybe. I always find it interesting how the different stages from different circuits work well together. I think Sluckey said at some point, pick a power amp and a preamp and glue them together. That's pretty much what I do. I'm not knowledgeable enough to invent something new.

[PRR]

....I had to watch "Seal Island" three times--they didn't pay me enough...

You can watch it again! The drama! The plotting! Romance. Suspense. Melodrama! Females in furs!