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JCM800 2204 Phase Inverter issue and other
JCM800 2204 Phase Inverter issue and other
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Old 11th November 2018, 05:15 PM   #131
SimoS is offline SimoS
diyAudio Member
Join Date: Aug 2018
Hello. Installed the new OT = no more redplating and full output power again
I'm in doubt, now, about trying however to reduce B+ (switchable?) to complete the transformation to a old style ('80) JCM800 2204. Your opinion?

In any case thanks again for your patience and your suggestions: I learnt a lot!
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Old 12th November 2018, 12:35 AM   #132
Koonw is offline Koonw
diyAudio Member
Join Date: Apr 2013
Congratulation! But you should protect the OT from shorting happened again in future:

1) Install a 100 ohms 2 watts resistor across the secondary, this acts as dummy when the speaker/load is accidentally pull from output jack.

2) Install diode protection in Primary as in newer Marshall amp

3) HT can be reduced by adding series resistor in each secondary of power transformer before the rectifier bridge. If max. AC current drawn is 200mA, then 100 Ohms resistor will drop 100*0.2=20V on each secondary AC tap. So 20*0.2=4 Watts, you can rate up to 10 Watts resistor. Alternately you can reduce the screen voltage by simply adding series resistor after choke T3. (Remember reducing screen voltage is more effective than reduce plate voltage in term of plate current reduction hence possible red plating)
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Old 12th November 2018, 09:51 AM   #133
turk 182 is offline turk 182  Canada
diyAudio Member
Join Date: Oct 2012
time to celebrate!
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