More Amp Construction

When you have lots and lots of extra terminals, getting things tidy is not so difficult. I ultimately should've added a second twelve lug turret board to this build.
 
When you have lots and lots of extra terminals, getting things tidy is not so difficult. I ultimately should've added a second twelve lug turret board to this build.
The pics were in no way a critique of your build. Just an example of what I wish I could come close to doing!
 
Here are the schematics if anybody would like to torture themselves a bit. 801A Filament Regulator.jpg
This is the regulator for the filaments (sorry about all the blank space). It could of course be substituted for something else. The raw incoming voltage can go as high as +12V, or be trimmed down significantly with the dropping resistor in the power supply, so there's a lot of flexibility here.
801A PSU and Amp 1.1.jpg
I've looked this over tons of times, and I'm pretty certain it contains all my changes. With this arrangement, you could use a series feed output transformer from whoever and stability is not a concern. The 10uF cap could be a 630V cap without any issues, and the 3.3uF screen bypass caps are just parts I had sitting around that fit exactly where I needed them to. The MBRF745G and L-200C are mounted to the chassis to help with cooling. The power supply choke is not labeled but is a Triad C-14X. The paralleled pairs of 270R/10W resistors are likewise a bit over spec but they fit really nicely. A single 130 ohm 5-10W resistor would be fine in each of those positions.

I had the amp setup to make a hair more power, but DC operating point stability on the first pentode gainstage was giving me fits, so I dialed things back a bit.
 
20190823_215659.jpg
This is a relatively simple amp on the inside. The first stage is a 7L7 pentode which feeds a 6BL7 that has one half acting as a shunt regulator for the other half that is a cathode follower that is directly coupled to the grid of the 805A. A Hammond 156C choke is used as a load for the 6BL7 cathode follower when the 805A grid is driven sufficiently negative. The 805A filaments are DC heated with a choke input filter. A bit of local feedback is applied between the 7L7 plate and the 805A plate to bring the 805A into a more workable condition when it comes to matching it to output iron. There is a bit of adjustable bias on the grid of the 6BL7 cathode follower which adjusts the 6BL7 cathode voltage/805A grid voltage to set quiescent operating current.

The parallel feed output transformers and plate chokes are custom made by Sowter, and the power transformer is a Bottlehead unit that goes in the Kaiju. I also got a little lazy and just used the HV power supply layout from the Kaiju as well but with a power supply choke to nudge the B+ up a little bit. Luckily all the necessary power supply chokes are off the shelf Hammond units.

With the Chinese 805A, the amp eeks out 24W. With American old stock 838 and 805 tubes, the amp makes just over 30W.
 
That is quite impressive. I like the way the wood side panels are tucked into the chassis.

Are these for you Paul or did you build them for someone else?
 
I hope this isn't taken as thread crapping but this wiring job has me speechless!

Artistically/aesthetically pretty... I appreciate it for what it is. Looks amazing. I do have questions though. How long are the current loops? Buss grounding looks pretty, but is there a better way? How many avoidable solder joints and dissimilar conductors are there? Are there some bends in wire mostly about aesthetics? Would film caps be better than the ‘lyrics in some of those positions... and could the aesthetics then be maintained?

Point is that every approach has compromises and I will take those that are orientated towards reliability, maintain ability, and performance.
 
The boss talked me out of bends and into smoother radii over the years. It doesn't look as good, but it is less stressful to the copper.

That is my thinking too.

Regarding my post #88, I was poorly just trying to mamke the point the point there are many ways to build, each with its own benefits and adversities - not trying to suggest onw was better than another. Weirdly, I woke up at 2:00am, regretting that I'd made post #88 in fear it might have dragged this great build thread off topic. Thanks for keeping it on track.
 
Very well executed Paul, I really like the aesthetic, small details that add up quite nicely indeed. A few questions, if you don't mind.

1 - Where did you get those sockets. I'm on the hunt for quality jumbo 4 pins.
2 - You have schematics? Looks like an interesting circuit, fairly simple as well.

Nice power output, might be well suited for an lf amp perhaps?
 
1 - Where did you get those sockets. I'm on the hunt for quality jumbo 4 pins.

These are just the standard Chinese 4 pin jumbo sockets. They are pretty annoying to mount, but I use #10 threaded standoffs and #10 rubber washers so I can get some tension on the hardware without worrying about cracking the ceramic. If you need McMaster Carr part numbers, I can look them up.

2 - You have schematics? Looks like an interesting circuit, fairly simple as well.
I'll probably take a few more months to quiet down the "what ifs" in my head before I have something fully ready to publish.
Nice power output, might be well suited for an lf amp perhaps?
Only by accident!
 
These are just the standard Chinese 4 pin jumbo sockets. They are pretty annoying to mount, but I use #10 threaded standoffs and #10 rubber washers so I can get some tension on the hardware without worrying about cracking the ceramic. If you need McMaster Carr part numbers, I can look them up.

I have plenty of that sort of hardware, thank you though. I have sandwiched rubber washers around ceramic sockets in the past for the same reason.

I'll probably take a few more months to quiet down the "what ifs" in my head before I have something fully ready to publish.

Totally understood.

Only by accident!

As the late, great Mr. Ross would say "happy little accident!".

In all seriousness I ask because I'm interested in a design to drive my mid-bass horns. Transmitting tubes are just damn cool, there's no way around it. Hence my interest. :D
 
More work underway. This will be a #45 headphone amp with Magnequest TL-404 output transformers. 20191014_153517.jpg
I was all set to order the chassis and decided to do a hum pickup measurement with the TL404s and had to completely revise the chassis design to orient them in a very specific way. They will now hang out on a sub panel mounted on the inside of the chassis. As a side bonus, wiring up the impedance selector will be far easier with just some short jumpers. Both the line level input and the headphone output get routed through copper tubing (mostly for fun).
20191014_153407.jpg
 
Ive thought about wiring through copper tubes as well, nice to see someone actually doing it!

The case work look fantastic so far!
 
Wow - really cool stuff - makes me want to build some tube amps once again. Since I already have PushPull - I'd like to build a stereo SET unit.

Maybe someday.
 
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