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red plating alert
Posted: Sat Mar 08, 2014 12:19 am
by thefatcyclist
- on and idling_01.JPG (26.59 KiB) Viewed 1850 times
- standby_01.JPG (26.46 KiB) Viewed 1850 times
I take it this is not good.
Just to remind, Biacrown DR103, outer tubes pulled to reduce power. Original EL34 ot there abouts.
pic one stand by
pic two on and idling
hum from amp and it appears near the plating tube,
What damage have I done or will do if not immediate amp doctor
Re: red plating alert
Posted: Sat Mar 08, 2014 1:58 am
by OldSchoolDave
thefatcyclist wrote:
What damage have I done or will do if not immediate amp doctor
Could burn out the tubes, depending on how long they've been exposed to those conditions and how stout they are.
Get it resolved ASAP.
Dave
Re: red plating alert
Posted: Sat Mar 08, 2014 8:48 pm
by mhuss
Try one of the two pulled tubes in place of the RP one and see if it helps.
Sadly, Hiwatts were built for the Mullards they came with, and modern EL34s are not always up to the task. You may need to have the bias mod (
http://hiwatt.org/Schematics/BiasCkts2.gif) done to get it to where modern tubes will run comfortably.
The problem is that the manufacturing tolerances aren't what they were back in the day, and some modern tubes need a bias voltage more negative than that required by xf2 Mullards.
--mark
