Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Lectroid on November 28, 2022, 02:43:50 pm
-
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.
-
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?
-
@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.
-
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?
-
Try this:
https://el34world.com/Forum/index.php?topic=26814.msg295241#msg295241 (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/ (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.
-
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?! :w2: 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.
-
@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?
-
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.
-
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.
-
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.
-
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.
-
@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?
-
Just checked, my mistake, it's a 385 that we are working on.
-
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.
-
@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
-
Trying a GIF - I usually mess this up
-
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.
-
@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! :laugh: 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.
-
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. :icon_biggrin:
-
....I had to watch "Seal Island" three times--they didn't pay me enough...
You can watch it again! (https://www.youtube.com/watch?v=CVRe-bJPHb8) The drama! The plotting! Romance. Suspense. Melodrama! Females in furs!