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Sunday, December 16, 2018

Tube of the Month : The 12AV5

Hi!

Last year the December tube was a beam pentode designed for horizontal deflection service in TVs. So let's have a look at a similar one this year: The 12AV5.




Like the 6FW5 shown last year, the 12AV5 makes a nice pseudo triode when the screen grid is connected to the plate.

It is also available as a 6.3V heater variant (6AV5) but I only have 12,6V versions. The 12AV5 has an Octal base and no top cap. The pinout is shown on the left. It has a rather low maximum plate dissipation of 11W.  So the maximum power which can be extracted from it in single ended triode service is 2-3W. These TV tubes can take some abuse and I would not be scared to run it right at the allowed limit. It would probably make a nice low cost alternative to the 45. For the complete technical specs, see the General Electric data sheet. Especially the 12,6V variant can be easily found for cheap. So no need to complain about the rising prices of NOS tubes. If you are on a budget, take a side step off the main stream. As aways let's have a look at the triode connected plate curves:




Here some 12AV5 made by Raytheon:





A nice chubby little tube.







For just 11W dissipation the plate looks massive.




Some close ups:







CBS 12A5GA:







General Electric:







For examining the internal construction, this one has to die:




Removing the glass:






Clipping off the base:






Heater wire partially pulled out of the cathode sleeve:





The heater:




The plate:




Cathode, grids and beam forming plate:






Removing the beam plate:









Separating cathode and grids:




The cathode:




Screen grid, graphite coated to increase heat dissipation:




Control grid, gold plated to decrease secondary emission:




Those TV tubes were well made and produced at a time when tube manufacturing technology was very mature.




And lastly some photos of the tube in operation.






Best regards

Thomas



Sunday, December 9, 2018

Amplifier Work in Progress

Hi!

A quick preview of 3 different amplifiers which are in different states of completion.





A set of 46 drive 46 amplifiers, but this time in landscape style and with Tamura output transformers.




Interstage will be a Tango.  Since they have different finishes, additional transformer covers will be placed over them. Due to the size of the Tamura it had to be mounted on a sub plate through a cut-out of the top plate.




300B mono blocks in tower chassis with 801A driver already finished, one the housing is missing.




Some pics of the internals.








And lastly a new set of ER887 drives ER845 mono blocks.




Assembly from top down.




 


Sub assembly with Output and Interstage transformer and some capacitors.




Build up of the amp, only the last level missing:





The power supply chassis is built in similar fashion.




Stay tuned for updates as these amps get finished.

Best regards

Thomas