Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: rockrink on August 14, 2020, 03:04:45 pm
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Ultimately, I would like to have an AB763 with verb and Trem, single is fine. I'd like a mid and a dwell control, similar to a Vintage Sound amp I had for a short time. And I wouldn't mind if the filter caps could be on the main board, eliminating the need for the dog house. I also prefer turret board builds.
I have years of experience working on my own tube amps -- fender twin, Fender Bassman, Peavey C50, Blues Jr. -- and I've done a few mods on the BJ (Fromel) and C50 (Blueguitar). I was a technician in the Army a long time ago, and back then, I was a NASA-qualified solderer. I realize that was a long time ago. I also realize that building a tube amp from scratch requires more specific experience than I have. Thus, I am seeking help building a path to an eventual scratch-build. I contemplated with the idea of building one of the commercially available kits, but I'm not sure how satisfying that would be and whether that expenditure would just delay me from my actual goal. Given my interest and limited experience, what suggestions would you guys have for me.
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Start here...
https://el34world.com/schematics.htm
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I should mention that I have read through most of the site before my post.
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Start here...
https://el34world.com/schematics.htm
Thank you.
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I should mention that I have read through most of the site before my post.
Ok then, more specifically:
https://el34world.com/Hoffman/files/Hoffman_AB763_1.pdf (https://el34world.com/Hoffman/files/Hoffman_AB763_1.pdf)
Replace R31 with a dwell control (maybe add it to the back panel near the driver tube)
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Maybe find a middle ground between *total scratch build* and *kit build *.
An empty head or combo cabinet can be bought new, or repurpose a used head/combo cab.
I recently scored a decent late 90s fender solid state 1 twelve combo cab, with good eminence fender speaker for $50. Its gonna make a nice AB763 here in a month or two (hopefully. )
I'll order a chass8s to fit the cab, then transformers and the rest.
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Here's how Doug eliminated the doghouse
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Maybe find a middle ground between *total scratch build* and *kit build *.
An empty head or combo cabinet can be bought new, or repurpose a used head/combo cab.
I recently scored a decent late 90s fender solid state 1 twelve combo cab, with good eminence fender speaker for $50. Its gonna make a nice AB763 here in a month or two (hopefully. )
I'll order a chass8s to fit the cab, then transformers and the rest.
Thanks for the reply. Your approach seems wise. And come to think of it, I've got a few speakers sitting around doing nothing. Is it easier to get a cab first and fit a chassis to it, or vice versa?
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Here's how Doug eliminated the doghouse
That is beautiful, isn't it. I would love to put something like that together.
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Here's how Doug eliminated the doghouse
That is beautiful, isn't it. I would love to put something like that together.
Well, that's why we're all here.
Something like 40 amps later and I'm addicted now as much as ever.
I'm just starting to get them looking that pretty.
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Go here and pick one of Steve's amps and follow his build. Can't go wrong. http://sluckeyamps.com/index.htm (http://sluckeyamps.com/index.htm)
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I'd pick one of Doug's amps, and build away. They are great sounding, classic animals that have been tamed and there is a lot of experience with on this forum.
It sounds like the circuit portion of the build won't be a big challenge for you. (LOL, but you be learning every inch of the way!)
The biggest challenge, I bet, will be the cabinet and chasis. Most (all?) of Doug's amps have an available chasis, inexpensive.
I personally design my chasis', and spend the bucks for a sheet metal guy to bend to the specs. Or, you can buy off the shelf stuff (mostly Hammond, but there are a bunch of small suppliers on eBay) -- either approach works.
Then, you can design and build your cab. One does need woodworking tools for this. Or you can buy pre-built on eBay. Or re-purpose an old amp.
Dealers choice!
But whatever you decide to do, just do it!
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Ultimately, I would like to have an AB763 with verb and Trem, single is fine. I'd like a mid and a dwell control, similar to a Vintage Sound amp I had for a short time. And I wouldn't mind if the filter caps could be on the main board, eliminating the need for the dog house. I also prefer turret board builds.
I was able to get a ab763 one channel with the trem deleted into a blues jr and it worked out pretty well. As others have said, the hard part is creating cabs and chassis unless you purchase those separate.. DIY is a little less expensive but takes time to learn to do. What tools do you have available and how much of this are you willing to fabricate yourself? You can get a blank chassis from a few suppliers and cut everything out yourself, or use someone like Synaptic to partially/fully fabricate one for you. Tell them which PT you want to use if you want them to cut that out. https://reverb.com/item/2816491-blackface-style-chassis-blank-w-optional-knockouts (https://reverb.com/item/2816491-blackface-style-chassis-blank-w-optional-knockouts)
Ill vouch for those folks, they made the blank chassis for the blues jr build. Someone else had done the same on this forum.
After that, Doug has parts lists in the store for the one channel AB763. Its a fantastic circuit. Well worth having. Ill be building another for myself.
Good luck. Welcome to the forum! Looking forward to your build.
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Thanks to everyone for the great suggestions. I have decided that I am going to start a little smaller than my original vision. I will build the Blackvibe AB763 by Rob Robinette with no reverb and no tremolo. I ordered the eyelet board from Doug over the weekend and bought a new/surplus chassis elsewhere that had nothing punched or cut. And I ordered a bunch of graph paper. I figure I'll get a little more build-related experience under my belt and then tackle the reverb/tremolo AB763 later.
I'll post on my progress, and there is a slight change (sarcasm) that I might need some help along the way.
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Good luck with the build and keep us posted! I would be inclined to suggest an even more simple build for first time and go with a single-ended blackface design perhaps.
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Well, I've ordered the eyelet board and a few parts from Doug. I went with the eyelet version because it was already designed and available on Doug's site. I'm sure I will learn the process for requesting specially built turret boards next time, but I need to get underway with this project before life throws something in the way.
I have also ordered an aluminum chassis which has not been punched, so I'm sure I'll learn from that process as well. Since I don't imagine I'll be building enough of these to justify the costs of a Greenlee punch set, I was considering a simple step drill bit (or set). I also think I'll be buying a metal blade for my jigsaw for the transformer cutout. Would you guys recommend a different approach to punching/cutting/drilling the chassis?
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I was using these cheap step bits from HF and they got me through a couple chassis. Once I got tired of melting aluminum I got some old individual punches off ebay. I wound up with 3/4", 7/8", and 1 3/16" and that seems to be enough for me.
The small socket that Doug sells takes the 3/4" hole. There are some other small sockets out there that take the 7/8".
https://www.harborfreight.com/power-tools/drill-driver-bits/step-drill-bits/2-piece-titanium-nitride-coated-high-speed-steel-step-drills-96275.html (https://www.harborfreight.com/power-tools/drill-driver-bits/step-drill-bits/2-piece-titanium-nitride-coated-high-speed-steel-step-drills-96275.html)
https://www.ebay.com/itm/Greenlee-Punch-Die-Knockout-1-3-16/383676034790?hash=item5954dfaee6:g:ivsAAOSw4cdfNYaf (https://www.ebay.com/itm/Greenlee-Punch-Die-Knockout-1-3-16/383676034790?hash=item5954dfaee6:g:ivsAAOSw4cdfNYaf)
https://www.ebay.com/itm/GREENLEE-3-4-CONDUIT-KNOCKOUT-PUNCH-ASSEMBLY-7-NOS/193482073848?hash=item2d0c6e26f8:g:te0AAOSwZ1ZezAx0 (https://www.ebay.com/itm/GREENLEE-3-4-CONDUIT-KNOCKOUT-PUNCH-ASSEMBLY-7-NOS/193482073848?hash=item2d0c6e26f8:g:te0AAOSwZ1ZezAx0)
https://www.ebay.com/itm/GREENLEE-1-2-CONDUIT-7-8-DIA-HOLE-KNOCKOUT-PUNCH/184400721830?hash=item2aef23b7a6:g:xosAAOSwzkZfNbcF (https://www.ebay.com/itm/GREENLEE-1-2-CONDUIT-7-8-DIA-HOLE-KNOCKOUT-PUNCH/184400721830?hash=item2aef23b7a6:g:xosAAOSwzkZfNbcF)
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I should mention that I have read through most of the site before my post.
I was using these cheap step bits from HF and they got me through a couple chassis. Once I got tired of melting aluminum I got some old individual punches off ebay. I wound up with 3/4", 7/8", and 1 3/16" and that seems to be enough for me.
The small socket that Doug sells takes the 3/4" hole. There are some other small sockets out there that take the 7/8".
https://www.harborfreight.com/power-tools/drill-driver-bits/step-drill-bits/2-piece-titanium-nitride-coated-high-speed-steel-step-drills-96275.html (https://www.harborfreight.com/power-tools/drill-driver-bits/step-drill-bits/2-piece-titanium-nitride-coated-high-speed-steel-step-drills-96275.html)
https://www.ebay.com/itm/Greenlee-Punch-Die-Knockout-1-3-16/383676034790?hash=item5954dfaee6:g:ivsAAOSw4cdfNYaf (https://www.ebay.com/itm/Greenlee-Punch-Die-Knockout-1-3-16/383676034790?hash=item5954dfaee6:g:ivsAAOSw4cdfNYaf)
https://www.ebay.com/itm/GREENLEE-3-4-CONDUIT-KNOCKOUT-PUNCH-ASSEMBLY-7-NOS/193482073848?hash=item2d0c6e26f8:g:te0AAOSwZ1ZezAx0 (https://www.ebay.com/itm/GREENLEE-3-4-CONDUIT-KNOCKOUT-PUNCH-ASSEMBLY-7-NOS/193482073848?hash=item2d0c6e26f8:g:te0AAOSwZ1ZezAx0)
https://www.ebay.com/itm/GREENLEE-1-2-CONDUIT-7-8-DIA-HOLE-KNOCKOUT-PUNCH/184400721830?hash=item2aef23b7a6:g:xosAAOSwzkZfNbcF (https://www.ebay.com/itm/GREENLEE-1-2-CONDUIT-7-8-DIA-HOLE-KNOCKOUT-PUNCH/184400721830?hash=item2aef23b7a6:g:xosAAOSwzkZfNbcF)
Thanks. It looks like the Greenlees are not as expensive as I had thought. I ordered the 9 pin Belton Tube Socket and the 8 Pin Belton Tube Socket from Doug. I was planning on simply measuring them when they arrive so I would know which size hole I needed to make. Based on the links sent above, I will probably get the knockout punches. I haven't used one in decades, but I recall they were a delight compared to other methods.
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Hoffman tells you what size holes you need for his sockets.
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Hoffman tells you what size holes you need for his sockets.
Thanks. I didn't notice that earlier. I guess I need to slow down.
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The punches are nice, but the step drills work just fine as long as you debur. No biggie either way.
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Step drills work, but Greenlee punches are sweet. If you like good tools and have the cash, you will not regret buying the punches.
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Progress Report:
Ultimately, I decided to go with Rob Robinette's Blackvibe 6v6, no verb, no Trem, and finally got started. I work full time, so this is more of a weekend project.
The tube sockets, transformers, choke, output jack, IEC connector, test points are all physically installed in the chassis. I started populating the eyelet board (bought from Doug), but I felt like two of the F&T caps were physically too large, so I have JJs on order. When they arrive, I will resume with the board.
Also, I am going to try to fashion a DIY faceplate and the material for that should arrive this week. That will likely be this weekend's project. After the faceplate is built, I will install it to the chassis and then install the pots, switch, input jack and pilot light to the chassis through the faceplate.
I believe in about two weeks, I'll be ready to apply power and then make some cabinet decisions.
Thanks for all of the tips so far, really helpful.
R
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Keep us posted please.
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Update: I spent a sizable chunk of the long weekend working on the build and it is all wired up. Tonight, I will do some continuity checks with a highlighter and the schematic and try to get a certain confidence level in the build. I picked up the parts for a lightbulb current limiter earlier today, so I will build that and maybe put the amp under power later this evening if my preliminary checks seem right.
I'll likely post an update tomorrow.
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Progress report: Last night, I mustered all of the patience I could and performed the continuity test that I had mentioned yesterday. I really wanted to just turn the amp on and start playing it, but boy was I glad I waited.
On the Blackvibe, there is a jumper from pin 3 to pin 8 of the Phase Inverter which ties the cathodes together. I had totally overlooked the jumper in the layout; however, when I got to that part of the schematic with my highlighter and I started to test continuity between pins 3 and 8, I noticed that pin 3 inside my amp did not have anything connected to it at all. This caused me to take a closer look at the layout and that's when I realized my mistake.
After fixing that omission and completing my tests, I powered her up. Sure enough, she passes guitar signal through to the output. This felt like a big moment in my first build.
As I started tweaking the dials, I noticed that there was a huge jump in volume early on the dial. It was almost like the amp went from silence to way too loud with nothing in between. I then found another mistake that I had made. . . grrr . . . I had ordered linear pots instead of audio pots. I believe this is likely the cause of the all or nothing volume. Unfortunately, I didn't have any A type pots around, so I ordered some from Doug. When they arrive, I'll install them and test again.
Tonight, I will likely measure bias and DC voltages. I'll report back when I have an update.
To anyone else attempting a first build, I highly recommend taking a highlighter to the schematic and checking continuity from left to right, marking the schematic as you go. Oh, and be patient when ordering parts. . .
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Congrats on getting her working and +1 on doing continuity tracing with a highlighter. That approach is discussed on the Forum here: "How to double check your amp wiring and find things you missed" https://el34world.com/Forum/index.php?topic=17701.msg178630#msg178630 (https://el34world.com/Forum/index.php?topic=17701.msg178630#msg178630)