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Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum

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Old 12th June 2018, 08:14 PM   #191
kodabmx is offline kodabmx  Canada
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You're welcome, Chris. I'm guessing it's unity. The tone circuit itself is a 20db insertion loss, though. Perhaps you can calculate the gain of the surrounding tube stages?
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Old 12th June 2018, 08:18 PM   #192
hendrixgr is offline hendrixgr
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I can, no problem! Tomorrow i will decide what to build as now i have new information and options.
Thank you again!
Chris
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Old 23rd June 2018, 10:26 AM   #193
hendrixgr is offline hendrixgr
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Just ordered some pcb for the PI only, the NFB circuit is enhanced and it works fine with the LED bias.
When i finish and test everything i will post the relevant files.
The Tone stack is not the final design, obviously some cleanup is needed.
Chris
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File Type: png James_tone_stack_pcb.png (145.3 KB, 113 views)

Last edited by hendrixgr; 23rd June 2018 at 10:31 AM. Reason: more information
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Old 25th June 2018, 10:05 PM   #194
thermo is offline thermo  United States
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When tubes were made, here in the USA, there was (I believe) a 20% tolerance. So you may have a +20% one and a -20% one. Try another.
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Old 29th June 2018, 08:09 AM   #195
hendrixgr is offline hendrixgr
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Hi.

Yes i found out that there is a relatively big difference between same maker's tubes.
This thing is also forcing me to alter my design in order to account for those differences.
Chris
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Old 16th July 2018, 10:29 AM   #196
hendrixgr is offline hendrixgr
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Default mixed fliaments in series?

Hi. I am thinking to series-parallel mix the various tube filaments as follows: I have 4 829b's that each needs 1.125A at 12.6V and 4 6SN7GT's that i will use in a 2P2S configuration (2 in parallel and then 2 paralleled sections in series) so the whole 6SN7 block will be fed with 1200ma at 12.6V Now i will use a 12V dc boost converter with CC and CV capability and i will set the voltage to 63Volts and the current limit to 1.125A. This will allow me to elevate the concertina 6sn7 filaments to 50-60 volts since they will be the first in the chain and use one power supply for all filaments.

Any opinion on my scheme is welcomed because i cannot think why this scheme shouldn't work. With constant current i gain low inrush current but i get positive temperature coefficient and a theoretical runaway condition (in practice it cannot happen) that the voltage regulation should address and solve.

Chris
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Old 16th July 2018, 01:08 PM   #197
kodabmx is offline kodabmx  Canada
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Why bother? The 6SN7 can handle -100V+200V HK voltage. Also if you elevate the heaters 60V for the phase splitter, you raise the heaters for all tubes, no?

Personally, I've never raised a heater, but I've exceeded the max voltage by at least 50V, and never had a failure. YMMV though.


Koda
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Old 16th July 2018, 02:05 PM   #198
hendrixgr is offline hendrixgr
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Hi.
You are correct about heater elevation and thank you for the information about the heater limit (it is very good to know actual experimental data) but i do gain simplicity because i need only one boost converter and low current which means thinner wire and less heat, don't i?
So you think that this scheme will work as far as the filament connection scheme is concerned?
Chris
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Old 16th July 2018, 08:10 PM   #199
6A3sUMMER is offline 6A3sUMMER  United States
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Reminder:

If you ignore the cathode to filament voltage ratings; and if the cathode is "floating/moving" as in either a true current sourced LTP, or a Concertina phase splitter, you can expect the filament to cathode to develop leakage resistance over time. That WILL affect the performance of those aforementioned circuits.
This has been discussed many times in threads on this site, but is often forgot.
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