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 NEW  Matt presents bias and operation data for the 6V6 tube in SE operation - 6V6 Single-Ended (SE) Ultra Linear (UL) Bias Optimization.

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PostPosted: 28 Apr 2015, 18:03 
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Hi Bruce - I don't need much gain at all so the 12AU7 is a poor choice for me to start with - the choice made because it is the lowest gain tubes I have on hand. ;)

Now the idea of a universal preamp has grown on me, so I'm going to give this a go. I'm sure that having the ability to change the gain so easily will come in handy down the road as I try and build different amps. Once I figure out how much drive the FirstWatt F5 really needs I'll build a lower gain preamp specifically for it.

Cheers

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PostPosted: 05 May 2015, 17:28 
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The chassis I had in mind is a touch on the small side so I am going to have to order a larger one. I really dislike working in a small chassis.

I'll also need to order some high voltage electrolytic power supply capacitors. What do you folks think about the Illinois Capacitors and F&T Capacitors and JJ brands?

Matt - for the power supply how much should the capacitors be upped from the 4S design.

Cheers

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PostPosted: 05 May 2015, 21:06 
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Gio wrote:
Matt - for the power supply how much should the capacitors be upped from the 4S design.
The two cathode followers only draw a combined 3mA. I'd leave the caps as shown in the 4S project.

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PostPosted: 01 Jul 2015, 22:27 
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So a while back I ordered a Hammond aluminum chassis for this project. A couple of weeks later I went to pick up the chassis and they had shipped a steel chassis instead. I had the option of returning it, but the steel one is black powder coated so I figured I would take it as I am never happy with my paint jobs.

I've always used aluminum chassis as they are easy to drill with a typical 3/8" hand held drill. The steel chassis is nicely painted so that got me thinking that I need a drill press to do a good job. I've got the workshop space now, so I got on kijiji and found a 12" delta drill press right in my neighborhood. So you would think I was off to drill the chassis with the drill press, but instead I've been side tracked. The drill press came with a oscillating spindle sanding attachment with dust port and an awesome DIY drill table complete with T-tracks, replaceable inserts and dust collection port. And naturally this led me to pursue a dust collection system. :lildevil:

For the dust collection system I purchased a "Dust Deputy", which is a simple dust cyclone that separates out some 99% of the matter into a 5 gallon pail with only the remainder fine matter sent to vac. Simple and inexpensive and it should work very well for the light duty use it will see.

Anyway, I think I've worked out most of the distractions now and the caps and sockets arrived last week so it's back to the preamp. I'll get some photos of the chassis and parts posted tomorrow.

Cheers

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PostPosted: 03 Jul 2015, 00:05 
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Attached is a photo of the chassis. I think it looks pretty sharp. It has a rough stain black powder coat finish and the wood sides are walnut. Note the label says 1444-22CWW but the chassis is actually 1441-22BK3CWW and they sent an aluminum bottom plate. Just as well, it is hidden and it will be easy to drill ventilation holes in the bottom.

I don't normally work with a finished chassis so I figure I will cover it with masking tape to mark it up for drilling and protection of the finish.

For the 3/4" tube sockets holes I was going to use a bi-metal hole saw or a step drill bit with a drill press. The metal chassis is 0.051 inches or 20 Ga. Any recommendations?

I'll use that decorative tube socket plate with the rectifier to hide the ventilation holes in the chassis top. I also have chrome tube shields I was thinking of using but that may be too much bling.

Cheers


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PostPosted: 03 Jul 2015, 02:49 
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Gio, nice finish.

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PostPosted: 18 May 2016, 17:40 
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hi

I build this pre with cathode follower.
i used 50kohm pot and cc 0,47uf.
it works perfectly but when i have follower tube on it gives me low freq hum.
without it no hum.
does anyone have any idea why that hum occurs.


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PostPosted: 05 Jun 2016, 09:50 
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HI, I have not finished my build yet. How are you turning the follower tube on and off?

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PostPosted: 26 Jan 2017, 20:41 
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any more updates on this build?
I'm looking at morphing my plans for the regular 4S to this to deal with my amp having fairly low input impedance. It looks like I could do it with a minimal amount of added parts but with 10k impedance on the amp my .47uf coupling capacitors likely won't work but fortunately, I went cheap there.


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PostPosted: 31 Jan 2017, 23:27 
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Hi - no updates on my end, I had to box this build up shortly after my last post. But it is back on the work bench now and I should be getting back on it soon.

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