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Tubelab Discussion and support of Tubelab products, prototypes and experiments

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Old 23rd January 2019, 01:20 AM   #51
kevinkr is offline kevinkr  United States
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After a 14 year run, the TSE must DIE!
Quote:
Originally Posted by baker8 View Post
The 5842 is getting expensive and hard to find. Would a board adapted for a D3A be a bad idea?
Unfortunately D3A have become quite expensive and rare. Individual tubes now run $40 - $100 each..
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Old 23rd January 2019, 01:42 AM   #52
baker8 is offline baker8  United States
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Quote:
Originally Posted by kevinkr View Post
Unfortunately D3A have become quite expensive and rare. Individual tubes now run $40 - $100 each..
Yikes! I didn't know that. Seems like just a few years ago I bought them for under $10 each.
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Old 25th January 2019, 04:58 PM   #53
tomchr is offline tomchr  Canada
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I guess I should sell mine then.

Tom
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Old 25th January 2019, 11:54 PM   #54
Tubelab_com is online now Tubelab_com  United States
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Seems like just a few years ago I bought them for under $10 each.......I guess I should sell mine then.
I think I paid $15 each for mine nearly 10 years ago. I could sell them, but I only have two and I would find a need for them right after I sold them......I did sell off my collection of Telefunken tubes last year, then used the funds to buy some "worthless TV tubes." OK, a lot of TV tubes, all for $1 each or LESS.
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Old 6th February 2019, 02:36 AM   #55
Tubelab_com is online now Tubelab_com  United States
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First Prototype assembly started. I spent a little bit of today soldering parts, and the rest of the day ordering $350 worth of components from Digikey. The Mouser order may get done tomorrow.
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File Type: jpg P2360438_x.jpg (644.0 KB, 330 views)
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Old 6th February 2019, 11:50 AM   #56
Mark Johnson is offline Mark Johnson  United States
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After a 14 year run, the TSE must DIE!
Drill holes appear to have a systematic misalignment towards 9 O'clock.
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Old 6th February 2019, 12:51 PM   #57
Tubelab_com is online now Tubelab_com  United States
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Yes, and it shifts as you move across the board. Lower right is worse case, upper left is OK. The next board will be different from this one. You can find several other issues if you look close enough.

This is a DIY proto board that was made using an iron on toner transfer method. My printer can't make two identical prints, and the paper itself goes through thermal shock when the hot iron hits it. These protos will have registration issues between the two sides and well as several other less than desirable traits like lack of plated through holes. They will never leave my lab, so I live with the drawbacks in order to eliminate the time and $$$$ for one or two off boards.

It is the fastest way to get a board made so that I can verify the layout and test various layout changes before dropping a kilobuck on quality made boards from a PC board house.

I do several of these over the course of designing something. When done, they may get saved, stripped for parts, or used for experiments. I went through maybe 6 or 8 board spins for the original TSE design since the amp design itself was new and still in a state of flux, as was the PCB layout. In this case there were minimal changes to the amp design itself, so there should be only one or two proto board spins. I will know more once this one sees power up and torture testing.

The TSE-II is pretty much the SAME as the original TSE, yet DIFFERENT.

The board is larger to reduce overcrowding with 300B's and fat 2A3's.

The parts list is being redone to use common parts that are available from multiple sources. Several different flavors of electrolytics and mosfets have been ordered for testing.

Unlike the original TSE, component price is not a selection criteria. The price difference between budget parts and good (but not stupid) parts is nothing in the overall amp cost.

The only change to the audio path was to add gate stoppers to the mosfets. Mosfets in general have become much faster than the old 2SK2700 used 15 years ago. The gate resistor adds some insurance against oscillation.

The filament supply has a new regulator, 3 input filter caps in parallel instead of one big one to lower overall ESR and improve ripple current capability. The goal was to make operation with 5 amps worth of 2A3's more reliable.

The layout was changed to improve separation between the filament current loops and the audio path ground point.

A zener diode / resistor pair was added to the mosfet positive supply to reduce mosfet power dissipation, and each TO-220 device now have their own standard size heat sink.

The parts layout is pretty much the same as before but things were moved around a bit to avoid thermal hot spots that were present in the old board when operated at high voltages.

This board (and all that follow) will be tested and optimized at B+ voltages from 250 volts to over 400 volts and a chart for resistor values at each voltage will be generated. All power supply caps are rated for 105 degrees C, 450 volts and chosen for ESR, ripple current capability, and lifetime.

The screw connectors as used in the SSE and SPP are now used in the TSE-II. Connections were added for a supplemental cap and choke, as in the SSE.
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Old 8th February 2019, 02:20 AM   #58
Tubelab_com is online now Tubelab_com  United States
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Tomorrow it's....smoking or non-smoking.
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Old 8th February 2019, 02:23 AM   #59
colnago55 is offline colnago55  United States
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Just a thought, would it be possible to add test points to the board?
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Old 8th February 2019, 05:04 AM   #60
zman01 is offline zman01  Bangladesh
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After a 14 year run, the TSE must DIE!
George,

Good luck with your experiments!

Looking at the proto PCB just remembered another aspect that can be (maybe) improved - please refer to the the MOSFETs and heat-sinks within the blue rectangle of the attached picture. In my experience, this place was a tight fit for the sinks and the height was a challenge - if your sinks are 1" tall, your PCB has to be mounted lower from the top, and the 5842 tubes become nearly invisible. Other option is to keep the heat-sinks exposed, but that might pose electrical hazards and might not be aesthetically acceptable for some folks.
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