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Red Plating??

I have a CLASS A KT88 amp that has an autobias circuit.  The company rep recommended SED 6550C Winged C tubes.  I purchased a quad of them.  They bias OK and they sound wonderful but I just noticed that they red plate a bit. If I can figure out how to do it I will attach a picture.

The red plating is just in the inner corner of one of the plates on all 4 tubes.  It looks as though I am looking at the filament through a translucent plate but I know that its red plating. 

https://imgur.com/a/RVLWPcf

Can I operate like this safely?  The bias does hold steady and does not fluctuate. The red plating does not change.  As a Class A amp this status should hold steady.  Of course, it does run hot. If all that it hurts is tube life, thats OK.  These are my best sounding tubes without a doubt.

chinook9

Showing 3 responses by chinook9

chinook9 OP
66 posts
 
ieales

I just checked my circuit voltage and found it to be 124 Volts.  The amplifier indicates its designed for 115V, 

Could I build a transformer to reduce the voltage??  I have built a number of electronic devices and probably have the required equipment.
chinook9 OP
66 posts
 
Thank you all for your input. I have sent a message to the company rep.  He was the one who recommended these tubes. 

atmasphere, you mention "a bit of red plating."  Would you consider the red plating shown in my photo a "bit"?  The amp "bias- checking" lights/circuit indicate that it is correctly biased. All four tubes have a similar amount of red plating.
chinook9 OP
66 posts
 
Great information being posted in this thread.  For the time being I am waiting to hear from the company rep but I'm not holding my breath. I'll use the KT88s until I get this resolved. 

Not sure if the bucking transformer will solve the problem but its worth probably worth the investment of $90 if it might work. 

I'd like to hear opinions on potential of the bucking transformer to solve the problem.  They are available in 3% or 7% reduction in voltage and it looks as though I should go for the 7% reduction if I get one.
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