|Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum|
Please consider donating to help us continue to serve you.
Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
||Thread Tools||Search this Thread|
|27th January 2007, 04:22 PM||#31|
Join Date: Sep 2004
Location: Boston, Massachusetts
Blog Entries: 6
Definitely twist all heater wires, this is particularly critical the low level input stage and driver stage. There should be no heater wire loop around the socket, arrange things so that the wires pass entirely around one side or the other of the socket, not both sides.
The filament circuit(s) should not be floating, if there is a center tap available it should be grounded or elevated above ground with a bypassed voltage divider. Elevating the filaments above ground will help with filament/cathode breakdown voltage ratings in LTP and cathodyne (split load) inverters by reducing the voltage difference between the two. Usually this also results in much quieter operation as it reduces leakage in the insulation from filament to cathode. Just be careful not to exceed the insulation rating of any tube filament sharing that filament supply.
There should only be one connection between the chassis and the amplifier ground. Use a star ground arrangement or buss grounding with only one point connected to chassis. There should also be a connection for mains safety ground to chassis right at the point where power enters the amplifier.
You should use rubber grommets anywhere wires pass through the chassis. (Output and power transformers)
Since you say it is relatively easy to rotate the output transformers 90 degrees I'd do this. This will virtually eliminate the mutual inductance between the power and outputs and greatly reduce coupling between them.
Grid stopper resistors should be used on all tubes - 1K should be sufficient for most types. These must be mounted right at the socket to be effective.
220 - 1K resistors on the screen grids of your KT88 will save you a lot of grief by preventing parasitic vhf oscillations in the output tube.
A number of use have had reliability problems with some small metal films in this location (me included) so I would recommend a 1W resistor and I generally used carbon film for this purpose.
"Extraordinary claims require extraordinary evidence." - Carl Sagan
|27th January 2007, 09:37 PM||#32|
Join Date: Jan 2005
thank you very much!!!!! i will follow your advices. This means almost re-asemble all the circuit but is a good moment to polish the aluminium
|Thread Tools||Search this Thread|
|Thread||Thread Starter||Forum||Replies||Last Post|
|2A3 or KT88 ?||6J7||Tubes / Valves||8||19th April 2009 11:52 AM|
|My KT88 SE project||JesseG||Tubes / Valves||8||20th April 2008 04:26 AM|
|Project choice for KT88||JDeV||Tubes / Valves||6||16th August 2005 07:27 PM|
|Kt88 Se||hacknet||Tubes / Valves||9||10th September 2004 08:19 AM|
|Would it be possible? OTL/OCL KT88?||Layberinthius||Tubes / Valves||4||24th January 2004 11:31 PM|
|New To Site?||Need Help?|