Fan & Meter Board Replacement
X54-1300-10
CTR Engineering Inc in the USA, has a replacement board for the TL-922. The original Kenwood part number for this board is X54-1300-10 and it is easily identified on the circuit diagram. This unit is a direct replacement but provides better than original features.
LINK: ctrengineeringinc.com/kenwood-tl922-x54-1300-10-boards
An issue I have not personally encountered is where some reported they have some arcing and subsequent carbon tracking issues.
What makes this board interesting, is that it allows one to adjust the fan run-on time after switching off the amp. CTR Engineering point out that when using the 3-500ZG with the graphite anode especially, it’s a good idea to maximise the run-on time. This off course prolongs the cooling of the tubes and limits heat soak that might stress the glass seals in the tubes.
In addition, it makes some design changes to improve the metering and adds meter protection, a vital mod in case of a plate to grid short. (due to a gassy tube perhaps)
I have not yet purchased this board but I am going to get one and install it. With this board being a drop in wire for wire replacement, it makes the install much easier. The attached pdf file is the instruction manual if you would like to take a look.
Under the “Web Links” section DG0OBU has detailed all the mods applied to his TL-922. One of those is changing the fan to 240 volt unit and then by using a piggy back board over the standard X54-1300-10 board, he has built a circuit to have adjustable run on timing from seconds to hours it seems. Not that you need hours mind you, but a wide range of adjustability. https://www.dg0obu.de/media/files/TL-922.pdf. It’s all in German, but how good having online translation available nowadays.
Image credit: W8JI and DG0OBU