Hi trobbins, did you resolve this in the end? I am now in the possession of an Oltronix LS107 which uses 3 EL34s connected as pentodes, It has some tasty looking Mullards in there now, so to replace them with a modern cheap EL34 is plan B.
No progress on any ss alternatives so far. I finished off the restoration as far as I could (I'm not at liberty to include the service manual and schematic), but with no 'need' for it so far it will just remain on the shelf for now.
Well done for getting the Oltronix.
It does make one muse over how to protect the EL34's, and how to balance them for dissipation when used in parallel - given that standard maintenance was just to replace them with matched valves. I partly restored a HP 716B a few months ago - it has six EL34's, of which four are in parallel and squeezed in to such a small footprint that I couldn't remove them without making a custom extraction tool, so left that for another time.
Well done for getting the Oltronix.
It does make one muse over how to protect the EL34's, and how to balance them for dissipation when used in parallel - given that standard maintenance was just to replace them with matched valves. I partly restored a HP 716B a few months ago - it has six EL34's, of which four are in parallel and squeezed in to such a small footprint that I couldn't remove them without making a custom extraction tool, so left that for another time.
This is a most interesting thread. As Chris pointed out in post #14 the ability of tubed to dissipate power at high temperature is a great advantage. The relatively new Silicon Carbide FET's can operate at elevated temperatures (175C) https://www.infineon.com/cms/en/pro...TwlyqbJ35xoCtwsQAvD_BwE&gclsrc=aw.ds#products
enabling the use of smaller heatsinks and dispensing with forced air cooling in some cases.
One needs to bear in mind "the tube" if used in a audio amplifier may see twice the B+ voltage, the Silicon Carbide FET's have this covered with voltages up to 2000 volts.
My thoughts are one could make a triode connected "tube", the 6.3 AC heater supply could be used via a small transformer to power the circuitry and make the device work in a similar manner to a genuine triode connected tube.
My colleague and I designed and built built a 50kW voltage converter using 6 Silicon Carbide FET's. the efficiency was over 96% , we never destroyed a FET during testing so the devices must be very robust!
I have no idea how well the Silicon Carbide FET's work in the linear zone.
I cannot see this project saving money, the cost in time will be high, others may benefit from any work carried out; at some stage it will be worthwhile. A FET tube could have pot adjusted parameters and even a microcontroller to watch over things, it could even have Bluetooth.
Good luck with the project.
Ken K
enabling the use of smaller heatsinks and dispensing with forced air cooling in some cases.
One needs to bear in mind "the tube" if used in a audio amplifier may see twice the B+ voltage, the Silicon Carbide FET's have this covered with voltages up to 2000 volts.
My thoughts are one could make a triode connected "tube", the 6.3 AC heater supply could be used via a small transformer to power the circuitry and make the device work in a similar manner to a genuine triode connected tube.
My colleague and I designed and built built a 50kW voltage converter using 6 Silicon Carbide FET's. the efficiency was over 96% , we never destroyed a FET during testing so the devices must be very robust!
I have no idea how well the Silicon Carbide FET's work in the linear zone.
I cannot see this project saving money, the cost in time will be high, others may benefit from any work carried out; at some stage it will be worthwhile. A FET tube could have pot adjusted parameters and even a microcontroller to watch over things, it could even have Bluetooth.
Good luck with the project.
Ken K
Revisiting this old thread. I was wondering why it was that many of these old regulated power supplies used EL34's. I did read somewhere that they were partly designed for this role with having higher than usual heater to cathode insulation, 400V in the article I read, but I see no evidence of that in the old tube datasheets.
Some tubes that were expensive then are cheap now because they are not audio types; is it reasonable to simulate with other tubes in LTSpice? Do modern guitar-amp friendly EL34s perform this type of donkey work?
Some tubes that were expensive then are cheap now because they are not audio types; is it reasonable to simulate with other tubes in LTSpice? Do modern guitar-amp friendly EL34s perform this type of donkey work?
In E235L electronic devices manufactured by PHILIPS and SIEMENS, G2 is mostly connected to pin-1 (according to the factory data, it is marked as internally used) together with pin.4, while in TELEFUNKEN, pin-1 is free, that is, sometimes it is not even on the base of the electronic device. Therefore, it cannot be said that the connection of the base of EL34 and E235L is the same, because G3 is connected to pin-1 of EL34.
Are E235L's really cheaper than EL34's? Hard to imagine, as their production has ceased decades ago, and as it is a SQ tube. Anyway, their cathode to heater voltage rating of +250 V still is much lower than these 400 V named above.
Best regards!
Best regards!