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12BK5 Hybrid Amp
12BK5 Hybrid Amp
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Old 30th January 2019, 07:42 PM   #11
Gnobuddy is offline Gnobuddy  Canada
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Quote:
Originally Posted by Printer2 View Post
I did a photo example of cutting and bending a similar chassis at one time
I remember seeing your pics some years ago, around the time I first found your posts about your 2W 6AK6 mini 5E3.

I want to use the C-purlin I found, rather than fold up my own chassis from flat sheet. That means I have to find a way to cut it cleanly without bending or collapsing the C-shape in the process. I do have access to a small metal-cutting band saw, but I think the weight of the saw coming down on the purlin might bend the metal and make an ugly cut.

I'm thinking, maybe if I cut a block of wood to fit tightly inside the C-Purlin right where the saw cut is to be made, it will keep it from collapsing.

I like working with aluminium, but steel is a different matter. It usually seems to involve bloodshed (my own blood, that is!), iron filings that go everywhere, and lots of time.


-Gnobuddy
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Old 3rd February 2019, 01:36 AM   #12
Printer2 is offline Printer2  Canada
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I like aluminum myself, don't come across a lot of it free though. Speaking of cheap, found a radio today for $20 that was built in Vancouver in the 1950's. I was not going to bother as the picture of it showed the grill area with a height for an 8". I thought the last thing I need is another five tube line powered amp with crappy tubes. But I took a chance on it because it was five minutes away and it is twenty degrees warmer than it was two days ago.

Painted top, who cares, didn't even look at the turntable. Looked at the back and I saw the 10" speaker and that is all I needed to decide to get it. Saw it had octal tubes, another plus, also a power transformer although I have enough of them. When I got it home found out it is suppose to have a 6K6 output tube, had a 6W6 in place. So I got a decent speaker and a output transformer for another SE amp, I have about 20 6K6GT's.

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Last edited by Printer2; 3rd February 2019 at 01:38 AM.
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Old 3rd February 2019, 03:31 AM   #13
Gnobuddy is offline Gnobuddy  Canada
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Originally Posted by Printer2 View Post
So I got a decent speaker
Is that a vintage Weber speaker? Looks like an Alnico magnet, too.

The type of magnet material makes no difference to speaker performance (it's the BL product that matters), but Alnico gets all the street cred.


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Old 3rd February 2019, 04:03 AM   #14
Printer2 is offline Printer2  Canada
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Or Weber copied a vintage style?
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Old 10th February 2019, 05:19 PM   #15
Printer2 is offline Printer2  Canada
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No I am not a horder, I could not help myself on this one it looks so cute. A small floor standing radio, I actually works and I payed $75 as well as drove an hour for it. Other than recaping the power supply will leave it stock. It does have a phono input and switch on the chassis which I can hook up a guitar preamp to. The person that had it refinished it and it looks pretty good.

http://pacifictv.ca/schematics/viking51-45data.pdf

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Somehow lost the image in the above post.


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I have wired up some more of the 12BK5 amp but the trip to get the radio and changing the arrangement of my workshop is taking up my time.

Last edited by Printer2; 10th February 2019 at 05:28 PM.
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Old 10th February 2019, 05:45 PM   #16
Tubelab_com is offline Tubelab_com  United States
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Quote:
I want to use the C-purlin I found,
I found a bunch of similar looking stuff, but it was a thinner gauge steel, used for running bundles of cat 5 cables through a building between the ceiling and roof. It was about the right size for small amp chassis, so I grabbed several of the smaller pieces.

I made a wood buck from cheap pine 2 x 4's that fit tightly inside and then put a clamp across the outside to squeeze it for a tight fit. Position the buck so that about 1/2 inch gets cut off each time you use it. I could then cut the the whole thing on a band saw without much blood loss. A big old speaker magnet near the cutting area helps collect the steel filings, but also makes some cling to the material.

I found that punching or drilling a clean tube socket hole in the stuff was a bigger job than cutting it, and I wound up leaving it all behind when I moved.
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Old 11th February 2019, 01:14 AM   #17
Gnobuddy is offline Gnobuddy  Canada
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Originally Posted by Tubelab_com View Post
...wood buck...clamp across the outside...punching or drilling a clean tube socket hole in the stuff was a bigger job than cutting it...
Thanks for sharing your method!

You have me wondering whether it's worth putting time into trying to work with this steel C-purlin stuff, or whether I should pitch it and just go hunt down some appropriately sized aluminium U-channel.

I've been using a set of three step-drills to make all the larger holes in my aluminium chassis, and the plywood boards I used for some builds. The step drills work wonderfully well in aluminium and wood, but I don't know how well they fare with sheet steel.

-Gnobuddy
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Old 11th February 2019, 01:16 AM   #18
Gnobuddy is offline Gnobuddy  Canada
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Originally Posted by Printer2 View Post
...I am not a horder, I could not help myself...
Now that's a very convincing juxtapositon.

Cute radio!


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Old 19th February 2019, 03:33 AM   #19
Printer2 is offline Printer2  Canada
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So I was buying online again and was looking at some 6AV6's for that little radio. While I was there I looked up some 35L6's, a reasonable price for them. I picked up a RCA Victor Model 45-EY-4 record player once and it had two 35L6's in P-P, which was unusual.



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It would make for a nice little low voltage amp, the only problem I have is with the 35V. I could use a laptop brick and a dc-dc converter to boost it up to 35V. Or I can go with a 12L6 or the like but for some reason it just seems to me a waste of capabilities. Mind you the 12L6 's might just last forever in the amp. I am going to have to think about it.
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Old 19th February 2019, 05:39 AM   #20
Gnobuddy is offline Gnobuddy  Canada
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Originally Posted by Printer2 View Post
35L6...Or I can go with a 12L6
You know the 35L6 has lower plate and screen dissipation ratings than the 12L6, yes?

35 volts is an odd one all right. But there are inexpensive 36V DC switching power supplies, and you can easily knock off the extra volt with a series 1N4007 diode or two. How about this one: https://www.digikey.ca/product-detai...783-ND/7681532

With a 1A rating, that power supply can also run three 12.6 -volt heaters in series, in addition to a pair of 35L6s. Maybe some 12AV6 or something similar?

If you want to go old-school and have lots of hum and heater-wiring grief, there are old-fashioned 60 Hz, 18V-0-18V transformers, like this one: VPP36-560 Triad Magnetics | Transformers | DigiKey


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