what brand of EL-34 came stock??

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what brand of EL-34 came stock??

Postby jcs on Sun Jul 15, 2001 7:09 am

i picked up an english made L-120 with RCA 6ca7s...what came stock?? this one has the voltage selector and i think is all 12ax7,correct? what is the plate voltage and bias range?? i bought as is...it may cost to fix,but i cant wait to get it up and running.......i will use this for clean, with my 71 50 marshall for crunch!!!!! jcs :cool:
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Re: what brand of EL-34 came stock??

Postby limeycity on Sun Jul 15, 2001 11:47 am

Hello JCS<P>The 120 would almost certainly have been equiped with Mullard EL34`s 6 in the 120<BR>There should be A single ECC81 in the preamp section it acts a a phase invertor for the output valves, all the other valves are ECC83`s or 12AX7`s The ECC81 is also known as a 12AT7 The 81 should not be changed for an 83 as it may oscilate under some conditions <P>The plate voltage is low for a valve amp at approx 375v dc The bias voltage is quoted as -36v dc but to get all 6 EL34 the same is quite hard to acheive At least there is two bias pots <P>The RCA 6CA7 valves are good valves and if OK it is a waste of money to replace them.They are just American equilivants for the EL34<P>As they run at a low ht voltage they tend to last a long time 120 watts from 6 EL34`s makes for quite a reliable amp
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Re: what brand of EL-34 came stock??

Postby Swarty on Sun Jul 15, 2001 12:48 pm

There is a better than not chance that the RCA 6CA7s are actually Mullard EL34s. If the bottles are about the same diameter as the base, they would not be a US 6CA7. If the bottles are wider than the base(like a taller 6L6), then they would be US tubes. Do not adjust the bias by a voltage chart, set each side to draw aprx 70% of the heat disipation (x3).
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Re: what brand of EL-34 came stock??

Postby jcs on Sun Jul 15, 2001 4:51 pm

these are the big bottle RCAs,which i have more of...i like them in my old metal face 50 fine....could you guys explain a little more on the biasing? also this amp says custom made.......any other tweaks these need to run safely?? jcs :)
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