• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

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Thanks.

I tried a test with a 1.5" hole saw. It needed persuasion to go deeper than the depth of the teeth. The saw stayed centered but the hole didn't turn out very clean, and that's after some hand sanding.

An externally hosted image should be here but it was not working when we last tested it.


I don't think a Greenlee punch would go through 1/4" metal. Not without a hydraulic press, anyway.

I'll think of a solution eventually. No rush.

Wrap a pice of sand paper around the holesaw and plunge it back through the hole several times until the hole begins to smooth out. Then add another layer of progressively finer grit. Repeat this until your hole is perfectly smooth. Usually two or three layers will do. This is how I have cut every large hole in 1/4” material. Here is an example.
 

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My present project, 845 PP.
At first some tests with output tubes only, driven by interstage transformer and audio generator.
Now with a Williamson style driver board. Not so easy to get +Ub (~720 V) for the tests.
 

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Wrap a piece of sand paper around the holesaw and plunge it back through the hole several times until the hole begins to smooth out.

Good idea. Nice work. Thanks, I will give this a try.

for what model of bmw these pretty cylinders / pistons?

They're Nikasil cylinders from a late-model R100, not sure which. I have a pair of matching big-valve cylinder heads, too. Parts are largely interchangeable across a wide range of models/years. I bought them because the price was "too good to pass up" and now they're sitting on my bench and one day after I'm gone my kids will put them in a dumpster.

I know this is the wrong venue, but if you're interested in pics of my motorcycles, I've put links at the bottom of this post.

The 942 cap should be a very good cap anyway.

I would think so. It seems to be competently constructed and well-reviewed in the reports I have seen online, if that means anything. They're expensive enough that you don't feel like you're buying bargain-basement junk, but not so much that you have to struggle to justify the price. The sweet spot, then, along the continuum of cost, fashion, and self-delusion.

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https://lh3.googleusercontent.com/2RF3M5T8BDJ5jfzZKo3XXe0J2MpSjQ84DOjYcSXrneby5zJyqAq9JIoQ68OKVm-EAi-CNKjeXFbkJQIKXaoKT8fPL4lycat9CQkL3Qa-UvDL8MK-o_5sqNjflKsmYilzEq2t6dVogPEEWsGx6B96GJAu5mzj-lji9LFBffxX6wsaLqKIU3gZCrMOtHWxjfkyHMIuw4-slaJZMnLmrIM2SjabJPT8KoqyAJdTcvLr_WCDQd6anizCE6DXHUJf5Bzu0oF2Km0vs2cEQjnbjsZEbtBzR33G527LFDGO7ozERIQskTahG8YGN3CYLetLqDPQvW7rkFJwAXtpNe3kowNKAQ7L4u_AElIaOr0t-LTTQIP4GF_uEAiLwOA6ITue592Q6TEgpCjW8T0kWkn44h2dMLmXBaSkddJlt2yPUZs0tWdT4eUAZnZaujbmlN4tzUQH0RdJardwNN1mVL6ACkrlsdLHkw4tjOCiYlz2tLW3O0jBRwdtxGigWD6DQg8NRSj3D6rcdrQc1exGztgaxMqZLbPzxO1dFxX9ZLiJl4CcXNWvuLJFFszTKB9j7gNSLP6iBqtl689-ntO86_D7_fswzQOXalRF7jKLrp0woWjVwQpeAl_g3VDp9wdCd_oM2p8r2a6rbIXterK1Grnrx7BRYPAg=w1167-h875-no
https://lh3.googleusercontent.com/ExmR0649Aa93qEzY2tDZepyflNsGI6DkUGyT-W19c8aQPXCcSWgoW2KgbaMhu3bBMnDBb7CowQxxO2b9ri6x5dxyAMW_Fk0DVohiEuyhn2SLpzyTc2CzMqRkpNGVvyjUqv722HAUjvSIwSzY_HSIxFEU5imDHfUxTDVv4-ll8Tugm9kLkqVayIDIT8qlIQ5xlrVAlQD7s03OOL2eMcxNwuGyG9KM6FOTCvxYPsNWu_OTR9DMMly0fgqAg2QO1Kx6kOnKsIaJrPCH_Sr_VEjjelJcI5OVJcf4Yx7hCDatOaN2DyPN0mQzM4Enye6Vo0GmIiRzGw2pcknJDkIDuwnJiLWqpZJuEgAngxMhcL-_qTqCLSbrUMRSlU377TuEznfiBaqUYGg6xxcme2Hx_v8w-llBqiZMUJ_EbghSxhbEtVNg2caKz6SAacFBrFSAhlzaLObqfLgQwU8gYfphoNHPqGm30YJ181nr5m5AgJ-3QovjBDSpqnxKMi2M7HkRHoyZBqpbFNw7MfGPRWlfFgrd_FDSDw5WyIffDx35Z2DhNeMgM3g8lQcguTCO8YC8-5Lt2WJhXLge0KVBX1PyH4J1r4MisXhtsMbeZh0Gnnp51L8ORK9roOqLRtxr68GghiuNmRSwFefhm1tCKXceHRMc7TQq=w657-h875-no
https://lh3.googleusercontent.com/nJjLRblVIsI9rpt5okhTEYiHlkvQlCitRPoQH40il3hUXe1pEo-eWPM8QAVCDcv0U18htcdUrwmgS9faFoKwaETFDRbKzXHQcd6yFmiDFgQ3zGUgsAAUSeV89-rdjyL6R9eiEq8I-qRVSLrudp0cUp2dcxyXJ7UfNWXL26Ze7H_VhQKzXzOeRQndBh-iKhbqFK_MyyaEHDIkfgbcNRvuqO9GB4vOfi0PC_lo9go0wUcHfoSXT2sKtm_eshGii2yJ1l8DXw4JuQIX0NyCsc6qP3Fw2xLdUXvaQSmXjSuKFDIL1IMHy8VWUY34AZmmA11UfwruHvcA6Lj6DA8PHu0oZUXg1y7GYrXIzF9xGPvDFhzxBF8G2ilBDu6BS3MXYGpixH7MwlqHZZpL3zGOJ0CwDjK1PBlAvLhbslz64zlHpCkgeY1MQKcahwX5BTI-M_vPLTf6dJhVxnMyEgqtDHv71IWWdqBWYd90kCJpr4g9DVnqAs0Pi_ftSG_FvIzpLmdIzlHN7CbbO6gY8DrYX8Odc8cEgWwh6OCKxii45GSWcwxXi0bbvodFYcaEyngI5e13fXNCsNxcYFALbYNR4hBZgEMmE-cE_7qKho8HBBoE4nHSJfsBnBbcA8Nv0mw3GHt6PMqv6CZgeHoUUr5-Hyc4R8W6=w1167-h875-no
 
you are welcome hpasternack :)
really beautiful bikes !!
i have a choper bitza /2 with r100 engine
and r75/6,r60/7,r100/7,r75/5,k75rt,k75s,k1100lt and other motorcycles
before your children decide to put your pair of piston cylinders in the trash, send me a mp, I qlqs engine block / 6 mk2 and / 7 waiting for piston cylinders, I would be happy to buy them they are not scratched ;)
 
Finished up the "Consolidation' preamp.

I consolidated a bunch of circuitry into a rather small chassis. There isn't much room left in there to add anything but it has Bluetooth APTX, 24/192 DAC, 128 step relay volume control, relay switched inputs, a nixie to tell which input you're on, those cheap tube level meters, latching relay that remembers if you're on coax or optical for the dac input, a buffer for the outputs, and a line amp good for 10V out for 1V in for driving the monoblocs I'm building using parts from other amps.

Took about three days...

Thought I'd share the pics.

The little transformer makes the power switch latch or not and turns on the rest of the box. 12V switcher powers the tube heaters, all those boards, and a boost converter for the B+. Theres a 200R resistor that acts as an inrush limiter which is switched out by the black relay. The toroid powers the DAC.

Sidenote: These pics were taken with my phone camera! I'm still getting over how good that nixie looks at full quality :)
Koda
 

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Finished prototyping, crossing fingers...
Input: 0 dB (0.775V) RCA, 50K stereo
Outputs: low ohm for 4-6 Ohm and high ohm, for 8-12 Ohm load.
Power: minimum 6W for <1% total harmonic distortions.
Soft asymmetric clipping, negative output resistance for damping of woofers.
Bandwidth: 10 Hz-90 KHz -3 dB, from 20 Hz full power.
Available versions with different output tubes:
EL34
5881/6П3С-Е
Raytheon VT127
4П10С
 

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