Sony TA-N55ES Bias Trimmer Pot Replacement Part Help

[squonk666]

Hello to all,

I'm looking for help regarding which bias trimmer resistor replacements (RT301 & RT351) to purchase as the original carbon trimmer resistors are no longer available for Sony ta-n55es power amp.

The sony part number (1-237-455-11) in the service manual only states that the resistance of the trimmer is 500 ohms , now i don't know the power rating as this is not stated.

Should i purchase a 0.5w bourns 25 turn pot to replace these or do i need extra power rating ??

Can anybody who has done the repairs on the TA-N55ES or similar amp help me with which part to purchase to replace?

Its really annoying the Sony do not include the power rating for the said parts, unless its not important ?

Thank you in advance.

 

[U230421]

I have had a N55. A 0.5W potmeter is sufficient.
One can calculate the exact power rating if a circuit drawing is available.
If the bias current is, say, 10mA, potpower is (10E-2)exp2 * 500 = 0.05W.

 

[squonk666]

Thank you Marbravo for your reply and help

Would you replace with a single turn pot or multi ?

The pin layout is important too.

 

[orbanp]

The power rating requirement is minimal, the bias current is not flowing through that pot, only the bias network current, which is a lot less than that stated 10mA.
A 25-turn pot is probably a better quality pot than a single turn one.
If it fits physically, then it should be OK.


Peter

 

[squonk666]

Thank you both for your reply , its greatly appreciated

The pin orientation is important , so i would need to identify the pins for the new replacement pots are of the same orientation as the original carbon pot.

There are 3 terminals on the original pot.

 

[Mark Tillotson]

Multi-turn cermet trimmers are definitely a good choice if it fits the footprint.

 

[squonk666]

Thank you both for your reply , its greatly appreciated.

The pin orientation is important , so i would need to identify the pins for the new replacement pots are of the same orientation as the original carbon pot.

 

[U230421]

Between two pins you will measure 500Ω independent of the position of the wiper. Notice where these fit in the pcb. Make a drawing of it. 90% change that the middle one is the wiper.


10mA if no 'rubber zener' is used, otherwise as stated by orbanp in #4.
If so, 0.1mA is running through the trimmer. Yields 0.000005W

 

[U230421]

...identify the pins...

Yes, the middle one is the wiper.

 

[squonk666]

thank you all for your help,

Can i substitute the Sanken output transistors 2sa1215 & 2sc2921 with 2sa1216 and 2sc2922 ?

Are there any alterations i would need to make to other components if its ok to use these instead ?

thank you