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Old 14th January 2018, 08:34 AM   #8191
Manta79 is offline Manta79  Netherlands
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Did it light up like nixies or neon ?
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Old 14th January 2018, 08:42 AM   #8192
Manta79 is offline Manta79  Netherlands
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One of the reasons I am interested is that I have an old Philips cinema tube amplifier, 1945+, that I would like to restore in its old glory. There is also a light bulb on it. What does a ballast do ?

Best, Richard

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Old 15th January 2018, 05:07 AM   #8193
Wavebourn is offline Wavebourn  United States
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Quote:
Originally Posted by Manta79 View Post
What does a ballast do ?
Kind of CCS. Resistance of the filament depends on it's temperature, so the higher is the voltage drop, the higher is the resistance.
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Old 15th January 2018, 06:25 AM   #8194
El Sid is offline El Sid  South Africa
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My self restored HH Scott LK-72

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Wow that is very very nice!
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Old 17th January 2018, 07:04 AM   #8195
dch53 is offline dch53  Australia
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Default 50W Williamson

Here are a couple of 50W Williamson monoblocks I built 18 months ago. Based on My KT88 Williamson Amp Build but with modifications to accommodate 6GU7s and 6550s and an LC power supply. I believe this was originally a GEC design.

There's 12.5dB of feedback.

For stabilisation I tried 47pF across the feedback resistor and various RC combinations across the V1A anode resistor but settled on 4k7 in series with 470pF across the V1A anode resistor.

In addition to the pictures of the units and circuit diagrams there are 5kHz scope shots of no added stabilisation and with the stabilisation (resistive load and 2uF load).

They sound great!

Thoroughly enjoyed the whole process of simulation using LTSpice, ordering parts, designing the physical layout, having the chassis' laser cut, bent, welded and painted, assembly and testing.

I learned a lot. Like if I ever build more, don't put the bias test points so close to the hot output valves!

The only major problem I had was electromechanical hum induced into the chassis' by the mains transformers (another thread) reduced to an acceptable level by putting sliced rubber grommets under the feet of the mains transformers.
Attached Images
File Type: jpg IMG_0058.JPG (325.1 KB, 1045 views)
File Type: jpg IMG_0068.jpg (399.3 KB, 1034 views)
File Type: png 5KHz No added stabilisation.png (5.8 KB, 980 views)
File Type: png 5KHz 4.7k + 470pF across V1 anode resistor.png (5.6 KB, 946 views)
File Type: png 5KHz 4.7k + 470pF across V1 anode resistor 2uF across load.png (24.9 KB, 149 views)
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Old 18th January 2018, 10:54 PM   #8196
Brice is offline Brice  United States
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Acrosound UL120
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Old 19th January 2018, 03:33 AM   #8197
gabdx is offline gabdx  Canada
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Originally Posted by dch53 View Post
Here are a couple of 50W Williamson monoblocks
Nicely done! I like how you placed a particular attention to placement of parts and crossing wires at 90deg. Must sound good.
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Old 19th January 2018, 06:56 AM   #8198
pelayostyle is offline pelayostyle  United States
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Originally Posted by dch53 View Post
Here are a couple of 50W Williamson monoblocks I built 18 months ago.....
Nice! Build looks good and I bet they sound great. It sucks having to wait so long for the Edcors but they're worth it.
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Old 19th January 2018, 07:02 AM   #8199
pelayostyle is offline pelayostyle  United States
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Valve wizard phono stage. Easy build and sounds very, very good. Built it with PCB female pins on a cap to allow for swapping the V2 tube between an au7 and at7. I think I've settled on the 12au7 in v2. Feel free to ask any questions.

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Old 20th January 2018, 07:00 AM   #8200
dch53 is offline dch53  Australia
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Nicely done! I like how you placed a particular attention to placement of parts and crossing wires at 90deg.
I wish I could take credit for that but it was purely accidental.
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